R4C Sherwood audio mod questions
I've been looking over documentation I've assembled on the Sherwood audio stage modification.? I have diagrams from the April 1979 HR article, from MODS.dk and from the files section here.? Since none of these except for the HR article are dated, I'm unsure which is the latest improvement.? Hopefully someone can point me in the right direction.? Apparently after the HR article, there were changes made as follows but I couldn't find an explanation for the changes: 1. The .22 cap and 1500 resistor on the input were eliminated, 2. The 200 uF cap on pin 2 was changed to 400 uF, the 390 ohm resistor was changed to 270 ohms.? Which version of the circuit is the best one to use?
?
73, Floyd - K8AC
|
I¡¯d go as far as to say that holds true for 95% of the OEM speakers. The Heathkit SB604 wasn¡¯t much to write home about either
Mike WB8VGE
toggle quoted message
Show quoted text
On Jan 2, 2025, at 10:19 AM, Jim VE7RF via < jim.thom@...> wrote:
On Wed, Jan 1, 2025 at 07:25 PM, Joseph K7CBR wrote:
<I confirmed beyond any doubt the old speaker was terrible.
IMO, the MS4 speaker has to be the worse speaker I have owned.? ?With the AC4 power supply installed in it, it doesn't leave much wiggle room for open cell foam and dynamat.? Replacing the driver was an option....that I did not pursue.? Bob Heil got that part right.? "It's no more than a 50 cent speaker....in a $50.00? box".?
|
On Wed, Jan 1, 2025 at 07:25 PM, Joseph K7CBR wrote:
<I confirmed beyond any doubt the old speaker was terrible.
IMO, the MS4 speaker has to be the worse speaker I have owned.? ?With the AC4 power supply installed in it, it doesn't leave much wiggle room for open cell foam and dynamat.? Replacing the driver was an option....that I did not pursue.? Bob Heil got that part right.? "It's no more than a 50 cent speaker....in a $50.00? box".?
|
Re: VE3EFJ third mixer mod for the R4C
?I took the easy way out on my yaesu xcvrs.......and used an external rack mount? Class A headphone amp. ( 200 mw per channel).? Simple Behringer 4 x channel Class A? headphone amp.? ?I use headphones 99% of the time.? Zero hiss.? But I took the output right off the analog product detector....and routed it externally to a class A? pre-amp....to feed the input of the? headphone amp.? ? Same output off the product detector was fed to the turntable input (with RIAA de-emphasis circuit removed)? of a small stereo preamp / amp....then? a pair of decent speakers....again, no hiss.??
|
Very true Jim. I am trying to confirm the VCO is off that far.?
Those are some strange readings you are seeing on your counter. Per the service manual the high VCO should free run at around 32 MHz. Operating range is 63.05 to 78.05 MHz.
On Wed, 1 Jan 2025 17:24:38 -0400
"Jim Harris via " <radiove1rb=[email protected]> wrote:
> Gary the frequency counter is hook to 5/24. I will check the input to the
> two 5 volt regulators and let you know. I do have? a scope but it only goes
> to 30 mhz but I know where I can get a good 100 MHz one. Will get that as
> soon as I can and have a looks at those outputs. Many thanks Gary for all
> your help otherwise I would be working in the dark.
>
> Jim VE1RB
>
> On Wed, Jan 1, 2025 at 4:45?PM Gary Follett via <xntrick1948=
> [email protected]> wrote:?
>
> > If that oscillator is showing anything real (~152 MHz) then it is being
> > selected. This selection is enacted by the application of +10 volts on
> > U502. The VCO board has no other information about the band selected by the
> > band switch.
> >
> > The only other information the VCO gets from the outside world comes in
> > via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as
> > well, and is the result of the 40 MHz Reference, the PTO and the VCO signal
> > divided by N (N being the selected number produced by the band selection
> > logic) and this is the signal that closes the PLL loop.
> >
> > However, even with the loop open and unlocked, the frequency at the output
> > of the VCO should never exceed 80 MHz,
> >
> > Where are you measuring the 152 MHz?
> >
> > If grounding RFC505 on the away end does nothing, try grounding the other
> > end. If still no change, then ground the physical junction at CR511A, B and
> > CR510 A,B. This should pull the frequency down a lot. If not, ground the
> > Drain of Q504 through a capacitor of about 0.01 uF. That should clearly
> > kill any oscillation and remove any output from the VCO.
> >
> > Then humor me on this one - measure the voltage on the inputs of both 5
> > volt regulators U501 and U502 when a low band (less than 15 MHz) and a high
> > band (greater than 15 MHz) are selected by the band switch. If there is a
> > switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I
> > would have a hard time deriving what would happen in this condition but I
> > am quite sure things would not go well.
> >
> > This is when an oscilloscope would be handy. You could look at the
> > waveform at the output of the VCO, at pin 5/24, the output of the VCO to
> > the radio. You should see? a nice sine wave of roughly constant amplitude
> > when either VCO is selected.
> >
> > Gary
> >
> > W0DVN
> >
> >
> > On Jan 1, 2025, at 1:50?PM, Jim Harris via <radiove1rb=?
> > [email protected]> wrote:?
> >
> > Gary I tried that ground on RFC505 and no change. Is it not getting band
> > information?
> >
> > Jim VE1RB
> >
> > On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via <xntrick1948=?
> > [email protected]> wrote:?
> >?
> >> If you are reading 152 MHz, the you should ground RFC505 on the end away
> >> from the varactor diodes. The frequency should come down.
> >>
> >> Gary
> >>
> >> W0DVN
> >>
> >> On Jan 1, 2025, at 11:58?AM, Jim Harris via <radiove1rb=?
> >> [email protected]> wrote:?
> >>
> >> Jim maybe this will help. I touched up several solder joints although
> >> they didn¡¯t look good but not cracked. I switched the input to the counter
> >> and it is reading 17 to 18 mhz
> >> <IMG_1166.jpeg>
> >> as the frequency is jumping around so is not locked. I wonder if that is
> >> a clue?
> >>
> >> Jim VE1RB
> >>
> >> On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via <radiove1rb=?
> >> [email protected]> wrote:?
> >>?
> >>> Good ideas Jim and I will get at doing that today. It is windy and
> >>> raining here quite hard. A good job inside hi hi. I will let you know how
> >>> it goes. Many thanks for the suggestions and help.
> >>>
> >>> Jim VE1RB
> >>>
> >>> On Wed, Jan 1, 2025 at 12:24?PM Jim Shorney via <jimNU0C=?
> >>> [email protected]> wrote:?
> >>>?
> >>>>
> >>>> At this point I am suspicious of that 1.3 MHz reading. That may be a
> >>>> spurious reading. It seems to me that the VCO should not be able to run
> >>>> there. What is the level of the signal? The frequency determining
> >>>> components are L502 and the varactor diodes. Resist the temptation to try
> >>>> to adjust L502. As a long time tech told me back in the dim past, when you
> >>>> have a failure "it is never the alignment".
> >>>>
> >>>> At this point I think I would inspect the solder connections in the
> >>>> high VCO circuit under magnification and good lighting. You could have a
> >>>> failed joint or via. Check the voltages on the three JFETs. C156 or C517
> >>>> could be suspect. You have a working low VCO to compare voltage and
> >>>> resistance readings to.
> >>>>
> >>>> On Wed, 1 Jan 2025 07:41:18 -0400
> >>>> "Jim Harris via " <radiove1rb=[email protected]> wrote:
> >>>>?
> >>>> > Yes Gary I did the ground on RFC505? when looking at the frequency on?
> >>>>?
> >>>> > the counter and it does drop a lot. So I guess you are saying the High?
> >>>>?
> >>>> > VCO is oscillating at 1.3 MHz . If that is the case there must be
> >>>> > something wrong on that board unless the info it gets is wrong. Hope
> >>>> > this helps.?
> >>>>
> >>>> --
> >>>>
> >>>> 73
> >>>>
> >>>> -Jim
> >>>> NU0C
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>?
> >>>
> >>>?
> >>
> >>
> >>?
> >
> >
> >?
>
>
>
>
>
--
73
-Jim
NU0C
|
Re: VE3EFJ third mixer mod for the R4C
Did you alter the feedback network to roll off above the speech range? May of the reference designs built around these are for hi-fi bandwidth. On Wed, 1 Jan 2025 21:07:48 +0000 (UTC) "Bob Loving via groups.io" <bob.loving@...> wrote: Many years ago, I designed a PC board for the TDA 2003 Audio Amplifier. Like some have noted, the hiss level was/is a bit too high if you listen when wearing "cans."? -- 73 -Jim NU0C
|
Those are some strange readings you are seeing on your counter. Per the service manual the high VCO should free run at around 32 MHz. Operating range is 63.05 to 78.05 MHz. On Wed, 1 Jan 2025 17:24:38 -0400 "Jim Harris via groups.io" <radiove1rb@...> wrote: Gary the frequency counter is hook to 5/24. I will check the input to the
two 5 volt regulators and let you know. I do have a scope but it only goes
to 30 mhz but I know where I can get a good 100 MHz one. Will get that as
soon as I can and have a looks at those outputs. Many thanks Gary for all
your help otherwise I would be working in the dark.
Jim VE1RB
On Wed, Jan 1, 2025 at 4:45?PM Gary Follett via groups.io <xntrick1948=
[email protected]> wrote:
If that oscillator is showing anything real (~152 MHz) then it is being
selected. This selection is enacted by the application of +10 volts on
U502. The VCO board has no other information about the band selected by the
band switch.
The only other information the VCO gets from the outside world comes in
via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as
well, and is the result of the 40 MHz Reference, the PTO and the VCO signal
divided by N (N being the selected number produced by the band selection
logic) and this is the signal that closes the PLL loop.
However, even with the loop open and unlocked, the frequency at the output
of the VCO should never exceed 80 MHz,
Where are you measuring the 152 MHz?
If grounding RFC505 on the away end does nothing, try grounding the other
end. If still no change, then ground the physical junction at CR511A, B and
CR510 A,B. This should pull the frequency down a lot. If not, ground the
Drain of Q504 through a capacitor of about 0.01 uF. That should clearly
kill any oscillation and remove any output from the VCO.
Then humor me on this one - measure the voltage on the inputs of both 5
volt regulators U501 and U502 when a low band (less than 15 MHz) and a high
band (greater than 15 MHz) are selected by the band switch. If there is a
switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I
would have a hard time deriving what would happen in this condition but I
am quite sure things would not go well.
This is when an oscilloscope would be handy. You could look at the
waveform at the output of the VCO, at pin 5/24, the output of the VCO to
the radio. You should see a nice sine wave of roughly constant amplitude
when either VCO is selected.
Gary
W0DVN
On Jan 1, 2025, at 1:50?PM, Jim Harris via groups.io <radiove1rb=
[email protected]> wrote:
Gary I tried that ground on RFC505 and no change. Is it not getting band
information?
Jim VE1RB
On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via groups.io <xntrick1948=
[email protected]> wrote:
If you are reading 152 MHz, the you should ground RFC505 on the end away
from the varactor diodes. The frequency should come down.
Gary
W0DVN
On Jan 1, 2025, at 11:58?AM, Jim Harris via groups.io <radiove1rb=
[email protected]> wrote:
Jim maybe this will help. I touched up several solder joints although
they didn¡¯t look good but not cracked. I switched the input to the counter
and it is reading 17 to 18 mhz
<IMG_1166.jpeg>
as the frequency is jumping around so is not locked. I wonder if that is
a clue?
Jim VE1RB
On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via groups.io <radiove1rb=
[email protected]> wrote:
Good ideas Jim and I will get at doing that today. It is windy and
raining here quite hard. A good job inside hi hi. I will let you know how
it goes. Many thanks for the suggestions and help.
Jim VE1RB
On Wed, Jan 1, 2025 at 12:24?PM Jim Shorney via groups.io <jimNU0C=
[email protected]> wrote:
At this point I am suspicious of that 1.3 MHz reading. That may be a
spurious reading. It seems to me that the VCO should not be able to run
there. What is the level of the signal? The frequency determining
components are L502 and the varactor diodes. Resist the temptation to try
to adjust L502. As a long time tech told me back in the dim past, when you
have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the
high VCO circuit under magnification and good lighting. You could have a
failed joint or via. Check the voltages on the three JFETs. C156 or C517
could be suspect. You have a working low VCO to compare voltage and
resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via groups.io" <radiove1rb@...> wrote:
Yes Gary I did the ground on RFC505 when looking at the frequency on the counter and it does drop a lot. So I guess you are saying the High VCO is oscillating at 1.3 MHz . If that is the case there must be
something wrong on that board unless the info it gets is wrong. Hope
this helps. --
73
-Jim
NU0C
-- 73 -Jim NU0C
|
Yes Gary that does interest me a lot. We will talk about that and make a deal I hope. Many thanks for the offer.
Jim VE1RB
On Wed, Jan 1, 2025 at 5:33?PM Gary Follett via <xntrick1948= [email protected]> wrote: You know, the VCO board in the TR7 is the same as the one in the R7. I happen to have a working R7 VCO board if this interests you.
Gary
W0DVN
Okay I will get it out and have a look see.?
Jim VE1RB On Wed, Jan 1, 2025 at 5:28?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: Well, your 30 MHz scope is not entirely useless. Even though the ~80 MHz VCO will be severely attenuated, you should still be able to see it and determine what it looks like That VCO signal is pretty stout at the point at which you are observing it (several volts per to peak).
Gary
W0DVN
Gary the frequency counter is hook to 5/24. I will check the input to the two 5 volt regulators and let you know. I do have ?a scope but it only goes to 30 mhz but I know where I can get a good 100 MHz one. Will get that as soon as I can and have a looks at those outputs. Many thanks Gary for all your help otherwise I would be working in the dark.?
Jim VE1RB On Wed, Jan 1, 2025 at 4:45?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If that oscillator is showing anything real (~152 MHz) then it is being selected. This selection is enacted by the application of +10 volts on U502. The VCO board has no other information about the band selected by the band switch.
The only other information the VCO gets from the outside world comes in via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as well, and is the result of the 40 MHz Reference, the PTO and the VCO signal divided by N (N being the selected number produced by the band selection logic) and this is the signal that closes the PLL loop.
However, even with the loop open and unlocked, the frequency at the output of the VCO should never exceed 80 MHz,?
Where are you measuring the 152 MHz?
If grounding RFC505 on the away end does nothing, try grounding the other end. If still no change, then ground the physical junction at CR511A, B and CR510 A,B. This should pull the frequency down a lot. If not, ground the Drain of Q504 through a capacitor of about 0.01 uF. That should clearly kill any oscillation and remove any output from the VCO.
Then humor me on this one - measure the voltage on the inputs of both 5 volt regulators U501 and U502 when a low band (less than 15 MHz) and a high band (greater than 15 MHz) are selected by the band switch. If there is a switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I would have a hard time deriving what would happen in this condition but I am quite sure things would not go well.
This is when an oscilloscope would be handy. You could look at the waveform at the output of the VCO, at pin 5/24, the output of the VCO to the radio. You should see ?a nice sine wave of roughly constant amplitude when either VCO is selected.
Gary
W0DVN
Gary I tried that ground on RFC505 and no change. Is it not getting band information?
Jim VE1RB On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If you are reading 152 MHz, the you should ground RFC505 on the end away from the varactor diodes. The frequency should come down.
Gary
W0DVN
Jim maybe this will help. I touched up several solder joints although they didn¡¯t look good but not cracked. I switched the input to the counter and it is reading 17 to 18 mhz ?<IMG_1166.jpeg> as the frequency is jumping around so is not locked. I wonder if that is a clue??
Jim VE1RB On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via ??<radiove1rb= [email protected]> wrote: Good ideas Jim and I will get at doing that today. It is windy and raining here quite hard. A good job inside hi hi. I will let you know how it goes. Many thanks for the suggestions?and help.
Jim VE1RB
At this point I am suspicious of that 1.3 MHz reading. That may be a spurious reading. It seems to me that the VCO should not be able to run there. What is the level of the signal? The frequency determining components are L502 and the varactor diodes. Resist the temptation to try to adjust L502. As a long time tech told me back in the dim past, when you have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the high VCO circuit under magnification and good lighting. You could have a failed joint or via. Check the voltages on the three JFETs. C156 or C517 could be suspect. You have a working low VCO to compare voltage and resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via?" <radiove1rb=[email protected]> wrote:
> Yes Gary I did the ground on RFC505? when looking at the frequency on?
> the counter and it does drop a lot. So I guess you are saying the High?
> VCO is oscillating at 1.3 MHz . If that is the case there must be?
> something wrong on that board unless the info it gets is wrong. Hope?
> this helps.
--?
73
-Jim
NU0C
|
Thank you for that info! You are 100% right about the MS-4 in stock form (its fidelity is pitiful though). I am more of an SWL type person, which is what motivated me to make changes to the MS-4. A less efficient speaker (larger voice coil and magnet) yet with a much better low, mid, and high range response, coupled with about 11 watts RMS of power, and changes to the cabinet making it masquerade as more of a tuned enclosure really made a drastic difference. Incidentally, the MS-4 easily goes below 100Hz now, and at times if I tune across some "hifi" hams, they are so overcompensating for the lack of response in everyone else's system, it makes my R4C about jump off the speaker with low frequency rumble. That is NOT a criticism of the hifi guys at all, just an empirical observation. Some of them sound like wide FM using the C-line, as those changes coupled with Frank's 2.8 filter really get it done.
If you have any solid ideas for changes in the noise blanker for the R4C I would listen. Its OK yet still is very limited.
CHEERS!
Joseph
On Wednesday, January 1, 2025 at 03:36:36 PM EST, Rob Sherwood via groups.io <rob@...> wrote:
Hi Joseph,
?
Initially I duplicated the low frequency roll-off of the stock amp, but later changed the input roll-off to be minimal.? I see a typo in the attached schematic.
The output coupling electrolytic C1 should say 330 uF not us.? That is likely the dominant cause of low frequency roll-off. ?The 330 uF could be increased to 470 uF or even 1000 uF, but I don¡¯t know whether an MS-4 speaker would produce any additional low
frequency audio.? Headphones would be a different matter.? I doubt there is any need to increase C2 in the feedback circuit, but I have never experimented with trying to extend the low end.?
?
I happen to use Icom SP-20 speakers on all my rigs, and while it reproduces 150 Hz quite well, it is really falling off at 100 Hz.
?
Rob, NC0B
?
From: [email protected] [mailto:[email protected]]
On Behalf Of Joseph K7CBR via groups.io
Sent: Wednesday, January 01, 2025 11:32 AM
To: [email protected]
Subject: [DRAKE-RADIO] AMP-4
?
Mr. Rob... Can you please remind me what the low frequency attenuation was for your AMP-4? Thanks!
On Wednesday, January 1, 2025 at 12:59:27 PM EST, Rob Sherwood via groups.io <rob@...> wrote:
My AMP-4 feedback loop was designed for about a 3 dB roll-off at 3 kHz.? Personal choice.? Rob, NC0B
> On Jan 1, 2025, at 10:10?AM, Jim Shorney via groups.io <jimNU0C@...> wrote:
>
> ?
|
Re: VE3EFJ third mixer mod for the R4C
Thank you, Paul, for the extended explanation.
Bob K9JU
On Wednesday, January 1, 2025 at 04:28:46 PM EST, Paul Christensen via groups.io <w9ac@...> wrote:
>Another change is to the Zobel network resistance. This network is the series R/C circuit between the output of the amplifier and circuit common (ground). It provides a resistive load for >stability of the amplifier at higher frequencies when encountering inductive loads (e.g., the speaker and the speaker leads). ? The network also helps to stabilize the amplifier from oscillating when switching loads between speaker and headphones -- especially if there¡¯s an open circuit condition at any moment between switching the loads.? ? Paul, W9AC
|
You know, the VCO board in the TR7 is the same as the one in the R7. I happen to have a working R7 VCO board if this interests you.
Gary
toggle quoted message
Show quoted text
On Jan 1, 2025, at 3:30?PM, Jim Harris via groups.io <radiove1rb@...> wrote:
Okay I will get it out and have a look see.?
Jim VE1RB On Wed, Jan 1, 2025 at 5:28?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: Well, your 30 MHz scope is not entirely useless. Even though the ~80 MHz VCO will be severely attenuated, you should still be able to see it and determine what it looks like That VCO signal is pretty stout at the point at which you are observing it (several volts per to peak).
Gary
W0DVN
Gary the frequency counter is hook to 5/24. I will check the input to the two 5 volt regulators and let you know. I do have ?a scope but it only goes to 30 mhz but I know where I can get a good 100 MHz one. Will get that as soon as I can and have a looks at those outputs. Many thanks Gary for all your help otherwise I would be working in the dark.?
Jim VE1RB On Wed, Jan 1, 2025 at 4:45?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If that oscillator is showing anything real (~152 MHz) then it is being selected. This selection is enacted by the application of +10 volts on U502. The VCO board has no other information about the band selected by the band switch.
The only other information the VCO gets from the outside world comes in via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as well, and is the result of the 40 MHz Reference, the PTO and the VCO signal divided by N (N being the selected number produced by the band selection logic) and this is the signal that closes the PLL loop.
However, even with the loop open and unlocked, the frequency at the output of the VCO should never exceed 80 MHz,?
Where are you measuring the 152 MHz?
If grounding RFC505 on the away end does nothing, try grounding the other end. If still no change, then ground the physical junction at CR511A, B and CR510 A,B. This should pull the frequency down a lot. If not, ground the Drain of Q504 through a capacitor of about 0.01 uF. That should clearly kill any oscillation and remove any output from the VCO.
Then humor me on this one - measure the voltage on the inputs of both 5 volt regulators U501 and U502 when a low band (less than 15 MHz) and a high band (greater than 15 MHz) are selected by the band switch. If there is a switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I would have a hard time deriving what would happen in this condition but I am quite sure things would not go well.
This is when an oscilloscope would be handy. You could look at the waveform at the output of the VCO, at pin 5/24, the output of the VCO to the radio. You should see ?a nice sine wave of roughly constant amplitude when either VCO is selected.
Gary
W0DVN
Gary I tried that ground on RFC505 and no change. Is it not getting band information?
Jim VE1RB On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If you are reading 152 MHz, the you should ground RFC505 on the end away from the varactor diodes. The frequency should come down.
Gary
W0DVN
Jim maybe this will help. I touched up several solder joints although they didn¡¯t look good but not cracked. I switched the input to the counter and it is reading 17 to 18 mhz ?<IMG_1166.jpeg> as the frequency is jumping around so is not locked. I wonder if that is a clue??
Jim VE1RB On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via ??<radiove1rb= [email protected]> wrote: Good ideas Jim and I will get at doing that today. It is windy and raining here quite hard. A good job inside hi hi. I will let you know how it goes. Many thanks for the suggestions?and help.
Jim VE1RB
At this point I am suspicious of that 1.3 MHz reading. That may be a spurious reading. It seems to me that the VCO should not be able to run there. What is the level of the signal? The frequency determining components are L502 and the varactor diodes. Resist the temptation to try to adjust L502. As a long time tech told me back in the dim past, when you have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the high VCO circuit under magnification and good lighting. You could have a failed joint or via. Check the voltages on the three JFETs. C156 or C517 could be suspect. You have a working low VCO to compare voltage and resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via?" <radiove1rb=[email protected]> wrote:
> Yes Gary I did the ground on RFC505? when looking at the frequency on?
> the counter and it does drop a lot. So I guess you are saying the High?
> VCO is oscillating at 1.3 MHz . If that is the case there must be?
> something wrong on that board unless the info it gets is wrong. Hope?
> this helps.
--?
73
-Jim
NU0C
|
Okay I will get it out and have a look see.?
Jim VE1RB
On Wed, Jan 1, 2025 at 5:28?PM Gary Follett via <xntrick1948= [email protected]> wrote: Well, your 30 MHz scope is not entirely useless. Even though the ~80 MHz VCO will be severely attenuated, you should still be able to see it and determine what it looks like That VCO signal is pretty stout at the point at which you are observing it (several volts per to peak).
Gary
W0DVN
Gary the frequency counter is hook to 5/24. I will check the input to the two 5 volt regulators and let you know. I do have ?a scope but it only goes to 30 mhz but I know where I can get a good 100 MHz one. Will get that as soon as I can and have a looks at those outputs. Many thanks Gary for all your help otherwise I would be working in the dark.?
Jim VE1RB On Wed, Jan 1, 2025 at 4:45?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If that oscillator is showing anything real (~152 MHz) then it is being selected. This selection is enacted by the application of +10 volts on U502. The VCO board has no other information about the band selected by the band switch.
The only other information the VCO gets from the outside world comes in via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as well, and is the result of the 40 MHz Reference, the PTO and the VCO signal divided by N (N being the selected number produced by the band selection logic) and this is the signal that closes the PLL loop.
However, even with the loop open and unlocked, the frequency at the output of the VCO should never exceed 80 MHz,?
Where are you measuring the 152 MHz?
If grounding RFC505 on the away end does nothing, try grounding the other end. If still no change, then ground the physical junction at CR511A, B and CR510 A,B. This should pull the frequency down a lot. If not, ground the Drain of Q504 through a capacitor of about 0.01 uF. That should clearly kill any oscillation and remove any output from the VCO.
Then humor me on this one - measure the voltage on the inputs of both 5 volt regulators U501 and U502 when a low band (less than 15 MHz) and a high band (greater than 15 MHz) are selected by the band switch. If there is a switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I would have a hard time deriving what would happen in this condition but I am quite sure things would not go well.
This is when an oscilloscope would be handy. You could look at the waveform at the output of the VCO, at pin 5/24, the output of the VCO to the radio. You should see ?a nice sine wave of roughly constant amplitude when either VCO is selected.
Gary
W0DVN
Gary I tried that ground on RFC505 and no change. Is it not getting band information?
Jim VE1RB On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If you are reading 152 MHz, the you should ground RFC505 on the end away from the varactor diodes. The frequency should come down.
Gary
W0DVN
Jim maybe this will help. I touched up several solder joints although they didn¡¯t look good but not cracked. I switched the input to the counter and it is reading 17 to 18 mhz ?<IMG_1166.jpeg> as the frequency is jumping around so is not locked. I wonder if that is a clue??
Jim VE1RB On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via ??<radiove1rb= [email protected]> wrote: Good ideas Jim and I will get at doing that today. It is windy and raining here quite hard. A good job inside hi hi. I will let you know how it goes. Many thanks for the suggestions?and help.
Jim VE1RB
At this point I am suspicious of that 1.3 MHz reading. That may be a spurious reading. It seems to me that the VCO should not be able to run there. What is the level of the signal? The frequency determining components are L502 and the varactor diodes. Resist the temptation to try to adjust L502. As a long time tech told me back in the dim past, when you have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the high VCO circuit under magnification and good lighting. You could have a failed joint or via. Check the voltages on the three JFETs. C156 or C517 could be suspect. You have a working low VCO to compare voltage and resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via?" <radiove1rb=[email protected]> wrote:
> Yes Gary I did the ground on RFC505? when looking at the frequency on?
> the counter and it does drop a lot. So I guess you are saying the High?
> VCO is oscillating at 1.3 MHz . If that is the case there must be?
> something wrong on that board unless the info it gets is wrong. Hope?
> this helps.
--?
73
-Jim
NU0C
|
Well, your 30 MHz scope is not entirely useless. Even though the ~80 MHz VCO will be severely attenuated, you should still be able to see it and determine what it looks like That VCO signal is pretty stout at the point at which you are observing it (several volts per to peak).
Gary
toggle quoted message
Show quoted text
On Jan 1, 2025, at 3:24?PM, Jim Harris via groups.io <radiove1rb@...> wrote:
Gary the frequency counter is hook to 5/24. I will check the input to the two 5 volt regulators and let you know. I do have ?a scope but it only goes to 30 mhz but I know where I can get a good 100 MHz one. Will get that as soon as I can and have a looks at those outputs. Many thanks Gary for all your help otherwise I would be working in the dark.?
Jim VE1RB On Wed, Jan 1, 2025 at 4:45?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If that oscillator is showing anything real (~152 MHz) then it is being selected. This selection is enacted by the application of +10 volts on U502. The VCO board has no other information about the band selected by the band switch.
The only other information the VCO gets from the outside world comes in via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as well, and is the result of the 40 MHz Reference, the PTO and the VCO signal divided by N (N being the selected number produced by the band selection logic) and this is the signal that closes the PLL loop.
However, even with the loop open and unlocked, the frequency at the output of the VCO should never exceed 80 MHz,?
Where are you measuring the 152 MHz?
If grounding RFC505 on the away end does nothing, try grounding the other end. If still no change, then ground the physical junction at CR511A, B and CR510 A,B. This should pull the frequency down a lot. If not, ground the Drain of Q504 through a capacitor of about 0.01 uF. That should clearly kill any oscillation and remove any output from the VCO.
Then humor me on this one - measure the voltage on the inputs of both 5 volt regulators U501 and U502 when a low band (less than 15 MHz) and a high band (greater than 15 MHz) are selected by the band switch. If there is a switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I would have a hard time deriving what would happen in this condition but I am quite sure things would not go well.
This is when an oscilloscope would be handy. You could look at the waveform at the output of the VCO, at pin 5/24, the output of the VCO to the radio. You should see ?a nice sine wave of roughly constant amplitude when either VCO is selected.
Gary
W0DVN
Gary I tried that ground on RFC505 and no change. Is it not getting band information?
Jim VE1RB On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If you are reading 152 MHz, the you should ground RFC505 on the end away from the varactor diodes. The frequency should come down.
Gary
W0DVN
Jim maybe this will help. I touched up several solder joints although they didn¡¯t look good but not cracked. I switched the input to the counter and it is reading 17 to 18 mhz ?<IMG_1166.jpeg> as the frequency is jumping around so is not locked. I wonder if that is a clue??
Jim VE1RB On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via ??<radiove1rb= [email protected]> wrote: Good ideas Jim and I will get at doing that today. It is windy and raining here quite hard. A good job inside hi hi. I will let you know how it goes. Many thanks for the suggestions?and help.
Jim VE1RB
At this point I am suspicious of that 1.3 MHz reading. That may be a spurious reading. It seems to me that the VCO should not be able to run there. What is the level of the signal? The frequency determining components are L502 and the varactor diodes. Resist the temptation to try to adjust L502. As a long time tech told me back in the dim past, when you have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the high VCO circuit under magnification and good lighting. You could have a failed joint or via. Check the voltages on the three JFETs. C156 or C517 could be suspect. You have a working low VCO to compare voltage and resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via?" <radiove1rb=[email protected]> wrote:
> Yes Gary I did the ground on RFC505? when looking at the frequency on?
> the counter and it does drop a lot. So I guess you are saying the High?
> VCO is oscillating at 1.3 MHz . If that is the case there must be?
> something wrong on that board unless the info it gets is wrong. Hope?
> this helps.
--?
73
-Jim
NU0C
|
Re: VE3EFJ third mixer mod for the R4C
>Another change is to the Zobel network resistance. This network is the series R/C circuit between the output of the amplifier and circuit common (ground). It provides a resistive load for >stability of the amplifier at higher frequencies when encountering inductive loads (e.g., the speaker and the speaker leads). ? The network also helps to stabilize the amplifier from oscillating when switching loads between speaker and headphones -- especially if there¡¯s an open circuit condition at any moment between switching the loads.? ? Paul, W9AC
|
Gary the frequency counter is hook to 5/24. I will check the input to the two 5 volt regulators and let you know. I do have ?a scope but it only goes to 30 mhz but I know where I can get a good 100 MHz one. Will get that as soon as I can and have a looks at those outputs. Many thanks Gary for all your help otherwise I would be working in the dark.?
Jim VE1RB
On Wed, Jan 1, 2025 at 4:45?PM Gary Follett via <xntrick1948= [email protected]> wrote: If that oscillator is showing anything real (~152 MHz) then it is being selected. This selection is enacted by the application of +10 volts on U502. The VCO board has no other information about the band selected by the band switch.
The only other information the VCO gets from the outside world comes in via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as well, and is the result of the 40 MHz Reference, the PTO and the VCO signal divided by N (N being the selected number produced by the band selection logic) and this is the signal that closes the PLL loop.
However, even with the loop open and unlocked, the frequency at the output of the VCO should never exceed 80 MHz,?
Where are you measuring the 152 MHz?
If grounding RFC505 on the away end does nothing, try grounding the other end. If still no change, then ground the physical junction at CR511A, B and CR510 A,B. This should pull the frequency down a lot. If not, ground the Drain of Q504 through a capacitor of about 0.01 uF. That should clearly kill any oscillation and remove any output from the VCO.
Then humor me on this one - measure the voltage on the inputs of both 5 volt regulators U501 and U502 when a low band (less than 15 MHz) and a high band (greater than 15 MHz) are selected by the band switch. If there is a switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I would have a hard time deriving what would happen in this condition but I am quite sure things would not go well.
This is when an oscilloscope would be handy. You could look at the waveform at the output of the VCO, at pin 5/24, the output of the VCO to the radio. You should see ?a nice sine wave of roughly constant amplitude when either VCO is selected.
Gary
W0DVN
Gary I tried that ground on RFC505 and no change. Is it not getting band information?
Jim VE1RB On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If you are reading 152 MHz, the you should ground RFC505 on the end away from the varactor diodes. The frequency should come down.
Gary
W0DVN
Jim maybe this will help. I touched up several solder joints although they didn¡¯t look good but not cracked. I switched the input to the counter and it is reading 17 to 18 mhz ?<IMG_1166.jpeg> as the frequency is jumping around so is not locked. I wonder if that is a clue??
Jim VE1RB On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via ??<radiove1rb= [email protected]> wrote: Good ideas Jim and I will get at doing that today. It is windy and raining here quite hard. A good job inside hi hi. I will let you know how it goes. Many thanks for the suggestions?and help.
Jim VE1RB
At this point I am suspicious of that 1.3 MHz reading. That may be a spurious reading. It seems to me that the VCO should not be able to run there. What is the level of the signal? The frequency determining components are L502 and the varactor diodes. Resist the temptation to try to adjust L502. As a long time tech told me back in the dim past, when you have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the high VCO circuit under magnification and good lighting. You could have a failed joint or via. Check the voltages on the three JFETs. C156 or C517 could be suspect. You have a working low VCO to compare voltage and resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via?" <radiove1rb=[email protected]> wrote:
> Yes Gary I did the ground on RFC505? when looking at the frequency on?
> the counter and it does drop a lot. So I guess you are saying the High?
> VCO is oscillating at 1.3 MHz . If that is the case there must be?
> something wrong on that board unless the info it gets is wrong. Hope?
> this helps.
--?
73
-Jim
NU0C
|
Re: VE3EFJ third mixer mod for the R4C
Many years ago, I designed a PC board for the TDA 2003 Audio Amplifier. Like some have noted, the hiss level was/is a bit too high if you listen when wearing "cans."?
The spec sheet has the device setup for ~40-dB of voltage gain set by the ratio of two resistors, one from the output to the "-" input (call it R1) and the other from the "-" lead to circuit common (call it R2). Circuit common is typically called ground. Note that for simplification, I am ignoring any dc blocking capacitors in the circuit. The audio input from the Volume/AF Gain control is to the "+" input of the device so the voltage gain is 1 + R1/R2.
By changing the ratio of the resistors to reduce the gain to approximately 20-dB. That makes a lot of difference in the amount of hiss heard when wearing headphones. This assumes there is plenty of drive for the lower gain amplifier which is proper audio design in my estimation. To me, the TR7 is a great example of a horribly designed audio amplification system!
Another change is to the Zobel network resistance. This network is the series R/C circuit between the output of the amplifier and circuit common (ground). It provides a resistive load for stability of the amplifier at higher frequencies when encountering inductive loads (e.g., the speaker and the speaker leads). One spec sheet suggested keeping the R value of the network to no more than 1-Ohm else possible instability of the IC amplifier.?
By the way, if my explanation of the Zobel network utility is incorrect, would someone provide a better explanation.?
FYI, Caveat Emptor and Your Mileage May Vary!
Bob Loving K9JU
Maryville, TN
On Wednesday, January 1, 2025 at 02:29:26 PM EST, Paul Christensen via groups.io <w9ac@...> wrote:
>I've seen that board on Osh Park. I like the purple one. ?
Jim, thanks for the reminder.? Wow, Oshpark now wants USD $53.60 per 3-board order.? It's much less expensive through JLCPCB at USD $3.50 for five boards and includes Global Standard Postal (i.e., slow) shipping.? The attached .ZIP Gerber file of the R4 amp board can be uploaded to JLCPCB.? HOWEVER, for anyone even remotely interested, I don't have a B.O.M. in a nicely formatted file.? That will happen but not in the next several weeks.?
Paul, W9AC
|
If that oscillator is showing anything real (~152 MHz) then it is being selected. This selection is enacted by the application of +10 volts on U502. The VCO board has no other information about the band selected by the band switch.
The only other information the VCO gets from the outside world comes in via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as well, and is the result of the 40 MHz Reference, the PTO and the VCO signal divided by N (N being the selected number produced by the band selection logic) and this is the signal that closes the PLL loop.
However, even with the loop open and unlocked, the frequency at the output of the VCO should never exceed 80 MHz,?
Where are you measuring the 152 MHz?
If grounding RFC505 on the away end does nothing, try grounding the other end. If still no change, then ground the physical junction at CR511A, B and CR510 A,B. This should pull the frequency down a lot. If not, ground the Drain of Q504 through a capacitor of about 0.01 uF. That should clearly kill any oscillation and remove any output from the VCO.
Then humor me on this one - measure the voltage on the inputs of both 5 volt regulators U501 and U502 when a low band (less than 15 MHz) and a high band (greater than 15 MHz) are selected by the band switch. If there is a switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I would have a hard time deriving what would happen in this condition but I am quite sure things would not go well.
This is when an oscilloscope would be handy. You could look at the waveform at the output of the VCO, at pin 5/24, the output of the VCO to the radio. You should see ?a nice sine wave of roughly constant amplitude when either VCO is selected.
Gary
W0DVN
toggle quoted message
Show quoted text
On Jan 1, 2025, at 1:50?PM, Jim Harris via groups.io <radiove1rb@...> wrote:
Gary I tried that ground on RFC505 and no change. Is it not getting band information?
Jim VE1RB On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via ??<xntrick1948= [email protected]> wrote: If you are reading 152 MHz, the you should ground RFC505 on the end away from the varactor diodes. The frequency should come down.
Gary
W0DVN
Jim maybe this will help. I touched up several solder joints although they didn¡¯t look good but not cracked. I switched the input to the counter and it is reading 17 to 18 mhz ?<IMG_1166.jpeg> as the frequency is jumping around so is not locked. I wonder if that is a clue??
Jim VE1RB On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via ??<radiove1rb= [email protected]> wrote: Good ideas Jim and I will get at doing that today. It is windy and raining here quite hard. A good job inside hi hi. I will let you know how it goes. Many thanks for the suggestions?and help.
Jim VE1RB
At this point I am suspicious of that 1.3 MHz reading. That may be a spurious reading. It seems to me that the VCO should not be able to run there. What is the level of the signal? The frequency determining components are L502 and the varactor diodes. Resist the temptation to try to adjust L502. As a long time tech told me back in the dim past, when you have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the high VCO circuit under magnification and good lighting. You could have a failed joint or via. Check the voltages on the three JFETs. C156 or C517 could be suspect. You have a working low VCO to compare voltage and resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via?" <radiove1rb=[email protected]> wrote:
> Yes Gary I did the ground on RFC505? when looking at the frequency on?
> the counter and it does drop a lot. So I guess you are saying the High?
> VCO is oscillating at 1.3 MHz . If that is the case there must be?
> something wrong on that board unless the info it gets is wrong. Hope?
> this helps.
--?
73
-Jim
NU0C
|
Hi Joseph,
?
Initially I duplicated the low frequency roll-off of the stock amp, but later changed the input roll-off to be minimal.? I see a typo in the attached schematic.
The output coupling electrolytic C1 should say 330 uF not us.? That is likely the dominant cause of low frequency roll-off. ?The 330 uF could be increased to 470 uF or even 1000 uF, but I don¡¯t know whether an MS-4 speaker would produce any additional low
frequency audio.? Headphones would be a different matter.? I doubt there is any need to increase C2 in the feedback circuit, but I have never experimented with trying to extend the low end.?
?
I happen to use Icom SP-20 speakers on all my rigs, and while it reproduces 150 Hz quite well, it is really falling off at 100 Hz.
?
Rob, NC0B
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Joseph K7CBR via groups.io
Sent: Wednesday, January 01, 2025 11:32 AM
To: [email protected]
Subject: [DRAKE-RADIO] AMP-4
?
Mr. Rob... Can you please remind me what the low frequency attenuation was for your AMP-4? Thanks!
On Wednesday, January 1, 2025 at 12:59:27 PM EST, Rob Sherwood via groups.io <rob@...> wrote:
My AMP-4 feedback loop was designed for about a 3 dB roll-off at 3 kHz.? Personal choice.? Rob, NC0B
> On Jan 1, 2025, at 10:10?AM, Jim Shorney via groups.io <jimNU0C@...> wrote:
>
> ?
|
Gary I tried that ground on RFC505 and no change. Is it not getting band information?
Jim VE1RB
On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via <xntrick1948= [email protected]> wrote: If you are reading 152 MHz, the you should ground RFC505 on the end away from the varactor diodes. The frequency should come down.
Gary
W0DVN
Jim maybe this will help. I touched up several solder joints although they didn¡¯t look good but not cracked. I switched the input to the counter and it is reading 17 to 18 mhz ?<IMG_1166.jpeg> as the frequency is jumping around so is not locked. I wonder if that is a clue??
Jim VE1RB On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via ??<radiove1rb= [email protected]> wrote: Good ideas Jim and I will get at doing that today. It is windy and raining here quite hard. A good job inside hi hi. I will let you know how it goes. Many thanks for the suggestions?and help.
Jim VE1RB
At this point I am suspicious of that 1.3 MHz reading. That may be a spurious reading. It seems to me that the VCO should not be able to run there. What is the level of the signal? The frequency determining components are L502 and the varactor diodes. Resist the temptation to try to adjust L502. As a long time tech told me back in the dim past, when you have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the high VCO circuit under magnification and good lighting. You could have a failed joint or via. Check the voltages on the three JFETs. C156 or C517 could be suspect. You have a working low VCO to compare voltage and resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via?" <radiove1rb=[email protected]> wrote:
> Yes Gary I did the ground on RFC505? when looking at the frequency on?
> the counter and it does drop a lot. So I guess you are saying the High?
> VCO is oscillating at 1.3 MHz . If that is the case there must be?
> something wrong on that board unless the info it gets is wrong. Hope?
> this helps.
--?
73
-Jim
NU0C
|
Okay Gary I will go do that right now.?
Jim VE1RB
On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via <xntrick1948= [email protected]> wrote: If you are reading 152 MHz, the you should ground RFC505 on the end away from the varactor diodes. The frequency should come down.
Gary
W0DVN
Jim maybe this will help. I touched up several solder joints although they didn¡¯t look good but not cracked. I switched the input to the counter and it is reading 17 to 18 mhz ?<IMG_1166.jpeg> as the frequency is jumping around so is not locked. I wonder if that is a clue??
Jim VE1RB On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via ??<radiove1rb= [email protected]> wrote: Good ideas Jim and I will get at doing that today. It is windy and raining here quite hard. A good job inside hi hi. I will let you know how it goes. Many thanks for the suggestions?and help.
Jim VE1RB
At this point I am suspicious of that 1.3 MHz reading. That may be a spurious reading. It seems to me that the VCO should not be able to run there. What is the level of the signal? The frequency determining components are L502 and the varactor diodes. Resist the temptation to try to adjust L502. As a long time tech told me back in the dim past, when you have a failure "it is never the alignment".
At this point I think I would inspect the solder connections in the high VCO circuit under magnification and good lighting. You could have a failed joint or via. Check the voltages on the three JFETs. C156 or C517 could be suspect. You have a working low VCO to compare voltage and resistance readings to.
On Wed, 1 Jan 2025 07:41:18 -0400
"Jim Harris via?" <radiove1rb=[email protected]> wrote:
> Yes Gary I did the ground on RFC505? when looking at the frequency on?
> the counter and it does drop a lot. So I guess you are saying the High?
> VCO is oscillating at 1.3 MHz . If that is the case there must be?
> something wrong on that board unless the info it gets is wrong. Hope?
> this helps.
--?
73
-Jim
NU0C
|
Floyd - K8AC
Jim Shorney
Paul Christensen
Rob Sherwood