Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: MikePR on September 03, 2015, 08:08:11 am

Title: Can i use these parts on a Hoffman AB763 Single Channel?
Post by: MikePR on September 03, 2015, 08:08:11 am

Have these parts that I want to see if It would be safe to use on a Hoffman AB763 Single Channel. Also if somebody has the Hoffman Lite version with reverb schematic laying around and can post it here I will appreciate it. I do not use vibrato but reverb.

Hoffman Specs                         My part Specs

PT - 354 vdc                               PT - 450 vdc       
       250 ma                                      270 ma
       6.3v/4a                                      6.3v/ 3.75a

OT - 50 watts                              OT - 50/60 watts
       4.0k ohm                                     4.2k ohm

CHOKE - 90ma                           CHOKE - 50ma
               4 Hy                                          4 Hy

REVERB                                    REVERB
DRIVER - 3.5W                          DRIVER - 3.5W
              14.5K OHM                                25K OHM

Title: Re: Can i use these parts on a Hoffman AB763 Single Channel?
Post by: sluckey on September 03, 2015, 08:32:15 am

That PT and OT should make a fine 6L6 AB763 such as Super Reverb. I'd want a bigger choke and a proper RT.

Doug has a single channel schematic. It also has bias vary tremolo but it's very easy to drop that off the schematic. Here's my schematic that does not have trem. It's for a 6V6 but only a couple parts need to change for a Super Reverb.

     http://home.comcast.net/~seluckey/amps/tdr/tdr.pdf (http://home.comcast.net/~seluckey/amps/tdr/tdr.pdf)

Title: Re: Can i use these parts on a Hoffman AB763 Single Channel?
Post by: 2deaf on September 03, 2015, 11:06:50 am

A 22921 reverb transformer has a primary impedance of 14.5K?  Wow, no wonder they strapped two 12AT7 stages to drive it.  For decades I thought the primary was 25K.

Title: Re: Can i use these parts on a Hoffman AB763 Single Channel?
Post by: MikePR on September 03, 2015, 11:16:55 am

Thx for the schematic. Which parts would you'll change to make it 6L6? Can you take the Master out and replace with Mid control? Also my Transformer only has 2 red wires with no ground wire, i was thinking going instead of the tube rectifier with ss. Here is something i've been working for a while now.