7591 rocket, pure magic

[azatplayer]

Ive had this hankering for ages to do something ampeg, and using the old 7591's. Dunno why really, just had.
So i got some of the new EH 7591A's in to try. Ive been dickin with an old mule chassis that currently had a rocket, mostly layout in it. I converted the few odd bits back out to stock rockt.
Its using liverpool iron, 5K2 OT about 400V plates.
I made a bit of a muff out of my first attempt at fixed bias, had too much and got blocking. While trying to figure that out i made it cathode biased and had it working straight up.
Was very bright and very bassy, i mean bright! And too much dooffy bass.
Farted around with it for a bit, then reread my post and answers i put up on these tubes. Inparticular Martins comments on the blocking. I adjusted the bias resistors to get in range, and voila!
Goit 400V plate, around 32ma biased, and it sounds real good.
I was hoping to get an octal amp right around AC30 output, between 6V6's and 6L6's, i think ive done that. Perfect wattage for gigging clubs. Im have 2 masters in this mule, ppimv and KOC's PI grid replacement thingy, which i prefer, holds its brights better.
They drive real easy too so the EL84 based circuit suits the tubes. That translates to this really sweet ramping up to the highs, like digging in response kinda leaps off the string and rises for a split. really cool.
I think im gonna mess with a little higher gain, and see what they sound like pushed with a hotter preamp.
My Newport is a little too thuddy down low, my old Hamer special sounds perfect, those old dimarzios are lovin it!
Strat and tele very good, if anything a little brighter. Thats with pots all at noon, so pretty tweakable right off the bat.
What great tubes!

[lacrebob]

I've been mostly a lurker here and have just one build completed - a scratch build of a tweed princeton 5F2A circuit.

I'm currently planning a 2x7591 Rocket build. I have the transformers, tubes, and a finished 1x12 combo cabinet together with a pre-drilled chassis.

My power transformer is a stancor 310-0-310 (@117v) and I think I'm going to use a stancor 3801 as the output transformer.

Since I'm nearly a rookie, I'm a bit concerned about changing power tubes and modifying a circuit.

Did you use a 15H choke, same resistors and electrolytic capacitors in the power section as is shown in the Rocket AO EL84 schematic?

[azatplayer]

Hey Bob. I did use the hammond 15H choke, but mine is SS rectified and has only 50uf on the first stage, the rest of the caps and values are the same.
Its quite pretty. I did not like it cathode biased tho. Totally different tone to fixed. If you look at the gibson GA30rvt schematic, you get an idea on the bias circuit and voltages. Tho mine is a standard marshall circuit with lower value resistors.
These are great tubes man, good luck!

[azatplayer]

Spent the day tweaking this amp, tried a bunch of stuff, and settled on what im pretty happy with. Changed out the cathodes on the first and sec stages, 2K7/.68 first stage and 1k5/22uf sec stage, and put in KOC's bootstrapped master which works nicely in this circuit.
Gonna try some larger grid resistors tomorro, i see 10K used a lot with these tubes. They are super sensitive to attack and rise really fast. Its such a wonderful thing for styles like, say Greg V. Very dynamic valves.
I feel they run up just a little fast, so am hoping the grid stops slow them a tad.
I like these tubes so much i just ordered some more. Got a double deluxe build i did ages ago settin on the shelf. Interested to hear that with 4 of these bad boys. Tho will have to drop in another OT, thinking a 50 watt plexi will work.
So cool to find something nice off the beaten track a little.