The method I described is an easy access way to monitor the voltage on pin 2 of the 6gk6 with the chassis in set, the center of the volume pot is more or less directly connected to that pin, by watching the voltage there, you are also watching the volts on that pin.

Yes that’s the green wire goes to pin 2. So now I have to change 2 .005 discs and got another tube coming hopefully Friday. Then put it all back together and hope no more load pulling down the b+.

Well putting the chassis back in so if I still have this b+ being pulled down then all I can come up with is a bad cap to ground I don’t think a resistor would do this because it just seems like maybe one b+ voltage is bleeding over to another via a cap to ground. Pulling all tubes one by one with chassis in hooked up didn’t show anything positive.

All back together and the audio output tube is new and still getting really hot fast voltages still low and the green wire on the volume pot goes directly to pin 2 and there is 280 ma at that pin the volume pot is 2 meg it measures 2.4meg if pin has to be zero I have no clue why there is 280ma there. Still looks like this audio circuit is pulling the b+ down b+ down means all other voltages go down with it. The volume pot has 3 connections green blue and ground which ground is on the body of the pot and one end of the pot maybe the ground is picking up stray voltage from somewhere else and back feeding the pot. I don’t know at this point. If the tube is at zero volts then it will run full but with 280ma then the tube should not run full even chassis out pin 2 still showed around 50-60ma. Now I have discovered that the 1st video 6aw8 and the video output 6hb6 are getting hot fast within 30 seconds being on so I’m off now to look at that circuit.

Hi Guys, It is good o see you have made progress on this set. So If the audio tube is
getting hot and is possibly the current draw, it should be easy to figure out what might
be wrong. First turn it on and hook up a quality audio signal to the volume control,
make sure you put it through a .1 uf cap and see how it sounds... Good quality or not?
Does the audio output transformer measure 930 Ohms? Is there approx 145V on pin 8?
If you are reading .25V on the grid & Center line of the volume control, check out R80,
R81, R82, be sure they are right.
Also there are other goodies to think about., like crudlies on the tube socket pins allowing
little bits of current to flow and give you small voltage at pin 2 the grid to the tube.
I Assume Timmy that your 280ma. at pin 2 is actually .28V small typo.
I Also found I kept making the same typo earlier in this thread saying 380ma. for the
power supply current, when it's actually 580ma, as others have correctly written......
Also you should be able to ground pin 2 without causing any harm, and see if the tube
runs cooler, & Your PS voltages return to normal.....

I'm a big fan of voltages being pretty close to what the schematic says, but .25V is kinda
small for that spot.

As it is, when you run the set do you get sound, or snow from the sound when you turn
up the volume ? does it sound like it should? Clear not distorted?

Also remember single tube audio output circuits like that are Class A Amplifiers, so the tube
is biased on anyway, and always, otherwise you would hear distorted sound as each
sound would be turning the tube on and off all the time. Class A Amplifiers are always
conducting, and the input signal smoothly changes the grid voltage & smoothly raises, &
lowers plate - cathode current to give you a nice smooth sound.



.

I could answer all you wrote if you want my number let me know it will only take a few minutes so much typing lol. The audio trans checks perfect 80-81-82 resistors perfect and after having the set on the last time I had an antenna on channel 3 fades alittle probably out of tune but channel 4 sound was perfect but heard no snow with antenna off and yes I made a mistake pin 2 is a green wire is the wiper set on it measured 280 mv But the tube didn’t red plate until I had the chassis out and found the 150 resistor burned. The tube just seemed to get really hot fast now I find within 30 seconds the 6aw8 and the video output 6hb6 get really hot fast I have read that low b+ is not good for tubes maybe things change with the tube conducing at low voltage. My initial finding was I had no video so maybe something in the video area causing all this.

It is always possible you have more than one problem. If you suspect the Video Output
tube is using too much current, then you need to do voltage checks at each pin & see
if you find any burnt looking parts in that circuit. It's also sourced to the 385V.

The video amp 6AW8A is also sourced to the 385V.

But if the audio out tube accounts for all the extra power supply draw, then we may be
getting ahead of ourselves.


.

That’s just it there is nothing I’m finding resistors check perfect it makes no sense I thought maybe something in the convergence but I don’t think there is any high voltage points there to pull it down.

keep in mind, as stated before , audio output tubes always tend to run hot, as do horizontal outputs, this is just par for the coarse and does not mean there is something wrong.

Ok maybe so but I still have the low b+ and no video and I went over the video amp and output and found nothing I did suspect the 1n60 but I do have sound.

If the sound is clear, and you replaced the cathode resistor, and that circuit seems ok,
then it's time to check the next circuit. It may seem frustrating because there is no
dead short, and everything mostly works, but somewhere you may have a tube
with bad voltages on it, improper biasing, and using too much current.
It will take time to find it, Most likely with tedious voltage checks.

.

You still have yet to get a decent DVM that has a decent amperage range to check what current draw you really have at L54 right after the voltage doubler.

And until you can do this correctly, as you have stated that the meter you have does not have the range to do so, you are just going on assumption.

GET A decent DVM and check the current at that point to see if it is indeed excessive.

this is an important step.

Going to try something I have been using a 10 foot extension cord to power this tv so with the resistance of the extension cord and the thermistor and using a power cord from a b&w tv very thin and an air conditioner running from same outlet maybe this will make a difference, excessive resistance would cause this.

Well that didn’t work but from the first day I plugged this set in it red plated one horizontal tube and it’s still doing that now only one tube and it’s now looking like the pulling down of voltage maybe in the horizontal the oscillator runs but after warm up plug in again the oscillator will not start again until it sets for awhile and cools down. I don’t know if the yoke would affect the horizontal oscillator from starting. This happened with the old flyback but I since changed the flyback with a nos one. Problem is the voltages across the board are still low it’s not like I can look at voltages and see that one rail is lower then the rest and go to that area b+ low everything is low.

hummmm Red Hot Tube Plates = Too Much Current.

Is G1 for each tube -45V?

Maybe you need to take a break from this tv for a few days......


.

The g1 was low to begin with so I turned it down more like not even a 1/4 up. Took the chassis back out to double check the 2 timing caps .0039 and .0068 it’s always possible I reversed them especially because the print on them is so small I should have used a magnifying glass that’s how small and yes I should get away from it. But only 1 tube, hmm.

here is the biggest help to know when hor osc is OK.

https://i.imgur.com/afNm19c.jpg

best investment you can make.

I know but it wouldn’t pay for me since I would use it once then put it in the closet lol ��

Not sure you are checking the right " G-1". We mean the G-1
of the hoz out tubes. They are in // to give enuf output.
Typical sets draw abt 210 ma this one IIRC 240, beyond most
hoz out specs. Thats why 2 HOT's. Others did it in the early days.
Admiral did & if you changed the FBT there were pages to mod the
set to use one 6KD6 H out NOBODY wanted to do them.
If that neg voltage is not there the tubes stay on too long.
See class C amps. !
Once one fries the other takes over. That one will overheat trying
to supply the HV but one cant keep up current demands.
Bottom line is without the proper G-1 voltage you will cook up expensive sweep tubes. Fix that FIRST if needed !

enuf fer now
Zeno:smoke:

This from the start didn’t do this all the time was random then it was ok now it started doing it again when the oscillator is running I have perfect hv. Maybe it’s because the b+ is low creating this. Only tube I can’t test is the damper.

So after this one your never gonna touch another TV again.... ever ????? :saywhat:

Stop making excuses for not investing in your hobby, screwdrivers & wire snips only go so far..... :rolleyes:

I bit rough but.....
We went out to a rib joint last week. I got a full rack & my squaw got
a half. It was a great feed & leftovers I measured my rack & it was
16" long. Next day I finished mine then the next day I took a dump and
it was just a memory. Nothing left but the CC bill.
A nice meter will usually last a lifetime unlike the ribs. Here today, flushed
tomorrow.......
So anyhows get the H OSC going FIRST ! The PS voltages are probably
a red herring.
And YES take a few days off. When we got a dog it got put aside & usually
another tech got it & fixed it fast. That tech was often the shop idiot !!

73 Zeno:smoke:
LFOD !

Unless you sell all your tube electronics or stop using them permanently you will encounter another problem where having a scope will be helpful. Test equipment is the one thing I'll probably never sell even if I were to dump 95% of my collection...I know if I sell it, a week later I'll need it bad enough to regret letting it go.

Dealing with this without a scope is like trying to win a marathon when one of your legs just got amputated yesterday and replaced with a peg leg... Dealing with this with a DMM that isn't sufficient for the job is like running that marathon with only one leg, and that leg is the peg leg...

That said if your meter has a dedicated DC Volts setting you can measure DC current as a voltage if you have a power resistor of a known value. Connect a 1 ohm or 10 Ohm power resistor in series with the cathodes, clip your meter across the resistor and measure DC voltage. DC current will equal measured DC voltage divided by resistance of that resistor...A 1 Ohm will make the math MUCH easier.

The shop idiot was a rotating position, Everyone got to be it at least once........

Same with Shop Genius....

Smoke a few high dollar Horizontal Output Transistors and your title changes fast!


.

Scopes are a funny thing. Up till the late 70's we almost never used them.
Then they became indisposable on new sets. So much so we started using them on old sets instead of plugging at them with a Simpson 260 or
RCA volt-ohmist. I thing almost any tube set can be fixed with a good meter
and a ringer for yokes & FBT's. It helped we bought the Sencore suite
then another all on crash carts. New stuff took the fustration out of
test leads etc. Sencore also used to publish a LOT of how to stuff
that was of great help.
Anyhoo time to finish my ale & hit the sack. & GB all my VK friends.

73 Zeno:smoke:
LFOD !

While I didn’t get an exact ma from L54 it does measure up perfect in ohms the ma would show higher then 580 if the voltage is being pulled down so obviously voltage is being pulled down and obviously affecting the horizontal oscillator so if everything I check from coils and resistors check good there is ceramic disc caps so if there is one leaking to ground back feeding another circuit causing this problem how can I get an idea if stray voltage is making it to ground. Is there a way to check ground in such a way to see if there is voltage there that shouldn’t be there.

In all the many sets I have restored, 10+ (lost count now), I have only had one occasion of an horizontal output tube red plating, ( Magnavox ), and this was due to a defective damper.
Truth is, you have picked a rather hard set to work on, even for experienced vintage TV buffs.

The dual horizontal outputs is a perfect example of this, not sure why Moto chose this over a single larger tube, because it only make it more complicated.
If you have not done so already, it is highly recommended that you get a matched pair of 6JM6s, where this is not critical, it will insure that the horizontal output circuit is working at optimal efficiency.

Yes I got 2 new RCA tubes and one started to red plate but I pulled the plug. So if the damper is bad would it pull the voltage down along with red plating a tube. I have a new damper I wasn’t able to check the one in the set. The only other thing I found that I missed was a 25 v150 uf cap to the contrast and brightness but it checks at 223 uf so I’m changing that one. It seems once chassis is in and the convergence and tuner are plugged in then the voltage drops but the convergence is low voltage don’t think it would pull b+ down the way it is.

New does not necessarily mean matched, though you may have difficulty finding them, they are sold in pairs that have been tested to work well together, no 2 tubes are exactly alike, and it prob won't matter THAT much, but in a situation such as this, it is always better to use a matched pair over a non-matched.
Like sold here.
https://www.vivatubes.com/nos-matche...uum-tubes-100/
out of stock :(

I had the last of the 28 tube Motorola's, the ETS908. We ran the set 5-8 hours a day! It only required a few tubes, here and there and never any circuit work.
It lasted about 10 years, used until the 23EG got too weak to show a decent picture. It still had the original 6JM6's.

I guess I'm just lucky that the 25AP22A in the Hoffman Colorcaster I found is in fair condition, it too originally came with a 23EG when it was new, still trying to find another tube, blue gun is weakest. :(

As it is now I’m going to look at the convergence panel which has 5 200v red caps. It also has a selenium diode don’t even know if that maybe shorted there was no smell to say it burned up but this voltage drop is when the convergence panel and tuner is plugged in. But have to check everything maybe this route will show something.

That most likely won't get you anywhere.

there is no bias going to the convergence circuits at all, it's fed by horizontal and vertical pulses from the respective transformers. No boas needed at all
the vertical output has a convergence tap on it, the horizontal shares the same feedback winding on the flyback that is used for horizontal AFC and color sync.
in fact, you can unplug the convergence circuits completely and still get HV, you will most likely see a partial collapse of vertical range.

I dont know half of what you guys know when it comes to these tvs but I don’t get why the voltage drops once they are plugged in. Can I test the selenium diode with a dvm.I have noticed that when the vertical is running you can usually here it at the yoke all my other color sets I was able to here it this one I don’t. So if the vertical is not running that maybe pulling down the b+ since there is a 385v on the primary side of the output transformer or maybe no running at the correct speed.well I know if the vertical quits then I have a horizontal line but maybe not running at correct speed.

the answer to that is no, for the most part, a DVM can not test selenium diodes, the diode test feature was made for SI/GE types which have a much lower junction barrier voltage, and thus trying to test selenium will always look bad to them.

I have said it, and so have many others, you need to get better equipment, because now, you are just going on assumptions, and as long as you are, you will keep going in circles no matter what you try to do.

You NEED a better DVM that can measure the current draw right after the main diodes, you need to know what the draw is with NO guessing. 580ma? more? less?

And as others have said, you need an o-scope.
is the ripple after L54 1.5v? more? less?

ALL OF THIS is important, And can't be done with what you have right now.

I know I know but I cannot spend crazy money for just this set nothing in stone that says I’ll be working on more sets in the future so with that said one day in the very near future I’ll post when it’s fixed. I have nothing else to do during the day.

Wasn't this set listed on eBay for like $225 before you bought it (I remember because before the ETF meet I was considering buying it)?

If you choose wisely you could get 4 scopes and a decent budget DMM for what this set cost.

It's definitely time to throw in the towel on this set and cut your losses.
You've learned from this encounter.
Don't feel bad; it happens to all of us in life.
There are future projects with your name written all over them.

I have pointed this out before.

https://www.amazon.com/AstroAI-Multi...882160&sr=8-34
https://www.amazon.com/Crenova-Auto-...1882412&sr=8-7
https://www.amazon.com/Multimeter-Co...1882412&sr=8-8
https://www.amazon.com/Ranging-Digit...1882412&sr=8-6


here is 4 examples of what I call cheap throw away DVMs, I have 3 like these, which I use for risky testing, and not afraid to damage them, 95% of the time they agree with my high $ Fluke meters, which i use when i want best accuracy, like alignments.
The cost is so low on these, no reason not to have 1 or 2.

here is just a few hand held o-scopes.
https://www.amazon.com/Quimat-Oscill...ustrial&sr=1-5
https://www.amazon.com/Oscilloscope-...ustrial&sr=1-3


not so cheap, and will take a bit to learn to use.