New Trainwreck Inspired 2 channel amp

[Fischerman]

I put a fuse holder in series with the OT center tap...IIRC I'm using a 500mA fuse. I wasn't sure if a 250mA would be big enough.

[UR12]

Very cool!

I would consider current limiting the variable power supply or, at minimum, include HT fuse. A shorted power tube will blow the mosfet in about 1 second.

Thanks Paul! I'll probably just fuse it. I did some calculations on KOC's current limiter and he has it set to about 1.8 amps before it kicks in. I have a 1 ohm resistor on my board that I use to take current measurments. (thought about maybe a front panel meter showing total current draw) I had thought about removing it and replacing it with a fuse but it would probably be better to move it to a fuse holder on the back of the amp so it is easily accessable in the event it needed changed. It's funny that when the mosfet blows it usually shorts Drain to Source and basically (after replacing the shorted tube)and fuse(s) the amp would still operate you just wouldn't have any variable b+. I have also included seperate cathode resistors and bypass caps for each pair of tubes so you could run this thing with two tubes pulled if you had to. Thanks man, I appreciate the input. It's hard to remember everything on a prototype.

I'll try and get the schematic on this thing posted this evening. I got the NFB hooked up last night that I had forgot to run and redid the footswitch wiring on the jack last night. Tonight I am planning on working on getting some of the relay popping tamed down a little and I will be building a cab for the amp this weekend

[paulruby]

By the way, I've been wanting to do a two channel amp in a combo for a while now. This might just be what I build. Just finished a liverpool chassis and love the sound. Have built Rockets and love the clean tone. This is a great idea... What I will likely do:

Shared input gain stage for both channels. They're the same... The rest of each channel will be separate.

Relay switching at the end of the channels to feed the power stage. Will likely use the liverpool power stage with NFB and presence. Are you disabling NFB for the rocket channel? (Sorry if I missed the answer to this above.)

Will make a relay-switched half power to enable a foot-switch boost. I've found half power to be nearly perfect for lead boost, which lends perfectly to a 4xEL84 amp.

I will likely not use power scaling and just use MV on the end of each channel and a global post-pi MV. Need more thought for this perhaps. Might use an airbrake.

[Richie]

Are you disabling NFB for the rocket channel?

Yep he is useing it in the switching.. Liverpool has the presence control,and Rocket has the cut control..when the channels are switched..these also switch. As to keep them as close as possible to being along the lines of the channel your using.
I'm building a 4x 6v6 amp in this same amp..so we can compare them.
It will have a few changes compared to Dana's amp. But Most will be the same.

[UR12]

The other problem you're going to run into is that since the liverpool has the extra gain stage and the Rocket has the CF the two channels end up out of phase. If you leave the NFB hooked up while in rocket mode the NFB will end up being in phase with that channel which would cause problems when you switch from one to the other. I am disconnecting the NFB, connectiong in the Hi cut and grounding the tail of the PI in rocket mode. This is reversed for Liverpool mode.

[Rick]

Beautiful work and implementation. Nice chassis too! hehe, I wonder where you got those....?

Rick

[UR12]

Hey Rick

Yea nice chassis for sure! It worked out great. Richie will be using the other for another one of these with 4 6V6s so we're putting them to good use. You might be getting orders for a few more if you want the work

[Rick]

Sure thing Dana, just let me know.
Rick

[Fischerman]

It is a nice looking chassis.

Dana/Rick - how is the chassis 'supposed' to be mounted in the cab? I don't see any of those carriage nuts (or whatever they're called).

What other chassis can/do you build Rick? Do you make an ODS chassis?

[UR12]

It is a nice looking chassis.

Dana/Rick - how is the chassis 'supposed' to be mounted in the cab? I don't see any of those carriage nuts (or whatever they're called).

What other chassis can/do you build Rick? Do you make an ODS chassis?

I will be punching the holes for the capture nuts, I just haven't done them yet. I wanted to see where the relay power supply board was going to end up before I punched the holes. I have the wood, tolex and new router bit to make the cabs this weekend. I am making changes to the schematic by adding Paul Ruby's suggestion for current limiting on the voltage regulator and will get the changes made and schematic posted as soon as I can. Schematic and a few pics have been sent to Bnwitt to do the layout also.

[UR12]

Here is a pic of the new cab for the amp.

[Beerman]

Oh Dana. That's a lovely bit of work..... next time I hear a drummer joke in the rehearsal room I'll be keeping my mouth shut, or perhaps holding you up as a contrary (albeit rare) example.

[gearhead]

Dana,

Check your PM.

[skyboltone]

Here is a pic of the new cab for the amp.

Is the front two piece, or did you cut a slot for the tolex/grill cloth juncture?

[UR12]

Here is a pic of the new cab for the amp.

Is the front two piece, or did you cut a slot for the tolex/grill cloth juncture?

2 piece, just like a Marshall 18watt, 2 x 12 combo cab is done. Richie came up with the idea to put the Blues Breaker grill cloth on the amp and I thought it just looked too cool with the white cab and black trim. He is doing a 4x6v6 version of the amp. Kind of a Express/Rocket amp with the same front /back panels and cab. Now that I finished the first one I get to build one more.