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

Hello, wow already February and so much to do in retirement! J 

 

I wanted to share something with the group that I found interesting. As I prepare to dig back into my Collins 51S-1 radio, I mentioned that I would start the process over and test all the tubes again. Previously tested on a B&K 747 checker… Since then I have added to my tube checker collection and decided to use my Heathkit TT-1 tester, so I went and validated the calibration again.. Tested a 6V6 and 5Y4 as they were just sitting on the side of my bench and easy to get to. They both checked good!

 

Then the fun began when I grabbed a 6C4 tube. Being a 7 pin tube it went into a different socket than the 6V6 or 5Y4 tube.

The tube began to act very erratic, On-Off, low then high, testing it for shorts showed no shorts.. At first I suspected a bad tube socket but further inspection showed no issues??? The tube was marked on the box as good with a GM reading of 2150..

So I dug up 4 other 7 pin tubes like a 6BA6, and several others… All checked fine with no problems. Put the 6C4 back in same erratic problem.. My brain began to go in many different directions!!!

 

So out came my Hickok 6000A, Jackson 658 and Weston 978 Military version it was time to try that 6C4 and see what I get…

6000A said the tube was Good??? But the meter did move a little, like a ¼ of an inch on the needle..

Then I tried the Jackson, and same results, tube was good but again a very small amount of needle movement, like 1/16 of and inch…

 

!!!!!! Then a big surprise happened, tried it in the Weston 978, same version as the 981 series.. and wow, the tube was acting erratic like it did on the Heathkit TT-1,,, What is going on here??????

 

So after some coffee and a bit of a rest, we do that at age 76, LOL,, we began to look at some literature in my "How To Use, Calibrate, Repair And Upgrade Tube Testers by Igor S. Popovich" A nice Birthday present and surprise from my son last November…

 

Their it was in clear print, The Heathkit has a built in 5KHz Oscillators to place signal on the Grid, and the Weston has a 1 KHz oscillator to also place a signal on the tube Grid under test.. Apparently the 6C4 was not happy with this test signal… A good reason why having different tube checkers can help out a lot, or at least one of the Top Testers available…

 

So I will definitely be using the Heathkit TT-1 with the Weston 978 standing buy when I go back and re-check the tubes in the Collins radio, wonder what I might discover???? I will report back with a follow up, still a few weeks out as I have several other projects now on the bench, like I said Busy in retirement, J

 

If you have had similar experiences please do share it with the group… Like one of you said early on the only real test for a tube is when it is working in the circuit it was designed for.

 

Robert WA6PHN,,

What do they sing,, "It Never Rains In Southern California", Sure!!!! L

 

 

From: Amateur-repairs@groups.io [mailto:Amateur-repairs@groups.io] On Behalf Of Robert Lonn WA6PHN
Sent: Sunday, January 21, 2024 2:32 PM
To: Amateur-repairs@groups.io
Subject: 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