1950 Philharmonic 8200 Audio Issues
 

Greetings everyone, last year as you may recall I had bought and went through the tedius process of electrically restoring a Philharmonic branded Meck TV which I got it working but am still having some issues with the Video IF alighment yet, but that's for another time, the real reason I'm posting is because my Philharmonic/Meck TV is having some audio problems, for some reason when ever I try to turn the Video IF Alignment screws my screwdriver slips out of the slot and hits the chassis.

Well I've had two times where that's happened to me and its taken out my audio section by somehow shorting out or blowing the 1st and 2nd sections of the 6T8 tube which is part of the Audio Section of the TV (part of it functions as the Audio Frequency Amp Stage) and I've lost the original Meck Branded 6T8
tube this way and a NOS RCA Branded 6T8 tube this way.

I checked all of the connections underneath around the 6T8 tube socket to see if there is anything around that area and the Video IF Trimmers that could be causing the short out to happen, and there isn't from what i can see. So I don't know what's going on.

Anyone have any ideas as to why my 6T8 tubes are going out prematurely when my screwdriver hits the top of the chassis of this TV?

Any help in this regard would be appreciated as I don't have very many 6T8 tubes left in my stash.

Not sure what is causing the issue, but to make it not happen again, put some heat shrink on the end of your screwdriver, leaving just enough blade exposed to fit the screw you are adjusting.

OK, I'll try that.

Could I temporarily use a 19T8 in this TV in place of the 6T8 for testing purposes?

I'm asking because I have a whole buttload of 19T8 tubes and no working 6T8 tubes currently.

I was thinking that I had heard (at least in series string sets anyways) that you could go slightly higher than the original rated tubes for testing purposes (e.g. 12BA6 in place of a 6BA6, and it wouldn't really harm the circuit).

I would say no to that substitution, it will push too much current though the 19T8, it is too far off.

OK, well then It looks like I'm gonna have to order some new 6T8s then.
Hopefully they aren't too expensive...:sigh:

The only really expensive tubes I've encountered in this hobby, are the horizontal output tubes for color sets.

If it is a ferrite core on a transformer you are adjusting you should use a non-metalic screwdriver.... metallic screwdrivers (in addition to being hard and having the potential to crack the core or the slot off the core) have magnetic effect on the core similar to the slug...so if you get something adjusted dead on it will stop being dead on as soon as you remove the screwdriver....the effect even happens with non-ferrous metal screw drivers. Copper and aluminum drivers change the inductance tuning in the opposite direction of ferrous ones (this can be used to ones advantage if a coil needs to be adjusted by knifting or has a stuck slug or other issue that makes you not want to adjust it more than once).

If you don't have a plastic screwdriver and don't want to wait on mail you could do what I used to do as a broke college student...take a defunct mechanical pencil (I think I used the bic ones with the clear outter barrel and black inner Barrell), pry off the stiff plastic pocket catch file or grind the end down to the blade size you need then super glue the other end of the catch into the inner barrel of the pencil to get a long handle (I still have 1 or 2 I made floating around here somewhere)...I also used to file down the weird alignment tool like plastic sticks that come with newer Weller soldering irons, but those didn't seem to turn out as well.

...and anything ever used as an audio amplifier or output in any device, ever. :D

Edit: maybe not 50C5s.

How are these 6T8s failing? Is the filament burning out? Are certain elements shorting out? Has the emissions gone down to zero? Failure in the triode section or failure in the diode sections or failure everywhere?

The nature of the failure might tell you what is taking them out.

This reminded of an AM/FM Zenith radio I had when I was a kid. I dug it up out of a pile under dad's bench and it worked, so I put it in my room. A month later, it quit. A tube tester showed a dead 19T8 so I put one in that dad had in stock and it ran a month or two and went dead. It wasn't a filament issue, the tube just went dead - low to no emission. I bought one more 19T8 at a parts store and that one lasted a couple of months and quit. I threw the radio out.

Now, I did put a lot of hours on the radio in that two or three months, sometimes leaving it running if I forgot to shut it off during the day and I used to sleep at night with it running on low, so the run time was high.

I don't know if the 19T8 was a lousy short lived design or if something was wrong with the radio, but I didn't know anything about them other than tube swapping at that point.

John

Especially if those horizontal output tubes are popularly used in Ham Radio transmitters, tube type CB Radios, and illegal tube type CB Radio not so linear Amplifiers, aka Splatter Boxes aka multiple Spread Spectrum devices. And also popular audiophile tube types in desirable vintage NOS. Fixed that for you!

Horz output tubes in legal CB radios? I've seen small-signal types* like 12BY7 for finals in legal rigs. OTOH, bootleg linears used a lotta horz output types like 6KD6, 6JS6 etc.

* "small signal" compared to power output types.

The alighment adjustments are small machine threaded metal setscrew style screws that thread into the coil, and the screwdrivers I'm using aren't magnetic, so I don't think that's the problem, and yes one of the adjustments is super stiff and hard to turn which is why the screwdriver slips on me so easily during the adjustment process.

I just all of the sudden have either one or two sections coming out completely dead, no emissions whatsoever, the filiments are still lighting but just no emissions, completely dead according to the tube tester, its usually the first two sections of the 6T8 tube that fail in that manner.

I have had it where the first section was dead and section 2-4 were fine, and I've also had one fail where sections 1, 3 and 4 were fine and section two was dead, and I've also had one where both sections 1 and 2 were dead and sections 3 and 4 were fine, so I don't know what to make of that failure pattern or that particular type of failure where various combinations of the first two sections of the 6T8 tube fail but the rest of the tube is fine, as I have never had this happen to me before.

What you describe here is exactly what this TV is doing with my 6T8 tubes, the only problem is that I've replaced pretty much every single paper cap in this TV and it has all new Electrolytics and I also replaced a ton of old out of tolerance resistors as well, also this TV has been barely used since I've got it up and running.

Now grant it those 6T8 tubes I had were all used tubes except for one of them so I really didn't know how many hours were actually on those tubes, the one tube that has me scratching my head about its failure is that I did have a NOS RCA 6T8 tube that someone on another electronics forum I was apart of a while back had sent me for an old Grundig Console Radio I had several years ago that had a intermittent EABC80 tube in it that was giving me troubles in that radio.

That NOS 6T8 tube failed just like the used 6T8 tubes I had, that one was the one that tested as section 2 having no emissions and sections 1, 3 and 4 had had plenty of emissions yet (it measured around the 80 to 90 marks on the emissions section of the tester's meter).

So Long story short this TV still seems to have a mysterious phantom lurking in it yet.

Another strange thing is that sometimes the audio will randomly come back on it own without me doing anything to it it'll just pop back on, but then it will go back out again if I try to adjust the IF adjustments and the screwdriver slips and hits the chassis again.
The other weird thing is that the only adjustment screw that this happens with is the 4th Video IF Adjustment Screw which is the only Video IF Adjustment Screw that is hard to turn for some reason, and is the only Video IF Adjustment Screw I have issues with the screwdriver slipping off of when trying to adjust it, because of how hard that adjustment screw turns.

I've got some 12BY7s in my tube stash that I don't have any use for, should I try throwing them on fleabay and seeing if I can make some money off them?!:scratch2::smoke:

Well I got some new 6T8 tubes and installed one of them into this TV and I got the audio to work just long enough for me to get the Video IF adjustments adjusted to where they should be so then I shut the TV off thinking the Audio issue was fixed, but then when I went to turn the TV back on again later on in the evening to make sure it was still working correctly and the audio was gone again and this time I didn't do anything to it to cause the audio to go away, it disappeared on its own this time, and I tried everything I could think of to try and get the audio to come back including swapping in another 6T8 tube and it wouldn't come back.

And I'm not sure what's going on with the audio on this TV as it was working fine until just recently.

Bad sockets?

Hmm, I'll look into that.

Well I figured out what part of my problem was with this TV's audio problem,
there was a resistor that came loose from where it was soldered to, which I had resoldered the loose resistor back to where it was supposed to go, but it didn't fix the audio issue like I thought it should of.

Below is the schematic with the areas in the audio section giving me troubles and the resistor that was loose that I repaired marked out as well.

OK, SO I think I figured out what's going on with this TV, I think it has something to do with the tuner, as I was able to get the audio to come back on again today but then when I went to readjust the IF again (as it was out of whack again) my screwdriver slipped and hit the chassis of the tuner itself and then both the picture and audio disappeared.

So it seems the tuner may need some work done to it.

Also another thing I've noticed is that my High Voltage and Vertical and Horizontal Oscillators don't start on the first try when I first turn on this TV, it usually takes 2 or 3 tries to get it to come on properly.

Any ideas as to what that's all about?

Both vert and horiz? Odd. I'm assuming it's been completely recapped and resistors are close in value.

Tubes would be my first suspicion followed by carbonized tube sockets then osc coils.

Have you scoped them to confirm the oscillators are not running?

This could also be thermal. You can try preheating the chassis with a heat gun and see if it starts reliably. If so, you may be able to pin it down with heat and freeze spray.

John

Yes, if the TV has been sitting for more than 24 hours and I try to turn it on, I don't hear the loud buzzing noise you hear when the TV's Vertical and Horizontal Oscillators and the High Voltage kick in, it doesn't kick in until I turn off and turn on the TV a couple of times.

The reason why I know that the oscillators aren't running for the Vertical or Horizontal is because It doesn't make the distinct high pitched whistling noise that the oscillators make when they are running, and when the High Voltage is running I can usually smell a little bit of an ozone smell when the high voltage first starts running, wheras when the High Voltage isn't running there isn't any ozone smell, also no picture shows up on the screen even after all the tubes have warmed up including the picture tube.

Yes the TV has been completely recapped and all out of tolerance resistors replaced with modern carbon film and metal film resistors.

I was able to get the audio to come back again but then when I went to readjust the video and audio IF transformers again because they drifted out of adjustment, so when I went to readjust the 1st Video IF adjustment which is on the Tuner Chassis, my screwdriver I was using slipped off the adjustment screw and hit the tuner chassis which then caused me to lose my picture and audio both this time around and when I try tapping the tuner chassis the picture flashes back on temporarily but then goes away again.

Which makes me think that my audio problems were and are related to the tuner.

What are your thoughts?

Just to be clear, when you lost the picture and sound, you were left with a blank raster with no snow, correct?

Sometimes we get lost trying to find a problem because of *too much* knowledge.

I would forget about the slipped screwdriver and troubleshoot this like it came in to my shop with no sound and no picture, so that means verifying all voltages in the tuner and IF section, and trying some tubes. Tubes become shock sensitive at times. Maybe the slipped screwdriver caused an overvoltage in one of your tube elements.

Since you seem to have a whole bag of what seem to be unrelated issues, I would again check the power supply voltages and scope them to make sure they're clean.

John

The picture went to a black blank screen, and no audio.

There are a couple of the Video IF tubes in the TV that are original to the set (they were Meck branded because they made the TV for Philharmonic).

Maybe I should try checking those tubes and replacing them with new ones?

Also I don't really have any 6AU6 tubes except what came with this tv, I do have some 6BA6 tubes which are listed as appropriate substitutes for the 6AU6.

Suspect all tubes even ones you have newly installed. One of the longest times I ever chassed my own tail troubleshooting was when I assumed that the damper on a set that had worked prior to a recap had to still be good afterwards....the tube had randomly died and it took me borrowing it to use it in another set for me to get past my stupid preconceived notion that it couldn't have just randomly died.

Is there HV? A problem in the tuner or IF will still leave a raster if the brightness is midrange or higher.

Maybe tapping around the tuner is causing a sympathetic vibration somewhere in the sweep section and restoring deflection and/or HV.

Again, troubleshoot this forgetting everything you know about the TV (other than it worked after being recapped).


I'm not one of those guys that says never use a tube tester; I have several and find them useful to a degree. But what you need instead of a tube tester at this point is a good meter and a good scope (and an iso trans if it's a hot chassis).

I would start with the basics. Check the HV. Arc the cap of the HV rect to the cage. Scope the horiz drive to the horiz output. Check DC voltages at the CRT. If it has raster, scope the video from the detector back through the IFs.

A signal generator or a dedicated device like a B&K 1070/1077B or Sencore VA48/62 will allow you substitute drive and low level signals to see what's good and what's not.

John

Well I figured out what the problem was and I got it working like it should now.
My power supply caps were shorting against the chassis and some of the resistors for the Power supply circuit.

Because of how cramped it was by the power supply area of the chassis, when I originally replaced the old power supply filter caps I had to just use a free floating terminal strip for the power supply filter caps because there wasn't enough room for me to get a soldering gun into the chassis to solder the terminal strip to the chassis without accidentally burning through wiring insulation.

So apparently what the problem was that I didn't get the terminal strip situated so that it was sitting completely horizontal against the chassis so that the filter caps weren't touching the chassis or anything else near it, so when I hit the chassis with the screwdriver when it slipped the vibration of the screwdriver hitting the chassis was causing the terminal strip to move just enough to short the filter caps to the chassis and other components nearby which is why i would loose my audio and then eventually my video as well.

So I fixed the filter caps and I now have video and audio again.

A note: This Philharmonic began as the company founded by Avery Fisher in 1937. Avery Fisher lost control of the company due to WW II production and the need for more capital for the business. Avery Fisher left Philharmonic Radio in 1945, and began Fisher Radio. John Meck acquired the remains of Philharmonic in the 1950 time frame.

Ok, so this Philharmonic had nothing to do with E. H. Scott and Scott Radio Labs and more to do with Fisher.

The horizontal output tubes for some years were popular for illegal CB Radio not so linear amplifiers, and for many amateur radio HF transceivers as well, the Yaesu FT 101 line, the Swan 350 as two well known examples. They were cheaper in this era than Eimac 3-500z or other RF tubes when these transceivers were new, or not very old.

The 12BY7 was more of a video output. They haven't obtained the value that 6LB6 tubes and the like have.

Very true. But some types of sweep tubes are expensive like the 6LB6, the 6DQ6 because of their use by Amateur Radio equipment and Illegal CB linear amplifier use. And yes, the 12BY7 was much more a video output tube.

John Meck Industries also acquired the remains of E.H. Scott and Scott Radio Labs in this time frame, so they're in this era, related companies. They died out in the 1960 time frame roughly.

OK, so then this was related to the E. H. Scott Philharmonic then. :scratch2:

Yes, corporate relatives in this era. As they were sister brands, under the John Meck Industries umbrella. The brands being Philharmonic Radio & TV, and E.H. Scott aka Scott Radio Labs.