Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bullkelp on October 04, 2024, 11:14:04 pm

Title: ab165 Bassman - whats the story with this layout?
Post by: bullkelp on October 04, 2024, 11:14:04 pm

Hi all

Im hoping to build a replica of this bassman clone. I was told its an ab165, but upon inspection its a little different. I cant find a kit that it resembles either. For what its worth it seems to use a mojo tone transformer which has a higher VAC than the fender schematic calls for and also appears to be cathode biased.

The other thing that is obvious is it only has three pre-amp tubes....

I realllllly like how it sounds and it works perfectly for the surf band I play in but the owner isnt wanting to sell. So im in the process of drawing out the layout and trying to build a clone of this clone!

Any thoughts about how this amp substnatially differs from a true ab165? How is there one less preamp tube? PT VAC difference likely to effect the sound (this is 710 VAC where as the fender code I think is 660 VAC both 250ma).

Also why would one go for cathode bias in such a build?

Ill try and post some pictures of the internals:

(https://imgur.com/XjsdF8B.jpg)

(https://imgur.com/3Otj5d7.jpg)

(https://imgur.com/T9YegJJ.jpg)

(https://imgur.com/UtJRhfa.jpg)

Title: Re: ab165 Bassman - whats the story with this layout?
Post by: bullkelp on October 05, 2024, 12:46:10 pm

Right
After a bit more reading Im assuming that the v2 that would usally cary the third gain stage for the bass channel has been removed?

Title: Re: ab165 Bassman - whats the story with this layout?
Post by: tubeswell on October 05, 2024, 04:53:52 pm

Maybe a 6G6b sans one preamp toob?. Can we expect a schematic? (Sorry - layout drawing is hurting my eyes)

Title: Re: ab165 Bassman - whats the story with this layout?
Post by: mresistor on October 06, 2024, 10:15:00 am

Why cathode bias?  The owner/player probably wanted more compression and sustain with an amp more easily overdriven. Maybe also wanted to not be bothered with having to check and adjust bias for every tube change or replacement.

Title: Re: ab165 Bassman - whats the story with this layout?
Post by: bullkelp on October 06, 2024, 12:38:36 pm

I think your right.
I used it for a recording not long ago and a couple live shows and it really does compress very nicely. One of the reasons id like to build one for myself :)

Title: Re: ab165 Bassman - whats the story with this layout?
Post by: bullkelp on October 06, 2024, 12:39:36 pm

Quote from: tubeswell on October 05, 2024, 04:53:52 pm

Maybe a 6G6b sans one preamp toob?. Can we expect a schematic? (Sorry - layout drawing is hurting my eyes)

Heya Tubeswell :)
Still finding my feet with drawing schematics....
Why do you say 6g6b rather than ab165?

Title: Re: ab165 Bassman - whats the story with this layout?
Post by: mresistor on October 06, 2024, 12:51:03 pm

Looks like the owner got the chassis from this vendor. http://www.solandfa.com/products-Bassman-Chassis-Kit.asp (http://www.solandfa.com/products-Bassman-Chassis-Kit.asp)


I'd say carry on and just copy the layout as your doing,  take lots of photos that you can refer back to.

Title: Re: ab165 Bassman - whats the story with this layout?
Post by: bullkelp on October 06, 2024, 06:03:26 pm

Good advice re: photos

Title: Re: ab165 Bassman - whats the story with this layout?
Post by: tubeswell on October 06, 2024, 06:23:21 pm

Quote from: bullkelp on October 06, 2024, 12:39:36 pm

Quote from: tubeswell on October 05, 2024, 04:53:52 pm

Maybe a 6G6b sans one preamp toob?. Can we expect a schematic? (Sorry - layout drawing is hurting my eyes)

Heya Tubeswell :)
Still finding my feet with drawing schematics....
Why do you say 6g6b rather than ab165?

Each channel with TB tone controls and a presence control. 4 preamp tubes. Looks like maybe blonde Bassman - Just a guess.