High voltages on Admiral 19A11.
 

Good evening gents,

I have been working on my Admiral 19A11 for some time now. This set has been completely recapped and all resistors replaced. Horizontal sweep transformer and filter choke have also been replaced. The set has been working fairly well, except for a vertical linearity issue (picture squashed at the bottom), which it has always had. I began to test voltages to try and track down this vertical linearity issue. However, I immediately noticed that all voltages were high across the entire set. Even at the 5Y3 tube (L.V, rect.). Pins two and eight should be 240VDC and are running around 266VDC. Pins four, and six should be 240VAC and are running around 292VAC. Any ideas where my issue may lie? My untrained, novice opinion is the power transformer. Nothing in the circuits really before the 5Y3 tube other then the power transformer. The transformer stays cool to the touch for about 40 minutes, then starts to warm up. Never gets too hot to touch, but does get fairly warm.

Any advice would be greatly appreciated. Thanks.

What's the AC line voltage on the set ? They typical spec out the voltages assuming it's 117, but it's often more like 125 these days. That will increase all the voltages in the set.

SAMS lists it at 117. The ACV at my plug is reading 115.5 right now.

I always seem to get higher voltages in sets and the ac voltage is 113 to 115 .

your lin issue could be the 6kv caps , what did you put there ? sometimes changing the value a little corrects the lin issue

mike

In photo from left to right the SAMS called for .005, .001, .001, .005, and .005 (all microfarads @ 6KV).

Replacements values are .0047, .001, .001, .0047, and .0047.

Thanks!

Very interesting regarding voltages when AC is 113 to 115. My house typically runs around 115.

Looks like ceramic discs for 6KV caps. They can be non linear. That may be your problem. I did that years ago on my Motorola TS-4 and it worked. One finally failled and the newer tubular 6KV caps perform much better.

Ah! Had no idea about the ceramic discs having possible issues. I will try replacing with tubular ones. Any ones specifically that I should be looking for? Brand? Assuming Mouser carries them.

Thanks again everyone. Guess this is how new guys learn, huh? :thmbsp:

I just did a search on Mouser for 6kV caps and all that came up was ceramic disc type. Any suggestions for where to get the tubular kV caps from?

Thanks.

I have gotten them from http://justradios.com/ or http://www.alliedelec.com/ .

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

You guys are great! Going to try using the tubular kV caps and I will report back results. :D

Ceramic caps have a peculiar property that causes the capacitance to vary as the voltage on them increases. So when you try to pass a sawtooth waveform through one, it gets "bent" causing the non-linearity.

Thanks Bob, I was wondering why a capacitor that measured correct on my checker would not work well in a signal-coupling or wave-shaping circuit.

Someone else on this forum has suggested that ceramics were good for bypass applications and not much else.

Here's a more in depth discussion on this topic. http://www.videokarma.org/showthread.php?t=260749

When I popped open my National TV-7, I was surprised to see original ceramic doorknob caps for the horizontal. So it seems that ceramics work fine in the horizontal, but not the vertical.

Using a much larger ceramic cap for the vertical should reduce or eliminate the non linearity.

Bob,

Thanks SO much for the explanation. Very interesting and noted. Cannot wait to swap out and see the result. I ordered the caps through Allied.

Thanks again everyone. Will post update in a few days with result.

Re: the higher voltages: I've found that it's not unusual for the measured voltages to be a bit higher than those in the Sams (or Rider's) manuals and don't sweat it as long as everything works OK, current draw is reasonable and the transformer stays cool.

After about 40 minutes, my power transformer does heat up. It does not get too hot to touch. It heats up so that if I put my entire hand on it, it is nice and toasty. I can keep my hand on it indefinitely without burning myself. Once it gets to this temp, it seems to stabilize there.

Not sure about this set in particular, but a hot tube next to a transformer can also warm it somewhat.

Phil Nelson

99.999% of my experience is in radio vs tv, but I'd consider it normal for a transformer to run warm but nowhere near "ouch" warm. Also, and again this is based on my very limited TV experience, it seems odd that the DC out (pins 2 and 8) of the 5Y3 would equal the AC in; I'm used to seeing it a bit higher, more in line with what you're measuring.

I'd be curious to hear what the TV experts have to say about that. Am I all wet, or what?

The 5Y3 tube is right next to the transformer. That tube runs very hot and I guess you are right, it could warm up the transformer some. My transformer never gets to "ouch" status.


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Don't forget when a lot of those manuals were written meters were resistive VOM's and possibly even VTVM's and not Digital meters, that are possibly reading peaks of the pulses coming through the rectifier, and possibly not the more lower average reading the older meters may have been indicating. Higher line voltage also a very valid factor....

:thmbsp: Yep , the voltage figures on the schematics were likely taken with a voltmeter with around 10K ohms per volt loading , wheras modern meters are much higher (Maybe 1 to 5 Meg per volt ?) . Since the new meter puts less load on the circuit the voltage reading is higher .

Solution = get a nice old VOM like my favorite , the old reliable Simpson 260 :D

PS , Most voltage charts will have a caption somewhere saying "Voltages measured with 10K per volt meter" or something similar .....

Again, great to know! Set seems to be working fine other than the linearity issue, which hopefully the tubular kV caps will fix. So guess that remains the best diagnostic tool of the set right now - working well.

Thanks.

This may be a wild goose chase . . . . . but it is worth a check.

Make the power transformer resistance check suggested at the bottom of Rider page 3-9 and continuing at the top of page 3-10 in the 19A1 Rider schematic downloadable at:

http://www.earlytelevision.org/tv_sc..._diagrams.html

Then make sure you are using the correct rectifier tube!

The 19A1 chassis was occasionally supplied with power transformers made for the 5U4G instead of the 5Y3. If the wrong rectifier tube is used, this usually produces lower DC voltage, but if a 5Y3 were used with the less common 5U4 transformer, the DC might be slightly higher. The wrong tube can also produce transformer overheating.

James

Since it's fun to irresponsibly speculate (lol), I think it's more likely that we're just spoiled by the precision of the test equipment we have available. It's nothing to read a couple hundred volts with .1V resolutin on a DMM, but takes some effort to read the same thing to within 10% on a typical analog meter (I'm thinking a "modern" 260 on the 500V scale.)

Most old consumer stuff used 10-20% tolerance parts, so I try not to get too hung up on the numbers. Back when I was in electronics school, one of my instructors (a grouchy old fart) was fond of saying "close enough for government work." Now that I'm becoming a grouchy old fart, I appreciate the simple brilliance of that statement.

I may make sure that the power transformer in there is the one for the 5Y3 rect. tube. I do recall seeing in the SAMS a production change note in the parts list next to the Power Transformer. That's what it must have been. Easy enough to track down info and switch to the 5U4 tube if need be. Thanks for that info.

Just read the Rider. Glad they supplied the resistance check, b/c when I first got the set I cleaned it up and REPAINTED the power transformer. HA! So any red dot that may have been there is long gone. I did tape off the part number and that remains and it is the correct part number. So the resistance check should reveal which transformer I have. Right now, the rect. tube in there is a 5Y3.

Always take lots of reference photos before doing any work :yes: Is there a tube chart inside the cabinet ?

There is. I believe that says 5Y3 for rect. tube.

'Member that the 5Y3 has a 2A filament and the 5U4 is 3A.

Yep , if you use a 5Y3 where a 5U4 is called for , you end up with a very HOT (overloaded) 5Y3

If you use a 5U4 where a 5Y3 is called for , you end up with a hot power transformer .....

Rider says Admiral used the same part number for both transformers and the red dot was not on the very early ones!

Jas

Well those tubular 6kV caps replacing the ceramic disc caps certainly did the trick. WOW!!! Thanks to everyone who posted regarding this issue. Height and linearity are now great! Check it out. Pics and link to video below.

http://youtu.be/QYb0SHafHZU

Looking pretty good! It's always fun when the picture suddenly shapes up.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html