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Re: S-20R mixer cct.
开云体育Jim & Tom? The Hexode signal grid has a max? or min? voltage of -3? presumably to the cathode [depends who you read] , but my conclusion from a Sylvania ??blurb? is that it can go as positive as -3 volts, and as negative as -30 where there is little transconductance, and so is often connected to the AVC, but apparently not in the S-20R. but that does not help the situation. As Jim says, on band 1 ?there is no ground, and I say there is no control of THAT grid voltage by ground, AVC or other, so it floats. On the other bands the bottoms of ?3,2,1 can be grounded [all depending] providing a DC ground ?but it goes thru the coil{s} so is strange to me. But band 1 is a real mystery to me too. ? ? Tom, I suggested a test for the bandswitch area? was it not practicle? ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Sunday, March 9, 2025 2:46 PM To: [email protected] Subject: Re: [HallicraftersRadios] S-20R mixer cct. #photo-notice ? Tom That is interesting.? The tube manual indicates that -3 volts should be there.? Have you replaced C5 and C8?? Minor leakage in either could cancel the expected negative bias on G3 of the 6K8.? From the QST article, I expect that there are unintended interactions when the expected voltages are out of spec. ? In looking at the schematic for the umpteenth time, I see how the upper band tank coils are returned to ground through switch 7D rotor that shorts the bottom of the band coils to ground.? Not sure how L13 is grounded when the band switch is in the BCB setting.? If you measure the DC resistance from the grid cap to ground you should measure R12 (33 ohms +/- 20%) plus the coil resistance for each band switch setting.? Is this the case??? ? Measuring from the switch side of R12, you should measure just the tank coil resistance to ground.? That resistance should increase as the band switch connects to the next lower tank coil.? If you don't see the coil resistance then perhaps the oscillator stator sections of either C1 or C2 is grounded? ? Likewise, the switch side of C37 should measure the LO coil resistance to ground for each band switch setting.? Like the above, each lower band coil resistance will be higher.? Is this the case? Remote troubleshooting is a s-l-o-w process, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy ? ? On Sunday, March 9, 2025 at 11:47:14 AM CDT, Allthumbs via groups.io <btse1@...> wrote: ? ? Thank you, Jim. The 6K8 control grid (grid cap) measures 0.00 vdc, pretty much as expected. ? Tom ? -- don??? va3drl |
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Re: S-20R mixer cct.
Tom That is interesting.? The tube manual indicates that -3 volts should be there.? Have you replaced C5 and C8?? Minor leakage in either could cancel the expected negative bias on G3 of the 6K8.? From the QST article, I expect that there are unintended interactions when the expected voltages are out of spec. In looking at the schematic for the umpteenth time, I see how the upper band tank coils are returned to ground through switch 7D rotor that shorts the bottom of the band coils to ground.? Not sure how L13 is grounded when the band switch is in the BCB setting.? If you measure the DC resistance from the grid cap to ground you should measure R12 (33 ohms +/- 20%) plus the coil resistance for each band switch setting.? Is this the case??? Measuring from the switch side of R12, you should measure just the tank coil resistance to ground.? That resistance should increase as the band switch connects to the next lower tank coil.? If you don't see the coil resistance then perhaps the oscillator stator sections of either C1 or C2 is grounded? Likewise, the switch side of C37 should measure the LO coil resistance to ground for each band switch setting.? Like the above, each lower band coil resistance will be higher.? Is this the case? Remote troubleshooting is a s-l-o-w process, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Sunday, March 9, 2025 at 11:47:14 AM CDT, Allthumbs via groups.io <btse1@...> wrote:
Thank you, Jim. The 6K8 control grid (grid cap) measures 0.00 vdc, pretty much as expected.
?
Tom
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Re: S-20R mixer cct.
Don, here's a photo of the underside in its as-found state. Not too bad but not something a sane person would plug in and turn on without at least replacing the electrolytics. Obviously it had seen some repairs over the years. I have since replaced most resistors and capacitors and replaced the old 2-wire power cord with a modern 3-wire.
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Tom
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Re: S-20R mixer cct.
Thank you, Jim. The 6K8 control grid (grid cap) measures 0.00 vdc, pretty much as expected.
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Tom
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Re: S-20R mixer cct.
开云体育Jim, interesting stuff? but I wonder, after your bold part You seem to have forgotten to emphasize ?“but in most designs the frequency shift caused by one is offset by the other so that good stability is obtained.”??? From my readings, ?in 1939/40, the 6K8 was the preferred mixer for all wave radios, not that it matters to Tom’s obstinant oscillator ?problem. Presently , I wonder what controls the hexode signal grid DC voltage, as using my eyes, it is not connected to ground, AVC, or anything. {a Riders book shows it to be ?connected to avc} ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Saturday, March 8, 2025 6:27 PM To: [email protected] Subject: Re: [HallicraftersRadios] S-20R mixer cct. #photo-notice ? Tom The following is excerpted from QST, February, 1941 ? "The high oscillator transconductances of the 6K8 and 6SA7 make them particularly suited for all-around usage. They oscillate strongly at high frequencies where L/C ratios are unfavorable. The 6A8 construction is not satisfactory for amateur usage because of instability in the oscillator. The oscillator electrode is a pair of rods located in the tube between the No. 1 grid and the screen. These side rods collect electrons from the cathode stream and the electrode current is controlled by the No. 1 grid. Unfortunately, changes in signal-grid or screen voltage also change the anode current. This conductance between signal grid and oscillator causes instability with variation in a.v.c. voltage. Fluctuations in screen voltage due to supply regulation also change the frequency ... skip... The 6K8 has been used extensively by the amateur and also the commercial manufacturer principally because it gives fair stability, and design problems are usually simple. The tuned-grid oscillator shown in Fig. 5 gives very little trouble and is easy to build.?The oscillator frequency is not independent of screen and a.v.c. voltages, but in most designs the frequency shift caused by one is offset by the other so that good stability is obtained. The 6K8 has an effect known as space-charge coupling which is experienced at high frequencies. This effect is as follows: The oscillator voltage on the No. 1 grid causes a fluctuation in the number of electrons in the region of the signal grid. The electron density changes at the oscillator frequency and as a result a displacement current flows into the signal grid. At high frequencies where the signal grid and oscillator frequencies are quite close, the impedance of the signal grid circuit at the oscillator frequency is quite high and as a result the displacement current produces an a.o. voltage across the signal grid circuit. This voltage, when smaller than the bias, reduces the gain of the tube slightly. Under extreme conditions it overrides the bias and causes rectification in the signal-grid circuit, causing a serious loss in gain. The coupling can be neutralized by a small capacitance - approximately 2 or 3 ??f d. - between oscillator and signal grids. Commercial practice is to use a condenser (known as a "gimmick") made by wrapping two pieces of wire together to give the desired capacitance. Neutralizing the space charge increases the gain and image ratio." ? The bold print above is my doing.? Perhaps a little attention should be given to other tube sections.? ?In your tube pin measurements, shown below, you do not measure the grid cap voltage.? If C5 is leaking then the 6K8 control grid will be positive which will have an affect on the triode oscillator section of 6K8 because of the common cathode. Just a thought, Jim -- don??? va3drl |
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Re: S-20R mixer cct.
Thank you, Jim. I will measure it and report. In the meantime, I just got back from a big swap meet and need to dig out from all my new treasures. ?
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Tom
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Re: S-20R mixer cct.
Tom The following is excerpted from QST, February, 1941 "The high oscillator transconductances of the 6K8 and 6SA7 make them particularly suited for all-around usage. They oscillate strongly at high frequencies where L/C ratios are unfavorable. The 6A8 construction is not satisfactory for amateur usage because of instability in the oscillator. The oscillator electrode is a pair of rods located in the tube between the No. 1 grid and the screen. These side rods collect electrons from the cathode stream and the electrode current is controlled by the No. 1 grid. Unfortunately, changes in signal-grid or screen voltage also change the anode current. This conductance between signal grid and oscillator causes instability with variation in a.v.c. voltage. Fluctuations in screen voltage due to supply regulation also change the frequency ... skip... The 6K8 has been used extensively by the amateur and also the commercial manufacturer principally because it gives fair stability, and design problems are usually simple. The tuned-grid oscillator shown in Fig. 5 gives very little trouble and is easy to build.?The oscillator frequency is not independent of screen and a.v.c. voltages, but in most designs the frequency shift caused by one is offset by the other so that good stability is obtained. The 6K8 has an effect known as space-charge coupling which is experienced at high frequencies. This effect is as follows: The oscillator voltage on the No. 1 grid causes a fluctuation in the number of electrons in the region of the signal grid. The electron density changes at the oscillator frequency and as a result a displacement current flows into the signal grid. At high frequencies where the signal grid and oscillator frequencies are quite close, the impedance of the signal grid circuit at the oscillator frequency is quite high and as a result the displacement current produces an a.o. voltage across the signal grid circuit. This voltage, when smaller than the bias, reduces the gain of the tube slightly. Under extreme conditions it overrides the bias and causes rectification in the signal-grid circuit, causing a serious loss in gain. The coupling can be neutralized by a small capacitance - approximately 2 or 3 ??f d. - between oscillator and signal grids. Commercial practice is to use a condenser (known as a "gimmick") made by wrapping two pieces of wire together to give the desired capacitance. Neutralizing the space charge increases the gain and image ratio." The bold print above is my doing.? Perhaps a little attention should be given to other tube sections.? ?In your tube pin measurements, shown below, you do not measure the grid cap voltage.? If C5 is leaking then the 6K8 control grid will be positive which will have an affect on the triode oscillator section of 6K8 because of the common cathode. Just a thought, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Tuesday, March 4, 2025 at 02:41:02 PM CST, Allthumbs via groups.io <btse1@...> wrote:
Newish member of this group, first time posting. I have an S-20R in need of repair. I am not a trained technician and am not particularly good at interpreting symptoms. However, I do have the chassis working just as it should from the grid of the first i.f. through the audio output. But the mixer stage is faulty—the LO is not oscillating. ? I have a voltage chart for an S-20R that was made up by a member of the Antique Radio Forum. The tube pin voltage readings on my chassis agree almost entirely with his chart, except for the 6K8 mixer. I’m posting the readings in the chart below. FYI—I took these readings with the chassis powered via a bucking transformer so that it runs on 117 vac. On the first line are his readings and on the second line, in red, are my own. FWIW, my voltage readings were made with a DMM, not a VTVM. ? ? If it helps, here's the mixer section: If you’re familiar with these sets, you might recall that the underside of the 6K8 socket is a bit difficult to access because the oscillator coil assembly partially covers it. Maybe the symptoms I’m posting will point to a solution that would mean I won’t face the daunting task of partially disconnecting and ?lifting the whole coil assembly.? :-) ? Any thoughts? Thank you, ? Tom |
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Fw: Re: [HallicraftersRadios] Off-The-Wall Question
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Justin:
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I didn't recognize your name in my initial response. I indicated I just
finished a manual for a HE-43C. When I was putting the mailing label on the
envelope, I realized it was for you. So it's on the way. Ah; the perils of
aging.
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Pete, wa2cwa
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----- Forwarded Message -----
Date: Sat, 8 Mar 2025 12:49:44
-0500
Subject: Re: [HallicraftersRadios] Off-The-Wall Question
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Lafayette HE-43C is not rare. It is identical to the HE-20C (which we sold
1000's of these sets - HE-20, 20A, 20B, 20C(relay and electronic switching
versions), 43C) except the 43C works on 110V AC and 6 volts DC. The 20C works on
110V AC and 12 volts DC. Other then that, they are identical. I just finished a
HE-43C manual for a customer. Both the HE-20C and 43C were made by United
Scientific Laboratories (USL) in Long Island City, NY.
A tunable receive and a crystal controlled transmitter was quite common
with a number of manufacturers in the early 60's. A Spot switch obviously was
common on these transceivers.
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Pete, wa2cwa
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On Sat, 08 Mar 2025 08:46:48 -0800 "Justin Bowser - KI5GKD" <justin.bowser@...>
writes:
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Re: Off-The-Wall Question
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For what its worth - the Lafayette mechnical filter Part Number in the
HB-600 is 1253-24.
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Pete, wa2cwa
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On Sat, 8 Mar 2025 17:35:22 GMT "k2orsfan via groups.io" <k4pf@...>
writes:
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Re: Off-The-Wall Question
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toggle quoted message
Show quoted text
Lafayette HE-43C is not rare. It is identical to the HE-20C (which we sold
1000's of these sets - HE-20, 20A, 20B, 20C(relay and electronic switching
versions), 43C) except the 43C works on 110V AC and 6 volts DC. The 20C works on
110V AC and 12 volts DC. Other then that, they are identical. I just finished a
HE-43C manual for a customer. Both the HE-20C and 43C were made by United
Scientific Laboratories (USL) in Long Island City, NY.
A tunable receive and a crystal controlled transmitter was quite common
with a number of manufacturers in the early 60's. A Spot switch obviously was
common on these transceivers.
?
The HB-600 had one major service bulletin. There were excessive failures in
the 2N2949 RF Power Amplifier so a board and circuitry with a different RF Power
Amplifier transistor was designed and circuit diagram and install instructions
were provided.
?
For a short period, The HB-600 was replaced by a HB-600A which had the
revised RF Power Amplifier already installed. There were also some other circuit
changes but don't recall what they were.
?
?
On Sat, 08 Mar 2025 08:46:48 -0800 "Justin Bowser - KI5GKD" <justin.bowser@...>
writes:
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Re: SX-100MK2A
开云体育Bob,Thanks for the tip, but no such marking on mine. Ray, W4BYG On 3/7/2025 22:21, Bob via groups.io
wrote:
-- "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 |
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Re: Off-The-Wall Question
开云体育For what it’s worth I converted an Eico CB transceiver to 10 meters (29.6) many years ago.? It was crystal transmit and VFO receive. ? Mike Langner ? From: [email protected] <[email protected]> On Behalf Of Justin Bowser - KI5GKD
Sent: Saturday, March 8, 2025 9:47 AM To: [email protected] Subject: Re: [HallicraftersRadios] Off-The-Wall Question ? Mike - It's solid state so no tubes or HV to worry about.? I've tested low-pass filters with my Nano VNA a long time ago and seem to remember that one channel is hooked to input and the other hooked to output. ? Pete - I'll give that a try and let you know.? I also got another rare/unusual bird coming, an HE-43C.? I've never seen a CB where you transmit with crystal and receive by VFO.? What I plan doing is to put in a circuit that replaces the crystals with an Arduino controlled 5351 module. ? 73, -- Justin B. |
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Re: Off-The-Wall Question
This may help if your bad filter was made by Kokusai: It seems that the insertion loss is pretty much the same as the Collins mechanical filters of the same era, about 20 dB. Good luck, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Saturday, March 8, 2025 at 02:55:07 AM CST, Peter A Markavage via groups.io <pmarkavage@...> wrote:
To rough test whether the mechanical filter is working, jury rig a .01 Mfd
cap disc capacitor from filter input to filter output. If volume and noise perk
up, filter is probably bad.
?
Since I worked at Lafayette and also did the service for most of the NJ
stores for a number of years, when we started closing the stores as part of
bankruptcy proceedings, all the service parts, cannibalized equipment, and
anything else the stores didn't want and were going to throw it away, it all
came home with me. So, I probably have the largest collection of NOS Lafayette
parts that still exists today although I've been trying to work down the pile
for the last 40 years.
?
I don't recall, since I don't have the file folder and manual?in front
of me, whether we issued any service addenda on the HB-600.
?
The HB-600 was the "top-of-the-line' solid-state base transceiver we sold
in 1966. It was also called the "CB Commander" (one of the marketing guys came
up with that tag). Also had a? 5 stage "unique RF Noise Silencer". It sold
new for $220.
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It made the front cover of the main 1966 Lafayette catalog.
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Pete, wa2cwa
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On Fri, 07 Mar 2025 21:54:26 -0800 "Justin Bowser - KI5GKD" <justin.bowser@...>
writes:
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Re: Off-The-Wall Question
?
toggle quoted message
Show quoted text
To rough test whether the mechanical filter is working, jury rig a .01 Mfd
cap disc capacitor from filter input to filter output. If volume and noise perk
up, filter is probably bad.
?
Since I worked at Lafayette and also did the service for most of the NJ
stores for a number of years, when we started closing the stores as part of
bankruptcy proceedings, all the service parts, cannibalized equipment, and
anything else the stores didn't want and were going to throw it away, it all
came home with me. So, I probably have the largest collection of NOS Lafayette
parts that still exists today although I've been trying to work down the pile
for the last 40 years.
?
I don't recall, since I don't have the file folder and manual?in front
of me, whether we issued any service addenda on the HB-600.
?
The HB-600 was the "top-of-the-line' solid-state base transceiver we sold
in 1966. It was also called the "CB Commander" (one of the marketing guys came
up with that tag). Also had a? 5 stage "unique RF Noise Silencer". It sold
new for $220.
?
It made the front cover of the main 1966 Lafayette catalog.
?
Pete, wa2cwa
?
?
?
On Fri, 07 Mar 2025 21:54:26 -0800 "Justin Bowser - KI5GKD" <justin.bowser@...>
writes:
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don Root
Jim Whartenby
Allthumbs
Peter A Markavage
Ray, W4BYG
Mike Langner