1966 BF Showman - Recommended Replacement Parts

[pdf64]

There doesn’t seem any point benefit in testing the amp with old, potentially faulty ecaps in place, particularly if it might have been a while since it was last powered up(?).

[PicknStrum]

There doesn’t seem any point benefit in testing the amp with old, potentially faulty ecaps in place, particularly if it might have been a while since it was last powered up(?).

I'm definitely changing the e-caps, so I agree there is no point in testing them. I'm just wondering if I start the amp up without any ecaps, will that allow me to see if the transformer is shorting. I guess I'm wondering details on this procedure. I've never started an amp up without the filter caps in place...

If I'm understanding you:

1. Remove all valves and all e-caps (without replacing ecaps for now)
2. put a good fuse in
3. plug into LBL and power up
4. The light will stay bright if the transformer itself is shorting?

Is that correct? Is there any way to differentiate a short in the PT vs. the OT?

Thanks for the help!

[Charlie Wilson]

Hello, photos of the amp?
CW

[PicknStrum]

I've cleaned up the tolex a bit, but here are some pictures of the inside and out:

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[PicknStrum]

....and a tube chart:

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[pdf64]

That’s correct, and let’s deal with shorts if they happen.

But if it did, the OT CT would be disconnected and power LBL reapplied to see if that stopped the bright bulb.

[PicknStrum]

That’s correct, and let’s deal with shorts if they happen.

But if it did, the OT CT would be disconnected and power LBL reapplied to see if that stopped the bright bulb.

So I got really antsy and had to go for it. I removed the valves and e-caps. The closest value fuse I had on hand was a 2-amp so I tried it with that. Plugged into the limiter with a 150w bulb and the bulb didn't glow at all. My thoughts were I'd done something wrong / hooked it up wrong or something. Tried it with a 75 watt bulb and same thing: no glow. So I grabbed a trusty 15w and voila, just a faint glow. So I know my LBL is at least working. I assume this is a good test indicating no shorts. If so, woohoo!!!

[Roe]

The tad audio caps made in germany are great

Aren't these rebranded F&T?

Probably but made to tad’s specs

[pdf64]

... I assume this is a good test indicating no shorts. If so, woohoo!!!

It’s a pretty good sign all is good

[Leo_Gnardo]

That photo of the amp box gives us a clue. That rectangular declivity in the bottom board was standard issue in the early 60's. I suspect your amp/cab combination is a "Frankenstein" - where someone mounted a newer chassis in an older box. No harm there, it's another adventure in the twisted history of a survivor of the 60's.

If you're attracted to using Solen film caps as filters - yes they are excellent quality and unlikely to break down with their 630V rating. FWIW Antique Electronics sells them (tubesandmore.com) so I would recommend you do some price shopping. Carr has been using them for over 20 years now, and I expect their Solen failure rate has been dam' near zero. Problem is, they're so big, they won't fit into the Fender "doghouse." About the Kemets, I don't know, never have had my hands, not even eyes, on them. If they're film caps with high voltage ratings, that's all well and good. I can tell you on rare occasions I've used a Panasonic 20 or 30 uF film cap as a first stage filter, rated 800 or 900V. One problem, they're not cylinders like most electrolytics. Their rectangular form means you need some ingenuity to mount one. That space inside the chassis between power transformer and main circuit board looks like an attractive landing zone. Affix cap there with big glob of epoxy, works for me, so far so good.

[PicknStrum]

That photo of the amp box gives us a clue. That rectangular declivity in the bottom board was standard issue in the early 60's. I suspect your amp/cab combination is a "Frankenstein" - where someone mounted a newer chassis in an older box. No harm there, it's another adventure in the twisted history of a survivor of the 60's.

If you're attracted to using Solen film caps as filters - yes they are excellent quality and unlikely to break down with their 630V rating. FWIW Antique Electronics sells them (tubesandmore.com) so I would recommend you do some price shopping. Carr has been using them for over 20 years now, and I expect their Solen failure rate has been dam' near zero. Problem is, they're so big, they won't fit into the Fender "doghouse." About the Kemets, I don't know, never have had my hands, not even eyes, on them. If they're film caps with high voltage ratings, that's all well and good. I can tell you on rare occasions I've used a Panasonic 20 or 30 uF film cap as a first stage filter, rated 800 or 900V. One problem, they're not cylinders like most electrolytics. Their rectangular form means you need some ingenuity to mount one. That space inside the chassis between power transformer and main circuit board looks like an attractive landing zone. Affix cap there with big glob of epoxy, works for me, so far so good.

The one reason we thought it may actually be the original cabinet with a re-cover is the tube chart. The tube chart absolutely looks like it's original to the cab. The chart itself has "Fender Musical Instruments." As far as I understand, this would've been on cabinets starting in the CBS-era in 1965 and later. The chassis and parts seem to be an amalgamation of '65 serial numbers (pots, choke) and '66 serial numbers / stamps (chassis, filter board). Either way, there is something funky going on for sure! Not sure when the declivity on the bottom was phased out but I'd be interested to know.

Also thanks to everyone for their inputs on parts. After all that, I decided to stick with F&T. I couldn't really find Kemets in values close enough and I really didn't want to modify the amp to fit the Solen's.

For main board and bias board ecaps, I'm going with Sprague. I'm going with new production carbon comps where needed and metal oxides on the screens.

I'll get some pictures up as soon as I get this baby back up and running.

[SoulFetish]

Yo, just to give you a heads up; years ago I scored a bunch of 10µF, 20µF, and 30µF high voltage film caps in ratings of both 500V and 700V. These were the Vishay MKP1848S series (designed with a low profile for tight spaces). I make scale vector images of all the components I use for layout purposes. So, if you allow for the 20% tolerance in your reservoir capacitors, here's the dimensions for a combination of 30µF/20µF/20µF/20µF rated at 700V each. I don't know what your exact available space is under the doghouse, but these might fit:

VishayMKP1848S_Showman_Filter_Dimensions.jpg

I'm pretty sure I still have a bunch of these, so I'd be willing to sell you a cap kit if you were interested. Not trying to solicit, just an offer (feel free to PM me).

[PicknStrum]

Yo, just to give you a heads up; years ago I scored a bunch of 10µF, 20µF, and 30µF high voltage film caps in ratings of both 500V and 700V. These were the Vishay MKP1848S series (designed with a low profile for tight spaces). I make scale vector images of all the components I use for layout purposes. So, if you allow for the 20% tolerance in your reservoir capacitors, here's the dimensions for a combination of 30µF/20µF/20µF/20µF rated at 700V each. I don't know what your exact available space is under the doghouse, but these might fit:

VishayMKP1848S_Showman_Filter_Dimensions.jpg

I'm pretty sure I still have a bunch of these, so I'd be willing to sell you a cap kit if you were interested. Not trying to solicit, just an offer (feel free to PM me).

Hey, thanks for the heads-up - those definitely appear like they would fit. I think I'm going to stick with F&T to try and at least keep it looking original with the axial caps on the original board. Thanks again!

[SoulFetish]

Yo, just to give you a heads up; years ago I scored a bunch of 10µF, 20µF, and 30µF high voltage film caps in ratings of both 500V and 700V. These were the Vishay MKP1848S series (designed with a low profile for tight spaces). I make scale vector images of all the components I use for layout purposes. So, if you allow for the 20% tolerance in your reservoir capacitors, here's the dimensions for a combination of 30µF/20µF/20µF/20µF rated at 700V each. I don't know what your exact available space is under the doghouse, but these might fit:

VishayMKP1848S_Showman_Filter_Dimensions.jpg

I'm pretty sure I still have a bunch of these, so I'd be willing to sell you a cap kit if you were interested. Not trying to solicit, just an offer (feel free to PM me).

Hey, thanks for the heads-up - those definitely appear like they would fit. I think I'm going to stick with F&T to try and at least keep it looking original with the axial caps on the original board. Thanks again!

No worries. Good luck with the restore

[PicknStrum]

Got some updates for you guys! I ended up getting some new parts in - I replaced on electrolytics in the entire amp. I replaced power tube grid stoppers and screen resistors. I also replaced a few of the resistors on the main board and the normal channel grid leak. See below photos.

Upon going through tests with my light bulb limiter and variac, everything seemed pretty good until I got to the V3 tremolo tube. With preamp tubes in but no power tubes, these are the readings I'm getting:

V3
Pin 1 - 405 V
Pin 3 - 0.2 mV
Pin 6 - 357 V
Pin 8 - 0.8 V

In looking at the schematic / layout: https://www.thetubestore.com/lib/thetub ... ematic.pdf

Pin 1 is way too high
Pin 3 and Pin 8 are way too low

I did test this with 2 different 12ax7s that are known to be good - same results. I checked all of the resistors and capacitors around that area and I'm not seeing anything out of whack. Wondering if it's possibly the socket itself... any thoughts?

Power Tubes

I decided to continue the startup procedure. I could tell the limiter dimmed a little bit after initial startup with power tubes but not enough that I was confident. With the limiter in, I got 323 VDC coming out of the rectifier and going to the power tube grids.

I decided to test without the limiter and the fuse survived! I measured about 415 VDC at the rectifier and power tube grid pins. It's still a bit low but very close to the Fender voltages. Part of that may be because I haven't biased it yet. The other thing is I wonder if that V3 is putting more of a load on it with the higher voltages I'm getting.

The output does not seem loud enough for 85 watts, however. I can turn that baby up to 7 fairly comfortably. For reference, it's way quieter than my Princeton and my 5e3, so something isn't right. The other thing is I'm getting a bit of static when I switch the standby to "play."

Summary
1. V3 voltages not right - any thoughts? I've checked the components in that area and they seem to be good

2. Power tube voltages are a tad low

3. The output volume is definitely low

4. Static with the standby switch (I'm least concerned with that at this point.

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