How to Blackface a Dual Showman with Master Volume

[ulbe]

I'm trying to blackface a Dual Showman Reverb, With the push/pull master volume. I think it is mid 70s.
I've found a lot of information regarding the changes to the bias and grounding, but have not found anything regarding how to get rid of the master volume.
So far I've checked some websites and the Gerald Weber video, in which he tells you to check out one of his books... is that a good source of reference?
Thanks guys, any help at all would be very appreciated.

[Blue Strat]

I don't think you'll find a step by step guide on this.

Basically, look at both schematics and observe the differences. Therein lies the answer.

[WaltC]

My initial question would be:
Why?
Does the amp need work anyway and you figure you might as well?
Lots of the SilverFace Fenders, if tuned up and working "right" sound pretty good, even the pull boost and master vol. ones.

If you know how to build a bias circuit, then you can covert the bias balance in yours to bias adjust, but I usually just add another pot to the balance pot circuit and get both bias voltage adjust and bias balance between tubes, makes it easier to match up the tubes and still get them working at the best level.

Just going through and swapping out any of the parts that are different between a mid '60's showman and a master vol. dual showman often will not get you where you want to go sound wise and can even be dangerous. The power trans. in the later models (100W MV and 135W ultralinear) can produce sig. higher voltages than the earlier models, so the values of the components will probably need to be different than in the earlier models to get the same general safe operating point, and the ultralinear model output trans. is completely different that the earlier ones and the screen supply is wired differently.

Be careful, those suckers can bite! Good luck and keep us posted...

[AL30]

The power trans. in the later models (100W MV and 135W ultralinear) can produce sig. higher voltages than the earlier models, so the values of the components will probably need to be different than in the earlier models to get the same general safe operating point, and the ultralinear model output trans. is completely different that the earlier ones and the screen supply is wired differently.

Be careful, those suckers can bite! Good luck and keep us posted...

Yep yep yep. If you've got a push/pull you may have the UL model. You'll need tp do a lot of surgery to get to a BF - including swapping transformers.

AL

[ulbe]

Thanks for all the comments, very much appreciated.
To the person that asks why... Well I just bought this amp used, it works fine, but it still has original caps, tubes and there is no reverb tank (someone took it out) It works, but I must say does not sound too great. Also, the master volume works, but when pulled, there is some noise introduced to the signal.

Since I really have no use for a master volume, as this amp is going to be used to play clean, I figured blackfacing it would get rid of the master. I could be wrong, and not need to blackface it. I have to re-cap and re-tube the amp anyways. I know part of the bad sound could be old tubes. Also, all of the myth about silverfaces sounding bad, has me biased. (I admit I have never actually done a real AB comparison. This amp, however, is not sounding as great as I think it could)

You guys got me thinking about the ultralinear issue... I have no idea if this is or is not ultralinear.... how do I find this out? The transformer reads:
Fender
022889
606-5-15

That makes it a 1975, right? I don't think they were doing ultralinears at that point, but I could be wrong. I understand this is a 100 watt amp, according to the person that sold it to me.

Thanks a lot!

[RedRock]

If your amp has a choke between the output transformer and the
power transformer on the outside of the chassis, your amp is not
U.L. If there is no choke, it is U.L.
You can remove the master volume easily in either case, and you
certainly don't have to "blackface" the circuit to do it.
Slightly to the right of the phase inverter (as you look at the amp from the back) you will see 2 220k resistors joined together in a "V."
Disconnect the long wire that is soldered at the tip of the "V."
This is the wire that goes to the Master volume control.
Then, back at the phase inverter,there is a long wire soldered
into the input side of the phase inverter cap (which is probably.01
mfd.). Disconnect this long wire. Then with a piece of hookup wire,
20 or 22 gauge solid or stranded, with insulation on it, (about two
or three inches long) solder one end of the hookup wire into
the tip of the "V" and the other end into the input side of the
phase inverter cap. You can clip off the other ends of the two master
volume wires at the master volume control and get them out of the
amp.Clip off the other two wires soldered to the master volume,
and follow them where they are attached to the circuit board.
They are the lousy early Fender distortion circuit. Clip them off where they are soldered to the circuit board and get them out of the
amp. You are done. Of course all of this is done with the amp
unplugged and the filter caps discharged. If you are unsure about
any of this, take it to a tech.
If it were my amp, I would simply leave the master volume in,
and not pull it out in its push-pull mode. When you pull it out
you activate that bad Fender distortion circuit.

[ulbe]

Redrock,

Thanks for the info. That was exactly what I was looking for. I know a little about amps, have read books, asked questions, seen people work on them, but still am not even close to being an expert.
I am going to try to look into what you said. Seems easy enough. And, yes, I will discharge the caps!:AOK
Thanks.

(by the way, the amp is NOT ultra-linear)

[WaltC]

Yup, what Redrock said.

I'd clean it up, de-oxit the pots and jacks, clean and re-tension the tube sockets, check the coupling caps for leakage and replace the filter caps with caps with the same values (uF) and at least as high a voltage rating, check/change tubes as necesary, check/change power tube bias/balance, buy a new tank (see Antique Electronics Supply, www.tubesandmore.com, among others) and check/replace the reverb cables, clean up, fix and/or replace the footswitch. Then play it for a while and see what you think. All the above should be done anyway whether you decide to "blackface" the amp or not, so you won't have lost anything and may find that the amp now suits you just fine w/ no further work.

If not, then drop us a line and we'll see what we can come up with...<G>

[ulbe]

I hope this question is not to retarded, but is leaving the master on 10 all the time, the same as removing it from the amp? In other words, is the tone changed at all if one leaves the master on, but on 10, as opposed to removing it all together from the amp? If there is no change in tone, then removing it seems kind of pointless...

[RedRock]

Leaving the master volume on 10 is like having a 1 meg resistor
connected to ground at the input of the phase inverter cap.
It creates just a very, very small loss of volume, and dulls the tone and note
attack to a really small degree. There is also a very small loss of highs
caused by the capacitance of the shielded cable going to and returning
from the master volume pot itself. In a bright amp, this can be
a good thing. In a dark amp, not so.