2. amps-preamps
  3. 132537-2693

Genalex GL GZ-34 Rectifier...Did I just get a bad one? Five months seems

like a terribly short lifespan. I bought it in May and spent the extra money to get a "good" tube. It sounded good while it lived. But it went in a fiery inferno last weekend.  Fortunately it only took out a fuse.

It was running in a Bob Latino VTA ST-70 Dynaco amp. It's a great amp but runs the rectifier a bit hard from my understanding. However the original tube lasted at least 3-4 yrs IIRC. I tried a SS rectifier. YUK!! I put the tube (a spare Sovtek) back in place I've had good luck with the KT-66 Genalex GL's and they have a good reputation (I think). Is this just the luck of the draw. IOW, even a new tube can have a short life span? Or is this odd? Is there any way to avoid it? I'd buy another Gennalex GL if it will last. But I can buy 2 Sovteks for the price of one GL. Sovtek sounds good too.

FWIW, The tube that failed was cryo treated. Could that make a difference in a rectifier tube? As always, Thanks for your help.
128x128artemus_5
atmasphere's avatar
atmasphere
11,979 posts
 
The tube was not the problem.

The original ST-70 design is hard on GZ-34s and they are the most likely tube to fail in the amp. Its fine as long as you don't push the amp hard, but if you are pushing hard, the limits of the rectifier tube can be exceeded.

The solution is dual rectifiers and there isn't the room on the chassis nor the capacity in the power transformer. If there is any big flaw in the ST-70, that's it- the rest of the circuit is really quite competent.

I've not heard the Bob Latino version, but it appears to have only one rectifier tube for both channels, so its going to have the same problem. The solution- if you like that amp, keep a stash of rectifier tubes on hand.
artemus_5's avatar
artemus_5 OP
1,992 posts
 
Ralph. It would make me feel better if you didn't know what you are talking about. But I know you do.. I have thought about keeping a bunch of rectifiers around. I am running through 93.5 db speakers but I am running it somewhat hard. I think my new Zyx cartridge is the culprit cause I wasn't playing quite as loud before. It sounds so doggone good though. But I know it is the bottleneck. I just ordered another Genalex Gold lion. This time not cryoed. Time will tell. Thanks for your response. Try to have some good news next time huh? (-: He said in jest)
trelja
3,224 posts
 
@artemus_5 consider folks who never previously built anything assembled all but a few of the 300,000 ST70s, the fact that most of them that came up on the used market sported their original (5AR4 and all) tubes, and the majority of that number still worked mostly fine even after all those many, many years.

Unless Bob's using too big a capacitor in the first position of the power supply, which WILL blow rectifier tubes with regularity, there's no need to sweat it.  Just get another 5AR4. I recommend spending for a vintage tube for best sonics and reliability. After that, sit back, and enjoy.
jond's avatar
jond
5,916 posts
 
Just realized I made a slight error in my initial post to this thread my amp uses a 5U4GB rectifier not a 5AR4. Sorry about that!
artemus_5's avatar
artemus_5 OP
1,992 posts
 
Trelja. Thanks for the encouragement.  I still think the cryo treatment is the main problem. It may be fine for the other tubes. But the different materials expand & contract at different rates,. This may work in tubes which aren't pushed as hard as the rectifier tube in the ST-70. But it isn't a good thing for a rectifier tube IMO. Other articles point this out as well. Jim  McShane is also of your opinion that a good rectifier shouldn't have any problem pushing the ST-70.  And, I got 3-4 yrs on the original tube. So, even though the rectifier is somewhat of a bottleneck its not the be all end all without remedy. I agree with you that hundreds of thousands were built and ran great. Certainly many were pushed as hard as I push mine with less efficient speakers
More to discover