Help with 12ax7 identification and GZ34 repair

[theprofessor]

I recently got a small lot of 12ax7's, 12ay's, and a GZ34 for a good price, and I'm trying to sort a few things out. First, what each of the 12ax7's is. Secondly, how to repair the broken guide pin on the Mullard GZ34.

Here's a photo of the 12ax7/ecc83 I'm unsure of. It's a short smooth plate with two star-shaped micas. Is it an EI (Elektronska Industrija Nis)?

 

[theprofessor]

And here's that Mullard (maybe GE-branded) GZ34, with the broken guide-pin. I've glued one back on before when I had it, but I don't have the broken pin for this one. I knew that going into the sale, but I figured I'd either repair it or just be careful to insert it with the correct orientation. I'd much prefer to repair it. Any experience with this?

 

[theprofessor]

These look to be four Chinese 12ax7's

 

[theprofessor]

Here's a Tungsram ECC83. I really, really like these in the second gain-stage of Blackface/Silverface Fender amps like a Deluxe Reverb.

 

[stefanhotrod]

Be careful not to stick this GZ34 the wrong way inside your amp . Can‘t help with the other tubes but I personally wouldn’t tinker and bother with the guide pin and throw that tube away, NOS or not.

 

[theprofessor]

This one was fun. The seams on the top of the envelope and the internal construction, as well as the print on the side, made me think first of a Mullard I63-type or the like. But it's an NEC Hitachi gold pin branded "Realistic Lifetime." These are sometimes referred to as Japanese Mullards. Thus the "Made in Japan" on the side.

Does anyone have any experience with these who can compare them to any other tubes I might know?

 

[theprofessor]

Finally, a GE 12ay7. I need to remind myself how the dot date code works. I made a whole thread on that once, I think...

 

[corliss1]

They make these dudes to fix the guide pin:

https://www.tubedepot.com/products/octal-tube-keyway-replacement

Just slide it over the existing tube, drop of silicone to hold it together, and you're good.

 

[theprofessor]

They make these dudes to fix the guide pin:

https://www.tubedepot.com/products/octal-tube-keyway-replacement

Just slide it over the existing tube, drop of silicone to hold it together, and you're good.

Excellent! Thanks. I'll see if I can find one of those for sale some place. I'd rather buy from Tube Depot, but it looks like the product is currently unavailable there.

 

[Dacious]

I have short plate NEC 12AX7 and 12AT7. Very smooth sounding. I think I have them in my Greta

 

[Wally]

Can’t help much except that GE is ..as best I can see of those dots...from the 9th week of either 1954 or 1974.

 

[corliss1]

They also sell (and other places too) plain octal bases. It would be more work than the type of part I linked, but I supposed you could rip the pins out of those and grind the base down to make that work. Or take apart a broken tube and do it to that.

 

[Wally]

https://www.tubesandmore.com/products/keyway-replacement-piece-octal-tubes

I would simply mark the base and keep it for myself. If they are good, the GZ34 and that GE12AY7 are the cream of that top, imho. I throw those Chinese 12AX7 tubes away....or limit their use to trem circuits. I have never heard one that had any musical qualities to it, and every A/B test in a tone processing position I have put to others has had the same result...no one has liked what they heard in comparison to any other tube.
Over 20 years ago a fellow brought in a BFDR that had been recapped and totally retuned. The tech put in new GT tubes.....all Ch8nese novels. He was complaining that the amp did not sound as good as it did before the service. I pulled V1 and V2...Chinese 12AX7’s. I installed a couple of new Russian 12AX7’s, and the amp came to life. I asked him what the tech charged him for those GT 12AX7’s.....$15!!! I showed him two new Chinese tubes just like the GT labeled tubes I had pulled out of his amp and told him that I would have sold them to him for $4 a tube. I have been listening to the, for a long time and again..have never heard one make musical sounds in a tone processing position.

 

[theprofessor]

Can’t help much except that GE is ..as best I can see of those dots...from the 9th week of either 1954 or 1974.

Thanks, Wally. Yes, I think you're right. To the right of the center column are two dots, one on the bottom of the left of those two columns (= odd year for "tens" digit) and one on the middle of the right of those two columns (= 4 as "ones digit). So either 1954 or 1974. It has a horseshoe getter. I'd need to do more work, but I'd guess 1954 at the moment.

Here's an example I once made up from a GE 6V6GTA I had.

 

[theprofessor]

https://www.tubesandmore.com/products/keyway-replacement-piece-octal-tubes

I would simply mark the base and keep it for myself. If they are good, the GZ34 and that GE12AY7 are the cream of that top, imho. I throw those Chinese 12AX7 tubes away....or limit their use to trem circuits. I have never heard one that had any musical qualities to it, and every A/B test in a tone processing position I have put to others has had the same result...no one has liked what they heard in comparison to any other tube.
Over 20 years ago a fellow brought in a BFDR that had been recapped and totally retuned. The tech put in new GT tubes.....all Ch8nese novels. He was complaining that the amp did not sound as good as it did before the service. I pulled V1 and V2...Chinese 12AX7’s. I installed a couple of new Russian 12AX7’s, and the amp came to life. I asked him what the tech charged him for those GT 12AX7’s.....$15!!! I showed him two new Chinese tubes just like the GT labeled tubes I had pulled out of his amp and told him that I would have sold them to him for $4 a tube. I have been listening to the, for a long time and again..have never heard one make musical sounds in a tone processing position.

I hear you on those Chinese tubes. I don't normally keep those around. I am very happy with what I got for the price I paid, though.

 

[VintageSG]

The Japanese manufactured valves are every bit as fine sounding as anything from Europe, North America ( Inc. Canada ) or the Eastern Bloc before the demise of mass production. The Chinese -can- make superb sounding valves, but they also make those ghastly things with the odd clips. They can be quite adequate in some positions, and I do have a couple of fine sounding Ruby 12AX7 HG+ examples, but I also have a box of Sino valves whose only reason for not being crushed under a booted heel is I'm a pack-rat by nature. There are some variants that are rated by audiophiles as highly as any modern production gets, and they're priced accordingly. The examples you have are for use bringing a new build up to power, as soldering dummies, as target practice or last resort examples to keep in a box, pack-rat fashion.
If you want to build a skronky, valve powered box of noise, they're very good for that. Starved plate overdrives and fuzzes are a natural habitat for them.

 

[theprofessor]

I'm a dumbo. That tube in post #1 is an RFT, as a member over at The Gear Page pointed out to me. I've had one or two of those before and even have pictures. The micas sure looked like RFT to me, but I did not recall that plate structure. Here are some pics of an RFT I used to have.

 

[radiocaster]

I throw those Chinese 12AX7 tubes away....or limit their use to trem circuits. I have never heard one that had any musical qualities to it, and every A/B test in a tone processing position I have put to others has had the same result...no one has liked what they heard in comparison to any other tube.

I have some, I didn't even buy them, they came with some piece of gear.

They were nothing to write home about in a clean amp, but in a master volume amp they sounded awesome, better than anything else. They say Ruby 7025SS/12AX7A, no longer made, but I think the Shuguang 12AX7B is equivalent.

 

[King Fan]

Prof, you’re right about the RFT star micas. East German IIRC, often well-regarded, said to give a good rock tone.

And I agree strongly with your plan to salvage the Mullard GZ34. I never seem to see 'em selling for less than $100-200.




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[muscmp]

for the broken key, i just mark on the base of the tube with a red marker. no need for actual repair of the key.

nice collection, prof!!

play music!