Fender Dual Showman Reverb with safety issues

[aiyiadam]

This amp still works.. I didn’t have the guts to power the amp, but the new owner had tried it.

I don’t have a lot of experience with those amps. I assume that the boards might have become too conductive. There is too much rust.. The eyelets and other soldering surface look too rusty & dirty and many solder joints look bad. The tube sockets might be used, if I can clean the solder lugs well enough. The transformers should be okay. The reverb tank seems to work.. I told him, that the amp needs much more that a filter cap job and we should build new boards with “very possibly” new components. Unfortunately the owner can’t invest much in this amp. He would prefer to leave it in this way and sell it in working condition.

Even if this amp doesn't harm anybody, there is a strong chance that its tubes or trannies can be destroyed.

I will advise him to do a minimal investment and make the amp considerably less dangerous. I think we should at least:

• Change the filter caps and related resistors and clean out their board.
• Clean and renew the main grounding connections.
• Change the diodes, build a new bias circuit and clean out the related board.
• Clean and renew PT, OT and choke connections.

Maybe you could have some suggestions?

[Jon Snell]

You may well be surprised.
Replace the capacitors in the dog house as they are definately wrong.
The Mallory decoupling capacitors are of excellent quality and I would not suspect any for faults.
The board has years of grime build up, washing it with IPA and a dry paint brush will deal with that.
On the whole, not too shabby at all.
I have restored worse.

PS;
You cannot tell a bad solder joint by just looking in this type of build, PCB yes but not solder on eyelets. The eyelets hold the solder, not conduct it. The solder does the business between component leads.
The PCB is probably not conductive.

[Helmholtz]

Agree with the above.

The amp should be from the early 70s (transformer codes will tell). Uses same components as my own 1972 DSR.
AFAIK all the amps from that era and before used black fiberboards.
So the board looks like a replacement.

Start with vacuum cleaner and dry paint brush or compressed air.

You might need some Deoxit D5 for jacks, tube sockets, switches and pots.

[aiyiadam]

Thank you for the valuable information. This restoration thing is not for me. I am possibly too obsessive.

I also assumed that the main board isn’t original. Its material is different than the other boards in this amp. It is multi-layered and textured. Looks actually like cloth.. The component values are written on the board and the eyelets look bigger than usual. I surely am not expert in solder joints, but many of them do look wrong and some of those are on the boards. And don’t those rusty eyelets contaminate the new solder, if I don’t clean them well enough?

The mallory caps seem to be mostly (or all) cathode bypass caps.. Coupling caps look like paktrons. Wouldn’t a new vishay 715P be more reliable now? And many components have possibly drifted. I am sure that many of them didn’t sound like this 50 years ago..

At the end, I think it still makes more sense to toss this strange white board and build a fresh one. Check all the components, replace if necessary. But it would be too time consuming and expensive.

So... If I can’t work throughly on this amp, I shouldn't accept any responsibilty for the potential problems. If the owner accepts this, I will change the bias and filter caps, clean the two related boards, sockets &jacks and leave the rest (and the rust) of this amp in peace...

[Chuck H]

With the exception of any moisture absorption I wouldn't expect the board to be conductive. The original black paper fiber boards could become conductive because of moisture (humidity) and/or repeated application of heat or high voltage could create semi conductive paths on the old black boards with the high level of carbon pigments. The latter is NOT a problem with the board in that amp. Only any possibility of moisture causing mild conductivity. FWIW I've NEVER seen a black fiber board (and yours isn't even black) that was so conductive as to be a safety concern. In all my history here and abroad I've never heard of a conductive board heating and causing a fire. But I have to also say that I don't speak for anything that COULD happen. Just that I've never seen or heard of such a thing. And...

Since your board is clearly not a black fiber board, but rather an unpigmented fiber board (with no carbon pigmentation) it is almost surely safer than any black pigmented board.

[aiyiadam]

Thank you Chuck H. Let me put here a closer photo of the board. This is like cardboard and it is coming apart.

[Chuck H]

That's ugly. And the level of grime on the black board that was preserved for the rectifier and bias wiring certainly COULD be conductive. The untreated plain fiber board that was used also seems to have been marked for eyelet spacing and components with a pencil. I don't suspect there's enough graphite there to be an issue but a pencil line is, technically, a semiconductor.

I may get some heat for saying so, but "I" would probably replace the whole board. Saving you the effort of trying to clean it as well as eliminating any variables in the result. I would probably make my own board from untinted G-10 that I have on hand. I've done two Fenders that way when the boards demonstrated conductivity that couldn't be eliminated by drying. Short of that you can probably find a suitable board here:

https://hoffmanamps.com/MyStore/perl...ER_ID=!ORDERID!

These are epoxy boards that don't suffer any conductivity due to the black coloration. There is no board specific for that amp but I think you could rebuild the whole thing on the AB763 Twin Reverb board. It may require some retrofitting for mounting.

[Mick Bailey]

That looks like a DIY board to me. Superficially it looks to be similar to the material that Traynor used, but much softer. Eyelets should be tinned brass and rust suggests otherwise. Sometimes excess flux can be mistaken for a problem, but is fine. I'd also perhaps rebuild it onto a new board, but it isn't the worst I've seen and I'd want to get it running first before coming to a decision and find out the total of what may be wrong with it.

[Axtman]

Definitely install a power cord with molded grounded plug! Also remove the "death cap".

I have worked on a few chasises that were so dirty I could not read the value of the components.In that case I took outside and sprayed it off with a garden hose then left it outside in the sun to dry for a day or two. I have not had any issues but I made sure the chasis was completely dry and that no water go in and/or drained out of the transformers.

[Chuck H]

Definitely install a power cord with molded grounded plug! Also remove the "death cap".

I have worked on a few chasises that were so dirty I could not read the value of the components.In that case I took outside and sprayed it off with a garden hose then left it outside in the sun to dry for a day or two. I have not had any issues but I made sure the chasis was completely dry and that no water go in and/or drained out of the transformers.

I've also heard of people using a pressure washer on cabinets and grill cloth! When you've got nothing to lose, right?

[Axtman]

I would never use a pressure washer! Just use a garden hose and maybe some Simple Green.

[Chuck H]

I would never use a pressure washer! Just use a garden hose and maybe some Simple Green.

Well... Being a house painter I know what a real pressure washer can/will do. It's probable the pressure washer being used by whomever wrote about that was one of those wimpy, homeowner electric jobbies. Which would probably be safe enough.

[aiyiadam]

It has been a while.. I had to wait for the components and It is cumbersome work..

Since I have taken everything apart, I had the chance to inspect most of the component much better.

• The DIY board was actually ordinary paperboard and the eyelets were possibly from the clothing industry.
• Three of the 25uf mallory cathode bypass caps were very far from 25uf. The screen resistors were also done.
• The 100K plate resistors and the coupling caps were okay. Since I wanted to keep some of the original amp, I have kept the coupling caps and the hissy resistors for now.
• The tinned cables were all okay. The untinned heater leads of the transformer were too rusty. I had to use sandpaper for getting some solderable surface.
• The reverb tank and the transformer seem to work. The reverb cables were damaged badly. I had to solder some new cables. However, the mechanical isolation of the springs is very stiff. It became even stiffer with my thick reverb cables. A new tank will probably work much better.
• Almost all of the pots including the bias balance pot are still okay. The master volume push-pull pot was broken. The MV doesn't seem to be necessary for those kind of amps and I have installed a presence pot instead. I have kept the bias balance pot and added an additional pot for changing the bias.
• The stand-by and power switches seem to be okay.
• Three of the jack switches don't work.
• All of the tube sockets seem to be fine.
• The pertinax bottom of the voltage selector switch was bent very badly. Tried to repair it, but I couldn't.
• One of the bright switches don't work.
• The power cable looks okay. Since it was partly damaged, I have shortened it about 30cm. Due to rust there was no proper grounding on the plug. I have cleaned it and soldered the small rivet in the center. However, I will still change the plug.

The new board is 3mm FR4 and is a bit smaller than the original. Therefore I had to lengthen the choke leads and the OT center tap. Installed a 500mA fuse. Done new heater wiring for the preamp. Used mostly 1W metal film resistors, F+T filter caps etc.

Well... Now I am almost done.. There is a problem: The ticking noise of the vibrato is driving me mad. I have soldered a 10n cap on the 10M resistor (for reducing the ticking) and a 22n cap across the 220K reverb resistor (for reducing the hiss). And I have played a bit with the lead dress.. Those well known mods helped a bit. At the moment I don't hear any ticking, when only the vibrato is on and there is no input. And when I am playing, I do hear a ticking. If I increase the reverb, I hear a swooshing noise. There seems to be a kind of coupling between the reverb and the vibrato. Additional to the lead dress, the grounding might be playing a role here.

I need to work on the vibrato noise and would appreciate any advice.

[Delta362]

I recently came across this article that discussed relocating a ground wire makes a huge difference in the ticking. I haven't had one in recently to try, but might be something to consider. See towards the bottom of this article.
https://www.effectrode.com/knowledge...-with-tremolo/

[g1]

I've never ever seen a reverb tank like that. Unless someone else has, I would say it is definitely not the stock part, so would not spend any time on it.
There is a wire that goes right up against the opto-coupler. If you did not try moving it when you played with lead dress, give it a try. I've had success with it reducing ticking sometimes.