My CTC-16XL Project. - Page 26 - Videokarma.org TV - Video

Yamamaya42 · #**376** 09-28-2019, 12:21 PM

9 pin test socket made, https://imgur.com/CGv43mR

waiting for 7 pin to arrive

Yamamaya42 · #**377** 10-04-2019, 10:36 PM

I now have insight on what happened to my IF section...
https://i.imgur.com/hlFwF2h.png

something is VERY wrong with the 2nd if, and thus it takes 1st down with it.
it is NOT bad tubes, cause i checked that.

I wont know for sure till i have the time to pull it all apart and check caps/ resistors / tube sockets.

freakaftr8 · #**378** 10-04-2019, 10:50 PM

Are the voltages off the 6JH6 1st IF correct? It's hard to read but c17 is tied to all those that goes to ground. is it shorted?

Yamamaya42 · #**379** 10-04-2019, 11:11 PM

Quote:

Originally Posted by freakaftr8

Are the voltages off the 6JH6 1st IF correct? It's hard to read but c17 is tied to all those that goes to ground. is it shorted?

if 2nd if is down then 1st can't work
the 2nd gives the plate bias to the 1st

not sure what it is yet, Remember i have a CTC-16-XL.
almost the same as the 16, but different in quite a few ways.

Yamamaya42 · #**380** 10-04-2019, 11:20 PM

Right now I am very suspicious of c12 ( c21 on the CTC-16 version ) , if that was leaky that may cause what I am seeing.

when i get around to pulling the chassis to try and fix this, i will most likely replace all the.001 caps

Yamamaya42 · #**381** 10-04-2019, 11:43 PM

on a unrelated note, I took a nibbler tool to my HV cage, to add even more airflow, this is the thermal scan after 15 min, w/o the fans.
https://imgur.com/XSifzsf

Tom9589 · #**382** 10-05-2019, 10:17 AM

Does anyone know why the second IF stage is "floated" above ground by about 150V? Is it an effort for using the second IF stage as a voltage drop to provide plate voltage for the first IF stage? Kind of like the audio output tube circuit in some B&W sets to provide an approx 140 volts source at its cathode. I see where RCA used this arrangement for many different models.

If the AGC were way off, the second IF could be biased such that the voltages for both the first and second IF could be way off. Go back and check the voltages on the first IF stage as well. There is a good chance they are off as well.

Yamamaya42 · #**383** 10-05-2019, 11:41 AM

Quote:

Originally Posted by Tom9589

Does anyone know why the second IF stage is "floated" above ground by about 150V? Is it an effort for using the second IF stage as a voltage drop to provide plate voltage for the first IF stage? Kind of like the audio output tube circuit in some B&W sets to provide an approx 140 volts source at its cathode. I see where RCA used this arrangement for many different models.

If the AGC were way off, the second IF could be biased such that the voltages for both the first and second IF could be way off. Go back and check the voltages on the first IF stage as well. There is a good chance they are off as well.

I only saw about 20-30v on pin 5&6 of the 1st IF ( should have been 160v) and nothing on 1,2,7 (less than 1v) , and so I look at the 2nd IF , and saw it had the plate voltage, but everything related to the cathode's flothed ground was very low. (30v)
even with 1st IF removed the cathode voltage was gone.

I can see WHAT is happening, but since I was probing with tube test sockets, it don't know why yet.

with 1st IF removed, should i not see 160v ( approx) on the cathode of the 2nd?
I'm just going to have to make time at some date to take it all apart and check all resistors / caps in the area again.

Yamamaya42 · #**384** 10-05-2019, 11:59 AM

another thing that may explain what i am seeing, this is doing EXACTLY what it did before i replaced R48 & R50, i put in 1/2 watt carbon film ones, it said to use 1/2 watt, perhaps they did not hold up, perhaps it's time to replace every resistor off that power line with 1 watt resistors. ( and the .001 caps )

EDIT-
It's looking more and more like that is what the problem is, seeing a good 300+ v at point 3, and on the far side of R51 getting power to the plate of 2nd IF. But there is crap at point 14 other side of R50, hardly 30v.
Time to change it again with a 1w and the filter caps.

freakaftr8 · #**385** 10-06-2019, 12:23 AM

Those .001 wax ceramic ELMENCO caps I have heard are usually either bad or going to go bad soon..

Yamamaya42 · #**386** 10-06-2019, 01:07 AM

Quote:

Originally Posted by freakaftr8

Those .001 wax ceramic ELMENCO caps I have heard are usually either bad or going to go bad soon..

I always thought those tube cap things were funny looking, but i never thought they would cause this much trouble :/

Electronic M · #**387** 10-06-2019, 10:34 AM

Quote:

Originally Posted by Yamamaya42

I always thought those tube cap things were funny looking, but i never thought they would cause this much trouble :/

The elmenco caps .001 and up are just wax caps in disguise.

Yamamaya42 · #**388** 10-06-2019, 10:49 AM

Quote:

Originally Posted by Electronic M

The elmenco caps .001 and up are just wax caps in disguise.

I had never seen caps like them before i saw them in this set, kinda took them for resistors, till they were pointed out as CAPs in the SAMs, guess i should have replaced them, as they are clearly a source of trouble now

Yamamaya42 · #**389** 10-07-2019, 08:41 AM

I'm guessing that this will be a good replacement for them.

667-ECQ-E10102KFB (mouser )

I'm in no big hurry to get IF working again, as it's working OK via video input, I will most likely wait till it gets cooler.

dtvmcdonald · #**390** 10-07-2019, 09:30 AM

Those caps are the usual caps if you want 1 kV, very reliable.

BUT ... why the "B" on the end???? That's NOT usual, as it means a crimp in the
leads. Normally for old sets one leaves the B off. And saves a couple of cents.