GZ32 in place of a GZ34 in Bogen Amp.

Jereostereo

Jereostereo

Active Member
Hello - I have a lovely Bogen AP-35 tube integrated amp. Very well built piece of gear. The tube lineup is 7408 (6V6), 12ax7, 6eu7, 12au7a, and GZ34. I have 6V6GT output tubes in it. They are vintage Magnavox and all the other tubes are good vintage also - except the GZ34 rectifier. I bought a JJ that seems to work fine - the amp sounds very good. However, I do have several vintage GZ32’s laying around. The allure of using all vintage tubes in it has me wondering...

Is the GZ32 an allowable replacement for this amp, and if it is would a vintage GZ32 be a possible sonic improvement over the replacement GZ34 JJ?

I don’t want to audition the GZ32’s until I am reasonably certain it won’t damage the amp.

Thanks!
 
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I read in the past from the tube gurus here that the rectifier tube being part of the power supply aslong as the voltages are right it doesn't really effect sound. It is the least likely tube to effect sound. Hopefully you get some answers soon.
 
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Wouldn't do it--the GZ32/5V4 is rated for significantly less current and somewhat less voltage than the GZ34/5AR4. Like tonyg88, I'm skeptical that the choice of rectifier tube (within proper ratings) affects the sound of the amp--this usually seems to be a guitar player observation related to 'sag' in the B+ power supply that ought not to be present in a stereo amplifier properly set up. Others may feel differently.
Dave
 
Dave is correct about the ratings. I would say "it depends". I was unable to find a schematic for the amp so I don't know the operating conditions.

If the voltage and current are low enough it might be OK. You might also have to reduce the size of the first cap if it's a cap input filter. From the standpoint of the pinout and heater current they are compatible. The direct equivalent of the GZ32 is the 5V4G.
 
Without picking my brain and/or looking them up, one tube has more of a voltage drop than the other so probably not a good idea.
 
GZ32/5V4 is rated for 175mA current. That's probably cutting it close. And you'll get quite a bit less B+. There's really no benefit to using it here.
 
Yep, I couldn't easily find the voltage drop comparison, but the 5AR4/GZ34 is very efficient without much drop and I would expect the 5V4G would be more (hence, less B+). Not knowing the circuitry of the amp, I'd be worried about marginal operation of the GZ32 with the significantly lower current rating.
 
Like everyone else has said, changing to a different rectifier likely will not alter the tonal signature of the amp. I've never noticed a difference except in guitar amps.
 
That amp runs 4 6v6s so it needs all the current of a GZ34. I would honestly stick with whats called for. They are still availablea new, and won't break the bank.
 
zackthedog said:
GZ32/5V4 is rated for 175mA current. That's probably cutting it close. And you'll get quite a bit less B+. There's really no benefit to using it here.
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I agree that there wouldn't be any benefit, other than being able to use a tube he is not using otherwise. The difference in voltage drop is not significant. The 5AR4 drops 17v and the 5V4G drops 25v.
Dave451 said:
Yep, I couldn't easily find the voltage drop comparison, but the 5AR4/GZ34 is very efficient without much drop and I would expect the 5V4G would be more (hence, less B+). Not knowing the circuitry of the amp, I'd be worried about marginal operation of the GZ32 with the significantly lower current rating.
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Yeah, that's why I said "it depends".
trainbuftony said:
That amp runs 4 6v6s so it needs all the current of a GZ34. I would honestly stick with whats called for. They are still availablea new, and won't break the bank.
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Just because it uses 4 6v6s doesn't really tell you much. You need to know how hard they are being operated.

For example, the Magnavox 88xx series uses 4 6v6s and a 6CA4 / EZ81 rectifier, which is rated at 150mA - 25mA less than the 5V4G / GZ32. BUT, according to the Sams the B+ is 265v and the current draw is only 100mA.

The Magnavox 175 also has 4 6v6s but it uses a 5U4GB. In that amp the B+ is 355v and the current draw is 160mA.

The 5V4G / GZ32 could actually be used in the 175 because it's rated up to 410v and 175mA but the 5U4GB will be under less stress. The 5V4G also says to use a maximum 10uf first cap when it's being run at maximum while the 5U4 allows up to 40uf at max. It also is rated for 460v at 265mA.

If by "new" you mean new production, I've read numerous reports that indicate they are not nearly as tough as old stock 5AR4s but they would probably suffice unless the circuit was running pretty hot.
 
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FlaCharlie said:
I agree that there wouldn't be any benefit, other than being able to use a tube he is not using otherwise. The difference in voltage drop is not significant. The 5AR4 drops 17v and the 5V4G drops 25v.

Yeah, that's why I said "it depends".

Just because it uses 4 6v6s doesn't really tell you much. You need to know how hard they are being operated.

For example, the Magnavox 88xx series uses 4 6v6s and a 6CA4 / EZ81 rectifier, which is rated at 150mA - 25mA less than the 5V4G / GZ32. BUT, according to the Sams the B+ is 265v and the current draw is only 100mA.

The Magnavox 175 also has 4 6v6s but it uses a 5U4GB, which is necessary because the B+ is 355v and the current draw is 160mA.

If by "new" you mean new production, I've read numerous reports that indicate they are not nearly as tough as old stock 5AR4s but they would probably suffice unless the circuit was running pretty hot.
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I've used current production GZ34s and never had a problem. Specifically the Sovtek with the notched plates. The older Svteks, though, were not too rugged.
 
Jazzbow said:
I've used current production GZ34s and never had a problem. Specifically the Sovtek with the notched plates. The older Svteks, though, were not too rugged.
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Again, so much depends on how hard the tubes are being run. In most cases they should be fine but I would not run them close to the maximum specs that are listed in the original data sheets, which were developed with what are now "old stock" tubes. Sadly, this seems to be the case with all the new production tubes, not just rectifiers.

I will say that I'm basing that opinion on what I've read of the experience of numerous others. There seem to be lots of comments out there about new production tubes, in general, not being as tough as old production. I've got old 5AR4s (Mullards, Amperex, and some American made) that still test as new after being used for 50 or 60 years.
 
No problem staying with the new production GZ34, but I am curious why old production G34’s sell for such high prices. Just durability?
 
Jereostereo said:
No problem staying with the new production GZ34, but I am curious why old production G34’s sell for such high prices. Just durability?
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Durability, reliability, and the fact that they sound better. Some folks will say it shouldn't matter but the quality and consistency of tube construction 50 years ago makes a difference sonically.
 
Based on my experience with the 5V4 vs. a 5AR4 in the same amp, I would expect around 20-30 volts drop in B+.
 
zackthedog said:
Based on my experience with the 5V4 vs. a 5AR4 in the same amp, I would expect around 20-30 volts drop in B+.
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For an amp with that sort of load (quad of 6V6s), that's exactly what my experience has been, too.

The 5v4 is a useful tool, when you NEED to reduce B+... an example was a Pilot SM245 I had here- B+ was a bit "out of control" on modern line voltage, with the original 5AR4, especially when individual tube bias was added to the four EL84 output tubes (so that the tubes weren't running on the ragged edge of plate current). A 5V4 got it right in the sweet spot- it sounded great, and was well within the acceptable operational parameters of the 5V4.

Regards,
Gordon.
 
Jereostereo said:
Hello - I have a lovely Bogen AP-35 tube integrated amp. Very well built piece of gear. The tube lineup is 7408 (6V6), 12ax7, 6eu7, 12au7a, and GZ34. I have 6V6GT output tubes in it. They are vintage Magnavox and all the other tubes are good vintage also - except the GZ34 rectifier. I bought a JJ that seems to work fine - the amp sounds very good. However, I do have several vintage GZ32’s laying around. The allure of using all vintage tubes in it has me wondering...

Is the GZ32 an allowable replacement for this amp, and if it is would a vintage GZ32 be a possible sonic improvement over the replacement GZ34 JJ?

I don’t want to audition the GZ32’s until I am reasonably certain it won’t damage the amp.

Thanks!
Click to expand...

I've been thinking about this post and I wondered what Bogen's logic was in using both 12AX7 and 6EU7 tubes in the same circuit? Not sure I've ever seen that before. Aren't they basically the same tube with a different pinout? Just the kind of thought you deal with when you occupy my mind space. :idea:
 
they are, but different heater config. The 6EU7 is only a 6.3v 300ma tube. 12ax7 can be either 6.3v 300ma or 12.6v 150ma. Without looking at the schematic I don't know if they ran the heaters differently but that would explain it. If its not that, frankly I have no idea why you'd mix those two.
 
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