Re: help on finding a subsitute for a blown feedthru cap please
Jim:
Answered this one yesterday....guess you didn't see it.
The four feedthroughs in your pic are all .001 uf? @? 350VDC.? K4OAH's Service Manuals tell us this kind of info and are highly recommended.? Available at K4OAH.com from Garery's wife.? Sadly we lost him in 2018.
However...the hole to the right of those four feedthroughs is missing the?+650 VDC lead which passes through a small piece of plastic tubing that should be in that hole.? I believe the original was a short piece of bare wire with a tiny loop at each end which helped to hold the insulator in place in that hole.? The insulator needs to be capable of handling the high voltage that?runs to the anodes of the 6JB6 finals.? I don't see the wire from the C-J connector on the back of the radio, but perhaps it is out of the picture?? FWIW, the original insulator was black in color, should originality be of concern.
73 Peter VE7PS
working on a T4X transmitter shown here
?
any help please ?
?
Thank you - de W6TTY
?
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Whentuning up my TR-4C, slowing increasing XMTR GAIN and peaking RF TUNE, there is a strange BLOP sound? from the speaker. Please see the attached video clip.
I suspected selfoscillation or a leak somewhere. First I checked the bandswitch and groundings, then I did the Mixer and RF Alignment before proceeding to Carrier Balance Alignment. Tubes were swopped one at a time, screen caps in the PA were replaced, and so were C61 between driver and PA and C129 on the wiper of carrier balance control (R85). Diodes in T14 were recently replaced.
Any idea where to look?
Thanks.
Peter OZ8CTH
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Re: R4C Sherwood audio mod questions
Sounds as if one of you has actually rotated the transformer 90 degrees.? I just took a look at that area of the receiver and decided that task ranks right up there with removing your own appendix.? I wonder if it wouldn't be possible to shield the PTO can with mumetal?? I have no idea what the material is like to work with, but it seems to be readily available.? And thanks for the comments on the capacitor value.? I'll finish getting my version of the AMP-4 board installed today and hopefully I'll have audio output.
?
73, Floyd - K8AC
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Re: R4C Sherwood audio mod questions
&²µ³Ù;¡±It is tedious to rotate the R-4C power transformer 90 degrees, but it really makes a difference.¡±? ? For the curious, the magnetic field created within the transformer couples to the PTO which is located directly in front of the transformer.? The field produced is much stronger in one orientation. ? ? As the R-4C dial is turned from 0 to 500 kHz, the PTO¡¯s ferrite slug moves closer to the transformer which results in even greater field coupling.? Audio from the crystal calibrator at 0 is cleaner than it is at 500 where a ¡°fuzzy¡± sounding carrier is heard.? That fuzziness is created by the 60 cycle sidebands shown in Rob¡¯s PowerPoint slides. ? Paul, W9AC ?
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Thanks Jim for the ideas. I had started the alignment and when I got to the BFO I could not get the frequency down to the correct frequency. So I am going to order a new crystal and replace iut?and hope for the best so I will eventually complete the alignment. I should have thought of that.?
Jim VE1RB
First thought was that you have the Calibrator button depressed but that should be obvious because you could tune away from it with the VFO. As much as you have been digging around in there you may have knocked some adjustments off. I would do the frequency alignment starting at section 3-1 (10V adjustment) and proceeding through section 3-6 in the service manual. The fixed passband pots in 3-6 are particularly prone to getting bumped and some ops have replaced them with 10 turn trimpots. But I recommend the full frequency alignment so you know everything is correct.
On Sat, 4 Jan 2025 17:38:15 -0400
"Jim Harris via " <radiove1rb=[email protected]> wrote:
> yes it was a very pleasant surprised when I turned it on and it worked, The
> problem I have now id that when i SWITCH FROM lsb OR usB TO cw i get a
> signal in the receiver 5 over 9 and if I press the morse key I hear the
> tone as well. It does not seem to mute that signal. I also noticed that if
> I use the PBT I can hear a tone and can swing the passband and I can go
> back and forth past it. Almost sounds like an oscillation. Any ideas?
> Thanks,
>
> Jim VE1RB
--
73
-Jim
NU0C
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help on finding a subsitute for a blown feedthru cap please
working on a T4X transmitter shown here
?
any help please ?
?
Thank you - de W6TTY
?
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You pretty well covered it. I was thinking also tube pins and receptacles and overall screw tightness in the plate circuit (including anode caps). It may look minty but we don't know how well it was treated when actually used. On Sun, 5 Jan 2025 03:44:29 +0000 (UTC) "Evan via groups.io" <k9sqg@...> wrote: Roger,
If it were me, I'd start by using a quality dummy load, and then measure the SWR on the input to the amp. ?Then I would make a visual inspection of the input/output bandswitch contacts along with the fixed capacitors that are part of the tuned output circuits. ?A complete visual inspection of all components in the RF deck is warranted, especially the tapped RF choke in the plate circuit.
Too, it might be helpful to log grid current for each band during testing, along with plate current, to establish a baseline for correcting problems. ? I would not recommend updating the power supply until basic operation is established. ?Too, you might want to think about a soft key interface for the PTT line.
The experts on the Reflector will be able to give you better advice as well.
73,
Evan, K9SQG
On Saturday, January 4, 2025 at 10:35:42 PM EST, Roger KW4EMF <rogerlhill@...> wrote:
I want to get my L7 going. Yes I know the voltages will kill you. I purchased the amp at a hamfest. It looks to be all original and in almost mint condition. The amp worked somewhat but the output seemed to be low except on 20 meters. It was around 1400 watts on 20 and around 400 watts on 40 and 80 meters. Now you cannot even tune it on 40 and 80 but can still get around 400 watts on 20 meters. The plate voltage didn't change. I have 2600 volts according to the meter on the amp. Just trying to decide where to start the trouble shooting process. I have a Harbach kit to go in the power supply to replace all those old capacitors but I don't think that is going to fix my issue.?Thanks?RogerKW4EMF -- 73 -Jim NU0C
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Roger,
If it were me, I'd start by using a quality dummy load, and then measure the SWR on the input to the amp. ?Then I would make a visual inspection of the input/output bandswitch contacts along with the fixed capacitors that are part of the tuned output circuits. ?A complete visual inspection of all components in the RF deck is warranted, especially the tapped RF choke in the plate circuit.
Too, it might be helpful to log grid current for each band during testing, along with plate current, to establish a baseline for correcting problems. ? I would not recommend updating the power supply until basic operation is established. ?Too, you might want to think about a soft key interface for the PTT line.
The experts on the Reflector will be able to give you better advice as well.
73,
Evan, K9SQG
I want to get my L7 going. Yes I know the voltages will kill you. I purchased the amp at a hamfest. It looks to be all original and in almost mint condition. The amp worked somewhat but the output seemed to be low except on 20 meters. It was around 1400 watts on 20 and around 400 watts on 40 and 80 meters. Now you cannot even tune it on 40 and 80 but can still get around 400 watts on 20 meters. The plate voltage didn't change. I have 2600 volts according to the meter on the amp. Just trying to decide where to start the trouble shooting process. I have a Harbach kit to go in the power supply to replace all those old capacitors but I don't think that is going to fix my issue.?
Thanks?
Roger
KW4EMF
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I want to get my L7 going. Yes I know the voltages will kill you. I purchased the amp at a hamfest. It looks to be all original and in almost mint condition. The amp worked somewhat but the output seemed to be low except on 20 meters. It was around 1400 watts on 20 and around 400 watts on 40 and 80 meters. Now you cannot even tune it on 40 and 80 but can still get around 400 watts on 20 meters. The plate voltage didn't change. I have 2600 volts according to the meter on the amp. Just trying to decide where to start the trouble shooting process. I have a Harbach kit to go in the power supply to replace all those old capacitors but I don't think that is going to fix my issue.?
Thanks?
Roger
KW4EMF
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Re: R4C Sherwood audio mod questions
Hi Paul,
?
I was reviewing my 2012 Hamvention Drake Forum presentation and came across a picture of the AMP-4 in my R-4C.? The inverting input has a 220 uF capacitor installed.?
There may well be some AMP-4s with 330 uF capacitors for the inverting input.
?
The bulk of the attached Drake presentation deals with drastically reducing the line-related sidebands on the R-4C PTO.? I know you and I found this solution
independently about the same time, likely in 2011.? R-4C owners may find this attached document interesting.?
?
It is tedious to rotate the R-4C power transformer 90 degrees, but it really makes a difference.? A hole punch makes the job mechanically easy even if there
is a good bit of work removing and reinstalling the wires.
?
We will likely never know why Drake mounted the transformer properly in the R-4, R-4A and R-4B, but mounted it incorrectly in the R-4C.
?
73, Rob, NC0B
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Paul Christensen via groups.io
Sent: Saturday, January 04, 2025 6:52 AM
To: [email protected]
Subject: Re: [DRAKE-RADIO] R4C Sherwood audio mod questions
?
On Sat, Jan 4, 2025 at 05:19 AM, Floyd - K8AC wrote:
>The text specifies the inverting input capacitor as 200 uF while the schematic shows it as 330 uF.
The computed -3 dB high-pass turnover frequency is 123 Hz for 330 uF, and 204 Hz for 200 uF.? Pick either one based on personal roll-off preference.
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Re: Another Mistake: L7 HV calibration pot ?
The pot is on the inside, accessible though the hole. It is at the low side of the dropping resistor string but yes, always use an insulated tool when anywhere near high voltages. You are poking a sleeping rattlesnake. The bottom side interlock is a microswitch in the AC line at one edge of the chassis bottom. It breaks the line when you take the bottom cover off. You can defeat it by slipping something under the edge of the chassis that is thick enough to activate it. The HV interlock is the vertical rod in the left rear corner behind the tubes. You can either set something heavy enough to push it down across that corner or you can insert an insulating material that can withstand full HV between the contacts that short together when the rod is up. Again, be VERY careful. This thing can kill you. Or if you are lucky it could only hurt you really bad. On Sun, 5 Jan 2025 00:59:47 +0000 (UTC) "amfone via groups.io" <amfone20000@...> wrote: Jim so how do I disable the interlocks with the top cover off? And the adjustment pot is on the back panel near the fan cover inside of the chassis or outside and is it hot as in use an insulated tool?
Thanks Tim -- 73 -Jim NU0C
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Re: Another Mistake: L7 HV calibration pot ?
There are two interlocks on the L7 RF deck. ?One on the top and one the bottom, right side.
Jim so how do I disable the interlocks with the top cover off? And the adjustment pot is on the back panel near the fan cover inside of the chassis or outside and is it hot as in use an insulated tool?
Thanks Tim
On Saturday, January 4, 2025 at 07:53:47 PM EST, Jim Shorney via groups.io <jimnu0c@...> wrote:
I think it is the hole near the center of the chassis just outside of the fan cover. I suspect they state that it is not user accessible because they don't want anyone messing with it who does not thoroughly familiar with the ways of high voltage. You need to adjust it with the top cover off and the interlocks disabled so you can measure the high voltage with a suitable high voltage probe. Any ordinary Voltmeter not buffered by a HV probe will complain loudly before it disappears in a cloud of smoke. The same might happen to an inexperienced technician.
If the resistors are indeed out of range there was a ham selling suitable high voltage rated resistors online for a while but I don't recall who it was.
On Sun, 5 Jan 2025 00:26:15 +0000 (UTC) "Evan via groups.io" <k9sqg@...> wrote: >? This is the revised revision of the original revised revision, subject to change, about the L7 HV calibration pot. ? Not sure if it is accessible from that hole between the two coax connectors on the rear panel. > I apologize for the confusion. ?Settling an estate, sleep deprived, etc. and not sure anything I'm posting right now has any credibility. > 73, > Evan, K9SQG >? ? On Saturday, January 4, 2025 at 07:14:35 PM EST, Evan via groups.io <k9sqg@...> wrote:? > >? My memory is failing. ? The HV calibration pot on the L7 ?is not accessible from the rear panel. > 73, > Evan, K9SQG? -- 73 -Jim NU0C
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Re: Another Mistake: L7 HV calibration pot ?
Yes Jim, HV doesn't give you a second chance. ?HV, like the air and sea, is terribly unforgiving of mistakes. ?I have Triplett and HP meters with ?probes and 10KV scales but even so, I don't touch them when dealing with HV and keep one hand in my pocket.
Thanks for your comments.
73,
Evan, K9SQG
I think it is the hole near the center of the chassis just outside of the fan cover. I suspect they state that it is not user accessible because they don't want anyone messing with it who does not thoroughly familiar with the ways of high voltage. You need to adjust it with the top cover off and the interlocks disabled so you can measure the high voltage with a suitable high voltage probe. Any ordinary Voltmeter not buffered by a HV probe will complain loudly before it disappears in a cloud of smoke. The same might happen to an inexperienced technician.
If the resistors are indeed out of range there was a ham selling suitable high voltage rated resistors online for a while but I don't recall who it was.
On Sun, 5 Jan 2025 00:26:15 +0000 (UTC)
"Evan via groups.io" <k9sqg@...> wrote:
>? This is the revised revision of the original revised revision, subject to change, about the L7 HV calibration pot. ? Not sure if it is accessible from that hole between the two coax connectors on the rear panel.
> I apologize for the confusion. ?Settling an estate, sleep deprived, etc. and not sure anything I'm posting right now has any credibility.
> 73,
> Evan, K9SQG
>? ? On Saturday, January 4, 2025 at 07:14:35 PM EST, Evan via groups.io <k9sqg@...> wrote:?
>
>? My memory is failing. ? The HV calibration pot on the L7 ?is not accessible from the rear panel.
> 73,
> Evan, K9SQG?
--
73
-Jim
NU0C
|
First thought was that you have the Calibrator button depressed but that should be obvious because you could tune away from it with the VFO. As much as you have been digging around in there you may have knocked some adjustments off. I would do the frequency alignment starting at section 3-1 (10V adjustment) and proceeding through section 3-6 in the service manual. The fixed passband pots in 3-6 are particularly prone to getting bumped and some ops have replaced them with 10 turn trimpots. But I recommend the full frequency alignment so you know everything is correct. On Sat, 4 Jan 2025 17:38:15 -0400 "Jim Harris via groups.io" <radiove1rb@...> wrote: yes it was a very pleasant surprised when I turned it on and it worked, The
problem I have now id that when i SWITCH FROM lsb OR usB TO cw i get a
signal in the receiver 5 over 9 and if I press the morse key I hear the
tone as well. It does not seem to mute that signal. I also noticed that if
I use the PBT I can hear a tone and can swing the passband and I can go
back and forth past it. Almost sounds like an oscillation. Any ideas?
Thanks,
Jim VE1RB -- 73 -Jim NU0C
|
Re: Another Mistake: L7 HV calibration pot ?
Jim so how do I disable the interlocks with the top cover off? And the adjustment pot is on the back panel near the fan cover inside of the chassis or outside and is it hot as in use an insulated tool?
Thanks Tim
On Saturday, January 4, 2025 at 07:53:47 PM EST, Jim Shorney via groups.io <jimnu0c@...> wrote:
I think it is the hole near the center of the chassis just outside of the fan cover. I suspect they state that it is not user accessible because they don't want anyone messing with it who does not thoroughly familiar with the ways of high voltage. You need to adjust it with the top cover off and the interlocks disabled so you can measure the high voltage with a suitable high voltage probe. Any ordinary Voltmeter not buffered by a HV probe will complain loudly before it disappears in a cloud of smoke. The same might happen to an inexperienced technician.
If the resistors are indeed out of range there was a ham selling suitable high voltage rated resistors online for a while but I don't recall who it was.
On Sun, 5 Jan 2025 00:26:15 +0000 (UTC)
"Evan via groups.io" <k9sqg@...> wrote:
>? This is the revised revision of the original revised revision, subject to change, about the L7 HV calibration pot. ? Not sure if it is accessible from that hole between the two coax connectors on the rear panel.
> I apologize for the confusion. ?Settling an estate, sleep deprived, etc. and not sure anything I'm posting right now has any credibility.
> 73,
> Evan, K9SQG
>? ? On Saturday, January 4, 2025 at 07:14:35 PM EST, Evan via groups.io <k9sqg@...> wrote:?
>
>? My memory is failing. ? The HV calibration pot on the L7 ?is not accessible from the rear panel.
> 73,
> Evan, K9SQG?
--
73
-Jim
NU0C
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Re: Another Mistake: L7 HV calibration pot ?
I think it is the hole near the center of the chassis just outside of the fan cover. I suspect they state that it is not user accessible because they don't want anyone messing with it who does not thoroughly familiar with the ways of high voltage. You need to adjust it with the top cover off and the interlocks disabled so you can measure the high voltage with a suitable high voltage probe. Any ordinary Voltmeter not buffered by a HV probe will complain loudly before it disappears in a cloud of smoke. The same might happen to an inexperienced technician. If the resistors are indeed out of range there was a ham selling suitable high voltage rated resistors online for a while but I don't recall who it was. On Sun, 5 Jan 2025 00:26:15 +0000 (UTC) "Evan via groups.io" <k9sqg@...> wrote: This is the revised revision of the original revised revision, subject to change, about the L7 HV calibration pot. ? Not sure if it is accessible from that hole between the two coax connectors on the rear panel.
I apologize for the confusion. ?Settling an estate, sleep deprived, etc. and not sure anything I'm posting right now has any credibility.
73,
Evan, K9SQG
On Saturday, January 4, 2025 at 07:14:35 PM EST, Evan via groups.io <k9sqg@...> wrote:
My memory is failing. ? The HV calibration pot on the L7 ?is not accessible from the rear panel.
73,
Evan, K9SQG -- 73 -Jim NU0C
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Re: Another Mistake: L7 HV calibration pot ?
This is the revised revision of the original revised revision, subject to change, about the L7 HV calibration pot. ? Not sure if it is accessible from that hole between the two coax connectors on the rear panel.
I apologize for the confusion. ?Settling an estate, sleep deprived, etc. and not sure anything I'm posting right now has any credibility.
73,
Evan, K9SQG
My memory is failing. ? The HV calibration pot on the L7 ?is not accessible from the rear panel.
73,
Evan, K9SQG
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My Mistake: L7 HV calibration pot
My memory is failing. ? The HV calibration pot on the L7 ?is not accessible from the rear panel.
73,
Evan, K9SQG
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Re: Small lamp reference for Drake L7
Tim,
Not sure what to say. ? All the L7s I've owned or serviced had an access hole on the back panel for inserting an insulated tool for adjustment. ?Now the one on the L4B is different though.
I "responded" to your message in the reflector with a different title so all is well.
73,
Evan
Evan
No I have not done that in the manual from Drake it notes " not user accessible" tell me about it.
Evan I have purchased many parts for the Drake amps from you in the past and have used them.
Sorry to Bill I did not realize I posted this wrong.
Thanks Tim
On Saturday, January 4, 2025 at 06:57:53 PM EST, Bill KJ5BNE via groups.io <whb5k@...> wrote:
You¡¯ve posted a new topic about meter shunts. ?Please go to the .io group and re-post your question with a new appropriate topic title. ?Otherwise people researching this issue in the future won¡¯t be able to find the original question and possibly useful responses.
Thanks & 73, Bill AI5RP ++++++++++++++++ Bill Blodgett Arlington, Texas
On Jan 4, 2025, at 5:35?PM, amfone via groups.io <amfone20000@...> wrote:
?
Hello group. I need to replace the meter shunts for the Drake L7, LV and HV reading low. From the schematic Drake used 8 2.3 meg 1/2 watt resistors it appears from the schematic and manual pictures they are located right behind the 3-500Zs. Any advice gladly accepted.
Tim
WB8UHZ
On Saturday, January 4, 2025 at 03:14:00 PM EST, Mohamed VA2MKX via groups.io <va2mkx@...> wrote:
Thanks a lot for the reference, appreciated ! :)
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Re: Small lamp reference for Drake L7
Evan
No I have not done that in the manual from Drake it notes " not user accessible" tell me about it.
Evan I have purchased many parts for the Drake amps from you in the past and have used them.
Sorry to Bill I did not realize I posted this wrong.
Thanks Tim
On Saturday, January 4, 2025 at 06:57:53 PM EST, Bill KJ5BNE via groups.io <whb5k@...> wrote:
You¡¯ve posted a new topic about meter shunts. ?Please go to the .io group and re-post your question with a new appropriate topic title. ?Otherwise people researching this issue in the future won¡¯t be able to find the original question and possibly useful responses.
Thanks & 73, Bill AI5RP ++++++++++++++++ Bill Blodgett Arlington, Texas
On Jan 4, 2025, at 5:35?PM, amfone via groups.io <amfone20000@...> wrote:
?
Hello group. I need to replace the meter shunts for the Drake L7, LV and HV reading low. From the schematic Drake used 8 2.3 meg 1/2 watt resistors it appears from the schematic and manual pictures they are located right behind the 3-500Zs. Any advice gladly accepted.
Tim
WB8UHZ
On Saturday, January 4, 2025 at 03:14:00 PM EST, Mohamed VA2MKX via groups.io <va2mkx@...> wrote:
Thanks a lot for the reference, appreciated ! :)
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Floyd - K8AC
Paul Christensen
Jim Shorney
Rob Sherwood