1966 BF Showman - Recommended Replacement Parts

[PicknStrum]

Hey all,

Wanted to get your opinion on something. I've asked this on a different forum but I believe the general consensus here is different - apologies if you've seen this thread on that other forum.

I recently picked up a non-functioning 1966 AB763 Showman. It's by no means mint. It's blonde so was likely re-covered, although, some on the other forum thought that it looked like Fender quality - it's highly doubtful that Fender covered a showman in blonde in 1966, from what I understand. Even if it was done by Fender, it's in pretty rough shape. The PT and OT have both been replaced. A previous owner has attempted some mods. All that to say, it's far from mint.

One thing it does have going for it is that the guts appear to be dang-near all original. I plan on replacing all of the electrolytics (on the filter AND main board). I'm also going to replace the resistors that read out of spec and/or obviously need to be replaced. Finally, I think I'm going to up the wattage on the screen resistors as it looks like one of them blew apart at some point.

My goal here is to retain as much of the '66 vibes, without being too crazy about it. As it's already far from mint, I guess I'm not super concerned about a loss of value.

Here's what I'm thinking:

1. F&T electrolytics
2. NOS Allen Bradley Carbon Comps for 1/2 watt resistor replacements
3. New production carbon comps for the screen resistors with a rating of at least 2 watts

Any thoughts / opinions on that?

I do have 2 additional questions (I'm going a, b, c, format on these ):

A. Should I need to replace any of the blue molded caps, is there a recommended replacement? At this point, I'm planning on yellow Mallory 150s as I really like them in my DIY Princeton Reverb.

B. Any reason that I should or shouldn't re-cover the cabinet?


Pictures to follow, of course!

[pdf64]

Carbon based resistors carry an inherent fuel load, so are about the worst choice for applications that might be subject to heavy overload, eg screen grid current limiters, HT droppers. ie they can catch fire and cause significant collateral damage if there’s a fault in the circuit they feed.
MO with a flame retardant coating are probably the most appropriate type.
Don’t overlook the bias supply ecap, use a replacement with a higher voltage rating than the original 50V. As there’s typically over 50V across it.
Consider replacing all diodes and adding HT fusing.
1ohm cathode current sensing resistors are very beneficial, especially in the case of amps such as yours, with parallel push - pull pairs of power valves.

[ChopSauce]

HT fusing? I read really bad things about that, but maybe you can clarify this topic for me ?



I wouldn't change the blue molded at all, firstly. Secondly, I'd manage to use the amp with the minimal changes required to having it safely operating, because - even though it is not "mint" - it still is a piece of history and I feel that it should be handled this way.

I do not know that much about amps, for sure, but I know about one odd Moto Guzzi would sold for pretty cheap and appeared to be a very rare model, with a load of genuine vintage parts, and a valuable hi$tory.

Of course, if you bought it with the intend to mod. it, this is another story, but it doesn't look like that.

Other than that good NOS resistors sound OK but are these really required to be changed?
(out of curiosity)

[Stevem]

Have you had it on and in warm up to see if the tubes light up and the filament voltage is close to normal?

[sll]

Kendrick Amplifiers sells bags of high quality electrolytic caps at a very good price.

[pdf64]

Kendrick Amplifiers sells bags of high quality electrolytic caps at a very good price.

Just curious - how are you assessing their quality?
Are there any specs beyond the basic nominal capacitance and rated voltage?

[sll]

Kendrick Amplifiers sells bags of high quality electrolytic caps at a very good price.

Just curious - how are you assessing their quality?
Are there any specs beyond the basic nominal capacitance and rated voltage?

Just my experience using them for restorations, conversions, and repairs, Kendrick's reputation for quality amplifiers, and their description of the difference of capacitor production.

http://www.kendrick-amplifiers.com/mm5/ ... _Code=0801

[PicknStrum]

I wouldn't change the blue molded at all, firstly. SOther than that good NOS resistors sound OK but are these really required to be changed?
(out of curiosity)

Someone attempted some mods at some point. There are a couple of leads that are clipped. I can probably just jumper them with wires and leave the originals in there. In addition to the clipped leads, there are some clipped wires. Not sure what the intentions were but I haven't dug too deep yet.

As far as the blue molded caps, I have no plans on changing them unless I somehow have an issue with them after start up.

Have you had it on and in warm up to see if the tubes light up and the filament voltage is close to normal?

Probably should've led with this but as it sits, I can't turn it on. Like I said there were some obvious mod attempts done to it. A screen resistor is blown in half and the fuse also needs replacing. I'm also not planning on starting it up until I change all of the e-caps.

I'll definitely look into the stuff you said PDF. I'm absolutely planning on changing the bias cap and will grab a higher voltage. I do like the 1 ohms for helping to bias so that's a definite possibility.

I'll also look into those kendrick caps, sll.

Appreciate all the advice!

[TUBEDUDE]

First check the conductivity of that crappy fiberboard Leo used. It could save you some misery.
The blue moldeds are pretty good. Just check your grids for leakage.

[Roe]

The tad audio caps made in germany are great

[ChopSauce]

The tad audio caps made in germany are great

Aren't these rebranded F&T?

[pdf64]

...Just my experience using them for restorations, conversions, and repairs, Kendrick's reputation for quality amplifiers, and their description of the difference of capacitor production.

http://www.kendrick-amplifiers.com/mm5/ ... _Code=0801

It’s great that they work well, and if they’re used in their own amps they should hopefully have a good operational life, but to me, that page reads like a snake oil advert.
eg claims of superior performance, but nothing to quantify that, and no detailed specs / characteristics.

[pdf64]

...as it sits, I can't turn it on. Like I said there were some obvious mod attempts done to it. A screen resistor is blown in half and the fuse also needs replacing...

You might not have a light bulb limiter (LBL), if that’s the case then I suggest your top priority should be to build one.
With all the valves and ecaps removed, and a good fuse, power up the amp via the LBL to check that the transformers aren’t obviously shorted.
Then use it after you’ve done the remedial works, before the valves go in, to check the voltages are good etc.
Then for first power up with valves fitted.

[ChopSauce]

...Just my experience using them for restorations, conversions, and repairs, Kendrick's reputation for quality amplifiers, and their description of the difference of capacitor production.

http://www.kendrick-amplifiers.com/mm5/ ... _Code=0801

It’s great that they work well, and if they’re used in their own amps they should hopefully have a good operational life, but to me, that page reads like a snake oil advert.
eg claims of superior performance, but nothing to quantify that, and no detailed specs / characteristics.

This kind of advertisement sometimes is here merely to justify the price of the final product. Kemet and Solen (non e-lytics) caps, amongst most often cited, seem to be really good ones, if one is willing to spend more than the average price. Not sure there's enough room for the Solen, though.

[PicknStrum]

First check the conductivity of that crappy fiberboard Leo used. It could save you some misery.
The blue moldeds are pretty good. Just check your grids for leakage.

Will do! I'll see if there is any leakage between the main board and the liner board with chassis. I'll also check grids on the blue molded.

...as it sits, I can't turn it on. Like I said there were some obvious mod attempts done to it. A screen resistor is blown in half and the fuse also needs replacing...

You might not have a light bulb limiter (LBL), if that’s the case then I suggest your top priority should be to build one.
With all the valves and ecaps removed, and a good fuse, power up the amp via the LBL to check that the transformers aren’t obviously shorted.
Then use it after you’ve done the remedial works, before the valves go in, to check the voltages are good etc.
Then for first power up with valves fitted.

I do have a limiter. Although this isn't my first rodeo, per se, it is my first restoration. Thanks for this suggestion! I was wondering how I could test the transformers. So I'm removing all electrolytics before doing this, correct? Including main board, filter board, and bias board? I understand removing all the tubes and getting a good fuse in there but want to make sure I'm clear on the electrolytics. I usually follow robrob's startup procedure.

...Just my experience using them for restorations, conversions, and repairs, Kendrick's reputation for quality amplifiers, and their description of the difference of capacitor production.

http://www.kendrick-amplifiers.com/mm5/ ... _Code=0801

It’s great that they work well, and if they’re used in their own amps they should hopefully have a good operational life, but to me, that page reads like a snake oil advert.
eg claims of superior performance, but nothing to quantify that, and no detailed specs / characteristics.

This kind of advertisement sometimes is here merely to justify the price of the final product. Kemet and Solen (non e-lytics) caps, amongst most often cited, seem to be really good ones, if one is willing to spend more than the average price. Not sure there's enough room for the Solen, though.

I'll look into the Kemet's for sure. I'm willing to spend a little extra as long as I don't get too carried away