This is a custom guitar amp I built inside a stripped 1950's Newcomb H-50 PA, using only excellent quality vintage components throughout: 1950's Sprague Bumble Bee / PIO caps, Ajax Blue Molded caps, Allen Bradley resistors, and 1940s/50s octal/loctal preamp tubes. The transformers are original.
I also loaded the amp with full set of vintage NOS/NIB tubes including 2 matching label Mullard GZ34s and a matched quad of late 50's Tung-Sol 5881/6L6GBs.
Summary description of the amp:
It's a modified Hi Power Tweed Twin using octal/loctal preamp tubes with a modified 6G15 outboard spring reverb built into the front end.
Detailed description:
The power supply is comprised of 2 GZ34 rectifiers for the HT supply and a 7Z4 loctal tube rectifier for the bias supply.
The power amp uses 4 6L6s, fixed bias, with a separate voltage divider PSU node feeding the screens grids (like the original Newcomb). Measured output before clipping: 56W.
The preamp supply is fed from a MOSFET voltage stabilizer to keep things mouse-quiet even with the fat bottle preamp tubes. The preamp tube filaments are also operating on quiet DC power.
The main preamp uses a 6C8G octal dual triode input stage and 2 7F7 loctal dual triode tubes in a traditional tweed twin/early Marshall type circuit, with an added resonance control to the negative feedback loop.
The reverb circuit is built into the front of the amp like an old Fender outboard unit, and it's basically the same circuit, but I used a 7N7 dual triode as the buffer stage / reverb input stage and a 7F7 as the 2nd verb / recovery stage.
When I got the amp, it still had one cool Altec line/mic transformer installed (octal base). So I used that transformer (driven by a parallel 7N7) as a reverb driver, using a high impedance 150ohm reverb tank.
The 3 reverb controls are mounted on a separate front panel which plugs into the back of the amp via an octal plug/socket. The VU meter is tapped off the speaker output, as is the XLR line out (600ohms). 4/8/16ohm selectable output.
13 tubes total! Will try to get a video clip posted soon.
