Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Justa on December 30, 2010, 05:26:09 am

Title: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: Justa on December 30, 2010, 05:26:09 am

I rebuilt my 74 SFTR completely a couple of years ago to original SF specs.  It works and sounds great.  In reviewing the component differences from SF to BF there appears to be very little to change.  I mainly want to try it BF for a few months and see if I prefer it.

I can leave the master volume as is, or shunt it out of the circuit or........   Does anyone have any ideas on useful mods that can be done with the master volume slot in the chassis?

Thanks!!

Title: Re: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: LooseChange on December 30, 2010, 05:54:59 am

I would leave the Master in.  It has a purpose and IMO it does not interfere with the BF setup if it is not turned down.

Title: Re: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: Justa on December 30, 2010, 09:18:24 am

Thanks LooseChange,
That seemed to be the most logical choice as it only has a little wire length I was worried about but it really hasn't been a problem so far.  This would also leave the amp more stock.  I really like my SF but for the few part changes thought I would try the BF config for a few months and see what happens.

Title: Re: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: nateflanigan on January 02, 2011, 09:15:34 pm

FWIW I've never understood why most of the internet scorns the master volumes on sf fender's.  Especially on a twin, I think it would make it much more versatile.  You could always switch it out for a pull pot to make it bypassable. 

Title: Re: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: Justa on January 02, 2011, 09:56:02 pm

I'm going to leave the master.  I was just wondering about the wire length and noise.  Actually I really like the amp as SF but thought after 38 years I wanted to do the BF mods and see for myself.  Should be an easy matter to convert back if I don't care for it.  Doug's parts should be here soon.

Title: Re: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: topbrent on January 03, 2011, 02:35:30 pm

I keep a master volume on that amp, but I would change the silverface pre-PI master volume to a post-PI master volume.


Better in every way....(imho)

Title: Re: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: DummyLoad on January 03, 2011, 11:52:38 pm

PPIMV or switchable cross-line a la matchless.

Title: Re: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: Justa on January 13, 2011, 02:53:19 pm

Update:
I completed the SF to BF on my 72 TR exactly per AB763 except leaving bias level plus bias balance that I had already installed.  Set plate dissipation to 65%.  Truthfully I was not expecting much of a difference and maybe some disappointments in the lows.  It is difficult for me to describe the difference in tone but after several days of playing it with different guitars I am really diggin the difference in tonal dynamics in the amp.  To my ears it sounds like there is a little more harmonic distortion that is very pleasing.  The lows are still plenty tight and not muddy.  Wish I hadn't waited 38 years to try this.

topbrent:
What is to be gained by a post PI master?  Is it just better tonally when you turn the master down than the pre PI master?  Up till this point I almost never use the master volume.

ISOTone:
Could you briefly tell me what PPIMV or switchable cross-line a la matchless is all about?  I am clueless on this stuff.

Thanks guys! 

Title: Re: 74 Twin Reverb SF to BF, What to do with Master Volume?
Post by: DummyLoad on January 13, 2011, 05:45:11 pm

PPIMV

(http://cfs6.tistory.com/upload_control/download.blog?fhandle=YmxvZzE0MjMxOEBmczYudGlzdG9yeS5jb206L2F0dGFjaC8wLzA1MDAwMDAwMDAwMC5naWY%3D)

cross-line MV