Rocket and Rectifiers

[RJ Guitars]

I've got a couple Mullards and they are good, no doubt about it. I've got a Sovtek in my KT66 Rocket amp right now that I can't say anything bad about... I was surprised myself. I was trying to find something so that I didn't have to pass around rectifier tubes in my different amps. The Sovtek is hard to tell from the others in a blind test in any one of a half dozen amps. I can't say if they all are like this, I only bought one of them.

I sent a note to the Tube Sargent and asked him what he had in a Mullard equivalent GZ34 in a current production tube and he had plenty to say about it... surprisingly he thinks Mullard were wonderful mostly because they were indestructable, but really didn't think of them as "Magic"? Interesting to say the least.

He recommended the Shugang Dragon for similar performance specifications to the Mullard with the Caveat that they will not last nearly as long. He also said that despite the cheap look to them the Soviet Mil spec 5AR4's were well made and sounded good.

He did seem to think that most of the old school true 5AR4's were good (Brimar, GE, Daystrom, Matushida) and they are also hard to find and quite expensive.

His ultimate recommendation was two 15 cent diodes and improve the specifications even above the Mullard... interesting to say the least for a guy who runs a vintage tube business.

Is there any guess as to why KF went with a tube rectifier in the Rocket rather than diodes like in the other Wrecks? He did say in his brochure that he kept all the good parts of the AC-30 and eliminated the bad ones... that would imply that the GZ34 must have been one of the good ones. In the Trainwreck pages he talks about some amps getting a "singing" quality from the use of tube rectifiers... I think the Rocket sings pretty sweetly myself.

rj

[Brad737]

Gents,

I prefer the old Mullard rectifiers myself. I have a buddy who used to work for GT, and he really educated me about tubes. The problem is that ALL currently available recto tubes suck compared to ALL NOS rectifiers. The problem with new recitifers is that they simply don't perform up to design spec with regards to current, voltage, etc. That's why the NOS rectifiers make a difference in tone. The amps are "allowed to" operated at full current draw and voltage. There's also another benefit of using NOS rectifiers. They literally last 15 to 20 times longer than any new production tubes. Check out www.guitaramplifierblueprinting.com and read Myles' Tube Primer. He has TONS of great info about tubes of all kinds on there.

Hope this helps,
Brad

[Zippy]

You give a compelling argument, Brad... to use a solid state rectifier (and a dropping resistor if you want to change voltage as a function of current draw.

BTW, there is no gain in a rectifier, Mullard or otherwise. It is, however, as you say, all about delivering voltage and current.

[RJ Guitars]

Gents,

I prefer the old Mullard rectifiers myself. I have a buddy who used to work for GT, and he really educated me about tubes. The problem is that ALL currently available recto tubes suck compared to ALL NOS rectifiers. The problem with new recitifers is that they simply don't perform up to design spec with regards to current, voltage, etc. That's why the NOS rectifiers make a difference in tone. The amps are "allowed to" operated at full current draw and voltage. There's also another benefit of using NOS rectifiers. They literally last 15 to 20 times longer than any new production tubes. Check out www.guitaramplifierblueprinting.com and read Myles' Tube Primer. He has TONS of great info about tubes of all kinds on there.

Hope this helps,
Brad

I went to the web site but he really doesn't help us much in understanding the differences between modern GZ34's and the old Mullards. He is in agreement with the Tube Sargent in that the Mullards last forever...

Zippy has it right that if the main idea is to meet the specs of a solid state diode, then why bother with a tube recto...?

In reading the Miles document on rectifiers he goes through a good description to show us the voltage recovery behavior for the various tube rectifiers, and no doubt some of them have a slow recovery and most of them drop a fair amount of voltage. The GZ34 is almost as fast a solid state diode. I recall Ken Fischer himself said that a GZ34 was the most like a solid state diode. This begs the question (although I wouldn't fight on either side of the fence), but why bother with a GZ34 in a Rocket?

Okay, tubes are a bit slower to recover when with your AC swing, but that same voltage has already been smoothed and filtered by the time it gets to your circuit. Can we can hear a "slow" rectifier tube response, especially if the best rectifier is essentially as fast as a solid state diode? But, if I still buy into the notion that a GZ34 sounds different than a solid state rectifier, I want more info on what is different about the filtered DC voltage from each of them. What do we hear because I can't grasp any reason how filtered DC voltage can be slow??? A voltage drop I understand and agree with.

Sag? we need to measure sag and maybe play with a VVR unit. GZ34's don't sag much. I'm talking about rectifier sag - Load down (compress) and then ramp back up. What time constant are we talking about? Is it mili-seconds or seconds? If it's seconds can you imitate with a VVR? When I play with the VVR I have a hard time hearing a small voltage drop... then we also have to consider that unless we've got these dudes cranked, we might be working in class A and there should be no sag...

I'll guess that KF used a GZ34 in a Rocket because he was making an amp based on the AC-30... and he could get good rectifier tubes. I won't declare myself a non-believer in GZ34's yet, but if indeed they add something to the mix, it has to be identifiable and measurable and I am looking for that understanding.

rj

[jaysg]

Sag? we need to measure sag and maybe play with a VVR unit. GZ34's don't sag much.

Interesting set of questions. One thing not immediately obvious is that when you set up a cathode biased amp that's pushing or exceeding the output tube's dissipation spec, there isn't a vast difference between idle and dimmed...therefore not much sag from the tube rectifier...which does lead to the question, 'why bother?'

[Zippy]

Tne thing not immediately obvious is that when you set up a cathode biased amp that's pushing or exceeding the output tube's dissipation spec, there isn't a vast difference between idle and dimmed...therefore not much sag from the tube rectifier...which does lead to the question, 'why bother?'

More heat?

[2tone]

Ken also spec'd a GZ34 for the Komet 60..The other Komets use SS rectifiers I believe. Also, there is an audible difference in rectifier brands and types. The GZ34 Mullard etc are superior in durability and low end response. However, since the Rockett uses 80 uf of filtering on the GZ34, which is way above spec for that tube, the life of the tube, even a Mullard, will be shorter in the Rocket. Russian, Chinese etc current production GZ's will have even shorter life, and I wouldn't use them at all. I even had a failure of a new Mullard GZ in my Rocket once, so they aren't all bombproof! Ken had a large stash of Mullard GZ34's and he would go thru a bunch of Mullard rectifiers to select one for each individual amp!! What a luxury. He said there were definite differences in each Mullard, enough to want to select the best one for each amp. He said one that didn't sound as good in one amp would sound better in a different amp...

[Zippy]

Also, there is an audible difference in rectifier brands and types.

Help me here. Why is there a difference in the sound of a rectifier?

[M Fowler]

[quote: help me here. Why is there a difference in the sound of a rectifier?]


Selective hearing.

[rawnster]

I was playing around with an amp last night that has duel rectification. I dropped in two of the NOS Mullard GZ34s. Very cool sounding, but almost too dark and chocolaty. If I keep them in, I'll probably have to re-voice the amp with a little brighter V1 tube. Too much of a good thing I guess.

[2tone]

I would not have believed that even different Mullard GZ 34s will sound different but it's true. Ken told me that several times. The rectifier is part of a tuned circuit in the power section. Having tried different rectifiers in several of my amps, I was surprised to hear differences that are not imaginary..Try it yourself. My ears aren't as good as Ken's but I can hear the differences. all the technical arguments will not change my mind either.

[M Fowler]

Starve your power tubes and it will change the tone of the amp. That is what the tube rectifier does based on which rectifier tube you put in that spot whether it is new, used or NOS. It is all about the sag isn't it?

Diodes don't have the drop, so you get a more powerful amp with completely different tone structure. Technically I couldn't explain it at all.
But with this diverse tone geeks we have some one can.

Mark

[Zippy]

Sag and drop aren't the same to me but I agree that it is ALL ABOUT THE VOLTAGE.

Rawnster, if you are in The Tone Zone, now is the time to measure some voltages. I hope that is not too subtle a hint.

[jerrydyer]

do rockets make a dissapatting noise when turned off .. thank you

[rawnster]

Rawnster, if you are in The Tone Zone, now is the time to measure some voltages. I hope that is not too subtle a hint.

Yes, I get the subtly of your hint. I'll get to it this evening.