'69 Super Reverb runs hot w/GZ34

[Bluewail]

I have a '69 (AA1069) Fender SR that has been gone over and blackfaced to AB763 specs by a reliable tech. As I understand it, it should be able to run either a GZ34 or a 5U4. The AA1069 circuit was designed for a 5U4 but the AB763 takes a GZ34. When I load in a GZ34 and bias it at 19 watts/tube using a CompuBias meter the plate voltage reads 495 and the amp runs REALLY hot, both the tube and the input xfmer. With the 5U4 and 19 watts/tube the plate voltage reads 470 and the amp runs MUCH cooler. So what's the story? Can I do something to run the GZ34 and have it run cooler? Any help would be appreciated.

[phsyconoodler]

Hmmm...something is afoot.....

Have you tried another GZ34?Is that a JJ by the way?Some have been having problems.
495v is rather high.It may be that the transformer doesn't like the higher voltage,but I would be inclined to think it's probably high current draw from a bad rectifier tube.

[Bluewail]

Actually it is a JJ. Let me swap it out and see what happens. It would not be the first bad JJ GZ34 I've had - in fact it would be the 4th.

[Bluewail]

Well I think you nailed it. I put in an old Amperex GZ34 and voila - 467v@ 19 watts/tube and no blistering heat. So this is now the 4th JJ GZ34 that went bad over the course of the last 5 years or so. 3 arced and burned up taking fuses with them and now this one. Never had another rectifier, new or NOS, go bad. In fact come to think of it, I've only had one JJ that worked correctly. I'll stick with the NOS or garden variety Sovteks for GZ34's.

Thanks for the help.

[davemccarthy707]

JJ=junk x 2. I do not use anything with JJ on it. Not rectifiers,power,or preamp tubes. Nothing but trouble here.

[Bluewail]

I like JJ's just fine normally, especially their ECC803s preamp tubes, EL-84's and the 6v6's. Something's just wrong with the design of those rectifiers though.

[davemccarthy707]

I've had too many problems with all their tubes. I just stay away now.

[jcs]

I wont let JJ rectifiers anywhere near my gear.

If the power tranny was designed for a 5U4 (which SF fenders often are) i would always keep around a few USA 5u4 for reference in the future, they are generally very rugged rectifiers and reasonable.

[slider313]

I would stick with a 5U4 in that amp.

[brad347]

JJ rectifiers do not have a good track record. I recommend not buying them anymore. But I bet you've figured that out after 4 out of 5 were bad!

However, they make the best new production 6V6 in my opinion... but that's not saying much. That's kinda like saying a car is the nicest one in the junkyard

[Prairie Dawg]

JJ rectifiers do not have a good track record. I recommend not buying them anymore. But I bet you've figured that out after 4 out of 5 were bad!

However, they make the best new production 6V6 in my opinion... but that's not saying much. That's kinda like saying a car is the nicest one in the junkyard

I'm not particularly pleased with their 6L6GCs-I had some problems with a customer's Boogie Mk II that seemed to be specific to JJ tubes. My old Russian wafer base 6L6GCs worked fine but the JJs produced shorts in one socket, blowing the same screen resistor-which was prolly marginal but hey. I ended up replacing the affected sockets to cure a problem I might never have had unless the customer wanted JJs.

Their EL84s seem to be rather good.

[brad347]

Yeah. The funny thing is they are kinda marketed as a "premium" product, and I run into lots of people that consider them as such. But in my opinion, besides the 6V6, they are no better than anything else, and sometimes worse.

[StratTone]

I also agree that there 6V6s are great tubes. The only other JJs that I like are the older 12ax7s they came out with that were great. I actually have about 6 that were given to me that have been in an amp for like 5 years that still test new and sound great. Now the new ax7s they have been putting out that is a different story........ Yuck.

[davemccarthy707]

Besides the rectifiers being a problem, I find their 6l6gc's do not fit in the older sockets nice at all. They like to arc out tube sockets. The pins are too small. There 12aXX type tubes are not much better. I just stay away. If I want new production 6l6's I go with TAD 6L6WGC.