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What GZ34 Rectifier tube for my '65 Vibrolux?


Greg_In_Michigan

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I found an original '65 Vibrolux in a dumpster late last year and I am now getting around to getting the parts I need to have it fixed. I had no problem with the parts I was searching for until I started looking for the GZ34 Rectifier tube. Most things I read pointed me to the NOS Mullards, but their price tag seems a bit high. I'm wondering if I really should get the Mullard, or would something like a Sovtek 5AR4 for $20 be OK?

 

I have found some Mullard NOS GZ34 on Ebay for $90-150. I could swing that, but it would mean I have to wait longer between buying the other components I need, and having all the parts professionally installed and the amp biased. With the $20 solution I can pretty much buy everything right now and get the thing serviced so I can be rocking right away!

 

I will be having the amp serviced by a tech who I am told was the amp tech for names such as Ted Nugent. Not sure if this is legit or not, but the guy who owns the local guitar shop seems pretty cool so I am hoping he isn't out to screw me over. I know I can do the work myself, but I have been strongly encouraged by some forumites in the past that I should have it done by a reputable tech as it would increase the resale value. I have no intentions of selling it, but I would still like to keep the value at its maximum.

 

Here is the list of parts I need/decided on. I chose these parts because they needed to be replaced (filter caps) or because the amp was missing them.

 

Cap Kit (ordered) - 5 X Sprague 16 uF 475V Aluminum Electrolytic Capacitors. Filter Caps, 7 X Sprague 25uf 25v Aluminum Electrolytic Capacitors. Cathode By-pass. 1 X Sprague 100uf 100v Aluminum Electrolytic Capacitors. Bias Circuit.

 

Speakers - 2x Weber 10F150T, light dope, 8ohm, 25W

 

Power Tubes - TAD 6L6GWC-STR

 

Rectifier tube - Sovtek 5AR4, or maybe a Mullard NOS GZ34?

 

Knobs - 2 knobs were damaged when this was thrown into the dumpster. The chrome center popped off. Should I leave the originals without the chrome center, or replace them?

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Nobody?
:wave:

Does the rectifier tube not make a tonal difference?

 

 

 

The rectifier just supplies the electricity. It makes more of a difference in feel than sound. That difference is more apparant as you play louder.

 

DO NOT "experiment" with different rectifier tubes without knowing exactly what you're doing. The wrong one can fry your amp in a hurry.

 

There are some options (depending on which type you need and what amp you have) where a different tube than the ones specified can get more sag at a lower volume...but again, don't screw around unless you know what you're doing. You asking here means you don't.

 

Use the specified tube...or do some Google-fu and get a more in depth answer about substitutions.

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Sovtek will work fine.

 

As noted the rectifier is there to convert AC to DC for the plate voltages. The way they affect the tone/feel of the amp is how they drop the voltage (compared to a solid-state rectifier) and how well they provide current. New manufactured 5AR4's are pretty accurate in their performance, though they do not last as long as a NOS tube.

 

Keep the original knobs, even if you replace them on the amp. None of the new ones are made exactly like the old ones were. You may however be able to transplant an inlay from a new to the old ones.

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I am not intending to experiment. My intention is to find the best components (within reasonable price) and supply them to the amp tech to overhaul the amp and do it correctly. I have not found any definitive information about the Rectifier tube so I thought to consult here.

 

Wyatt is a great resource. :thu:

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I am not intending to experiment. My intention is to find the best components (within reasonable price) and supply them to the amp tech to overhaul the amp and do it correctly. I have not found any definitive information about the Rectifier tube so I thought to consult here.

 

 

Let's say that the performance difference between a Sovtek and any NOS 5AR4/GZ34 isn't any different than the difference between any two brands of NOS tubes.

 

Mullards are very well regarded for consistency and people really seems to like how they perform. I have a few, though they are in hi-fi's I built. They are good tubes, but I really couldn't speak to a difference in sound from them. And, in general, you'll get 5 times the life out of a NOS rectifier than a modern one, which makes the NOS competitive in price vs. life. Conceivable, you could go the rest of your life on one NOS 5AR$, assuming you aren't a professional gigging several nights a week, but there is also the chance you turn your amp off standby one day and have a $150 tube fizzle prematurely.

 

A good NOS deal are JAN Philips/Sylvania 5V4's, which are actually relabeled 5AR4's. It was easier to just relabel the tube to meet a military contract for 5V4's, for their purpose, the difference wasn't important. They can be found for $75-90.

 

BTW, those 12F150's can be really efficient...blow the heads of the first few rows efficient. When they say "aggressive," they mean it.

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I've read lots of recommendations for the 10F150T. I am only a bedroom player so I don't necessarily need insane volumes with massive headroom. I have my Twin Reverb RI for that. I thought the 25W light doping would give me a bit more breakup at earlier volume levels. At least, that's what I have read.

 

What other speakers should I consider? I would like mild breakup from the amp with a very warm tone.

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Sovtek GZ34's are kinda known for reliability problems, might want to check out a JJ GZ34 from a reliable outlet like KCA. Lord Valve, or Valvequeen (member here)

 

http://www.kcanostubes.com/content/jj-5ar4gz34

 

Here's a slightly used GE for $50..

https://www.kcanostubes.com/content/anos-ge-5ar4-lightly-used-test-new

 

I use these in Early Marshalls with absolutely no issues, (and my presonal Vibrolux) as bulletproof as Blackburn Mullards.

 

You basically buy these once....not unusual to find these still strong in 40 year old Voxes/Marshalls.

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I've read lots of recommendations for the 10F150T. I am only a bedroom player so I don't necessarily need insane volumes with massive headroom. I have my Twin Reverb RI for that. I thought the 25W light doping would give me a bit more breakup at earlier volume levels. At least, that's what I have read.


What other speakers should I consider? I would like mild breakup from the amp with a very warm tone.

 

 

The Webers are a good call, I'd suggest an attenuator to get breakup where you like it, then use the attenuator to drop volume.

Weber have some great choices...

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Sovtek GZ34's are kinda known for reliability problems, might want to check out a JJ GZ34 from a reliable outlet like KCA. Lord Valve, or Valvequeen (member here)


 

 

I was hesitant to get into this, because there are those who think Sovtek is less reliable than JJ and vice-versa, and equally so with the Chinese tube. Everyone seems to have their favorite and think the others are junk. But I have yet to see a consensus on the matter.

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I was hesitant to get into this, because there are those who think Sovtek is less reliable than JJ and vice-versa, and equally so with the Chinese tube. Everyone seems to have their favorite and think the others are junk. But I have yet to see a consensus on the matter.

 

 

Never said that, Sovtek tubes are as reliable as most new production tubes, as long as they have been burned in, and weeded out properly.

 

Not many retailers do, hence the:

"Guess new **** aren't as good as ***, I just had a one of a pair die after a month" and

"Q.C.'s crap-had a pair drift 12 .ma apart in a weekend" posts you often see here.

In my experience, from my vendors, less variances in J.J. GZ-34's in amps I see in my day to day. Sovteks can vary a bit, and can make the amp sound a bit different (sag/voltage drip). Not good when one goes in a studio, the back-up goes in, and the amp sounds different.

This is just my experiences with these the last decade of having J.J.+Copper Caps to add to the usual suspects.

 

(Get the G.E. It's only $30 more)

 

You pick up a tip or two in 32 years as a full time amp/guitar tech.....

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