Fender Amp "Master" Volume DILEMMA...........

[Pastortom]

Pardon me, as usual, for asking a question that may be very simple for the learned amp wizards here......Trust me when I say that you're ALL appreciated.

If you're familiar with Fender Silverface amps from the 70's, you're probably aware that the faceplates can determine the actual value (and most certainly affect the appearance) of the amplifier.  The faceplates are NOT being reproduced, since a crackdown by Fender's lawyers (so I understand)........The blackface plates can be found, but NOT silvers.  Hence, my dilemma.

I'm a perfectionist at heart, and can't STAND "relics".....I have to restore my amps in order to sleep at night. 

My problem is this:    I picked up a silverface Twin Reverb model with the master volume over by the pilot light.  The faceplates were modded by Fender to allow this extra pot......OTHERWISE, a new blackface faceplate could replace the ratty damaged silverface.  My QUESTION:    Can I ELIMINATE the master volume simply and neatly, retaining the normal volume control on the left?  If I was a cob artist I'd just pre-set the pot, then wrap it and isolate it inside the chassis, then install the blackface, and VOILA'..no master.  BUT, I'd like to actually eliminate it...........

IS THERE a very simple solution, and if so, WHAT exactly would it be?  Again, forgive me if it's simple and obvious.......I sometimes is a moron.

[mresistor]

Well here's the schematic for it, I think you can remove the MV but it will take someone looking at the schematic to see how...... someone with more experience modding twins.....
What does the push-pull switch do on the MV? The MV twin is surely different than the AA270 Silverface Twin. Does yours have the line out, if so the bottom schematic is the one to use.  

Silverface MV Twin Schematic
SF MV Twin with line out
 

[Pastortom]

No line out, and no push-pull function..........Just a straight 'no frills' master volume.

[mresistor]

can you post a couple of pics of the innards? also is there a tube chart inside the cab that tells what model ? or on the back of the chassis? Is it an AA270 or AA769?

[FYL]

IS THERE a very simple solution, and if so, WHAT exactly would it be?

It's usually very simple : just remove the MV pot and the associated glue - can be a simple treble bypass cap or something more complex, go AB763 style. As easy as that.

We need to know which model / main board for more specific info.

[plexi50]

I have had 3 Silverface masters in the past 2 months that at request asked for the master volume pot be removed

Each owner asked to have the master pot put back in after the removal

These amps are not nearly as loud without them or have that breakup

These amps are just basically LOUD and is hard to dial in that sweet spot with a master

They are what they are without some other board value changes

Like FYL said: AB763 style is a good choice

[mresistor]

So you guys are saying to rebuild the board to AB763 specs? Shouldn't be too hard.

[FYL]

So you guys are saying to rebuild the board to AB763 specs? Shouldn't be too hard.

Not a full rebuild, but selective component changes. If your TR is compatible, of course (UL models are a royal pain in the neck).

[phsyconoodler]

I recently removed the master on a silverface twin and it sounded just fine.I simply followed the AB763 layout and removed and replaced only the necessary components to accomplish the job.While I was in there I switched it to a bias adjust from the bias balance system and was able to get the tubes working a bit harder than 25ma.It sounded quite nice.
  I did not notice it having any less volume that it did with the master though.

[eleventeen]

If I am understanding your esthetic priorities correctly:

There's also the option of replacing the faceplate with a BF real or repro one; and moving the MV pot, as is, to either the extension speaker jack; or, changing the dual RCAs that are for the rev/trem footswitches to a stereo 1/4" jack and plug and moving the MV pot into a freed-up hole. Offhand, I'd kind of prefer the 2nd option. Because 1: It's easily conceivable that a user would want to use an extension speaker with a Twin (prob not so much with say a Deluxe) and 2: Completely reversible. Well...OK, you'd lose 4" on footpedal cable if you ended up reverting to factory stock.

[Pastortom]

Well, I hadn't considered moving the pot......I definitely would not put it anywhere on the faceplate.......BUT, on the back of the chassis I would consider if it was a "clean" job.......I wouldn't want to disturb any of the existing jacks though.......I would probably move it to an open spot on the chassis and drill a new hole for a nice installation.   That's a possibility............BUT, don't know.........gotta consider eliminating it........

[Pastortom]

My circuit is an   A-49593 .......and here's a pic of the chassis.......The master volume pot is hooked to the fat black leads going to the far left.

[eleventeen]

Wouldn't even have to unsolder anything on the MV control to move the current wires and pot as a unit to one of the rev/trem jacks.

As for altering (for example) the trem footswitch jack, geez, it's one wire shorted (or not) to ground. Big deal.

Personally, if you do not wish to rebuild the amp to AB763 (pretty easy) I would move the MV, if you wished to retain it (and I think there's very good reason to do so per some of the above comments and my own experience) to the trem footswitch hole on at least a trial basis: Decide/figure out if you can abide that control on the back panel in the first place. EVEN IF you decide to change to AB763, there's plenty of good reason to add a MV and you'll need a place for it if you so decide. 

btw: stumbled onto this, may be useful for you: http://www.diyguitarist.com/GuitarAmps/TwinReverb.htm

[FYL]

My circuit is an   A-49593

A-49593 is the serial number, probably a late '72 model. Judging from the board pic probably based on the AA270.

[sluckey]

Remove the two wires from the MV lugs (not talking about the ground wire or shields). Solder the two wires together. Throw the pot away.

A neater way to do this would be to follow those two fat black wires back to the board. Unsolder them from the board. Solder a jumper between the eyelets you just unsoldered the fat black wires from. Throw the pot away.

Here's the schematic for that amp... http://www.el34world.com/charts/Schematics/fender/fender_quadreverb_100w_nomstrvol.pdf

[jojokeo]

I don't think that type of master vol sounds bad to have at all? I have a number of amps w/ that set-up/style (pre-pi). What's the big deal people make w/ this particular amp/set-up that causes people to groan or complain about them? I don't get the bad rap they get?
I was thinking it was a ppi type before I saw the schem.

[eleventeen]

IMHO, since they came out, people have heard this vintage amplifier and ALL the circuit changes (mostly goofy) that were made from AB763 to AA270 both with their ears AND their eventually-developed knowledge of the component changes AND their general disdain for the quality decline right-after-CBS-took-over Fender. When people see that MV control, all those synapses go off in their minds. That MV control, that extra knob sitting there, is just the most overt sign of what's behind the front panel. I don't especially think the MV control in particular is all that offensive; some like it, some don't, vanilla/chocolate, personal preference. It's just IMO this visual trigger that sets off all the hatred for the complete set of post-CBS mods that weren't well received at the time and have only seemed to get stinkier over time. I recall very well when silverface Fender amps came out. They were disdained EVEN THOUGH when they first came out, they were utterly identical (electronically) to their AB763 ancestors and remained so for perhaps 2-3 years.

I'm plenty guilty of this, I'm sure. ALL the major manufacturers went through pretty noticeable quality "hits" right around 1970-1971-1972. Fender, Gibson, Martin. Maybe a 1970 SG Standard is just as good a guitar as a 1963 SG or a 1976 or a 1998 or a 2006 SG; and the same for a Martin D-18, but it has always seemed to me that for US musical instrument manufacturers, they all went through some kind of dark age of quality control during the early 70's. In a lot of ways, those were pretty cruddy years for a lot of things.

[jojokeo]

Yes, I understand the history and lived it too. But, I didn't know anything back then when I was 10 and got my first used '63 Black Face Tremolux except the salesman telling me those advantages and how it would be worth money someday. My response was mainly from after seeing the schematic. I should know that as I have one stacked away behind a bunch of other amps. I haven't played it for a couple years or so. I should sell it but it isn't a priority at the moment and I know I won't get much from it either. It sounded great to me though It was to have had the MV modded in some way w/ a complete tune up when I bought it 20 years ago and didn't know the difference between a 12ax7 or a 12au7.

[FYL]

I don't think that type of master vol sounds bad to have at all?

It's quite crude technically and impacts treble response and tone.

It's also not very useful: a TR is the epitome of a loud'n clean amp, with little pre disto. Why bother with an approximative MV?

[sluckey]

Why bother with an approximative MV?

I guess it depends on the purpose of a master volume control. Back in the day, I always thought a mv was useful when 2 players were using the same amp (TR in this case). Each player set his volume with the separate channel volume controls. Once the mix was right, use the MV to set the overall level up/down. Same thing on the old Bogan PAs. Individual level control for each mic, MV to set the overall level.

That's what I believe Fender had in mind when they put a MV on the TR. I don't think anyone back then considered turning the mv down and cranking the volume up to get a little preamp overdrive/distortion out of a TR. That's what your fuzz box was for. I think the idea of using a MV to help create an overdriven tone at lower levels is relatively new.

[FYL]

Back in the day, I always thought a mv was useful when 2 players were using the same amp (TR in this case).

Good point.

[jojokeo]

I don't think that type of master vol sounds bad to have at all?

It's quite crude technically and impacts treble response and tone.

It's also not very useful: a TR is the epitome of a loud'n clean amp, with little pre disto. Why bother with an approximative MV?

To me it's no different than having a number of vol or gain pots for each stage such as in the TOS amp. If you find certain controls (or even grid resistors) minimize treble response too much you put a treble bleed cap across it or a small treble filter network. Just naming a few of Tubenit & Geezer amps like the 56T, Little Wing, TOS, Carolina Blues, etc. not mention many other commercial amps - all use this style of "MV". I don't really consider it being a true master volume - rather an overall preamp volume control. This is similar to what's described earlier but that doesn't make it necessarily a "tone robber" no more that a "smoothing cap" across a load resistor or any other hi requency filtering methods. (Unless you read Gerald Weber books) 
To me, a true master volume is performed in the power stage or using something like the VVR control.

[FYL]

To me it's no different than having a number of vol or gain pots for each stage such as in the TOS amp.

The TOS uses a different disto architecture, with the overdrive section playing a major role. You can control it thru the drive and level controls, which aren't MVs. It's more a crunch to OD amp than a clean to absurdly loud amp like the 100W Twin Reverb.

To me, a true master volume is performed in the power stage or using something like the VVR control.

Yep. My fave MVs are located at the PI (a bootstrap in a cathodyne) or post-PI (most KF type 2 and their derivatives), plus Power Scaling or it's VRM, VVR, etc. equivalents selectively applied. But it all depends on the kind of amp and it's disto structure.

[jojokeo]

To clarify and understand where you're coming from then, you're saying "why put a master volume on an amp that's meant for loud and clean?"

[FYL]

To clarify and understand where you're coming from then, you're saying "why put a master volume on an amp that's meant for loud and clean?"

Yes. The TR was - and still is - one of the loudest clean amps around.

[J Rindt]

One nice thing about these later Fenders was the more accessible location of the rectifier and bias circuit. You do not have to access it very often, but when you do, it is nice to have it between the PT and the circuit board......
Good Luck

[Pastortom]

Well, after taking some careful measurements on the back of the chassis of this master Volume model Twin Reverb, I decided NOT to monkey with the stock circuitry............

There was JUST enough factory lead wire to relocate the Master Volume control to the ONLY free and open location on the chassis......directly between the back faceplate and the chassis number stamping.  It's perfectly centered so that the knob will not block the numbers or hit the plate.  All in all, a very clean and easy relocation.    (a purist might disagree with the "new hole"...but I ain't worried about it much).

Relocating the Master Volume allowed me to "restore" the amplifier cosmetically, albeit without the silver faceplate......The blackface fits perfectly over the existing chassis, and eliminates the Master Volume..........I happen to like the blackface looks, so I'm pleased with the way it turned out.

I wish someone would pay for licensing and start reproducing the silverfaces though.......I LOVE the look of a nice clean silverface.especially with the original turquoise grillcloth (which they ALSO do not reproduce....there's a "wanna-be" out there, but it's really gaudy.....the stripe is FAR too wide, and it's NOT metallic like the originals).

Here's the finished job........Piece o' cake.

[mresistor]

Nice work PTom. Put a little black knob or a chickenhead knob on it. Does this amp still have the original electroytic caps in it?

[Pastortom]

I haven't looked under the cover yet.......they did a little work in there, so I'm hopin' they freshened it up........

[J Rindt]

Aren't those all the original bypass and bias caps?

[jojokeo]

Just a little outloud thinking here - but if the pot were still in place I think it's an interesting thought to turn that into a variable NFB or maybe a true presence control? Blackfacing w/ a bit of attitude 

[Pastortom]

Yeah, the blue caps look all original.............Amp sounds really nice as-is...........Hate to mess with it, BUT that "presence" control sounds intriguing........