Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: vicentebd on July 19, 2015, 08:42:04 pm

Title: AB763 Deluxe_Reverb OD
Post by: vicentebd on July 19, 2015, 08:42:04 pm

I'm planning use ,the normal AB763 channel, for a OD channel.
 Like the schematic below.
there is some advice for this mod :think1:
take the od idea from "Bassman & Dumblish OD & reverb"
Tubenite post... very useful

(http://s7.postimg.org/yxsy64w5z/AB763_Deluxe_Reverb_OD_rev2_mv.jpg) (http://postimg.org/image/yxsy64w5z/)

Title: Re: AB763 Deluxe_Reverb OD
Post by: DummyLoad on July 20, 2015, 12:56:43 am

V2b feeds relay with DC which very likely is more than small signal relay is rated for. however, of most concern is that when relay contacts 1&2 are closed, the same DC hits the grid of V1A then V1A will cease to exist. V1b does not have a complete circuit: cathode is not grounded, so at least you won't hear the pop when V1A goes into it's death throws... R1 (68K) is moot.


add a coupling cap at TP16, V1B we presume is a grounded cathode amp, needs a bias resistor to ground or a (-) supply.


--pete 

Title: Re: AB763 Deluxe_Reverb OD
Post by: tubenit on July 20, 2015, 05:51:36 am

Change the 22uf cathode caps to 4.7uf or 5uf ................. the 22uf will be VERY muddy sounding.

with respect, Tubenit

Title: Re: AB763 Deluxe_Reverb OD
Post by: vicentebd on July 20, 2015, 06:20:15 am

   DummyLoad  tubenit Thanks for the advice -"....V1b does not have   ...4.7uf or 5uf..."
I Will buy the parts and build, so soon I will give a feedback

Best regards vicente

Title: Re: AB763 Deluxe_Reverb OD
Post by: sluckey on July 20, 2015, 08:16:04 am

Quote

"....V1b does not have   ...4.7uf or 5uf..."

That's because it shares C11/R24 with V2B. V1 pin 8 connects to V2 pin 8 but is not shown on your schematic. Probably be a good idea to separate the shared cathodes with this mod. Use two 1500Ω rather than one shared 820Ω.

You can avoid the dc issues if you insert the OD circuit on the right side of C12 rather than the left side.

Title: Re: AB763 Deluxe_Reverb OD
Post by: vicentebd on July 20, 2015, 04:44:13 pm

Update I added  cap  4.7uf , ground v1B pin 8 and Master volume.
I Will use 33k resistor on stop grid I think will prevent rádio interference
About MV another idea?
(http://s7.postimg.org/yxsy64w5z/AB763_Deluxe_Reverb_OD_rev2_mv.jpg) (http://postimg.org/image/yxsy64w5z/)
got some parts today so hapy enthusiastic
(http://s3.postimg.org/83wya65lr/IMG_1034.jpg) (http://postimg.org/image/83wya65lr/)