SOLVED Tube Identification based on circuit

[PunchySunshine]

Hello you Wonderful Wizards!
I'm restoring a small homemade tube amp and I've run into a road block. I've replaced all the filter caps. The only caps left are the two "tone" caps but I'm about ready to replace those as well JIC. They measure at 8nf and their label says they should 5nf. The sound I'm getting out of the amp is weak. The filaments are all getting voltage and lit. I made a diagram in hopes that someone here can get me going again. The rectifier is a 6x5GT. That is the only tube I can properly identify. I think the power tube is a 6v6 but I can't tell and I don't have a clue what the pre tube is other than is ISN"T a 6SJ7 like I was hoping. I know it's a long shot but maybe @RetiredUnit1 or @Chuck D. Bones or @owlexifry has some clue for me to get me going on this again. I just feel so very close but yet so far!
View attachment 63009

 

[RetiredUnit1]

Wow they look like REALLY dirty tubes. There are people that can recognize tubes on their internal things, but I'm not one of them. You might want to try using a soft sponge moistened with some warm water and detergent and removing that grungy stuff. You may see some light etching to reveal their identities.

Hey, kinda hard to see, but is that a schematic printed on the chassis underside? You may want to also check the values of those old carbon comp resistors. I've seen 68k resistors drift way up to 2M. And those wax caps are guaranteed to be leaking. Modern substitute for .05uf is .047uf. You don't see .05 much, someone probably has them tho....

Could you post a picture of the entire inside of the chassis? I just like to see them, lol.

I do see a stop sign on the 6V6GT. That's a valuable tube, the stop signs 6V6 are as good as it gets for vintage tubes. I have about 20 in matched pairs that I got on an eBay auction for a stupid low price because it was Christmas eve. I'm not sure what the guy was thinking, I'm the only one that bid on it....(not for sale or trade)

 

[jessenator]

Whatever you do, don't use isopropyl alcohol! Some labels are resilient, but some will just scrub right off. Ask me how I know

 

[PunchySunshine]

Wow they look like REALLY dirty tubes. There are people that can recognize tubes on their internal things, but I'm not one of them. You might want to try using a soft sponge moistened with some warm water and detergent and removing that grungy stuff. You may see some light etching to reveal their identities.

Hey, kinda hard to see, but is that a schematic printed on the chassis underside? You may want to also check the values of those old carbon comp resistors. I've seen 68k resistors drift way up to 2M. And those wax caps are guaranteed to be leaking. Modern substitute for .05uf is .047uf. You don't see .05 much, someone probably has them tho....

Could you post a picture of the entire inside of the chassis? I just like to see them, lol.

I do see a stop sign on the 6V6GT. That's a valuable tube, the stop signs 6V6 are as good as it gets for vintage tubes. I have about 20 in matched pairs that I got on an eBay auction for a stupid low price because it was Christmas eve. I'm not sure what the guy was thinking, I'm the only one that bid on it....(not for sale or trade)

Wow..yer amazing! So the stop sign one is the 6v6....I'm an idiot! My gut was telling me but I'm just not experienced enough to understand yet. I'll try gently cleaning the tubes with your method and report back. No iso alcohol needed.
I'm not sure the schematic on the bottom is this one, but there are definitely transformer symbols among others that can't be made out.
As requested, more pics sir!

 

[RetiredUnit1]

Wow..yer amazing! So the stop sign one is the 6v6....I'm an idiot! My gut was telling me but I'm just not experienced enough to understand yet. I'll try gently cleaning the tubes with your method and report back. No iso alcohol needed.
I'm not sure the schematic on the bottom is this one, but there are definitely transformer symbols among others that can't be made out.
As requested, more pics sir!

As mentioned Iso is out!

Well that definitely looks like a schematic. This is what a Marshall 2203 looks like, you can see the preamp and power tube symbols. If there's any tubes on the schematic on that chassis, I'd bet a nickel that it would have the name of the tube printed next to it!!!

 

[PunchySunshine]

As mentioned Iso is out!

Well that definitely looks like a schematic. This is what a Marshall 2203 looks like, you can see the preamp and power tube symbols. If there's any tubes on the schematic on that chassis, I'd bet a nickel that it would have the name of the tube printed next to it!!!

View attachment 62238

Amazing! after a gentle cleaning can confirm the 6v6gt "stop sign"
Not so lucky on the other tube but a win is a win in my book!
I've investigated the drawings a little more and found a parts list. The full part numbers are covered by the terminal strip but here are the pics I've gotten JIC. I can't thank you enough for helping as much as you have already amigo! I got a big fat sac for ya next time I'm in SoCal..

 

[PunchySunshine]

Updated schematic.

I'll start getting some voltage readings now that we know two of the three tubes. I just ordered the last two cap replacements. Thanks for the heads up on the modern replacements. I checked the resistors against their color codes and they read fine. I'll be sure to double check 'em though! I sure do appreciate the help sir!

 

[RetiredUnit1]

Updated schematic.
View attachment 62315
I'll start getting some voltage readings now that we know two of the three tubes. I just ordered the last two cap replacements. Thanks for the heads up on the modern replacements. I checked the resistors against their color codes and they read fine. I'll be sure to double check 'em though! I sure do appreciate the help sir!

I'm remarkably free from the ravages of intelligence today, Monday-itis is sort of a permanent state of being for me. Fortunately I'm retired and the only chore to do today is put the trash cans out for tomorrow pickup.

This sure looks good! What graphics package are you using, just wondering. I have to jump through hoops to get Visio to put lines around lines. I do it by duplicating the line, making it black and thicker, moving it to a back layer, then re-centering around the original line. A royal PITA but it works.

 

[RetiredUnit1]

This is my latest drawing. It's a blackface princeton reverb AA1164. Might sound odd, but I'm particularly proud of the phillips head screw illustration. It's very realistic and three D ish. And the SOZO logo on the capacitors. I manually traced around a picture of a real one and shrunk it down to size.

I haven't touched this in a couple months since Harvest. Just not in the mood, spending a lot of time cleaning house. After my wife passed away back in 2021 I just sort of closed the door on a few rooms that were *a mess* and I've been spending my time cleaning, sorting, trying to decide what to sell and what to keep. It's exhausting....

 

[PunchySunshine]

This is my latest drawing. It's a blackface princeton reverb AA1164. Might sound odd, but I'm particularly proud of the phillips head screw illustration. It's very realistic and three D ish. And the SOZO logo on the capacitors. I manually traced around a picture of a real one and shrunk it down to size.

I haven't touched this in a couple months since Harvest. Just not in the mood, spending a lot of time cleaning house. After my wife passed away back in 2021 I just sort of closed the door on a few rooms that were *a mess* and I've been spending my time cleaning, sorting, trying to decide what to sell and what to keep. It's exhausting....

View attachment 62318

That looks great! I totally get the being proud of a Phillips head graphic. These things can get tedious. I just use DIY Layout Creator. It's freeware that I believe is open source. I prefer open source apps even if it's a little basic.
I also hear you with the exhaustion of cleaning and grieving. That's ultra hard on a guy.
My heart is with you brother.
I turned 49 today and I get to have my first endoscopy on Wednesday. Yay.

 

[RetiredUnit1]

That looks great! I totally get the being proud of a Phillips head graphic. These things can get tedious. I just use DIY Layout Creator. It's freeware that I believe is open source. I prefer open source apps even if it's a little basic.
I also hear you with the exhaustion of cleaning and grieving. That's ultra hard on a guy.
My heart is with you brother.
I turned 49 today and I get to have my first endoscopy on Wednesday. Yay.

Well Happy 49th Birthday Punchy!

The Ass-Cam. I hate those. The prep is the worst part. Not eating for a day then drinking a gallon of laxative. Ugh. Do yourself a favor DO NOT REFRIGERATE THE PREP JUICE.

I did that the first time and got hypothermia so bad I became unable to move. I did manage to crawl under the covers and eventually warm up, but my wife came into the room to see where I'd gone to and I couldn't even say "help me". A truly scary experience.... not to mention messy as I couldn't get up to go to the bathroom when the laxative kicked in.

 

[RetiredUnit1]

DIY layout creator, ah I checked the facebook page it's by Doug Hoffman. I used to buy components from him 20 years ago before I got a business license and a wholesale account with CE Dist. He's a really great guy, runs the EL34world forum. I thought I had it on this machine but I think it was on my old laptop. Before the 'spilled wine disaster' smoked it.

 

[PunchySunshine]

Well Happy 49th Birthday Punchy!

The Ass-Cam. I hate those. The prep is the worst part. Not eating for a day then drinking a gallon of laxative. Ugh. Do yourself a favor DO NOT REFRIGERATE THE PREP JUICE.

I did that the first time and got hypothermia so bad I became unable to move. I did manage to crawl under the covers and eventually warm up, but my wife came into the room to see where I'd gone to and I couldn't even say "help me". A truly scary experience.... not to mention messy as I couldn't get up to go to the bathroom when the laxative kicked in.

So scary! That's great advice. I'll be sure to not refrigerate.
My father in law said the same....the prep is the worst part. My artist buddy said it's the best 10 minute nap of your life.
I had no idea Hoffman wrote that. Now I gotta donate something. That guy IS great! A wonderful resource of information for newbs like me.

 

[RetiredUnit1]

So scary! That's great advice. I'll be sure to not refrigerate.
My father in law said the same....the prep is the worst part. My artist buddy said it's the best 10 minute nap of your life.
I had no idea Hoffman wrote that. Now I gotta donate something. That guy IS great! A wonderful resource of information for newbs like me.

I have a VERY high tolerance to alcohol and drugs. I watched the whole procedure, including the polyp removal, and when wheeled to the recovery room started to get up. The nurse said "whoa, hang on there, you can't be ready yet. Squeeze my finger." I started to squeeze and she said "OK STOP YOU'RE READY". Guess I squeezed too hard, lol.

It's a great buzz tho, very much like smoking a huge fatty.....

 

[PunchySunshine]

I came across this page:

Identify Unmarked Vacuum Tubes

rec.antiques.radio-phono.narkive.com

Which pointed me to this:

http://www.tubebooks.org/tubedata/ge_essential_characteristics.pdf

Which has handy little diagrams to help you narrow down the possible tubes based on pinout and continuity.

I've ordered a couple of different low cost preamp tubes to test this theory out as well as the proper tone cap replacements. I must have been loopy when I ordered those last ones because I got .047 instead of .0047. Doh! Keep you posted on the progress!

 

[Erik S]

Disclaimer - I know absolutely zero about tubes.

I did recently bring home a box of old tubes and some literature about tubes though.

If I understood your post - it looks like you’re trying to ID a sylvania tube, and I happen to now have some 1950s sylvania technical manuals, so I wondered if there was any way I could look it up from your photo.

It looks to me like it matches a T9 “RETMA outline” and it’s got 6 pins on an octal base with one standing alone.

I found two matches for a t9 tube with a compatible base diagram.

Either a 12sf5 / GT, or a 6p5GT.

I don’t know enough to know those are possibly right or whether they could work in your application, but it was a fun exercise.

Let me know if there’s anything useful I might be able to look up in there.

 

[PunchySunshine]

Disclaimer - I know absolutely zero about tubes.

I did recently bring home a box of old tubes and some literature about tubes though.

If I understood your post - it looks like you’re trying to ID a sylvania tube, and I happen to now have some 1950s sylvania technical manuals, so I wondered if there was any way I could look it up from your photo.

It looks to me like it matches a T9 “RETMA outline” and it’s got 6 pins on an octal base with one standing alone.

I found two matches for a t9 tube with a compatible base diagram.

Either a 12sf5 / GT, or a 6p5GT.

I don’t know enough to know those are possibly right or whether they could work in your application, but it was a fun exercise.

Let me know if there’s anything useful I might be able to look up in there.

I too know nothing! I sure appreciate you taking some time on this exercise. The 12sf5 won't work due to the pinout. But the 6p5GT is SPOT ON! Great stuff!
It seems this style base has filament on 2+7 while missing pins 4+6. Plate is on 3, Cathode on 8 and grid is 5
I just ordered at 6L5G and a 6C5GT as they match pinout and are only $7 a piece. If they don't work I'll give the 6p5GT a try @ $30 a tube. :*(
Good news on voltage readings, @RetiredUnit1 was absolutely 100% correct. The tone caps I left in were SUPER leaky. Maybe that will just fix it I won't even need to ID this mystery tube.
Either way, I agree, I'm having a blast learning this old school tech finally.

 

[Erik S]

I also found this for possible substitutions in case one of those looks right.

 

[RetiredUnit1]

Can't wait to hear it, such a simple design!

This is what I use to test my capacitors at full voltage for leakage before I use it in an amp. I test *everything*. Pots, switches, caps, resistors, tubes, jacks, fuses in the holder (a two fer), output transformer for continuity in the primary and secondary and no continuity between them.

I have a Sencore TC162 tube tester, it's got a cool feature that can tell you how much life a tube still has. And it's solid state, and tests transistors as well. It's a LOT easier than putting it together and THEN having to look for the faulty component.

Like christmas lights. Test those before hanging, right? I put those up yesterday. And I have the aches and pains in my legs and shoulders to prove it!!!!

I like blue, can you tell???

 

[PunchySunshine]

Update:
I changed the last two coupling caps @5nf (at least I think they're coupling caps) and it's a lot cleaner tone but still really soft.
The 6C5GT works! as a replacement preamp tube but there isn't a change in loudness.
I'll take some voltage readings today but the only thing left is the carbon comp resistors that all read fine with the DMM (but that don't mean they are). I may just shotgun them and try a new rectifier tube JIC as they are the last remaining possibilities it seems. The filament circuit is only getting 5.9 instead of 6.3. It seems like that would make for soft output.

Also, HAPPY HOLIDAYS!!
Here's our xmas lights. I use the gutter hooks from amazon and it only take 20-30 minutes for setup.