Friday, October 28, 2011

Bassman RI Harp Amp Project - Update

Here is the latest on the Bassman RI project:

-From right to left the preamp tubes are RCA 12AY7, and two JAN Philips 5751.

-The power tubes are Tung Sol new production 6L6.

-The rectifier tube is a JAN GE 5R4 brown base.

Bruce Collins at Mission Amps installed adjustable bias pots, biasing the power tubes rather cold. He also repaired a faulty tube socket under one of the power tubes. Other than that the circuits remain stock.

The speakers are two Weber 10A125-O on top, an Eminence Lil' Buddy hemp cone speaker on the lower left, and one of the original alnico blue speakers on the lower right.

We tried many different combinations of tubes in all the sockets before arriving at this configuration, which sounded best. We both like a big fat organic tone, with a punchy low end and some sparkle without being edgy. I like a harp amp to sound wide.

This amp sounds good. In Bruce's shop I could get it to 5 on the volume before it started to ring, and the sound was big with a nice warm tone. It is not as naturally crunchy as my Chicago 32-20 amp but it has it's own set of virtues. That old Coke-bottle full-wave rectifier gives it a very cool sag, and the alnico Webers compress nicely as you put some pressure on the amp. It makes about 40 watts in this configuration and is quite loud. It weighs 62 pounds.

I plan to leave it like this for a while, and I'm looking forward to flogging it at a gig we are playing Saturday night Oct 29 for a Halloween Party at a country club. I promise... sound samples will be coming soon.


Joe's Blues Blog said...

I like those blue frame Eminence speakers in the reissues. I like the old ones better than the LTD reissues.

Big Ernie Fuller said...

I'm curious, did Bruce change any resister values or anything when you changed your pre-amp tubes, or did you just plug & play?