transformer for rocket

[pancho510]

I looking for to purchase 120v input and an output trans 8 ohms or multi tap
for a rocket build any recommendations.

[RJ Guitars]

I have been informed more than once that the Dynaco 470 is "the output transformer" for a Rocket. Some of the well informed guys around here will go a bit further to say look for one of the old ones with the cloth covered wire... you can still get them on EBAY.

The power transformer story is a bit harder to unfold... we've believed for a long time that a somewhat low B+ is key to the Rocket sound... the Heyboer Rocket PT was a 260-0-260 secondary. Lately some info has surfaced that might indicate that the Stancor 8356 was used on at least one of the early Rockets. This tranny has a 117v primary and a 270-0-270 secondary... this is getting pretty close to AC-30 voltages so an original AC-30 tranny might work as well. Currently JM uses the same Pacific PT in the Rocket as is used in the Liverpool - 250-0-250 secondary.

Be cautious about comparing all those secondary voltages though, some of them use a "loaded" voltage rating while others use an "unloaded"...

So take it all in and see which one you like... historically I think you'll find most of the really great Rocket clones were made with the lower voltage trannies... but there are some awesome sounding units starting to show up using a 270-0-270 tranny as well.

YMMV

rj

[Mark]

Perhaps a dedicated Rocket transformer is an idea.

It could have 270-0-270, 260-0-260, 250-0-250 voltages.

I find with a 260-0-260 secondary I have typically 306VDC and this has the valves running hot. I think the valves would have been "happier" with 290VDC?

The other option is a Zener diode and this is definitely worth a thought.

[RJ Guitars]

... The other option is a Zener diode and this is definitely worth a thought.

I like this idea. I have been thinking about using a Zener on a switch that will take the center tap straight to ground for full power or through the Zener for a voltage drop. It's a relatively low voltage across the Zener and would give you a quick voltage drop to help you hear the difference in real time.

[Clyde]

What value would you recommend RJ, and for what voltage drop? Thank-you.

[Drew.12345]

I scored a NOS 8356 several months ago on EBay.
Once I fired up my Rocket and started checking voltages I realized I was getting about 340v on the plates.
I actually tried a daisy chain of five 5w 10v Zeners in series to drop the B+ down to 290. Problem was that this got so hot (within minutes) the solder melted between diodes and wires started to become unsoldered.
I've since ordered a 50w Zener to drop the voltages down but had to up the bias resistor in the mean time to keep the tubes within spec.
The amp sounds great to me but still leaves me curious to compare with lower voltages.