Rocket build

[camden_guitarist]

Hi there people,

I know, a lot of people have been asking around for half power Liverpools and Rockets and such. For my next project I'd like to build a small Rocket combo. The idea is to get either an old chassis or maybe a discarded SS amp and drill the holes myself.

My question is: what kind of transformers should I look for? 18W Marshall types or more likely Fender Deluxe ones?

Cheers,

Paul.

[M Fowler]

Just my two cents worth, I would get the marshall style combo chassis from turretboards.com and then grab their 18w heyboer marshall tranny set have a face plate made drill your holes and your set.

Mark

[hairyandy]

Hmmm. Well, as the Rocket is essentially an AC30 platform, I would think that you'd be best to go more in the way of something AC15-ish transformer-wise. The West Labs 15w set would probably be perfect, like in the Matchless Lightning. Also, check out the Brownnote Voxy Brown for something that could probably be turned into a more Rocket-like amp. I think the 18w Marshall is barking up the wrong tree---not really much in common there.

My $.02,

Andy

[Structo]

Voxy Brown

[M Fowler]

Also the Matchless Spitfire originally a 15w more commonly use the West Labs tranny set as you said.

However, Ken Watts has used the 18 watt heyboer tranny set and it works very well the design is in the circuit so it isn't going to be like a Marshall 18 just because you use the trannies?

I build this amp and it is a nice sounding amp.

Mark

[hairyandy]

However, Ken Watts has used the 18 watt heyboer tranny set and it works very well the design is in the circuit so it isn't going to be like a Marshall 18 just because you use the trannies?

I build this amp and it is a nice sounding amp.

Mark

I agree Mark. I was just thinking the West Labs set would be a little more "correct" in the Vox sense. I'm sure the 18-watt Heyboers sound fabulous!

Andy

[Travst]

Tom... I'm interested to know more about the amp in that layout.

[Bear]

I'm contemplating a 15w Rocket, too. What rectifier to use? GZ-34 seems maybe a bit overkill and NOS is expensive. I'm pretty sure I've seen vintage and recent Vox using EZ-81, along with all the 18w Marshalls and derivatives. Is it going to behave like the GZ-34, though?

Thing to watch on the West Labs and other Matchless-spec 15w transformers is that they use 4k impedance, same as for 30w, rather than 8k. You can do the mismatch (re-match?) on the secondary to correct, but if you don't, it might be hard on the output tubes. I'm just guessing that the lams are spec'ed more towards rock than chime (see discussion of lams and the A470 Dynaco iron), which might be better for a general-purpose amp. I'm still on the fence of which way is better for my purposes.

Bear

[collinsamps]

Having built more than a few vox'esque and Matchless platforms using Heyboer 18watt trannies I can tell you based on experience, that barring the slightly higher B+ (290-0-290) which is compensated for by changing the power stage cathode bias resistor value and a dropping resistor here and there for correct preamp voltages, the difference tonally in the 18watt OT and the vox ac-15 or matchless OT used in a Vox or matchless style circuit is negligible. I've started using it for all 15 - 20 watt builds on my Bristol and Hawk. as a result.

[M Fowler]

As you can see the circuit may seem the same as the matchless posted earlier at first glance but they are not and all use the 18 watt Heyboer tranny set. They make great amps.

Mark

[dartanion]

The Heyboer 18watt set should work well. Also, use an EZ81 as it is barely taxed with a pair of EL84s.

[Bear]

That is a cathodyne/concertina PI on the Voxy Brown, right? Anyone tried that design that can comment on the output drive?

(I'm thinking Rocket Lite: use the unused triode of V2 as a concertina PI, omit V3, use just a pair of EL-84's, and ditch the rectifier tube for diodes, which becomes a 'Pool supply. Four nonal tubes allows a compact build, and I'm not sure the loss of PI gain in a Rocket is going to be that critical. If it loses too much, I suppose the cathode bypass cap can be added on V1a.)

Bear

[Structo]

That is a cathodyne/concertina PI on the Voxy Brown, right? Anyone tried that design that can comment on the output drive?

(I'm thinking Rocket Lite: use the unused triode of V2 as a concertina PI, omit V3, use just a pair of EL-84's, and ditch the rectifier tube for diodes, which becomes a 'Pool supply. Four nonal tubes allows a compact build, and I'm not sure the loss of PI gain in a Rocket is going to be that critical. If it loses too much, I suppose the cathode bypass cap can be added on V1a.)

Bear

Looks like a long tailed pair to me.

[dartanion]

That is a cathodyne/concertina PI on the Voxy Brown, right? Anyone tried that design that can comment on the output drive?

(I'm thinking Rocket Lite: use the unused triode of V2 as a concertina PI, omit V3, use just a pair of EL-84's, and ditch the rectifier tube for diodes, which becomes a 'Pool supply. Four nonal tubes allows a compact build, and I'm not sure the loss of PI gain in a Rocket is going to be that critical. If it loses too much, I suppose the cathode bypass cap can be added on V1a.)

Bear

Looks like a long tailed pair to me.

LTP is correct. A concertina PI would change the tone quite a bit and how the preamp and power amp interact. An LTP contributes some gain whereas the concertina does not at all.

[Bear]

Dang, you're right. I have trouble working from layouts -- I don't "see the Matrix."

Other than less gain, what's the diff in tone?

Bear