Starting new 50-60 watt Rocket Reverb

[ronman]

Would transformer set from a fender blues deville work with this build?

[M Fowler]

I'm not sure what the specs are for those transformers, it looks the Hot Rod Deville set would work so is the blues Deville close?

[RJ Guitars]

Ultimately it always come to the question of what you want to accomplish. In building my original Rockster I wanted to try to retain a lot of the Trainwreck circuitry and performance of the Rocket amp while changing to an octal output section. Normster actually did this before I did using 6V6GT tubes and also adding reverb. Dr. Fowler has taken things to yet a higher plane by running up the watts a bit higher, building on a larger platform, and adding reverb. I enjoy watching the progression of amp designs and I think his amp took things in a good direction... albeit looking more Fenderish all the time. An octal Rocket shares a great coincidence of common parts and circuit design with the 59' Bassman so in many ways they are not that different to start with.

I would say the Deville trannies probably would work, but there are at least two possible differences in philosophy in how Trainwreck and Fender specified their transformers. IMHO - These will be key to determining if they work for you.

1) Secondary Voltage

All the trainwreck amps had B+ voltages below the standard that Fender typically used. This can be huge as far as amp tone and headroom goes. I couldn't find the primary voltages for the Blues Deville so it's possible they are similar to a trainwreck amp. I did see a note that indicated they were 40 watts output, that is pretty close to an octal Rocket. Don't see any show stopper here.

2) Output Transformer Size

Trainwreck is famous for using lots of mass and a conservative rating on their output iron. Fender on the other hand usually went a little on the lean side. In addition to the size, the design and materials are likely not the same either. Again I don't see any show stopper here but probably a big influence on the tone.

In the end I think they would work and probably work really well. I would guess that your amp might sound a lot like a Fender. If that is agreeable to you and especially if you already have the transformers I'd say do it. If you build it I would be very interested in the results... I have a Hot Rod Deville set of iron on the shelf .

Hope that is a useful perspective toward your questions.

rj

[ronman]

Here are the specs on the transformers.

Power transformer
450 vdc @ 270mA
6.3 vac 3.75 a
-72.2 vdc @1.5mA or -33.4vdc @59mA

Output Transformer
60 watt
4200ct

[RJ Guitars]

450VDC is definitely hotter than a Trainwreck. If I can crudely run the math backwards I'd say that is roughly a 320-0-320 power transformer, pretty standard stuff for Fender amps.

I think this will add headroom and take away some of the lower end and harmonics that a Typical Trainwreck Rocket gives you from the power tubes. It also has the preamp tubes running at a higher voltage than the typical Rocket and that will again change the sound of things. Should make a great amp but I expect you will have to work it pretty hard to get it to crunch. There are some tricks you can play to bring the B+ down if you want to have it more Wreckish.

The OPT I can't say anything more than I already have except it matches up pretty well to EL-34's, 6L6GC's, or KT-66's (my favorite).

I am an experimenter more than cloner so from my perspective you have enough variables to keep it interesting and worthwhile. If it sounds cool then you might start a trend. If nothing else you have everything there to turn it into a great surfer rock amp with the addition of reverb.

rj

[ronman]

Are there any great amps that I can build with these transformers?

[M Fowler]

I would build the Rocket with that tranny set should work perfect for an Octal version.

[Zippy]

I would build the Rocket with that tranny set should work perfect for an Octal version.

+1

Just pay attention to the dropping string to adjust your preamp voltages.

[RJ Guitars]

It's fun to guess what it might sound like but I would agree with Zippy and Mark Fowler, build the Rocket and give it a listen. If it's not "brown" enough you can always drop in a zener and lose a few volts if that matters.

Zippy might be on to something with his comment on the dropping string. Since so much of the amp behavior is determined by the preamp section you might help yourself by trying to match up the preamp voltages with the Rocket values.... tons of stuff you can do after the fact.

Also, if you can get one of the true engineers to comment (Cliff Schecht is quite good for example) they are very good at helping us understand how it all works together and maybe take a bunch of the guess work out of things in dialing in an amp to get what you want out of it.

rj

[Cliff Schecht]

My only thoughts are that I tend to get pretty anal about getting my voltages right, but for a reason. As others have stated, having a higher B+ than an amp calls for will dramatically affect the tonality and feel of the amp. I think 320-0-320 is way too high for a Rocket if you are going for that sound, but you can adjust the cathode bias resistor (increase it quite a bit) and add additional resistance the B+ dropping string to compensate for high voltages. In every Fender amp I've built I spend a lot of time tweaking the power stage so that my voltages are on par with the actual amp I'm trying to duplicate.

For high B+ you run into other problems though. The original Rocket and 59 Bassman circuits run the output tubes more like triodes than pentodes. When your B+ is too high, you end up dropping the B+ from the plate to screens quite a bit which already makes the output stage act like a pentode stage instead of a triode stage which dramatically affects the sound and feel (pentodes are brighter with less damping for a given bias condition). Methinks you'd be better off using that power transformer for a Fender/Marshall build or perhaps an Express.

[M Fowler]

Cliff essentially what I am building is a 5f6a Fender Bassman and actually in this build I wired the tone stack Marshall Plexi style so I actually should have posted it in the technical section because it no longer is a Rocket.

Mark

[Ian444]

Mark, it would also be close to a JTM45 then too? It's hard to know who copied who in the late 50's. Fender Super 5f4, Bassman 5f6, 5f6a, JTM45, Gibson GA-70, Vox top boost. Anyway it seems to be a nice sounding universal front-end for whatever power amp section one might choose to use. Well, that's the impression I'm getting. Sounds great with little 6P1P tubes making 10W also And the circuit is over 50 years old, amazing. KF must have liked it too or he wouldn't have done the Rocket. I wonder if the Rocket was in some way a tribute, or saying, "you guys got it right".

Cliff, what do you mean by "The original Rocket and 59 Bassman circuits run the output tubes more like triodes than pentodes."
I can only see pentode connection, the Bassman schem I have shows 430V on the 5881's?

[Normster]

Are there any great amps that I can build with these transformers?

3.75A filament current is cutting it too close for EL 34s. As long as you're OK with 6L6/5881 outputs, the power transformer will work.

As for great amps, maybe something along the lines of a Top Hat Ambassador. It's kind of a mix of Fender Twin preamp, Dumble tonestack, and Vox AC50 poweramp. Very versatile and tweakable.

A Rocket with 6L6/5881s would probably sound killer as well. Adjust the dropping string to match preamp voltages if you like, or just give it a shot and see if you like it. You can also play around with the PI cathode values. Maybe try 470R/10K, 820R/22K, 1k2/47k, etc. Different breakup characteristics for different values.

[Cliff Schecht]

Mark, it would also be close to a JTM45 then too? It's hard to know who copied who in the late 50's. Fender Super 5f4, Bassman 5f6, 5f6a, JTM45, Gibson GA-70, Vox top boost. Anyway it seems to be a nice sounding universal front-end for whatever power amp section one might choose to use. Well, that's the impression I'm getting. Sounds great with little 6P1P tubes making 10W also And the circuit is over 50 years old, amazing. KF must have liked it too or he wouldn't have done the Rocket. I wonder if the Rocket was in some way a tribute, or saying, "you guys got it right".

Cliff, what do you mean by "The original Rocket and 59 Bassman circuits run the output tubes more like triodes than pentodes."
I can only see pentode connection, the Bassman schem I have shows 430V on the 5881's?

This hit me only somewhat recently after playing around with biasing on my 59 Bassman build in conjunction with something that Andy posted. Yeah the plates are up at about 420-430V, but the screens are only a few volts below this. For the tube to act like a pentode you have to have a relatively large voltage difference between the plate and G2 (let's say 50-100V depending on the amp, maybe more for higher B+'s), otherwise the output stage "looks" like triode strapped pentodes and should be biased using the triode curves.

[ronman]

Does some one have a layout for a tophat.