so. I didn't want a 'meedly-meedly-meedly' noodler amp....

[chief mushroom cloud]

I was just going to build a small 2xEL84 version of an AC30....but....
The design considerations:
I'm not a multiplenotenoodler or a chinga linga strumalonga playabuncha samefuckinchordsastheotherguitarplayer kinda player....nor a SUNN((O)) guy with theheadofagoat on my guitar kinda guy either......
I play bits. I don't play ALLTHEFUCKINTIMEINASONG. Bits. Accents, small repeatable runs (as written), atmospheric vol swells, and I don't fucking jam or improvise.....that shit makes no musical sense to me. Bits.
I play a Strat w/ Kinmans and an Agile w/ TVJones (and a Shergold Masquerader as soon as I can get it refretted).
So I need an amp that works for song 'bits' So I started w/ an AC15.....and expanded from there. I have Merlin Blencowe's 2nd edition preamp book, and realized some useful things. And I like the TB circuit...but the Treble/Bass control leaves a little to be desired. Good EF86s are hard to come by, and eventually go microphonic.
So I grabbed a /13 ERT33 sch and used his 5879 preamp. I grabbed a Top Hat King Royale w/ Cheese sch and used his TMB circuit. I added a dash of Merlin, a dash of UL, a dash of AC15, and a dash of Southpark....and came up w/ this: (see attached).
It works well. No values were calculated...just tried values until it I liked it. It has usable tones all over the place at any volume. It does not have super gain. It has the 'right' amount of gain AND NO MUD. It can be dialed in to any holes available around the singer, keys, above the bass, and drums.

[LeftyStrat]

Interesting. Did you compare with and without UL connections? I've never tried UL. Some people seem to hate it, but the Dr. Z Route 66 uses it and sounds pretty good.

This is very similar to something I've been contemplating ever since I heard a Vox AC10 Twin.

[chief mushroom cloud]

I built an earlier version non-UL...and sold it (it had Heathkit OT, but I didn't use the UL taps). I built this using the UL taps on a whim...because frankly, I was curious. I like it a LOT better. Those Heathkit OTs are fantastic.

I also tried it w/ the OT CT pre choke...and it sounds very different and LOUDER (well, definitely more clean headroom). I also tried it w/ a 12BZ7 in PI....and it's very cool if I want to hammer the fuck out of the EL84s....but it wasn't what I was going after.

I have an AC30CC that was given to me, so I gutted it...I have an A470 OT I want to try in it w/ a much lower voltage PT (220-0-220 375mA)...but w/ stock Vox TB & 5879 preamp (as in this one).

I never really thought about UL all that much until I played thru a Marshall Major....and then I knew the next build I was going to try it.

[Masco]

Humm, looks interesting. That's a fairly large 220 Rk, is it loud enough?
I'd like to hear that one.

[chief mushroom cloud]

Humm, looks interesting. That's a fairly large 220 Rk, is it loud enough?
I'd like to hear that one.

There's a 1k 2W pot in parallel to bias it. I bias to 13W per '84...
I've dialed it up to 15W but anything over 13W...the tone gets ratty.

[dcribbs1412]

Thanks chief
Very cool ideas
I've got a 6.6K UL OT that I wanted to do something a little different with.
I may give this a shot ....maybe with some 6V6's
again thanks for sharing this.

Darin

[Masco]

Humm, looks interesting. That's a fairly large 220 Rk, is it loud enough?
I'd like to hear that one.

There's a 1k 2W pot in parallel to bias it. I bias to 13W per '84...
I've dialed it up to 15W but anything over 13W...the tone gets ratty.

Was that in your drawing before? I think I'm going nuts...

[chief mushroom cloud]

Humm, looks interesting. That's a fairly large 220 Rk, is it loud enough?
I'd like to hear that one.

There's a 1k 2W pot in parallel to bias it. I bias to 13W per '84...
I've dialed it up to 15W but anything over 13W...the tone gets ratty.

Was that in your drawing before? I think I'm going nuts...

yes...it's always been in there....works very well, too.

[Masco]

Wow, you must be sitting on top of a mountain of trophyfol Wimas.

[chief mushroom cloud]

Wow, you must be sitting on top of a mountain of trophyfol Wimas.

I had some left over from an AC30 build, but most of the caps are el cheapo polyester and some left over Ero caps....
I got lucky several years ago before everyone realized that eBay.de was a gold mine for Wimas at better than bargain prices.
From this experience...I'm convinced that the overall sound is largely the circuit topology, power supply voltages, OT, speaker cab design, and speaker choice. Everything else seems to have relatively insignificant impact (in the big picture).

[randalp3000]

I like the adjustable bias, does it work well?

[chief mushroom cloud]

I like the adjustable bias, does it work well?

Really well. I've put this in a few amps (10-15W cathode biased)...
The pot is a 1k linear 2W w/ nut collet....
I know some people say, "it's cathode biased...so it's self biasing..". Well, that's somewhat true up to a point. I tried RCAs, Phillips, and Soviets...and had to adjust it for each pair to get SAME plate dissipation. There was a 3W difference between the RCAs and Phillips.....
Sure...cathode biasing is self biasing...uh huh. Not with the NOS stuff that's out there now.