1954 Philco high b+ issue.....
 

First..... I'm so excited to be posting again after many years of.... well... not able to acquire more TV's.... My parents moved to Oregon last summer brining with them my Dads old college TV.. A 1954 Philco 22BU4001. I worked on it years ago as my first electronics restoration when I was in 8th grade(mid 90's) I was featured in Popular Communications... Well I butchered it. When I pulled the chassis just a few months ago I found I removed the silicon diodes replacements out of the power supply. I even stole the replacement electrolytics from the sweep/power supply chassis. Numerous cold solder joints were found, leads falling off... Two resistor leads were connected to the wrong terminal. I found two resistors that should have been in series were actually connected in parallel. I was 13 at the time, and 32 now. I know I should have started practice on a radio, not a 50's TV. Following the schematic I fixed almost all my errors. . rewired the power supply etc..

I'm plagued by a sync issue both vertical and horizontal, and the AGC/gain. I know many will argue about my power supply, but as I threw away the original selenium rectifiers as a kid and also stole the silicon replacements for another project I found two Federal seleniums on ebay.. This set when working properly will be used on a variac at 115 volts, which is what I've been using for my tests...

B+ is 238volts... Schematic is 245(at 117VAC) so I'm not concerned that the selenium rectifiers aren't supplying enough voltage.. Its my 130 volt B+ circuit that's causing my issues.

The 130v B+ is tapped off the 245b+ via a 2.5k 8 or 10 watt power resistor R29. I'm using a 2.6k 10 watt and I'm reading 40 volts high... My 130 is actually 170v. The original power resistor is disconnected but in the chassis. Years ago I just replaced it assuming it was out of tolerance. I measured it and its nearly 4.0k so I assumed Sam's mislabeled the value. I jumpered in the old power resistor to check the 130 volt B+.. The same reading as before.. 40 Volts high.. How is that possible with two very different resistance readings?

I took some voltage readings in the sections that use the 130v B+. the 3 6CB6 IF stages all show the correct plate voltage of 120 and 115, but the screen voltage is 170 where the 130v connects to. The plate and screen voltages are both derived from the "130v" source but pass through the IF cans to the plates.. Why is the plate voltage ok when the screens measure 170? The screen voltages should match plate voltages. Again the 6U8 sync amp, plate voltage is ok, but pin 3 measures 170. Video output tube 12BY7 is the same with the same high screen voltage.

I've checked the wiring of the 130v sections via the schematic and nothing seems miswired. What else should I check? The only thing left in my opinion is to disconnect the 245 volt source from the 130b+ and measure to see if there is 40 volts.. The other thought would be to disconnect one by one the 130 volt sections and see if the voltage drops to normal.

I get sound and video will connected to the digital tuner but the AGC/gain/contrast is overdriven. At min contrast its still excessive.... Sych isn't stable either.. Those sections use the 130v...

I'm a airline pilot and am gone from home for 4 days. I scanned a partial schematic for reference before I left.
The schematic is found in Sams set 227 Folder 10..

Please offer and suggestions.. I've been going at this for a couple months(not every day of course). My wife thinks I'm wasting time.....

A voltage source that is too high when others are normal means something using
that 130v is not working. With all circuits working the current draw will cause a voltage
drop across r29 so it all works out to 130v. Check those circuits not working, be sure
all the tubes are working, correct voltages all around. A tube turned off will not draw
its share of current, making a smaller voltage drop across r29.

Open load resistor, or tube in cutoff, possibly 2 problems. A single tube, or 2 section
tube not lighting up.... no current flow.... Be sure all wiring problems have been found.
double check, everyone overlooks things...

.

How do I isolate one of the 130 v circuits if all the voltages are the same on all the 130v circuits? Would pulling one tube at a time and measuring the voltage on a correctly working 130V circuit increase the voltage further? If the voltage doesn't increase then I've found the culprit circuit...right?

You did give me some food for thought. One of the IF 6cb6 tubes wouldn't light up unless it was wiggled in the right position. When I get home I'll resolder the terminals on the tube sockets in the IF stage. I'll also go over some resistors I might have missed.

Thanks,
Matt Davala

You say you have sync issues so that area might be a good place to start.

sync issues come from

Clipped signals from the IF/video amps (tubes resistors agc).

ineffective sync separater action (tubes resistors coupling caps).

A scope is the most effective way to see where the problem is. You look at the signal going into the separator if good then its the separator that is the issue. If its not correct then trace back all the way back to the video detector.

You can also try signal injection of a composite signal at the video detector, sometimes the levels and direction of the a composite signal from a DVD will correctly drive the video. Care should be taken when ever hooking up testing devises or signal injection to make sure there are no voltage potentials to worry about, and esp if there is a hot chassis.

here is a brief demo of a sync sep checkout with a scope.

https://www.youtube.com/watch?v=Flg5LwBadHI


your schematic shows a plug that connects up the out form the sync sep to the horz and vert circuits, I would start with checking to make sure that the pins are clean and making good contact there.

You don't need a scope if you see a significant voltage problem.
You don't need to disconnect any items as this would turn off other items and drive
the 130v up higher as you have stated. Something is already not working, open resistor,
tube off, open coupling transformer.... you need to do plate voltage checks on the circuits
listed above that process the signals you are lacking. Look there first.

And be sure r29 is the correct value, 2.5k or 2.6k don't matter, but making a mistake
like 1.5K is not good.... just double check correct value.

.

So I got home from work after being gone for 4 days. Got to do some troubleshooting on the Philco. I did a resistance test of the IF tube pins and my 6U8 Sync tube. Nothing was too far off.

Something that did correct my voltages is very unusual to me. I've been picking up FM stations... that's not the point though.... When I put my voltmeter on pin 5(plate) of the v5 6CB6t 3rd IF tube the sound cuts out and voltmeter shows 115 volts. I took another voltmeter to pin 6 at the same time and the voltage was spot on 115 volts. Like it should. I removed the voltmeter off pin 5 and the voltage on pin 6 shot up to 170.
If I hold the voltmeter on pin 5 on v5 and check other voltages on the other IF tubes including the 130B+ source it actually shows around 134..
40 volts less only when I hold the meter to plate. Remove the voltmeter and check voltages... up 40 to 170V. I did the same voltmeter test on the on the 2nd IF stage and got the same results and voltages for the b+ and other tubes.
It was not the same case when I put the meter on pin 5 of the 1st IF stage. Voltages were still wonky.

my lack of electronic knowledge leaves me baffled at this time. The resistance checks on pins 5 and 6(screen and plate) for all 3 IF tubes were correct. I show no open coils or transformers connected to the IF sections.....
I'm hoping that this TV will be finished soon.. Its been tough TV. I have 9 other TV's that all worked after a complete recap and some resisitors. This one has been a real pain....

Thanks for the help!
Matt Davala --Beaverton, Or

What kind of meter are you using? Is it digital?
Your description of the problem sounds like there's a strong powerline ripple on the 130V line, possibly due to a miswired filter cap. Your sync/AGC problem would suggest this also.

Try measuring the 130V with an analog meter (digital meters tend to go nuts on complex waveforms).

yes I was using two digital meters for my test.. I would have to make a trip out to my inlaws to borrow an old analog meter.

I'll go back over my filter caps tomorrow. Still baffled why connecting the voltmeter probes dropped the voltage 40 volts to normal.... Both tube pins connect to the same b+ source, just the plate passed through the IF can.. I keep the one meter on the screen and one on the plate and each time I move one meter off the plate the other voltages jump 40 volts.. Something to do with the added resistance of the meter?

Thanks for helping!
Matt D

I'll tack in another 10MFD cap on the 130V line tomorrow and make sure its grounded well.

Adding the cap to the 130 B+ made no difference. I'm checking my AGC over again to make sure its all wired correctly. The two cathode resistors of the 1st and 2nd IF should be 47ohms, they read near 80. Think that would be far enough off to cause a problem?

I'm thinking AGC because when I put the meter on the some points in the AGC circuit it drastically changes the 130 B+ voltage. The AGC in this Tv is an absolute nightmare.

Thanks,
Matt D

Got some higher grid voltages on the 1st and 2nd IF. Should be -.2v and -.1v respectively. I show -1.7 volts and -1.0 volts. What should I check? Seems like those values are quite off for grid voltages?

if its keyed agc, look for a .1ish cap that filters the AGC, again a scope works well here, I generally will scope the AGC after the filter to make sure there is no hash on it. If you do not have a scope and suspect AGC you can just clamp it with a variable DC power supply. With out the correct equipment (scope, vtvm) you can try feeding a composite video signal into the grid of the video amp (pull an IF tube out) and see if you get a good clean pic and video. If you go this route just make sure the chassis is not hot and isolate DC with a cap (a .1 is plenty) when connecting the comp video up. You can get a comp video from most DVD players. Sometimes it will no work due to phase differences but most of the time it works. It may not be strong enough but will tell if the sync is prob is before or after the video detector.

Could I use a small battery as a dc supply for the AGC? Right now the AGC is operating in the - voltages... What voltage battery should I use?

its very hard to read that little schematic but i see its not keyed but just taken off the output from the video out. I think I make out a .15 cap that prob acts as a fillter, again a wild guess but if that is bad it would make the AGC be all over the place. I would just clamp it with a DC source, thats the fastest way without a scope.