Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jrusto on April 17, 2024, 10:17:03 am

Title: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: Jrusto on April 17, 2024, 10:17:03 am

I have taken a PRRI gutted it and built the Hoffman PR.  Killer cleans but it doesn’t break up until after 7 on the dial.  I used an Allen TO20 output transformer to clean up the flubbiness rather than the stock PRRI OT.  I was used to getting a hint of break up at 4 on the dial without deafening the neighborhood.  I only use this amp at home so I don’t really need loud. 

I have compared the original PR schematic to the Hoffman and have found that the Hoffman has a grid stopper and a grid resistor that the original schematic does not show.  If I remove those, will I get closer to the breakup characteristics of my original PRRI or Original PR. 

With the Allen OT and bias set to 23, I am getting a little over 20 watts dissipation.  Pretty loud. I would like to get back down to closer to the 12 to 15 watts.  I know, not much difference but still a goal. 

Any thoughts?

Title: Re: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: sluckey on April 17, 2024, 10:49:53 am

Put the stock PRRI OT in the amp. Any joy? The resistors that Hoffman added should not be a factor.

Title: Re: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: Jrusto on April 17, 2024, 11:07:05 am

Thanks Sluckey.  I had already gone through my stuff to find it.  While I am in there, I am going to add a Raw control and slow the tremlo down.

Thanks again

Title: Re: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: shooter on April 17, 2024, 11:07:40 am

Quote

Killer cleans but

since it's a home amp where "time" isn't critical, throw all your pedals in front, tweak as needed, no soldering required.

Title: Re: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: Bieworm on April 21, 2024, 01:53:08 am

Did you use the same speaker?

Title: Re: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: ac427v on April 21, 2024, 06:46:19 pm

What would happen if OP biased it cold? ie 50%?

Title: Re: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: Jrusto on April 24, 2024, 08:31:06 am

Quote from: shooter on April 17, 2024, 11:07:40 am

Quote

Killer cleans but

since it's a home amp where "time" isn't critical, throw all your pedals in front, tweak as needed, no soldering required.

I have a few pedals but i want the amp on the edge at a lower volume.  The most I want to carry is a boost and maybe one more dist/overdrive.  Right now I am useing an Analog Man King of Tone Clone which sounds great but I am hearing pedal sounds where I want to hear amp breakup.

Title: Re: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: Jrusto on April 24, 2024, 08:32:11 am

Quote from: Bieworm on April 21, 2024, 01:53:08 am

Did you use the same speaker?

Yes using the same Weber 10F10T 25W light dope.

Title: Re: Super clean and loud Hoffman Princeton Build. Too clean?
Post by: Jrusto on April 24, 2024, 08:41:50 am

Quote from: ac427v on April 21, 2024, 06:46:19 pm

What would happen if OP biased it cold? ie 50%?

I have it biased at 23mA
Bias Probe   Plate Voltage   Plate Dissapation
23.0                  422                  9.7
23.0                  427                  9.8

6v6 Max plate disapation is 12Watts so I am running at 81%.  I could definetly lower it some and I will try and see what happens.  I believe Sluckey was on the right track with the output transformer up grade I did.

Going to change Allen TO20 back to the stock Fender OT when I get back off of vacation.