Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Lizard King on November 03, 2011, 07:01:32 am

Title: Picked up '65 Bassman BF, naturally I can't leave it alone - suggestions???
Post by: Lizard King on November 03, 2011, 07:01:32 am

The tube sticker says AA165 but it's really an AB165.  I found an article that talks about creating an AA864/AB165 hybrid so that's what I'll probably do - remove a couple caps and turn the hum control into a true bias adjust and get rid of the funky feedback circuit.

Anyway, while I'm in there does it make any sense to upgrade the caps on the circuit board?  I haven't opened the can yet to see if the filter caps need replacing.  The caps look OK on the board but as long as I have the iron heated up I might as well replace them if recommended.....or do you let sleeping dogs lie in this case?

Thanks all....love this forum (and store).

PS.
I was also thinking of adding a 100 Ohm wire wound resister to the power supply to imitate tube sag....

PPS.
That half used 7025 is gnawing at me......

Title: Re: Picked up '65 Bassman BF, naturally I can't leave it alone - suggestions???
Post by: bigsbybender on November 03, 2011, 08:47:23 pm

Really just changing the bias circuit and removing those 220k resistors from the plates make all of the difference in this amp.  I suggest playing it a bit with those mods before doing anything else.

Just that and the volume on like 7......sounds great!

Title: Re: Picked up '65 Bassman BF, naturally I can't leave it alone - suggestions???
Post by: SoundmasterG on November 04, 2011, 05:39:05 am

That AA864/AB865 mod does sound good. I built it into my own amp with some large OT's and it is a really good sound. I never finished the amp though and got sidetracked, but I do like that mod. I would leave all the signal caps intact and just replace the electrolytics if they look moderately old.

Greg

Title: Re: Picked up '65 Bassman BF, naturally I can't leave it alone - suggestions???
Post by: Lizard King on November 04, 2011, 05:55:02 am

Thanks both.....I'll probably take the minimalist approach.  I don't want to do anything that can't be undone in case I decide to sell it down the road....

Funny story.  Someone had added a grounded plug.  But instead of taking it all the way back to the amp and grounding the green wire, they just spliced it into the existing wire a few inches out from the amp.  The round wire was cut off.  Hard to believe someone would be that naive (read stupid) about electricity.

Title: Re: Picked up '65 Bassman BF, naturally I can't leave it alone - suggestions???
Post by: tubeswell on November 04, 2011, 05:43:49 pm

Quote from: Lizard King on November 04, 2011, 05:55:02 am

Someone had added a grounded plug.  But instead of taking it all the way back to the amp and grounding the green wire, they just spliced it into the existing wire a few inches out from the amp.  The round wire was cut off.  Hard to believe someone would be that naive (read stupid) about electricity.

And downright lazy