Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: wittyjeff on August 04, 2020, 11:55:50 am

Title: Need advice on the Bias circuit of a Bassman
Post by: wittyjeff on August 04, 2020, 11:55:50 am
I'm planning to build a Bassman clone that's based mostly on the AA864 but will contain the various improvements and mods that have become popular over the decades.  The problem is that I'd like to use a power transformer that is not a specific Fender replacement.  All the parameters of the one I have are acceptable... except that it doesn't have the 54V secondary for the bias circuit.  Are there any work-arounds out there to get that bias circuit to function properly without that winding?  I've attached the schematic I've drawn up so far (feel free to point out any other mistakes you see on it).
Thanks in advance for your help.
Title: Re: Need advice on the Bias circuit of a Bassman
Post by: sluckey on August 04, 2020, 01:07:28 pm
Copy the bias circuit in this schematic. May need to slightly adjust the value of the BIAS RANGE resistor.

     http://sluckeyamps.com/phoenix/phoenix.pdf
Title: Re: Need advice on the Bias circuit of a Bassman
Post by: wittyjeff on August 04, 2020, 01:59:03 pm
Quote
Copy the bias circuit in this schematic.
sluckey: As always, an excellent idea and I will implement it.  That's exactly what I needed, thank you.
Just for intellectual curiosity, what are your thoughts on instead converting the AA864 Bassman to cathode bias following the Deluxe 5E3 circuit?
Title: Re: Need advice on the Bias circuit of a Bassman
Post by: sluckey on August 04, 2020, 02:13:04 pm
Not something I want to do.
Title: Re: Need advice on the Bias circuit of a Bassman
Post by: vampwizzard on August 04, 2020, 02:32:50 pm
Quote from: sluckey on August 04, 2020, 01:07:28 pm
Copy the bias circuit in this schematic. May need to slightly adjust the value of the BIAS RANGE resistor.

     http://sluckeyamps.com/phoenix/phoenix.pdf

+1 for this. Did it on a hammond to bassman conversion. Worked perfectly.