rjguitar Rocket build

[Mark]

I wonder why KF used these type of polypropylene caps instead of the more commonly available 715's?

The other question is polyester caps come in the same package as these caps how did "we" work out they are polypropylene and not polyester?

[sepulchre]

Some 715P & 716P, particularly the higher voltage ones, are series wound so the outer foil cannot be connected to the lowest impedance. That may have something to do with it, I don't know.

[Jackie Treehorn]

I think the 716P didn't come on the market until 1989 or so, and the 715 has copper clad steel leads.

Good question about the Panasonic caps. I've got some that I bought at a surplus store thinking they were the polypropylene, but after a bit of research, turns out they were polyester.

The k40y's are very nice, too.

[njwrecks]

very nice work mate!! thanks for sharing..

[RJ Guitars]

Mark - hope you don'y mind a Hi-jack or maybe recycle of this thread... I came across some interesting AC-30 info that I thought would be of interest to the Wreck-Rocket crowd but not really anything that seemed worthy of a new thread.

http://www.petecornish.co.uk/queen.html

It is interesting to hear what he did to the Brian May amps in helping them to run cooler and make them more stable. Some of these ideas bring those AC-30's closer to a Rocket configuration just by getting rid of a lot of unused circuitry... but does Brian May use the Top Boost or the normal channel?

I was also somewhat pleased to see that he did away with the GZ34 rectifiers and went with solid state. The GZ34 is a very cool tube that gets us near SS performance... is it that it's just hard to let go of the glow for posterity's sake or do they really have magic in them?

[Colossal]

Hi RJ,

According to Greg Fryer who builds Brian's amps, he is just using one gain stage, no tone stack, and straight into the PI. The absence of the tone stack gives a good boost in gain. The front end is still hit with a treble booster.

As for the GZ34 vs. SS, I had a 4xEL84 test bed operating at AC30ish voltages into a 4k3 OT with a GZ34. It had a Trainwreckish power supply (the 1k resistor between the plates and screens). The tone was huge, beautifully full and clear, and 3D. Switching over to diodes just absolutely killed all of it. Distortion went from smooth and complex to buzzy and harsh. Sounded like a Crate or something. Completely flattened it out.

[RJ Guitars]

Hummm... that circuit kinda sounds like a Songwriter, which I have been tweaking my own here lately. It has minimal signal loss because of it's very unique set of tone controls and surprising amounts of gain considering the minimal tube compliment. The big surprise for this particular unit was the unexpected flavor... better than decent sound.

I am still trying to gather intel on the GZ34 thing... Ken Fischer stuck with it on the Rocket as did Dr. Z in his Z-Wreck. Do you think the tube behavior can be coaxed out of the SS rectifier with some circuit wizardry or are those $80 rectifiers really magic?

Thanks Colossal for the info.... it's always nice to get your input on these tweaking and technology questions.

[Colossal]

Hummm... that circuit kinda sounds like a Songwriter, which I have been tweaking my own here lately. It has minimal signal loss because of it's very unique set of tone controls and surprising amounts of gain considering the minimal tube compliment. The big surprise for this particular unit was the unexpected flavor... better than decent sound.

I am still trying to gather intel on the GZ34 thing... Ken Fischer stuck with it on the Rocket as did Dr. Z in his Z-Wreck. Do you think the tube behavior can be coaxed out of the SS rectifier with some circuit wizardry or are those $80 rectifiers really magic?

Thanks Colossal for the info.... it's always nice to get your input on these tweaking and technology questions.

RJ,

That test bed power amp, at the time and for the conditions I was referring to above, was mated to a very high gain preamp. That amp was nothing short of magical (if I do say myself). I definitely attribute the feel, sound, and response to the rectifier tube. There was a depth and 3D reverb quality to it. The distortion was very smooth but shimmering. Excellent definition and separation. I did use a Mullard GZ34, but I was also able to get the same sound out of a Sovtek GZ34 (which is what Dr. Z tubes his amps with). Whether emulating the dynamic response with resistors in series with diodes would produce the same results, I didn't test. Switching over to SS diodes, all the magic evaporated. It was way too fast. I have come to really dislike amps that are too immediate and the note just wants to come on fast but die right after. I like an amp to respond to my left hand, like an extension of my fingers. If it's a fight, then the amp isn't for me.

[RJ Guitars]

...I have come to really dislike amps that are too immediate and the note just wants to come on fast but die right after. I like an amp to respond to my left hand, like an extension of my fingers. If it's a fight, then the amp isn't for me.

Tell me - is this what is referred to as or related to the "Slew Rate" performance of a tube?

I can recall discussions with those close to KF and it was reported that one of his favorite things about the EL-84 was it's fast slew rate... wondering how that all fits together with what you've observed?

[Aurora]

Somehow those two arguments seems to contradict each other, - or.....
If the GZ34 has some sort of slow turn-on, that would be ruling the respons, even if the EL84 is fast enough. Still, - the onset of a tone will have a response time or rise time of several milliseconds...... ??

Have any of you experimented with different SS diodes? There are soft recovery, schottky - etc.etc ? Response time will also be dependant on size of filter caps in combination with series R of any chokes, or plain resistors in capacitor banks....

[RJ Guitars]

Somehow those two arguments seems to contradict each other, - or.....
If the GZ34 has some sort of slow turn-on, that would be ruling the respons, even if the EL84 is fast enough. Still, - the onset of a tone will have a response time or rise time of several milliseconds...... ??

Have any of you experimented with different SS diodes? There are soft recovery, schottky - etc.etc ? Response time will also be dependant on size of filter caps in combination with series R of any chokes, or plain resistors in capacitor banks....

Certainly the two observed behaviors and the associated descriptions seem contradictory, but I'm not savvy enough to be sure if we are comparing apples to apples...

It would be quite interesting to know if any of those other types of diodes or combinations of parts could accomplish the GZ-34ish behavior... I don't expect we are the first to ask this question - is anybody aware of other diodes/component options beyond the typical 1N4007 diode array -- with the hope of finding something similar to a tube GZ-34 behavior?

[Aurora]

While just idling around last night, I did some googling. What I found was a fairly credible report of a guy really doing some serious measurement, in trying to replace a GZ34 with Mr.Mr's Coppers SS replacements. While the resistor/choke sag is farily easy to figure out and replicate, what he found was that the GZ34s internal resistance actually decreased with increasing current draw. If the old GZ's really are tone gold in this context, that behaviour is rather more tricky emulate. I don't have enough experience with guitars to say what this will do to the response of the amplifier.

[Colossal]

While just idling around last night, I did some googling. What I found was a fairly credible report of a guy really doing some serious measurement, in trying to replace a GZ34 with Mr.Mr's Coppers SS replacements. While the resistor/choke sag is farily easy to figure out and replicate, what he found was that the GZ34s internal resistance actually decreased with increasing current draw. If the old GZ's really are tone gold in this context, that behaviour is rather more tricky emulate. I don't have enough experience with guitars to say what this will do to the response of the amplifier.

I've found that a lot of people naysay tube rectifiers as being one more point of failure and that their behavior can be simply simulated with a series resistance which matches the internal resistance of the tube rectifier. But, as noted above, their response is non-linear, so the matter isn't quite so simple.

Of interest is a statement by Allan Holdsworth (one of my absolute favorite artists) who said at a clinic "Many guys get hung up on tube amps versus solid state. To me, the most important tube in the amp is the rectifier".