wierd mod on Fender S/Face

[Harry the Horder]

I have a wierd mod on my Fender silverface {wired by Dan Torres)
on V5 that's the vibrato valve across pins 4 -9 going down to ground on chassis is a small trim pot. any ideas on what this does ?? :?
And what are your thoughts on removing pre-amp valve cans to improve tone as described in "The Tube Amp Book" is it truly beneficial?
Harry the Horder.

 

[Boogiebabies]

4,5 and 9 are for the heater elements. It may be some kind of hum trim pot.

 

[fdesalvo]

Mention the name Dan Torres and you quickley learn that people either love him or hate him. He's regarded as a hack by some of the most respected techs in the field. At the same time, some find him innovative and informative.

 

[Monsta-Tone]

He's both a hack and the author of a decent "Tube Amps for Dummies," style book.

Much of what is in the book is not what he sells as mods now, or what he will tell you over the phone.


The book is very good as a 1st book on Tube Amps, but most things should be taken with a grain of salt. It's poorly edited, written (like most books on the subject) with more opinion than fact, and some of the mods just don't work the way they are drawn.

It does, however give you the layout of a typical Tube Amp, and it explains the parts fairly well. The Bias Charts are handy too.




It does sound like some sort of Hum Ballance. On many older Fenders, the Filament Supply has 2-100 ohm resistors to Ground to create a Ground Reference for the Supply. They basically take a 100 ohm resistor from each of the 2 Filament taps on the Power Transformer to Ground.

This only occurs in the amps that don't have a Green/Yellow wire coming out of the Power Transformer to the Chassis Ground.

The Torres book describes this fairly well. Your mod may be due to an aging Power Transformer and drifting voltages within the Transformer.




As for the "Pre-Amp Valve Cans," these are there to keep stray noises (hum, etc.) from being induced into the tube.

They are also heat sinks and keep the tubes more cool than they would otherwise be.

And, they keep tubes in older sockets fairly well.



Every other book that I have read states very clearly and consicely that these should remain on. I have noticed in my personal amps that my Preamp tubes seem to become Microphonic sooner when they are removed.

 

[Monsta-Tone]

I forgot:

I have a Blackface Bandmaster that either came from Torres, or was done as an older kit.

The workmanship was terrible. There were 2 added relay circuit boards that were just floating. Also, the lead dressing was bad and there was lots of hum.

Lastly, whoever did the mods turned the amp into a 100 watt amp with a huge Hammond transformer. They used a guitar patch cord to power the speakers. The transformer's epoxy coating is melted and looks shitty. This thing has gotten hot.




I've seen a few other amps that Torres's shop has done and the workmanship is not good.




It's like taking your Mercedes to a Yugo mechanic. Just because you know your way around an amp or car doesn't necessarily mean that you know how to do the work cleanly.

I run into this a lot in my day job, Home theater and Automation. There are many Audio or Automation guys that can do great things, but their stuff keeps breaking and looks like ****. Some people just don't take much pride in the way their work looks.

 

[Harry the Horder]

Hi Guys 8) Thanks for the replies to my post. I see what you mean about the workmanship the wiring looks like spagetti junction ( that's a saying we have in dear old England) It actually refers to a Highway intersection that is a complete mess and even locals got lost on it for days.about the same as trying to follow the wiring. What books do you advize for reading up on valve amps :?: So far I have The Tube Amp Book,Inside Tube Amps (Dan The Man),and once it arrives Gerald Webers latest Book plus 4Hour DVD (I love a good film.Ref. cans I was just curious as Dan the Man recommends removing cans to improve tone but I say if it ain't broke don't fix it. :!: Thanks again Harry the Horder.

 

[wolfgang6505]

Trim pot? for vibrato....I been checking out ,using fenders for almost 15 years now and I've never heard of this.

My most recent fenders are \
64 Tremolux
64 bandmaster
71 bandmaster (hottrodded)

 

[Harry the Horder]

Well I said it was weird I cant really understand why it has been fitted with a variable pot I shall probably bin it when I do the blackface mod!
Harry the Horder :lol:

 

[Monsta-Tone]

Harry,

You could probably remove it, but it may be there because your original Power Transformer has drifted a little off spec. This happens naturally to a certain extent and is usually nothing to worry about.

If you remove it and notice a hum, then I would put it back in.

If you can't see it, and have a couple of beers, you probably could just forget about it.




If you do happen to remove it, don't do it while you are Blackfacing the amp. All too often, I see people do a bunch of mods, and then have lots of problems with the amp.

I do 1 mod at a time. Then I test the amp. It is way too easy to make a mistake and not see it. If you have done many things in the amp, it is too distracting to find the problem right away.

It may take longer, but you'll be much more happy with the results. Plus, you may notice that you can vary certain capacitor values and get some really sweet results.

 

[fdesalvo]

Yep, that's what I was thinking- tube vibrato via fluctuating bias!

Trim pot? for vibrato....I been checking out ,using fenders for almost 15 years now and I've never heard of this.

My most recent fenders are \
64 Tremolux
64 bandmaster
71 bandmaster (hottrodded)

 

[Monsta-Tone]

I didn't even think about the fact that the amp might not have had Vibrato from the factory.


What model is it?

 

[Harry the Horder]

Thanks for everybodys help and advice It's a Fender Twin Reverb circa Jul 26th 1971 Harry the Horder