GZ-34 and the Rocket

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Mark
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GZ-34 and the Rocket

Post by Mark »

I have from time to time ponder if the GZ-34 was actually needed in the Rocket at all and in particular the Mullard GZ-34.

I had my Rocket on the bench on the weekend. I put a 100mV 500hz signal into the amp, I had the CRO measuring the output and my multimeter measuring the B+ rail.

I was a little surprised the rail was so stable, normally I'd expect the rail to decrease as the amp started to clip. The rail didn't decrease as the amp clipped and it finally decreased when the volume control was set at 4 o"clock onwards.

I later remembered that Kevin O'Conner had said much the same in one of his books.

This makes me wonder if the Rocket wouldn't be better served with solidstate rectifiers and a power transformer with a (guess-timation here) 220-0-220vac secondary.

I'd like to hear from other Rocket builders on their observations.
Yours Sincerely

Mark Abbott
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Colossal
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Re: GZ-34 and the Rocket

Post by Colossal »

Mark,

Have you tried substituting diode rectification in the Rocket?

A couple of years back, I had a chassis that was set up as a Rocket, then it mutated into slight variants, then into a very high gain preamp. The filtering was 50uF across the board with a Mullard GZ34 powering it. In the high gain mode, the sound was magical with this power supply. Warm, but clear and articulate, with this wonderful depth that was truly three dimensional. At that time, the chassis had a TW style PT with 300-280–0-280-300 taps with 50R 25W on each secondary, going into the GZ34. It was of course no longer a rocket at that point, but I did put a pair of UF4007 diodes on a switch so I could switch between tube and SS rectifiers. In SS mode, the tone immediately changed. It became far too immediate and sounded fizzy, it just killed the whole amp. Switched back to that GZ34 and there was the magic. I never did really scope that amp as I ended up moving and I had to shelve things for a little while.

FWIW...
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geetarpicker
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Re: GZ-34 and the Rocket

Post by geetarpicker »

Ken himself (back in the day of course) told me he equipped all of his Rockets with Mullard GZ34s as they were the only tube in his opinion that could take the filtering load in that amp. That said, these days perhaps there are some current production rectifier tubes that are better than what was available then. I've had good luck with JJ GZ34s in my Fender blackface Deluxes, but I don't own a Rocket original or clone to comment.
matt h
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Re: GZ-34 and the Rocket

Post by matt h »

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Mark
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Re: GZ-34 and the Rocket

Post by Mark »

Hi Matt

I agree entirely, I calculate the difference in voltage is roughly fifty volts, this will cause the amp to be signicantly brighter. This would account for the fizziness or buzziness in a Rocket/AC-30 type amp.

The question still remains do we really need the GZ-34 in the Rocket.

Glen just out of curiosity what has lead you to think there are newer rectifier tubes which match the old Mullard? I don't doubt it is possible, but the current mantra is there is nothing like NOS. I'm not sure this generalisation applies to all tubes.
Yours Sincerely

Mark Abbott
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Re: GZ-34 and the Rocket

Post by matt h »

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KellyBass
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Re: GZ-34 and the Rocket

Post by KellyBass »

Would a copper cap be a quick way to test SS rectification...at least for "feel"?

One of these days, I'm going to take some crapped out tubes with metal bases, some UF's and zeners and build a few different ones for this purpose.
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Re: GZ-34 and the Rocket

Post by matt h »

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Mark
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Re: GZ-34 and the Rocket

Post by Mark »

I did think about using the Weber Copper Cap, but they don't get a lot of love for various reasons. It does seem like a good idea for the Rocket user, but in the long run, I'm inclined to think regular diodes and zener would be sufficient.

I've tried two GZ-34's one being a Mullard and the other being a Chinese Mullard copy and they both sounded the same to my ear.
Yours Sincerely

Mark Abbott
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Re: GZ-34 and the Rocket

Post by Jackie Treehorn »

There was a thread that resurfaced on TGP regarding the copper caps. Someone measured a GZ34 and observed that its internal resistance was not constant, but varied with the load. It dropped less voltage as the load increased.

So, it may well be contributing something extra special with its sag. I've had really bad luck with the current JJ. What I did in my ST70 was put a couple 11 amp IXYS hexfreds in series with a JJ. I'm curious if that removes the effect. It solves the reliability, though.
Mark
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Re: GZ-34 and the Rocket

Post by Mark »

Hi Jackie

I think the GZ-34 might get more mileage in an amp like a JTM-45 where there is more sag in the amp (if that occurs as I've never owned or worked on one).

The rail in the Rocket is very stable till the waveform is SIGNIFICANTLY squaring off. I'm using a Magnetic Components power transformer which is HUGE.

P.S. I"M USING CAPITALS AS I'M LARGELY BEING IGNORED TODAY. :wink: :lol: :oops:
Yours Sincerely

Mark Abbott
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Re: GZ-34 and the Rocket

Post by matt h »

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pdf64
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Re: GZ-34 and the Rocket

Post by pdf64 »

My WZ34 just contains 1N4007 rectifier diodes, a thermistor and 2 x 39 ohm resistors in series.
It doesn't seem to perform very closely to a GZ34, dropping rather more voltage under heavy load.

Ken indicates that the Ruby GZ34 is very close to the Mullard http://music-electronics-forum.com/t26515/#post229390
I'm using a Magnetic Components power transformer which is HUGE
Bear in mind that rectifier tubes have a requirement spec for a series resistance with their plate circuit. In 60s PT designs, this seems to have been generally provided by building resistance into the B+ winding.
I fear that transformer manufacturers may have forgotten about that, user preference perhaps being that PTs stay as cool as possible in operation, this requirement acting in opposition to adding resistance to a winding where that could be avoided.
If rectifier tubes then fail, it's because modern tubes are rubbish, right?
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