Metalwork - Lathe and Mill topics

Sunday, 21 January 2024

Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

I will keep this all in mind for sure 👍!!

On Jan 21, 2024, at 1:31 PM, Don Root VA3DRL <drootofallevil@teksavvy.com> wrote:

Robert , that method likely wont to much. I was mainly suggesting that many applications of tubes are not at one bias voltage. Variable Mu tubes are often have the bias controlled by the AVC. For the tube to do its job, it has to work as intended over a wide range of bias voltages/ gains.
Your testers likely test that the tube can provide lots of transcconductance[Gm] [gain, sort-of]. however when the bias is say minus 20 V, they don't bother to do another test the Gm ,, But they do/ can test for gas. It the tube is gassy it mucks-up the tube operation so it cant operate at small gain/ plate current so the tube can't throttle-back to low amplification.
I think I just saw that a 6SK7 has a normal Gm of 5000, but should throttle -back to only 10, [micro-Mhos] I think.
reading back; many 1930's gas tests were not very sensitive, but likely your testers have a good separate gas test using a marked "gas"switch. I wonder if you have tried that on the tube in question?

On Sat, Jan 20, 2024 at 07:56 AM, Robert Lonn WA6PHN wrote:

Not sure about that till I get further into this.. Sometimes I will turn the Bias up and down just to watch how the meter responds.. Not very scientific..
--
73 don va3drl

Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Robert , that method likely wont to much. I was mainly suggesting that many applications of tubes are not at one bias voltage. Variable Mu tubes are often have the bias controlled by the AVC. For the tube to do its job, it has to work as intended over a wide range of bias voltages/ gains.
Your testers likely test that the tube can provide lots of transcconductance[Gm] [gain, sort-of]. however when the bias is say minus 20 V, they don't bother to do another test the Gm ,, But they do/ can test for gas. It the tube is gassy it mucks-up the tube operation so it cant operate at small gain/ plate current so the tube can't throttle-back to low amplification.
I think I just saw that a 6SK7 has a normal Gm of 5000, but should throttle -back to only 10, [micro-Mhos] I think.
reading back; many 1930's gas tests were not very sensitive, but likely your testers have a good separate gas test using a marked "gas"switch. I wonder if you have tried that on the tube in question?

On Sat, Jan 20, 2024 at 07:56 AM, Robert Lonn WA6PHN wrote:

Not sure about that till I get further into this.. Sometimes I will turn the Bias up and down just to watch how the meter responds.. Not very scientific..

--
73 don va3drl

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Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

They did this so that there could be a number of different voltages used for the filament voltage for "portable" or mobile use.
You have to be very careful when wiring up the AC cord for Collins or you can easily wire it for the wrong voltage.
Also of note is often with extended use the alignment key on the 11 pin (IIRC) on the socket in the chassis can wear and the plug inserted incorrectly and zip go all of your tubes as well.
The 51S1 was uses extensively by the ASA (Army Security Agency) in the Vietnam era. It was used as a light receiver where the big boat anchors were a little cumbersome. Two were used in helicopters for RDF (and other unspecified uses).
When used with the Collins transmitters of the series they would allow almost full coverage of the range.
All of this is from a very poor memory of way back then.
JD
KE4MD

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Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Not familiar with it at all, so this is just a guess. But perhaps to create a smaller magnetic filed around the filament leads? 1 amp vs 4 amps means much small magnetic field.

Again, just a guess

Will N4JBD

On 01/21/2024 11:58 AM CST Robert Lonn WA6PHN <roblonn@cox.net> wrote:

Not sure Electrically why Collins did this type of Filament set up, but it must have been for a very sound engineering reason..

This is a link to a short 1 minute Video of the filament circuit and 25.2 Volt AC power transformer. If your familiar as to why this was done this way, it would be appreciated to share your knowledge.. The KWM-2A has a somewhat similar setup for some of its tubes..

Robert WA6PHN

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of Gary WB6OGD
Sent: Friday, January 19, 2024 8:58 AM
To: Amateur-repairs@groups.io
Subject: Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Robert,
Good advice.
I am no expert but I believe you can't rely too heavily on any tube tester. The actual circuit where the tube goes is the best tester.

I downloaded the 51s1 manual just to have a look. The BFO is one tube. I would try another, there are probably many types that could substitute
there if you don't have a good spare. I am thinking it maybe has a filament to cathode short or leakage of some kind that lets the AC filament signal onto
the BFO signal. But just a guess.
73,
Gary
WB6OGD

Grownups never understand anything by themselves and it is tiresome for children to be always and forever explaining things to them,

Antoine de Saint-Exupery in The Little Prince

Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Spent an hour going through the 51S-1 Schematic to get myself familiar with the layout again.. Interesting is the 25.2 Volts AC used to feed all the Filaments in the 6 volt tubes.. You basically have 4 tubes in series, with several stages divided with dropping resistors and filter capacitors.. I did get some feedback early last year that someone who had the same issue found a cold soldering connection/Bad Capacitor on one of the filament of a tube..

Not sure Electrically why Collins did this type of Filament set up, but it must have been for a very sound engineering reason..

This is a link to a short 1 minute Video of the filament circuit and 25.2 Volt AC power transformer. If your familiar as to why this was done this way, it would be appreciated to share your knowledge.. The KWM-2A has a somewhat similar setup for some of its tubes..

https://www.youtube.com/watch?v=x4S52RDGNgM

Robert WA6PHN

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of Gary WB6OGD
Sent: Friday, January 19, 2024 8:58 AM
To: Amateur-repairs@groups.io
Subject: Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Robert,
Good advice.
I am no expert but I believe you can't rely too heavily on any tube tester. The actual circuit where the tube goes is the best tester.

I downloaded the 51s1 manual just to have a look. The BFO is one tube. I would try another, there are probably many types that could substitute
there if you don't have a good spare. I am thinking it maybe has a filament to cathode short or leakage of some kind that lets the AC filament signal onto
the BFO signal. But just a guess.
73,
Gary
WB6OGD

Saturday, 20 January 2024

Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Not sure about that till I get further into this.. Sometimes I will turn the Bias up and down just to watch how the meter responds.. Not very scientific..

BTW, I was watching a YouTube video on someone restoring a 1960's vintage tube table top AM radio..

He dripped some contact cleaner into the tube socket, OK nothing new there, but then he scrubbed the pin sockets with something??? I could not figure out what he was using?? So I asked him and then the light went off in my head… I think I will use these on the radio just to be sure everything is nice and clean..

Robert WA6PHN

https://www.walmart.com/ip/GUM-Proxabrush-Go-Betweens-Cleaners-Moderate-10-Count/740700598

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of Don Root VA3DRL
Sent: Friday, January 19, 2024 10:53 PM
To: Amateur-repairs@groups.io
Subject: Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Robert , thanks for your words. I did read your stuff.

If they all test the tube at the same bias and get the same results, that is good.

Do any of them call for testing at a more negative bias as well ?? as a "normal" bias?

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of Robert Lonn WA6PHN
Sent: Friday, January 19, 2024 10:43 PM
To: Amateur-repairs@groups.io
Subject: Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Don, as I mentioned in my other post, see below, I now have 4 tube testers and they are precision high end devices, hopefully they can expose any tube issues that might come up.. Robert WA6PHN

When I first did this I only had a B&K 747 tube checker, but last year I visited an estate sale and picked up 3 nice tube checkers…

A Heathkit TT-1, A Triplet 3444A and a Hickok 539C.. Good to be the first on site at 6:30am so I could get the pick of the litter.. Also grabbed all the Tubes, probably around 850 or so..

I think I will start with the 539C checker first and if anything seems strange I will check it on a different checker.. The TT-1 was calibrated by me, and it was very close, the 3444 and 539C tracked very close to the calibrated TT-1.. I did replace all the old capacitor in the Hickok and Triplet and a few in the Heathkit..

The Heathkit TT-1 has a built in " I think" a 5 KHz oscillator that they modulate on the grid of the tube.. ???? Maybe I should use that instead of the 539C, may reveal something with a questionable tube.. We will see how all that goes,, Let The FUN BEGIN, after all it is Ham Radio!!! J

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of Don Root VA3DRL
Sent: Friday, January 19, 2024 7:13 PM
To: Amateur-repairs@groups.io
Subject: Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Robert and all

Re "I am no expert but I believe you can't rely too heavily on any tube tester. "

Well if it "reads bad" it likely is bad.

if it "reads good" it may well be good under the condition it is being tested at.

Most TTs measure Gm [where amplification is part of the intent in the tube.]

If you have a variable Mu tube you really want to know if it works properly with a small bias. But you want it to also work properly at a large negative bias

.. if you don't test it down there you might not know it has too hi a gm .. maybe that is where the gas messes things up like Jacques said.

I recently saw other postings somewhere the front end tube tested ok … but did similar things

.. but we need to get the books out on the details

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of Gary WB6OGD
Sent: Friday, January 19, 2024 11:58 AM
To: Amateur-repairs@groups.io
Subject: Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

--
73 don va3drl

Friday, 19 January 2024

Re: [Amateur-repairs] Creating a LSB and USB Test Signal!!

Robert , thanks for your words. I did read your stuff.

If they all test the tube at the same bias and get the same results, that is good.

Do any of them call for testing at a more negative bias as well ?? as a "normal" bias?

Don, as I mentioned in my other post, see below, I now have 4 tube testers and they are precision high end devices, hopefully they can expose any tube issues that might come up.. Robert WA6PHN

When I first did this I only had a B&K 747 tube checker, but last year I visited an estate sale and picked up 3 nice tube checkers…

A Heathkit TT-1, A Triplet 3444A and a Hickok 539C.. Good to be the first on site at 6:30am so I could get the pick of the litter.. Also grabbed all the Tubes, probably around 850 or so..

Robert and all

Re "I am no expert but I believe you can't rely too heavily on any tube tester. "

Well if it "reads bad" it likely is bad.

if it "reads good" it may well be good under the condition it is being tested at.

Most TTs measure Gm [where amplification is part of the intent in the tube.]

If you have a variable Mu tube you really want to know if it works properly with a small bias. But you want it to also work properly at a large negative bias

.. if you don't test it down there you might not know it has too hi a gm .. maybe that is where the gas messes things up like Jacques said.

I recently saw other postings somewhere the front end tube tested ok … but did similar things

.. but we need to get the books out on the details

--
73 don va3drl