Another New One.... - Videokarma.org TV - Video

mkoser · #1 04-01-2008, 12:58 PM

So I'm still very new to Old Tv's... but I picked up another one...

This one is an Admiral 16R12.

I got if for 10 bucks, so i'm not out too much.

The audio works fine, but I have no high voltage at all.

The High Voltage tube inside the cage does not glow at all. I have an exact same spare tube out of a different set, but that didn't solve the problem.

A quick visual didn't find any broken leads, exploded capacitors, or anything else obvious.

I don't have a sams for this set, since I just bought it.

Does anyone have any info on this set?

Would someone be able to give me a clue where to start? I'd like to get the set functional before I attempt to recap it..... just so I know where I'm starting at.....

Thanks

Matt K

cdmarion · #2 04-01-2008, 04:38 PM

Hi Matt,

I consider myself a begginer when it comes to TV's also, having re-capped only one tv. That being said, the first thing I'd look for is a blown fuse near the HV. My admiral has a .25A 250V fuse near the flyback.

Just keep in mind that if there is a fuse and if it is blown, there's probably a reason it's blown. Be carefull and good luck.

wa2ise · #3 04-01-2008, 05:13 PM

I have an Admiral 24R12 set, diagram:

which may be similar

mkoser · #4 04-01-2008, 05:33 PM

Quote:

Originally Posted by cdmarion

Hi Matt,

I consider myself a begginer when it comes to TV's also, having re-capped only one tv. That being said, the first thing I'd look for is a blown fuse near the HV. My admiral has a .25A 250V fuse near the flyback.

Just keep in mind that if there is a fuse and if it is blown, there's probably a reason it's blown. Be carefull and good luck.

Hello.

Thanks for the input. That's the first thing I checked.... The fuse is good. I've got voltage at the fuse....

I'm still looking!

Thanks,

MK

Old1625 · #5 04-01-2008, 08:54 PM

You need to check the horizontal output tube (6BQ6 in the offered schematic--not sure how similar or different these sets are...) the horizontal oscillator tube (6SN7), the damper tube (6W4), and the HV rectifier there in the doghouse you have opened up in one of your posted images.

The term "familiar ring" comes into being here; the horizontal sweep action in older sets was very much audible to younger people; I could be in the next room as a kid and be able to tell by the sudden change in pitch of that high "dog-whistle" sound emanating from the TV of the day that the horizontal hold had broken off lock. I'd be in there to rectify the problem by reaching behind the set to twiddle the horizontal coil before either of my parents were able to get out of their chairs. It does a kid good to keep their parents wondering at times.

If you can hear that 15,750 cycle pitch then your abilities to rapidly troubleshoot an old TV set are raised to stratospheric levels, as you can listen to the set and say: "No horizontal sweep--I can't hear a peep!" And such info will quickly lead you to the culprit. A weak sound of that pitch means that it is reaching the horizontal output tube, and the tube is too whipped to do enough to make the this high-pitched sound of normal volume. No sound and you know you need to look back further into the oscillator stage.

If there is adequate supply to the horizontal output tube, and it is not getting sweep signal from its feeding stage then its plate will be glowing a vivid red, and it will in short order kill itself in such case, as the negative bias it needs to keep its current in check is derived by the signal of the driving stage.

Pull your horizontal output tube and look at its "getter" spots--those spots of silvering that seem to be sprayed onto the inside of the glass--and asses their condition. If you look at a new tube, and then look at the one in your set, you will learn to discern a differenct between the two. A faded-to-brown, non-lustrous spot--or such that may be contaminated with spots of gray or white--is an indication of a power tube that needs to be replaced.

I hope this old fogey rambling of mine will somehow get you aimed in the right direction. Good luck in your troubleshooting--and enjoy! I always did....

mkoser · #6 04-01-2008, 10:29 PM

thanks for your help.

You are correct. I don't hear that "whine" you normally hear. I pulled the horizontal output tube and looked at it. The getter spot seems to be shiny, which fades to clear. No brown, white, or otherwise...

I am currently in the market for a tube tester. I used to have one, when I was in high school, but that's long gone now.....

I think my next course of action is to find a tube tester and give these tubes a test.. Wouldn't it be great if it was just a crappy tube?

I did notice, that simply metering at the fuse, I have 360 volts dc at start up, which fades in about two seconds to 260. The schematic above shows there should be 210. Is this simply because my line voltage is higher than what it was when this set was built? Or is this an indicator of another problem somewhere else?

Sorry I'm kinda dumb at this right now.... To be honest, I musta had lucky picks with the radios I have recapped in the past. I've only had to change out obviously bad grey tubes and swap cap for cap..... I've not really had to do much trouble shooting.

Thanks again for your help,

matt k.

wkand · #7 04-01-2008, 11:58 PM

Another easy test is to use a neon bulb electrical testr and hold it close to the cap lead on the Horiz Out tube withthe set running. If it glows you have Horiz-Osc, and output functioning. The HV Rect tube gets it's filaments from the inductive pickup of the flyback.

If you have an oscilloscope, you could check waveforms at the control grid of the H-out tube, but never use a scope to check HV out.

Swapping paper caps in the horiz sectons may be your only recourse to find out if the set is worth fxing. Measure DC voltages around the osc tube .

Good Luck!!!

Another Old Fogey

mkoser · #8 04-02-2008, 10:52 AM

Hi. Thanks for the reply.. I don't have a tube tester, much less an oscilloscope so that's not a possibility right now...

I swap out all tubes listed above from a set that has functioning high voltage, and I had the same result.... No high voltage.

Here are the voltages around the Osc tube.

P 1 8vdc
P 2 93vdc
P 3 13vdc
P 4 0
P 5 120vdc
P 6 13vdc
P 7 0
p 8 0

?????????????????????????????????

Thanks,

Matt K.

Old1625 · #9 04-02-2008, 11:09 AM

How about pin voltages on the horizontal output tube....? (Don't measure the plate cap!!! ) That you are getting no whistle indicates that either the output tube is getting no signal from the oscillator, or that the output tube itself is open, or not getting its supply voltage. The screen grid supply voltage could be killed by an open supply resistor, or a shorted bypass capacitor as shown going from screen grid to cathode. If the output tube is getting its required supply voltages, and there is no oscillator drive signal to the control grid the output tube will likely have its plate turn very red. It will kill itself or blow the fuse in short order if that happens.

mkoser · #10 04-02-2008, 01:47 PM

Ok. Thanks again.

Here are the voltages on the Hoz output tube

1 0vdc
2 0 vdc
3 0 vdc
4 182 vdc
5 0vdc
6 100vdc
7 0vdc
8 8 vdc

Any idea what this tells me???

Thanks,

Matt K.

Old1625 · #11 04-02-2008, 02:27 PM

There is likely insufficient or no drive to the output tube!!!! Your cathode current is about 60mA above the maximum recommended for the tube if the cathode resistor is indeed 47 ohms as shown in the schematic, and you're indeed reading 8 volts across it. There should also be a negative voltage reading on pin 5 if your set is like most. That is grid bias developed by the drive signal. You need to check for defective components-- such as a trimmer capacitor shorted to ground or perhaps an open phase or width coil.... Recheck all components to make sure they are within spec, and none of the capacitors leaky.

Don't run the set long under these circumstances or you will be in the market for a new output tube. If the plate isn't glowing red intially it will start soon.

mkoser · #12 04-02-2008, 02:35 PM

Hello, well, I was poking around in the set and I found a cap that was bulged and leaking wax out of it.

it is a .1mfd at 400 volts.

I replaced that cap and then powered the set back up.

Now, i'm getting that dangerous glowing red hot output tube condition you warned me about. oh yeah... and still no high voltage

as soon as I noticed the tube glowing, I pulled the plug....

Any other caps or you would check right away?

MK

Old1625 · #13 04-02-2008, 02:43 PM

You must have pulled a leaky bypass capacitor that was loading down supply to the output tube--probably the screen grid bypass. This certainly is an omen.

You need to check all the components in the network between the oscillator circuit and pin 5 of the output tube. You could have open or shorted capacitors, and/or resistors way off spec. Check the horizontal drive control, as well as the phase and frequency coils as applicable.

Beware that there may be dissimilarities between the posted schematic and what you have in your set.

RetroHacker · #14 04-02-2008, 02:44 PM

I'd go ahead and repcap the whole horizontal section. You're going to have to recap the entire set anyway...

-Ian

mkoser · #15 04-02-2008, 02:47 PM

I think I will just flippen start recapping the set. I mean, whats a few bucks in caps and a few hours worth of work.

I do need to find the sams for this specific set. The one posed above looks very similar to what I have, but I think I want to have the exact one for this set.

Anyone have any idea where I could get my hands on one?

thanks
Matt K.