1950 Philharmonic 8200 Audio Issues

[vortalexfan]

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.

[maxhifi]

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.

[vortalexfan]

Originally Posted by maxhifi

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).

[maxhifi]

Originally Posted by vortalexfan

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.

[vortalexfan]

Originally Posted by maxhifi

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...

[maxhifi]

Originally Posted by vortalexfan

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

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

[Electronic M]

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.

[AlanInSitges]

Originally Posted by maxhifi

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

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

Edit: maybe not 50C5s.

[Tom9589]

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.

[JohnCT]

Originally Posted by Tom9589

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?

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

[KentTeffeteller]

Originally Posted by maxhifi

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

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!

[old_coot88]

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.

[vortalexfan]

Originally Posted by Electronic M

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.

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.

[vortalexfan]

Originally Posted by Tom9589

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.

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.

[vortalexfan]

Originally Posted by JohnCT

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

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.