Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on January 09, 2012, 07:31:58 pm

Title: Master Volume On 100 Watt SF Twin
Post by: plexi50 on January 09, 2012, 07:31:58 pm

Is there a better way to wire the master volume pot on a 1977 SF Twin Reverb?

Title: Re: Master Volume On 100 Watt SF Twin
Post by: stratele52 on January 10, 2012, 04:03:43 am

A new double pot after the phase inverter tube V6A, 12AT7 is most of the time the best master volume.
But can you fit a double pot in the front of your amp, in place of the master volume pot ? I don't remember if is enough room.

Title: Re: Master Volume On 100 Watt SF Twin
Post by: stratele52 on January 10, 2012, 04:13:23 am

http://metroamp.com/store/index.php?main_page=product_info&products_id=498 (http://metroamp.com/store/index.php?main_page=product_info&products_id=498)

This how it look for parts, Probably it work fine on your amp , not sure. I have to do some more research.

Title: Re: Master Volume On 100 Watt SF Twin
Post by: LooseChange on January 10, 2012, 05:17:30 am

Never took a close look at that circuit.
I think the Master on the SF is a bootstrapped circuit and should work pretty well.
I'm used to that Master on the 135's that has a pull pot. I usually replace those with a simple 1meg pot that grounds the grid like any volume pot. Ands remove the added components.

Title: Re: Master Volume On 100 Watt SF Twin
Post by: Geezer on January 10, 2012, 07:00:03 am

I just got, not one, but TWO of these beasts! Haven't had time to look & see if they are 100w or 135w models, but both have the MV w/ pull boost. One is an international model w/ the voltage selector, the other a domestic US model.

A friend who owns a music shop has had them in his back room for 10 to 15 years & I don't know (nor did he) what is wrong with them.

Anyway, the deal is that I get them both working, then keep the one I want & give him the other back.

I'll be having LOTS of questions on these, as it's been a LONG time since I worked on any other amp than my own builds & designs. It will be several weeks before I can look at them, but I am very interested in any MV options out there.

Thx, G

Title: Re: Master Volume On 100 Watt SF Twin
Post by: plexi50 on January 10, 2012, 09:27:45 am

It's been a few years as well since the last time i had one of these. I have heard that this master sounds bad and most people dissconect them all together. The reason for me asking if there is a better tone option in using a master in this amp. To be honest i dont think you can do a whole lot with 100 watts in making it sound great at lower volume levels. It is what it is. LOUD! JMO

Title: Re: Master Volume On 100 Watt SF Twin
Post by: chuggy on January 10, 2012, 03:15:57 pm

See site below for PPIMV install using the original MV contol panel hole on a Vibrosonic Reverb, same amp but with a 15 in speaker.

https://sites.google.com/site/jimdramps/home/harness-the-beast

Jim R