Planning my next build (simplified AC15ish)

[aon]

Hi,

I've started thinking of my next amp build... Attached is a schematic I've come up with.

The preamp is pretty much straight off the Trinity TC15 and the power amp is more or less a standard AC15. I attempted to put in a lar-mar style master volume too. Because of better availability I've been thinking of using a 5Y3 (probably JJ 5Y3S) as the rectifier. I also upped the filter caps to 22u / 10u because these are easier to get. Does this seem sensible? Also I'm not entirely sure if the 300V-0-300V PT is the best option, or should I go for a lower voltage?

[sluckey]

370DX or 270DX would be a better choice but your 372BX may be OK since you plan to use a 5Y3 (hopefully a NOS). If I had a 372BX on hand, I'd give it a try, but if I had to buy a PT I'd get the 370DX or 270DX.

I used a small 315-0-315 PT from a Hammond AO-39 amp to build your circuit and had a B+ of 325V.

BTW, you need to connect a .1µF cap between V2 pin 7 and ground. Or, you could add one more tube and have a more versatile amp...

     http://sluckeyamps.com/dual_lite/dual_lite.pdf

[aon]

370DX or 270DX would be a better choice but your 372BX may be OK since you plan to use a 5Y3 (hopefully a NOS). If I had a 372BX on hand, I'd give it a try, but if I had to buy a PT I'd get the 370DX or 270DX.

I used a small 315-0-315 PT from a Hammond AO-39 amp to build your circuit and had a B+ of 325V.

BTW, you need to connect a .1µF cap between V2 pin 7 and ground. Or, you could add one more tube and have a more versatile amp...

     http://sluckeyamps.com/dual_lite/dual_lite.pdf

I don't know about NOS but sources I kind of trust say that TAD 5Y3WGTB and JJ 5Y3S should have voltage drop that's close to NOS tubes.

Yeah I looked at various transformers and the 372BX seemed like the easiest one to get with the 370DX being a custom order everywhere I normally get stuff from. But, looking again, Digi-Key has plenty of the 370DX in stock and it's not even all that expensive so maybe I could use that instead. Could probably get pretty much everything from there in the same order...

Heh, indeed your dual lite is so close that I might borrow heavily from at least the layout ;)

I'm wondering about the tone control you have on the Marshall side. Does it add significant tone-shaping ability in addition to the post-PI tone cut?

Any particular reason you went for a shared screen resistor on the output tubes?

[sluckey]

I'm wondering about the tone control you have on the Marshall side. Does it add significant tone-shaping ability in addition to the post-PI tone cut?

The Marshall side sounds good but quite different from the Vox side. I mostly prefer the Vox side.

Any particular reason you went for a shared screen resistor on the output tubes?

Haha. That's a copy/paste from the Marshall 1974 18 watt schematic. Never thought about it until just now. If doing over I'd use two screen resistors but I suspect you would never know the difference based on amp sound/performance.

Here's what the amp looks like...

     http://sluckeyamps.com/dual_lite/dual_lite.htm

[aon]

Something weird going on, can't add attachments when posting (get a HTTP 500 error) and if I try to add an attachment to an already posted message, it disappears!

Anyway, I went down the 18-watter wormhole last night and I think that I like the idea of a "Superlite TMB" with cascaded 12AX7 gain stages as the second channel. Would post a schematic but can't, as every image hosting site appears to be blocked at work but not this forum

[aon]

Another try with the schematic attached... I think I'll keep the inputs as one separate jack for each and handle channel switching "outboard", that way I can run separate signal chains into each channel since that's something I've often thought would be nice to do. Probably I'll start putting together the design for the chassis and layout next.

[sluckey]

Nice drawing. RV1 will not work as drawn.

[aon]

Oops, thanks for catching that! I updated the drawing.

[burt_toast]

Your 2.2nf (.002uf) cap on your "cut" control seems small compared to Vox's .047uf - like it would only roll off super high frequencies. Maybe that's what you're after, I dunno. Maybe someone smarter could chime in - heh...

[sluckey]

AC-15 uses .005µF.

https://el34world.com/charts/Schematics/files/Vox/Vox_ac15.pdf

[burt_toast]

Ha! Okay then, back to lurking for me :)

[aon]

Ha! Okay then, back to lurking for me :)

Yeah, there are a few values that differ between various schematics and could be a point for experimentation. The cut capacitor is definitely one of them. I think .002u came off Trinity TC15 initially but good point, I probably should have .0047 at hand too.

Much appreciated that you guys actually look at the schematic and catch this stuff ;)

[aon]

I've been working on the layout for the last couple of days. It's attached along with an updated schematic.