Rectifier tubes, the hidden "sweetness" of electronic gear, vintage and new, guitar amps and stereo.

The preamplifier tubes on that amplifier are two 6SN7's. The single 6SL7 is the rectifier tube.

 

A 6SL7 is not a diode, it's a double triode.

jeff

 

It's an odd comment that's for sure. I have 6SL7s as the driver tube in my SETs - the rectifier is a GZ37.

 

You're definitely right. It is. But if a triode can't be used to rectify a circuit, I have no idea what the hell the odd tube out is for! I would kill for a wire schematic of my amplifier. Impossible to find. I've searched and searched for one. There are two of every other tube size in that amp. It's just that single 6SL7 tube in between the two 6SN7's.

 

It would seem to be odd as a rectifier, but, then again, my phonostage, Viva fono, uses two 300b tubes as rectifiers.

 

Yeah that's an odd configuration! 300b's are also triode tubes. It also sounds like a pretty cool phono stage.

 

My Bob Latino 120 and my Opera Consonance both have tube rectification. It was a huge factor in choosing the Consonance.

 

Maybe it's being used for voltage gain, which is what the tube was designed for.

A 300b is not a diode either.

jeff

 

Is it possible to use a triode as a rectifier?

It seems so. From 1933

http://aip.scitation.org/doi/abs/10.1063/1.1749182

 

Can't view any of the docs.

jeff

 

I just posted this in another thread, but thought I should copy it here as well...

Last night I was doing some reading up on rectifier tubes. Right now there is a Sovtek GZ34/5AR4 in my '59 Fisher X-100, but from what I read they are well-regarded for ruggedness, but not so much for performance; something to do with plate voltage being too low. Vintage Mullards are said to be rugged and excellent-sounding. I almost pulled the trigger on a Matsushita - made in Japan supposedly with Mullard/Phillips tooling and said to be equal to a British Mullard.

Just this morning on eBay I spied a Sylvania-branded GZ34/5AR4, made in Great Britain by Mullard, for $52.75 shipped and I hit the BIN. That's at least 50% off the price of a Mullard-branded tube, so I think I made a good choice (hopefully).



Blackburn factory, made the 2nd week of December 1972:

 

I run a GE 5AR4 rectifier in my Bell 2440 integrated amp. It's probably the original. Also an RCA 5Ar4 in my Scott 299C.

If the "cheaper" (not really sure if they are) Russian tubes are not giving "to-spec" supplied plate voltage, then I would not use them. Plate voltage is very important, as this is the source that feeds into the filter caps for all of the supplied source voltages, i.e. 470, 370 100, what have you...

I do not understand how vintage rectifier tube branding difference affects sound, as long as the voltage is there, and the caps are keeping the DC filtering clean. I had no idea that the rectifier tubes affected the sound. I've only rolled 12AX7's, and tend to like smooth plate Tele's. There must be something to it as everyone is saying.

IMO the vintage amps deserve the real deal vintage tubes, as that's what they were designed around.

 

My understanding is that the rectifier's characteristics impact how "stiff" the power supply is and it is a combination of elements including the specs (which are available on those tube data sheets), along with the circuit design.
I have rolled many rectifiers in my Allnic phono stage, and they all affect the sound to a noticeable degree. I was using a first series Mullard fat base (the tube made after the more desirable and costly metal base) and have rolled Tung-Sol, old RCA (there is one with double 'angled getters' that isn't crazy money that is supposed to sound great in the Allnics) and a few others. The phono stage unit is still in current production and is supplied with a new Chinese tube (i forget which, I can look it up). I'm currently using a GEC U-52, and it presents more "air" and detail while still providing rock steady bass.
The guitar amp guys want "crunch" which is as I understand it "tube sag" from the rectifier. In hi-fi, that distortion is undesirable. I verified with the manufacturer/distributor that my various substitutions were permitted to stay within warranty.
I do use a vintage Mullard in my Quad II power amps, just as Peter Walker intended.
Rectifier rolling is still cheaper, for the most part, than small tube rolling or unobtanium power tube rolling. The WE rectifiers tend to be very pricey, but that has as much to do with the brand desirability as it does with the sound. I think I posted earlier to this thread DubStep Girl's Massive Rectifier shoot-out. Definitely worth reading if you haven't seen it.

 

Sylvanias are good too.NOS Sylvania GZ34s can still be found for under $40.

See above.

This place still has a few left.

5AR4/GZ34 by SYLVANIA - Buy or Repair at Radwell - Radwell.com

 

That's the same as the one I just bought, I believe. Made by Mullard.

[EDIT] Maybe not... the one on the Radwell site says "USA" under the logo.

 

thanks, but they're not GZ32s

 

Mullard GZ34 in my AB764 based Deluxe Reverb clone. Sounds great.

 

You said you've had trouble with the GZ 32 in your Quad IIs- I presume the older, original version of the amp and not the reboot?
I know at the time I was having mine restored, someone raised the possibility of using the GZ 34 in it- not sure what if any changes were involved in the circuitry, but might be worth exploring if you are having issues with the original tube type. I put NOS Mullard GZ 32's in mine, but haven't run it long enough since restoration to encounter any problems. You live in the land of the original Quad- there have to be some pretty good folks there on tweaking the amp-- mine were sympathetically restored, with minor improvements- including power cord socket so I didn't have those Jones plugs or whatever they are called.

 

They can be adjusted to take almost any valve. Lots changed them to take EL34s, but then they no longer sound like Quads. 34s don't work as stock, mine are stock.

 

I was focusing only on the rectifier, since that's where you said you had an issue. Mine are pretty much stock in terms of tube configuration- KT 66s on the power tubes. Sound glorious through a restored pair of old Quad ESLs. My comment was only meant to address what I thought you said was a repeated failure of the standard rectifier tube, and I know some have used the GZ 34 but don't know what that change would involve in terms of circuitry.
NB: did you mean GZ 34 when you typed EL 34?

 

I found an Amperex labeled 5AR4/GZ34 in my small tube stash. It says "Made In Great Britain".
Is it made by Mullard?
The internals look identical to the image you posted above.

 

Probably... look for the Mullard factory codes:
Tube enthusiast: know your tube codes.

 

Okay - Top row is hard to read since its mixed underneath the bugle boy icon.
Top row = 1 or 4, 3, 2.
Bottom Row = B, 2, I, 2.

So - I'm guessing Mullard (Blackburn, Great Britain), 2nd Week of 62. or '72?

 

Yes