Imperial Stout - new build dummy check

[burt_toast]

Hey guys,


So, I've had this old Precision Electronics PA30 for ages--a 1960s PA head which originally had 3 6EU7s, 2 6L6s, and a 5U4. It's been different things over the years, and some of 'em not bad. In my own lockdown depression, I decided to rip it all out (leaving only trannies and octal sockets) and try more of a proper build. My last amp was an AO35 based on a Hoffman Stout and I love it, so starting there, this one's got 2 12AX7s, 2 EL34s (cathode biased), and an octal solid state rectifier hockey puck.


Instead of cascading the first stage, I kept it very Plexi, with a single pre-jumped input and dark/bright pots. LORDY! I LOVE this thing! I still have some hum I have to chopstick out of it, but easily the best sounding amp I've ever had (and I've had a lot!)! Sounds like old Angus Young with the PPIMV down, and Rush/Sabbath first albums when cranked - perfect!!!


My questions for you guys are:
Any glaring mistakes/issues on my schematic?


Original Precision Electronics schematic said 350vac on power tranny secondary (I think, can't find it now), and I'm guessing it's around 30 watts at 8ohm, but sounds quieter than that to me - like 15-20w. Small output tranny? I must admit, I haven't checked voltages yet--was too excited--not smart, I know..


Whatcha think?
thanks,
Scott


ps, mains tranny says 220v on schematic because it's baked into the jschem item--my first time with this program, too. love it!

[sluckey]

Input jack... 1M should connect between tip and sleeve and switch should connect to sleeve.

[jordan86]

Love the name! Make sure you put Russian tubes in it. 🍻

[tubenit]

Just a thought to consider...……………………

What about using a mosfet CF ?

With respect, Tubenit

Correction:  you  need a coupling cap between the treble pot and the LTPI.  Like your .02 or a .01

[burt_toast]

Input jack... 1M should connect between tip and sleeve and switch should connect to sleeve.

Oops, thx Sluckey - it is like that in the amp - drawn wrong.

[burt_toast]

Just a thought to consider...……………………

What about using a mosfet CF ?

With respect, Tubenit

Hmm, will investigate. Thx Tubenit

[tubenit]

I've used the mosfet CF in a few amps always with success and is currently in my HoSo56 "the minimalist".

I can NOT tell any difference in tone between a mosfet CF and a tube CF.

There's a good article on this here:  http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm

[burt_toast]

Schematic corrected, thx Sluckey.


My meter's at work, so can't check voltages now - will post 'em then. At that point I can also ask better questions about my power supply resistors - I don't know the theory/math behind this stuff, so I have to with my gut, and use proven ideas (as you can see). Been staring at amp schematics since Aspen Pittman's 1st edition paperback, but my real understanding still falls apart like the binding in that book!


Hey Tubenit, if I don't plan on using a tone stack, do I still really need a CF?

[tubenit]

Hey Tubenit, if I don't plan on using a tone stack, do I still really need a CF?

Your current schematic is fine as it is. 

The one I posted would add another gain stage prior to the LTPI.  It simply seemed to me to be a "better" use of the second triode of V1.  However, that is merely my own preference and not necessarily truly "better".   And would allow a little more of the Marshall-ish topology in the preamp. 

You could use one of the V1 triodes without a CF to add another gain stage similar to a Fender Blackface Deluxe non-reverb.
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_ab763_schem.pdf

With respect, Tubenit