Admiral 30A12 restoration - Page 2 - Videokarma.org TV - Video

W4rtc · #16 05-17-2013, 05:14 PM

Hi Bob
Send a address and I will send you a box of five fuses. 1/4 amp one inch long 1/4 inch dia.
Joe

bandersen · #17 05-17-2013, 09:00 PM

Thanks, I'll take you up on that offer

This set has become rather frustrating. Especially since it was working fairly well on mostly original components. Now that it's been fully recapped, I still have some nagging issues remaining.

1. Excessive width. I need to reduce the width by about 30% so something has to be way off. I've replaced all the caps and checked/replaced all resistors. Also swapped the 6BG6 HOT and adjusted the drive and width controls. All that had minimal effect. Time to check the few mica caps I guess.

2. The tuner has some nasty issues. When adjusting the fine tuning the picture cuts out. I have to tweak the channel knob to get a clean picture. I have cleaned the contacts but I think it's time to pull it out for a closer inspection.

3. I don't get any picture until the brightness is about 3/4 clockwise. The CRT tests very good but the cutoff test stinks. Perhaps I need to alter the grid bias ?

4. Sound stinks. Hopefully it's just an alignment issue.

Oh well, if it was easy it wouldn't be much of a challenge now would it

wa2ise · #18 05-18-2013, 04:21 PM

I see a selenium rectifier just to the right of the power switch in your above picture. Those are known to go bad. What does it do in your set?

bandersen · #19 05-18-2013, 04:28 PM

Good eye. It's tied to the 6.3 VAC filament supply and I believe it creates a small negative bias for a few tubes. It's definitely on my list of many things to check

bandersen · #20 05-18-2013, 10:05 PM

I was just looking through all the caps I clipped out of this set and was surprised that about half are Dumont branded. Most of the rest are Cornel Dubilier with a few Sprague and Micamold in the mix.

bandersen · #21 05-19-2013, 06:47 PM

I've spent far more time on this set than I ever expected trying to track down the excessive width issue.
Finally, as I was about to abandon all hope, I noticed the huge power resistor in the HV cage was cold! An ohmmter confirmed that it was open.

Now where to find a replacement ? Luckily, I have an entire space 30A1 parts chassis but it too was bad.

So, I pulled one from another of my Admiral sets,. Ugh! All three are bad

I'm guessing this was either a common point of failure back in the bad or they go bad just sitting idle over the years.

I have a coupe more sets to scavenge from otherwise I'll cobble something together.
Regardless, I'm going to have to find a source of replacement 5,300-6,300 ohm 50W resistors if I want to get all my sets working properly.
Note the taps are 500 ohms apart and used to correct horizontal linearity if needed. All my sets use the center tap so that would be 5,800 ohms.

Geist · #22 05-19-2013, 08:17 PM

Hi All;
Bob, It looks like it is the same as what is used by RCA in the 630, and 830 type of sets.. Possibly more, or other RCA early TV's.. The Flyback also looks like it could be the same..
THANK YOU Marty

bandersen · #23 05-19-2013, 08:49 PM

I pulled one from every Admiral set and chassis I have and they are all bad

Quote:

Originally Posted by Geist

Hi All;
Bob, It looks like it is the same as what is used by RCA in the 630, and 830 type of sets.. Possibly more, or other RCA early TV's.. The Flyback also looks like it could be the same..
THANK YOU Marty

Yes, it both looks the same and is the same value. So I suppose I could borrow a good one from my 630TS.

This was Admiral's first TV on the market so I bet they were cautious and cloned RCA's HV design.

wa2ise · #24 05-19-2013, 09:13 PM

If the open is between the 2nd and 3rd terminal (counting from the bottom) and if the ohms between the 2nd and 3rd, and the 3rd and 4th terminal are supposed to be 500 ohms, connect terminals 2 and 3 together (to bridge the open) and connect the wire that was on the 3rd terminal to the 4th (top) terminal.

bandersen · #25 05-19-2013, 09:18 PM

Great idea, but unfortunately it's the main element that's burned out in all seven

bandersen · #26 05-19-2013, 11:54 PM

I dug up a 7500 and put 20K in parallel to get about 5500. I'll replace it as soon as I track down something more suitable.

Yep, that did the trick

Now I'm curious. If I had realized it was bad right away and replaced it without doing the full recap, how well would the set have worked

kvflyer · #27 05-20-2013, 08:16 AM

Well Bob, how about going to Mouser or one of the other vendors and just getting a few of the values that work and just putting a single one in? (If I understand correctly, the taps are for selection to get the right width?)

Possibly, you could find a hollow power resistor and just mount it in the same place, or alternatively, just use resistors similar to the ones you are trying temporarily.

I have to thank you for your tenacity. You find and attack all of the "Tough Dog" problems and come up with solutions so that when we get going on a project, you have already found and fixed it!

Oh yeah, it looks great!!!

Geist · #28 05-20-2013, 08:33 AM

Hi All;
Bob, Congratulations on getting the Admiral going.. I find that interesting, in that even if it is mostly the same design, the Bad section in the one in my 8T30 is the one between the second and the third lugs (500 Ohms) and not the first section of 5800 Ohms.. Is is the First section that is bad in all of your resistors that you have checked ??
THANK YOU Marty

bandersen · #29 05-20-2013, 12:54 PM

Quote:

Originally Posted by kvflyer

Well Bob, how about going to Mouser or one of the other vendors and just getting a few of the values that work and just putting a single one in? (If I understand correctly, the taps are for selection to get the right width?)

Possibly, you could find a hollow power resistor and just mount it in the same place, or alternatively, just use resistors similar to the ones you are trying temporarily.

I have to thank you for your tenacity. You find and attack all of the "Tough Dog" problems and come up with solutions so that when we get going on a project, you have already found and fixed it!

Oh yeah, it looks great!!!

According to the service info, you use he center tap unless you can't get hor. linearity by adjusting the linearity and drive controls. However, it clearly does affect the width too.

The only 50W fixed tubular resistors available are 5K, 7.5K or 10K. Coincidentally, the 7.5K are on sale at Allied so I ordered a few along with some 20K power resistor to put in parallel. There are also adjustable 50W 10K resistors, but the power rating is proportional to the tap position. So if I put it around 6K, I've reduced it to a 30W resistor.

Quote:

Originally Posted by Geist

Hi All;
Bob, Congratulations on getting the Admiral going.. I find that interesting, in that even if it is mostly the same design, the Bad section in the one in my 8T30 is the one between the second and the third lugs (500 Ohms) and not the first section of 5800 Ohms.. Is is the First section that is bad in all of your resistors that you have checked ??
THANK YOU Marty

The first section is bad in every resistor I checked

bandersen · #30 05-20-2013, 02:07 PM

I forgot to mention that I've already shocked myself on the twisted leads of the 10K power resistors sticking outside the cage while reaching for the drive control.

I now have a nice little burn mark on the side of my thumb.
It's been quite a while since I shocked myself and I think I was overdue.