Re: Off-The-Wall Question
Hi Justin – ? First, I suggest you verify that the mechanical filter is bad. Easy enough to do with a signal generator and a scope. Try to match required in and out impedances with resistors. You should be able to see the passband on the scope while tuning the generator. The ceramic resonator filter will probably need to be matched to the existing circuit. So, the Z in/out of both filters need to be known. You should also check and see to make sure there are no DC voltages going to the transducers of the mechanical filter. While in a good design this is avoided, it is possible that the grid bias is going through it. If it is, you will have to re-route the grid bias. A schematic would definitely be helpful. Good luck – 73 – Mike ? Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 908-902-3831 ?
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From: [email protected] <[email protected]> On Behalf Of Justin Bowser - KI5GKD
Sent: Saturday, March 8, 2025 12:54 AM
To: [email protected]
Subject: [HallicraftersRadios] Off-The-Wall Question? Hi, Y'all!? Been a while since I bugged the collective so now I have a question.? It's not Hallicrafters related but there is such a wealth of knowledge around here I figure somebody might be able to help. I picked up an old Lafayette HB-600 CB which is ailing.? I turn it on and get a slight hiss from the speaker and when I key the mic I show about a 5 watt carrier but no modulation.? That's just a little background info so here is where things might get interesting.? I decided to go through the alignment procedures and have injected 455 KHz at the proper point and heard exactly zero tone so I started working forward and after I got past a mechanical 455 KHz filter and an IF can I got a good solid tone and could peak the next two IF cans.? I have a stock of mini 455 IF transformers and I have ordered a ceramic 455 KHz filter from an AliExpress seller.? should the ceramic filter work as a drop in or might I need to do some modifications? I know some may look at messing with an old CB as tantamount to blasphemy but CBs and SWL is what got me into Ham Radio when I was a wee shaver.
|
Hi, Y'all!? Been a while since I bugged the collective so now I have a question.? It's not Hallicrafters related but there is such a wealth of knowledge around here I figure somebody might be able to help.
?
I picked up an old Lafayette HB-600 CB which is ailing.? I turn it on and get a slight hiss from the speaker and when I key the mic I show about a 5 watt carrier but no modulation.? That's just a little background info so here is where things might get interesting.? I decided to go through the alignment procedures and have injected 455 KHz at the proper point and heard exactly zero tone so I started working forward and after I got past a mechanical 455 KHz filter and an IF can I got a good solid tone and could peak the next two IF cans.? I have a stock of mini 455 IF transformers and I have ordered a ceramic 455 KHz filter from an AliExpress seller.? should the ceramic filter work as a drop in or might I need to do some modifications?
?
I know some may look at messing with an old CB as tantamount to blasphemy but CBs and SWL is what got me into Ham Radio when I was a wee shaver.
?
73,
--
Justin B.
KI5GKD
|
Ray,? On the back of my sx-100 it is stamped in rather large letter?
? ? ? ? ? MARK-2? ?A.? Bob w8exv
On 03/07/2025 7:21 PM EST Ray, W4BYG <w4byg@...> wrote:
?
?
I missed the earlier threads on this subject. My SX-100 SN 132612 has black knobs. There is no indication inside or outside if it is a ""Mark" model. Is there a list somewhere that relates serial numbers to when it was manufactured?
Ray, W4BYG
On 3/7/2025 17:17, Anthony W. DePrato via groups.io wrote:
Hallicafters used 3 knob designs over the years. the knobs on your unit were the last of the black knobs.
they? switched to Gray in the 60's but kept making the black knobs for the older receivers they were still selling
also look inside at the chassis it should say either run 2 or run 3.
73 Tony wa4jqs
?
On 3/7/2025 11:32 AM, Bob via groups.io wrote:
Tony, you say I have one that was next to the last run. How did
you determine that? Bob w8exv?
On 03/06/2025 11:18 AM EST Anthony W. DePrato via groups.io <wa4jqs@...> wrote:
?
?
Bob:
good luck with the sx 100 you have the next to last run if i recall had so many that i collected over the years it is hard to recall hihi.
but i can say this the sx 100 is a great receiver after i restored mine had a ham drop by to look at another receiver and then talked me out of mine.
73 Tony WA4JQS
On 3/5/2025 11:22 PM, Bob via groups.io wrote:
Tony, thanks for the reply, will remove all of them also. Bob w8exv
On 03/05/2025 3:54 PM EST Anthony W. DePrato via groups.io <wa4jqs@...> wrote:
?
?
NO do NOT leave them in the radio they like to go off like an M80
73 Tony WA4JQS
On 3/5/2025 12:38 PM, Bob via groups.io wrote:
My sx-100mk2a has several black cat caps, woud it be ok to leave these in
or replace them also.
? ? ? thanks in advance Bob w8exv
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
--
"The world is desperate for a faith that combines two things: awestruck sight of unshakable divine Truth, and
utterly practical, round-the-clock power to make a liberating difference in life"... John Piper
|
I missed the earlier threads on
this subject. My SX-100 SN 132612 has black knobs. There is no
indication inside or outside if it is a ""Mark" model. Is there
a list somewhere that relates serial numbers to when it was
manufactured?
Ray, W4BYG
On 3/7/2025 17:17, Anthony W. DePrato
via groups.io wrote:
Hallicafters used 3 knob designs over the years. the knobs on
your unit were the last of the black knobs.
they? switched to Gray in the 60's but kept making the black
knobs for the older receivers they were still selling
also look inside at the chassis it should say either run 2 or
run 3.
73 Tony wa4jqs
On 3/7/2025 11:32 AM, Bob via
groups.io wrote:
Tony, you say I have one that was next to the last run.
How did
you determine that? Bob w8exv?
On 03/06/2025 11:18 AM EST Anthony W. DePrato via
groups.io <wa4jqs@...>
wrote: ?
?
Bob:
good luck with the sx 100 you have the next to last run if
i recall had so many that i collected over the years it is
hard to recall hihi.
but i can say this the sx 100 is a great receiver after i
restored mine had a ham drop by to look at another receiver
and then talked me out of mine.
73 Tony WA4JQS
On 3/5/2025 11:22 PM, Bob via
groups.io wrote:
Tony, thanks for the reply, will remove all of them
also. Bob w8exv
On 03/05/2025 3:54 PM EST Anthony W. DePrato via
groups.io <wa4jqs@...>
wrote: ?
?
NO do NOT leave them in the radio they like to go off
like an M80
73 Tony WA4JQS
On 3/5/2025 12:38 PM, Bob
via groups.io wrote:
My sx-100mk2a has several black cat caps, woud it
be ok to leave these in
or replace them also.
? ? ? thanks in advance Bob w8exv
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC
HONOR ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS
3Y0PI ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR
ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI
ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR ROLL
CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS
WA4JQS/KC4 WA4JQS/ZS1
--
"The world is desperate for a faith that combines two things: awestruck sight of unshakable divine Truth, and
utterly practical, round-the-clock power to make a liberating difference in life"... John Piper
|
Tom? I don’t know what tests you have done on circuitry in the area . You verified the LO does not work [on any band] and no matter the new tube, so It seems something else is wrong , as Jacques said, “open or shorted”, and I would add “is not right as in leaky cap, off tolerance etc”. It is possible, but not likely that the Hexode circuit is bad and wrecks the LO, ….but not ?likely. ? That really leaves the triode and its circuits. Practical testing depends a lot on what is accessible, so it is hard for us to make a test plan. The problem could be near the tube cathode, grid, plate or further away in the bandswitch and coils. Perhaps you can look at the switch , coils, caps all as one. If I see ok, 1)???? ?the contacts of the 2 band switch wafers? SW-7E & F? should be DC floating above ground?? [no DC voltage when on?? and Hi resistance to gnd when off. ??]?? ?on each band. ? 2)???? and there should be continuity from side to side [thru coils] on every band ?resistance test ?
?
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From: [email protected] [mailto:[email protected]] On Behalf Of Allthumbs via groups.io
Sent: Friday, March 7, 2025 6:24 PM
To: [email protected]; Jim Whartenby via groups.io
Subject: Re: [HallicraftersRadios] S-20R mixer cct. #photo-notice? At the moment, Jim, my only other radio using a 6K8 is a home brew rcvr. The oscillator portion works just fine with this tube. -- don??? va3drl
|
Jacques No need to apologize, like you said, "or almost nothing" can fool a tube tester!? <grin>? My practice in tube testing, after looking at the getter, is to do a critical short test and then the gm test.? If the TUT passes these tests, even if the gm is a bit below spec, I keep the tube.? Like I said, the final test is in the circuit.
There are four frequency bands, so there are four LC tank circuits.? Probability would indicate that all of the tank coils and capacitors could not all be defective at the same time.? I don't know if Tom has looked at the other bands to see if the tank circuits are functional using his GDO.? If C1 and C2 are not shorted, then running the tuning and band spread capacitors to the fully open position, so that the tanks are at the highest operating frequency, will take them out of the circuit.? The goodness of the tank circuits can now be verified with the GDO.
So that leaves the band switch rotor contact to possibility be open, C37, C33 to be shorted (I guess open is still a possibility), R7 and R9 to be open with a hair line crack or badly out of tolerance and there is the possibility that the ground connection for the tank inductors has been lost.? I assume that all of these issues have been eliminated using resistance measurements.? If this is the case, then the tube or the tube socket are all that are left to investigate. Regards, Jim
Jim, I’m sorry but… All depends on the tester you use…. Nothing (or almost nothing) can fool my AVO VCM-163. ? For the S-20R of Tom problem. Something is open in the feedback path of the LO. Or short to GND, whatever…. This is a very simple plate-to-grid feed back path, so it HAVE TO work ! ? 73, Jacques, VE2JFE in Montreal ? ? OK, do you have other receivers that use a 6K8?? Do the other 6K8s that you tried in the S-20R also work in that receiver? Tube testers will tell you when a tube is bad but not if it is good.? The final test is in the circuit. Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Friday, March 7, 2025 at 02:28:52 PM CST, Allthumbs via groups.io <btse1@...> wrote: The 6K8 is NIB and tested on an I-177 for both gas and transconductance. I have also tried my other two 6K8's.
On 03/07/2025 11:32 AM PST Jim Whartenby via groups.io <old_radio@...> wrote: I wonder if the 6K8 is a little gassy?? It seems to me that the plate potential could overwhelm the high impedance of the triode grid circuit if some gas is present.? Is a known good 6K8 available to substitute? Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Wednesday, March 5, 2025 at 10:31:49 PM CST, Jacques_VE2JFE via groups.io <jacques.f@...> wrote: Hi Don. Any tube having a “floating” control grid, a heated cathode and a positive plate voltage cannot pass any current, because the electron flow will charge the grid highly negative and this will prevent any plate current going thru. If a hi-impedance voltmeter (say having 10Meg ohms input) is connected between that grid and GND (or cathode), it will show a negative grid voltage. There is tubes such polarised in some audio circuits: cathode directly connected to GND and a hi value of grid to GND resistor (typically 10Meg). For that reason, measuring a positive voltage from a “floating” grid respective to GND is not possible. In the 6K8 case, as the LO is not working and R7 is ± 47k ohms, the grid is practically at the same positive potential than the cathode. ? 73, Jacques, VE2JFE in Montreal ? Hi Jacques? Your words seem good to me until “IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all”… I don’t understand that. ??“could not be measured at all”… ?means zero or negative volts only?? . ? So what is setting the grid volts? As I see it, R7 is the only path from the grid to to B+ or B-minus. ? I will have to try again to redraw the circuit.. and read some tube theory again.. ??? ? ? Hi Don, simple: the 6K8 is made as a triode + hexode, sharing the same cathode, so the cathode bias resistor (R8) voltage depends on both the triode and hexode sections. So even if the triode section does not work as intended, there is still some current coming from the hexode… That being said, when the LO works normally from the triode section, the triode grid voltage have to be negative because the triode works in class C, and the grid current, charging the coupling capacitor (C37) results in a negative MEAN voltage to the grid. ? In the Table of voltages below, the grid is about at the same voltage than the cathode, which is an unmistakable sign that the oscillator is not working. And as the triode section is drawing all the current it could, this result in lower triode plate voltage and also in a lower screen grid voltage on the hexode part, and etc. ? IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all… ? 73, Jacques, VE2JFE in Montreal
--
don??? va3drl
|
At the moment, Jim, my only other radio using a 6K8 is a home brew rcvr. The oscillator portion works just fine with this tube.
?
Tom
On 03/07/2025 2:25 PM PST Jim Whartenby via groups.io <old_radio@...> wrote:
?
?
Tom
OK, do you have other receivers that use a 6K8?? Do the other 6K8s that you tried in the S-20R also work in that receiver?
?
Tube testers will tell you when a tube is bad but not if it is good.? The final test is in the circuit.
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
?
?
?
?
The 6K8 is NIB and tested on an I-177 for both gas and transconductance. I have also tried my other two 6K8's.
?
Tom
On 03/07/2025 11:32 AM PST Jim Whartenby via groups.io <old_radio@...> wrote:
?
?
I wonder if the 6K8 is a little gassy?? It seems to me that the plate potential could overwhelm the high impedance of the triode grid circuit if some gas is present.? Is a known good 6K8 available to substitute?
Jim
?
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
?
?
?
?
Hi Don.
Any tube having a “floating” control grid, a heated cathode and a positive plate voltage cannot pass any current, because the electron flow will charge the grid highly negative and this will prevent any plate current going thru.
If a hi-impedance voltmeter (say having 10Meg ohms input) is connected between that grid and GND (or cathode), it will show a negative grid voltage.
There is tubes such polarised in some audio circuits: cathode directly connected to GND and a hi value of grid to GND resistor (typically 10Meg).
For that reason, measuring a positive voltage from a “floating” grid respective to GND is not possible.
In the 6K8 case, as the LO is not working and R7 is ± 47k ohms, the grid is practically at the same positive potential than the cathode.
?
73, Jacques, VE2JFE in Montreal
?
Hi Jacques? Your words seem good to me until “IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all”…
I don’t understand that. ??“could not be measured at all”… ?means zero or negative volts only?? .
?
So what is setting the grid volts? As I see it, R7 is the only path from the grid to to B+ or B-minus. ?
I will have to try again to redraw the circuit.. and read some tube theory again.. ???
?
?
Hi Don, simple: the 6K8 is made as a triode + hexode, sharing the same cathode, so the cathode bias resistor (R8) voltage depends on both the triode and hexode sections.
So even if the triode section does not work as intended, there is still some current coming from the hexode…
That being said, when the LO works normally from the triode section, the triode grid voltage have to be negative because the triode works in class C, and the grid current, charging the coupling capacitor (C37) results in a negative MEAN voltage to the grid.
?
In the Table of voltages below, the grid is about at the same voltage than the cathode, which is an unmistakable sign that the oscillator is not working.
And as the triode section is drawing all the current it could, this result in lower triode plate voltage and also in a lower screen grid voltage on the hexode part, and etc.
?
IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all…
?
73, Jacques, VE2JFE in Montreal
--
don??? va3drl
?
?
|
Jim, I’m sorry but… All depends on the tester you use…. Nothing (or almost nothing) can fool my AVO VCM-163. ? For the S-20R of Tom problem. Something is open in the feedback path of the LO. Or short to GND, whatever…. This is a very simple plate-to-grid feed back path, so it HAVE TO work ! ? 73, Jacques, VE2JFE in Montreal ? ? OK, do you have other receivers that use a 6K8?? Do the other 6K8s that you tried in the S-20R also work in that receiver? Tube testers will tell you when a tube is bad but not if it is good.? The final test is in the circuit. Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Friday, March 7, 2025 at 02:28:52 PM CST, Allthumbs via groups.io <btse1@...> wrote: The 6K8 is NIB and tested on an I-177 for both gas and transconductance. I have also tried my other two 6K8's.
toggle quoted message
Show quoted text
On 03/07/2025 11:32 AM PST Jim Whartenby via groups.io <old_radio@...> wrote: I wonder if the 6K8 is a little gassy?? It seems to me that the plate potential could overwhelm the high impedance of the triode grid circuit if some gas is present.? Is a known good 6K8 available to substitute? Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Wednesday, March 5, 2025 at 10:31:49 PM CST, Jacques_VE2JFE via groups.io <jacques.f@...> wrote: Hi Don. Any tube having a “floating” control grid, a heated cathode and a positive plate voltage cannot pass any current, because the electron flow will charge the grid highly negative and this will prevent any plate current going thru. If a hi-impedance voltmeter (say having 10Meg ohms input) is connected between that grid and GND (or cathode), it will show a negative grid voltage. There is tubes such polarised in some audio circuits: cathode directly connected to GND and a hi value of grid to GND resistor (typically 10Meg). For that reason, measuring a positive voltage from a “floating” grid respective to GND is not possible. In the 6K8 case, as the LO is not working and R7 is ± 47k ohms, the grid is practically at the same positive potential than the cathode. ? 73, Jacques, VE2JFE in Montreal ? Hi Jacques? Your words seem good to me until “IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all”… I don’t understand that. ??“could not be measured at all”… ?means zero or negative volts only?? . ? So what is setting the grid volts? As I see it, R7 is the only path from the grid to to B+ or B-minus. ? I will have to try again to redraw the circuit.. and read some tube theory again.. ??? ? ? Hi Don, simple: the 6K8 is made as a triode + hexode, sharing the same cathode, so the cathode bias resistor (R8) voltage depends on both the triode and hexode sections. So even if the triode section does not work as intended, there is still some current coming from the hexode… That being said, when the LO works normally from the triode section, the triode grid voltage have to be negative because the triode works in class C, and the grid current, charging the coupling capacitor (C37) results in a negative MEAN voltage to the grid. ? In the Table of voltages below, the grid is about at the same voltage than the cathode, which is an unmistakable sign that the oscillator is not working. And as the triode section is drawing all the current it could, this result in lower triode plate voltage and also in a lower screen grid voltage on the hexode part, and etc. ? IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all… ? 73, Jacques, VE2JFE in Montreal
--
don??? va3drl
|
Tom OK, do you have other receivers that use a 6K8?? Do the other 6K8s that you tried in the S-20R also work in that receiver?
Tube testers will tell you when a tube is bad but not if it is good.? The final test is in the circuit. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
The 6K8 is NIB and tested on an I-177 for both gas and transconductance. I have also tried my other two 6K8's.
?
Tom
On 03/07/2025 11:32 AM PST Jim Whartenby via groups.io <old_radio@...> wrote:
?
?
I wonder if the 6K8 is a little gassy?? It seems to me that the plate potential could overwhelm the high impedance of the triode grid circuit if some gas is present.? Is a known good 6K8 available to substitute?
Jim
?
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
?
?
?
?
Hi Don.
Any tube having a “floating” control grid, a heated cathode and a positive plate voltage cannot pass any current, because the electron flow will charge the grid highly negative and this will prevent any plate current going thru.
If a hi-impedance voltmeter (say having 10Meg ohms input) is connected between that grid and GND (or cathode), it will show a negative grid voltage.
There is tubes such polarised in some audio circuits: cathode directly connected to GND and a hi value of grid to GND resistor (typically 10Meg).
For that reason, measuring a positive voltage from a “floating” grid respective to GND is not possible.
In the 6K8 case, as the LO is not working and R7 is ± 47k ohms, the grid is practically at the same positive potential than the cathode.
?
73, Jacques, VE2JFE in Montreal
?
Hi Jacques? Your words seem good to me until “IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all”…
I don’t understand that. ??“could not be measured at all”… ?means zero or negative volts only?? .
?
So what is setting the grid volts? As I see it, R7 is the only path from the grid to to B+ or B-minus. ?
I will have to try again to redraw the circuit.. and read some tube theory again.. ???
?
?
Hi Don, simple: the 6K8 is made as a triode + hexode, sharing the same cathode, so the cathode bias resistor (R8) voltage depends on both the triode and hexode sections.
So even if the triode section does not work as intended, there is still some current coming from the hexode…
That being said, when the LO works normally from the triode section, the triode grid voltage have to be negative because the triode works in class C, and the grid current, charging the coupling capacitor (C37) results in a negative MEAN voltage to the grid.
?
In the Table of voltages below, the grid is about at the same voltage than the cathode, which is an unmistakable sign that the oscillator is not working.
And as the triode section is drawing all the current it could, this result in lower triode plate voltage and also in a lower screen grid voltage on the hexode part, and etc.
?
IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all…
?
73, Jacques, VE2JFE in Montreal
--
don??? va3drl
?
|
Hallicafters used 3 knob designs over the years. the knobs on
your unit were the last of the black knobs.
they? switched to Gray in the 60's but kept making the black
knobs for the older receivers they were still selling
also look inside at the chassis it should say either run 2 or run
3.
73 Tony wa4jqs
On 3/7/2025 11:32 AM, Bob via groups.io
wrote:
Tony, you say I have one that was next to the last run. How
did
you determine that? Bob w8exv?
On 03/06/2025 11:18 AM EST Anthony W. DePrato via
groups.io <wa4jqs@...> wrote: ?
?
Bob:
good luck with the sx 100 you have the next to last run if i
recall had so many that i collected over the years it is hard
to recall hihi.
but i can say this the sx 100 is a great receiver after i
restored mine had a ham drop by to look at another receiver
and then talked me out of mine.
73 Tony WA4JQS
On 3/5/2025 11:22 PM, Bob via
groups.io wrote:
Tony, thanks for the reply, will remove all of them
also. Bob w8exv
On 03/05/2025 3:54 PM EST Anthony W. DePrato via
groups.io <wa4jqs@...>
wrote: ?
?
NO do NOT leave them in the radio they like to go off
like an M80
73 Tony WA4JQS
On 3/5/2025 12:38 PM, Bob via
groups.io wrote:
My sx-100mk2a has several black cat caps, woud it be
ok to leave these in
or replace them also.
? ? ? thanks in advance Bob w8exv
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR
ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI
ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR
ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS
WA4JQS/KC4 WA4JQS/ZS1
--
Anthony W.DePrato WA4JQS
CQ DX HALL OF FAME #39
DXCC HONOR ROLL CW PHONE RTTY
CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
|
The 6K8 is NIB and tested on an I-177 for both gas and transconductance. I have also tried my other two 6K8's.
?
Tom
On 03/07/2025 11:32 AM PST Jim Whartenby via groups.io <old_radio@...> wrote:
?
?
I wonder if the 6K8 is a little gassy?? It seems to me that the plate potential could overwhelm the high impedance of the triode grid circuit if some gas is present.? Is a known good 6K8 available to substitute?
Jim
?
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
?
?
?
?
Hi Don.
Any tube having a “floating” control grid, a heated cathode and a positive plate voltage cannot pass any current, because the electron flow will charge the grid highly negative and this will prevent any plate current going thru.
If a hi-impedance voltmeter (say having 10Meg ohms input) is connected between that grid and GND (or cathode), it will show a negative grid voltage.
There is tubes such polarised in some audio circuits: cathode directly connected to GND and a hi value of grid to GND resistor (typically 10Meg).
For that reason, measuring a positive voltage from a “floating” grid respective to GND is not possible.
In the 6K8 case, as the LO is not working and R7 is ± 47k ohms, the grid is practically at the same positive potential than the cathode.
?
73, Jacques, VE2JFE in Montreal
?
Hi Jacques? Your words seem good to me until “IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all”…
I don’t understand that. ??“could not be measured at all”… ?means zero or negative volts only?? .
?
So what is setting the grid volts? As I see it, R7 is the only path from the grid to to B+ or B-minus. ?
I will have to try again to redraw the circuit.. and read some tube theory again.. ???
?
?
Hi Don, simple: the 6K8 is made as a triode + hexode, sharing the same cathode, so the cathode bias resistor (R8) voltage depends on both the triode and hexode sections.
So even if the triode section does not work as intended, there is still some current coming from the hexode…
That being said, when the LO works normally from the triode section, the triode grid voltage have to be negative because the triode works in class C, and the grid current, charging the coupling capacitor (C37) results in a negative MEAN voltage to the grid.
?
In the Table of voltages below, the grid is about at the same voltage than the cathode, which is an unmistakable sign that the oscillator is not working.
And as the triode section is drawing all the current it could, this result in lower triode plate voltage and also in a lower screen grid voltage on the hexode part, and etc.
?
IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all…
?
73, Jacques, VE2JFE in Montreal
--
don??? va3drl
?
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I wonder if the 6K8 is a little gassy?? It seems to me that the plate potential could overwhelm the high impedance of the triode grid circuit if some gas is present.? Is a known good 6K8 available to substitute? Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
Hi Don. Any tube having a “floating” control grid, a heated cathode and a positive plate voltage cannot pass any current, because the electron flow will charge the grid highly negative and this will prevent any plate current going thru. If a hi-impedance voltmeter (say having 10Meg ohms input) is connected between that grid and GND (or cathode), it will show a negative grid voltage. There is tubes such polarised in some audio circuits: cathode directly connected to GND and a hi value of grid to GND resistor (typically 10Meg). For that reason, measuring a positive voltage from a “floating” grid respective to GND is not possible. In the 6K8 case, as the LO is not working and R7 is ± 47k ohms, the grid is practically at the same positive potential than the cathode. ? 73, Jacques, VE2JFE in Montreal ? Hi Jacques? Your words seem good to me until “IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all”… I don’t understand that. ??“could not be measured at all”… ?means zero or negative volts only?? . ? So what is setting the grid volts? As I see it, R7 is the only path from the grid to to B+ or B-minus. ? I will have to try again to redraw the circuit.. and read some tube theory again.. ??? ?
From: [email protected] [mailto:[email protected]] On Behalf Of Jacques_VE2JFE via groups.io
Sent: Wednesday, March 5, 2025 7:47 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-20R mixer cct. #photo-notice ? Hi Don, simple: the 6K8 is made as a triode + hexode, sharing the same cathode, so the cathode bias resistor (R8) voltage depends on both the triode and hexode sections. So even if the triode section does not work as intended, there is still some current coming from the hexode… That being said, when the LO works normally from the triode section, the triode grid voltage have to be negative because the triode works in class C, and the grid current, charging the coupling capacitor (C37) results in a negative MEAN voltage to the grid. ? In the Table of voltages below, the grid is about at the same voltage than the cathode, which is an unmistakable sign that the oscillator is not working. And as the triode section is drawing all the current it could, this result in lower triode plate voltage and also in a lower screen grid voltage on the hexode part, and etc. ? IF the R7 were open, a positive grid voltage (quite close to the cathode one) could not be measured at all… ? 73, Jacques, VE2JFE in Montreal
--
don??? va3drl
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Re: Looking for SR-500 Tornado, Maybe SR-160
Scott,
I have a PS-150, if interested. ?Contact me off list if you’d like it. ?I’m good on QRZ.
73, Bill AI5RP ++++++++++++++++ Bill Blodgett Arlington, Texas
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Show quoted text
On Mar 6, 2025, at 11:53?PM, Scott WA9WFA via groups.io <whitebear1122@...> wrote:
? Hi, I’m looking to buy a Hallicrafters SR-500 Tornado transceiver and PS-500 in good physical and preferably working condition. ?If I can’t find an SR-500, I would consider buying an SR-160/PS-150.
In 1970 a friend borrowed me an SR-160 when I first got my General, and I had a wonderful time working 75, 40, 20 meter SSB with it until I left for military duty after high school graduation. Here I am some 54 years later looking for some of that wonderful nostalgia of the SR-160/SR-500. ?Thanks. ?
73, Scott WA9WFA
--
?
73,
Bill
AI5RP / KJ5BNE/AE
Arlington, Texas
|
Tony, you say I have one that was next to the last run. How did
you determine that? Bob w8exv?
On 03/06/2025 11:18 AM EST Anthony W. DePrato via groups.io <wa4jqs@...> wrote:
?
?
Bob:
good luck with the sx 100 you have the next to last run if i recall had so many that i collected over the years it is hard to recall hihi.
but i can say this the sx 100 is a great receiver after i restored mine had a ham drop by to look at another receiver and then talked me out of mine.
73 Tony WA4JQS
On 3/5/2025 11:22 PM, Bob via groups.io wrote:
Tony, thanks for the reply, will remove all of them also. Bob w8exv
On 03/05/2025 3:54 PM EST Anthony W. DePrato via groups.io <wa4jqs@...> wrote:
?
?
NO do NOT leave them in the radio they like to go off like an M80
73 Tony WA4JQS
On 3/5/2025 12:38 PM, Bob via groups.io wrote:
My sx-100mk2a has several black cat caps, woud it be ok to leave these in
or replace them also.
? ? ? thanks in advance Bob w8exv
--
Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
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Anthony W.DePrato WA4JQS CQ DX HALL OF FAME #39 DXCC HONOR ROLL CW PHONE RTTY CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
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Re: Looking for SR-500 Tornado, Maybe SR-160
Scott:
if you do not find an SR 500 Contact me via my qrz email . i have
a recapped SR-150 with supply in excellent shape and working.? i
removed it from service last Oct. when i started using my restored
SR-400/HA20 combo.
it is in Somerset Ky. and i will be glad to put it back on the
air for a qso with you. i am on 3.657 sat and sun nites at 00:00z.
with W4OP N8CBX N4CJM an other BA restorers.
73 Tony WA4JQS
On 3/7/2025 12:52 AM, Scott WA9WFA via
groups.io wrote:
Hi, I’m looking to buy a Hallicrafters SR-500
Tornado transceiver and PS-500 in good physical and preferably
working condition. ?If I can’t find an SR-500, I would consider
buying an SR-160/PS-150.
In 1970 a friend borrowed me an SR-160 when I
first got my General, and I had a wonderful time working 75,
40, 20 meter SSB with it until I left for military duty after
high school graduation. Here I am some 54 years later looking
for some of that wonderful nostalgia of the SR-160/SR-500.
?Thanks. ?
73, Scott WA9WFA
--
Anthony W.DePrato WA4JQS
CQ DX HALL OF FAME #39
DXCC HONOR ROLL CW PHONE RTTY
CALLS HELD VP8SSI VP8BZL V31SS 3Y0PI ZS8JQS WA4JQS/KC4 WA4JQS/ZS1
|
Looking for SR-500 Tornado, Maybe SR-160
Hi, I’m looking to buy a Hallicrafters SR-500 Tornado transceiver and PS-500 in good physical and preferably working condition. ?If I can’t find an SR-500, I would consider buying an SR-160/PS-150.
In 1970 a friend borrowed me an SR-160 when I first got my General, and I had a wonderful time working 75, 40, 20 meter SSB with it until I left for military duty after high school graduation. Here I am some 54 years later looking for some of that wonderful nostalgia of the SR-160/SR-500. ?Thanks. ?
73, Scott WA9WFA
|
Jacques,? yes, but why is it that positive while not oscillation??? And what is preventing ?oscillation over all the bands and frequencies? ?.. it could be anything upset in the LO loop And most likely is a part common to all bands ?c33 and c37 ?bandswitch ??c7 c8?? And then resistors …Dunno
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From: [email protected] [mailto:[email protected]] On Behalf Of Jacques_VE2JFE via groups.io
Sent: Wednesday, March 5, 2025 11:32 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-20R mixer cct. #photo-notice? Hi Don. Any tube having a “floating” control grid, a heated cathode and a positive plate voltage cannot pass any current, because the electron flow will charge the grid highly negative and this will prevent any plate current going thru. If a hi-impedance voltmeter (say having 10Meg ohms input) is connected between that grid and GND (or cathode), it will show a negative grid voltage. There is tubes such polarised in some audio circuits: cathode directly connected to GND and a hi value of grid to GND resistor (typically 10Meg). For that reason, measuring a positive voltage from a “floating” grid respective to GND is not possible. In the 6K8 case, as the LO is not working and R7 is ± 47k ohms, the grid is practically at the same positive potential than the cathode. ? ?? -- don??? va3drl
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Re: S-20R circuit "analyisis" difficulties
Richard, yours in black from previous, my adder in red Not sure I understand your question so feel free to disregard this
if its nonsense.
T-10, 11, 12, 13 are the plate tank of the RF amplifier stage. The
common connections go to B+ the other side go to one side of the the
band switch. ? The secondary coils go to the other side of the bandswitch
which then goes to the signal grid of the mixer tube. ?Yes , and the secondary coils? seem to be tied together at the bottom? ..but ?otherwise floating so how does it couples to the grid unless inherent capacitance holds the common bottom to ground.
I was hoping to keep this topic about the circuit ?and not the Problems in Tom’s radio.
????
-- don??? va3drl
|
Re: S-20R circuit "analyisis" difficulties
Thanks Tom for New schematic? .. did he just do it?? C38 does not seem to be connected as in Richards version.. see below please verify one way or the other.
From: [email protected] [mailto:[email protected]] On Behalf Of Allthumbs via groups.io
Sent: Thursday, March 6, 2025 7:57 PM
To: [email protected]; don Root
Subject: Re: [HallicraftersRadios] S-20R circuit "analyisis" difficulties
?
Attached is a pdf of a crystal-clear re-drafting of a S-20R schematic. Perhaps it will be of use to anyone working on one of these sets.
All credit to the author whose username on the Antique Radio Forum is bcascisa
On 03/06/2025 3:36 PM PST don Root <drootofallevil@...> wrote:
An aside from ongoing topic ??S-20R mixer cct. ?…
While trying to “see” how the LO circuit works? things got me in a big knot.
C38 seems to run from some osc tanks back to the mixer RF tank area.
When I follow that I get to? the common [not ground] of the coils/transformers RF tanks? and found them to be floating = strange to me.
I am using Richard’s posted Handbook [ ohh thanks? RICHARD, GOOD SCANS] ?
IN ORDER TO separate lines so I could see I had to shift stuff and here is where I got.?? Maybe I got something wrong so need somebody to check my “re-draughting”
--
don??? va3drl
--
don??? va3drl
|
I posted this in another response but it fits here. Beside using a
GDO as an indicating wave meter or as a grid dip oscillator it is
possible to use it as a hetrodyne detector. In order to do this it must
have a headphone connection across the meter. The advantage of using it
this way is that the sensitivity is much greater than in the other
arrangements. One listens to the headphones and tunes for a beat. The
coupling need not be nearly as tight as in the other applications.
However, I tested this using my Millen GDO to listen for the LO of
an S-40A. Western Electric very high impedance headphones. could not
hear a beat when coupling to the antenna lead. The LO output there is
very low so its quite possible coupling more closely to the LO might be
audible. However, too tight coupling will shift the oscillator or even
kill it.
Using a separate receiver is a better way to hear the LO. Should
work from radiation out the antenna terminal or from the tube. Keep in
mind that the LO will be displaced from the signal frequency by the IF
frequency. For lower bands nearly always above the signal but in many
all wave receivers the highest band or two bands will have the LO below
the signal.
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Show quoted text
On 3/5/2025 9:41 PM, Jim Whartenby via groups.io wrote: Tom
Depending on your model of GDO you can either use it to generate a
signal and look for a dip in "grid" voltage at resonance as power is
absorbed by the LO tank circuit or you can use it as a "receiver" and
monitor whatever frequency is generated by the LO.? In either case the
GDO coil has to be closely coupled to the oscillator coil under test.
If the LO tuned circuit is good then you should be able to verify that
the LO tank circuit is adsorbing power form the GDO.? If you have not
verified this then I would first suspect that the distance between the
GDO coil and the LO coil is too great so no coupling is taking place.? I
have a GDO but have never used it.? I prefer to use a working receiver
as a tester since it is much more sensitive.
There is also the slight possibility that when you replaced components,
you may have mis-wired something or the dreaded previous owner did the
deed.? This is something that we have all done at one time or another,
especially if we have taken a break halfway through the process.? I
believe Jacques asked if you had double checked the LO circuit wiring
but I don't remember your answer.
An open LO coil is easy to ohm-out but an open tank or coupling
capacitor is a bit more of a problem.? Then there is the issue of a
broken or shorted wire to the tuning capacitor oscillator section or a
faulty band switch segment.? I would closely eyeball things in the LO
before resorting to any more digging into the chassis.? Even verify the
replacement component values.? I have sometimes transposed resistor
stripes so it helps to verify resistors values with the VOM or DMM.
Regards,
Jim
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
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Ray, W4BYG
don Root
Jim Whartenby
Allthumbs
Jacques_VE2JFE
Anthony W. DePrato