1966 BF Showman - Recommended Replacement Parts

[pdf64]

It’s an awfully bad idea to test and play an amp that hasn’t had its idle anode or cathode current checked.
The HT voltage may be getting pulled down by a massive current draw from the power valves.

The trem oscillator voltages require the footswitch plugging in an closing, otherwise both triode sections are in cut off.

[sluckey]

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

Nothing wrong here...

V3 voltages are exactly what they should be when you don't have a footswitch plugged in. If you had checked voltages on pins 2 and 7 you would see they are big negative voltages. So, the tubes are cut off and not conducting, which means plate voltages will be high and cathode voltages will be zero.

The voltages on the schematic were taken with the footswitch plugged in and contacts closed (or a jumper on the FS jack). This removes the negative voltage from the grids, allowing the triodes to operate normally, and results in the voltages you see on the schematic.

[PicknStrum]

It’s an awfully bad idea to test and play an amp that hasn’t had its idle anode or cathode current checked.
The HT voltage may be getting pulled down by a massive current draw from the power valves.

The trem oscillator voltages require the footswitch plugging in an closing, otherwise both triode sections are in cut off.

Valid point...I let my excitement get in the way

Cool I'll check voltages again after I bias and engage the tremolo.

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

Nothing wrong here...

V3 voltages are exactly what they should be when you don't have a footswitch plugged in. If you had checked voltages on pins 2 and 7 you would see they are big negative voltages. So, the tubes are cut off and not conducting, which means plate voltages will be high and cathode voltages will be zero.

The voltages on the schematic were taken with the footswitch plugged in and contacts closed (or a jumper on the FS jack). This removes the negative voltage from the grids, allowing the triodes to operate normally, and results in the voltages you see on the schematic.

Thanks for that awesome explanation Sluckey! I'll check again after biasing and getting a footswitch plugged in.


Any thoughts on the lower output? Maybe after I bias it will be in better shape. I won't play it again until after biasing.

[pdf64]

Regarding the control settings (ie ‘not much output on 7’), unless the exact Fender spec tapers are used, they can’t be referenced to typical Fender settings. Regular audio tapers will be rather different, in regard of the vol and treble controls at least.

[sluckey]

My Twin Reverb (same as Showman but with reverb added) will make your ears bleed on 7!

[PicknStrum]

Thanks again for your guys' help!

So after messing with the bias for a while, I decided to look at the power tubes and one of them was not heating up at all - prior to that I couldn't get the amp biased very evenly (makes sense in retrospect). Now I've got it biased at 40mA and 47mA - I'm toying with the idea of throwing in 1 ohm resistors to bias as opposed to the center tap resistance method (which is what I've been using up until now on this amp). The volume seems a lot better and the amp is less thin with 4 working power tubes.

I did get a pedal plugged into the tremolo and it's working great. The voltages seem to make much more sense now.

I'm really down to 2 minor issues:

1. There is a ticking with the tremolo - it speeds up and intensifies with the tremolo controls. The only thing that took the ticking away is when I put my meter probe on pin 6 of the tremolo socket.

2. I have quite a bit of static sound when taking the amp off of standby. There is a large static noise that lasts for about 5 seconds or so...

Hoping to iron those out but at this point I'm very happy with everything!

[sluckey]

The attached service bulletin "may" solve the vib tick... Sometimes a conductive fiber board is the culprit. See one fix in pic...

[PicknStrum]

The attached service bulletin "may" solve the vib tick... Sometimes a conductive fiber board is the culprit. See one fix in pic...

Thanks for posting that! I went ahead and followed the service bulletin. The tick is about 80% gone I would say. Good enough for me to leave it alone. I can only really hear it at 5 or higher which is more than I use anyway.

Also, the static seems to have disappeared. Not sure why - possibly because I've been working my standby switch a lot...I also messed with re-seating the tubes. I'm still getting that "electrical surge" sound upon startup but I think it's just the caps charging. It lasts about a second. I'm calling it done! Thanks again for all of the help

I'm a happy camper! Here is a photo of the amp back in it's cleaned-up cabinet:

IMG_5058.JPG

[sluckey]

Very handsome amp. First time (maybe the only time) I ever saw one was about '66. Walked into a teen club with my date, trying to look cool. The out of town band was playing We Gotta Get Out Of This Place by the Animals. They had two blonde Showman stacks and a blond Bassman stack! I may have drooled a little.

[PicknStrum]

Very handsome amp. First time (maybe the only time) I ever saw one was about '66. Walked into a teen club with my date, trying to look cool. The out of town band was playing We Gotta Get Out Of This Place by the Animals. They had two blonde Showman stacks and a blond Bassman stack! I may have drooled a little.

Haha, I love it! Definitely check out the gear before anything else. Your date can wait!

[SoulFetish]

The attached service bulletin "may" solve the vib tick... Sometimes a conductive fiber board is the culprit. See one fix in pic...

Thanks for posting that! I went ahead and followed the service bulletin. The tick is about 80% gone I would say. Good enough for me to leave it alone. I can only really hear it at 5 or higher which is more than I use anyway.

Also, the static seems to have disappeared. Not sure why - possibly because I've been working my standby switch a lot...I also messed with re-seating the tubes. I'm still getting that "electrical surge" sound upon startup but I think it's just the caps charging. It lasts about a second. I'm calling it done! Thanks again for all of the help

I'm a happy camper! Here is a photo of the amp back in it's cleaned-up cabinet:

IMG_5058.JPG

If you're still getting some "ticking" after performing the modification, try swapping out the oscillator tube with another make. It's weird, but I've had a problem with some JJ 12AX7's exacerbating the problem in this position. In fact I was just working on a Deluxe Reverb this morning that had this problem, and swapping the new JJ out for one the customers old pre's in a different position solved the problem. The new JJ was otherwise quiet and preformed fine in another position within the amp.

[PicknStrum]

The attached service bulletin "may" solve the vib tick... Sometimes a conductive fiber board is the culprit. See one fix in pic...

Thanks for posting that! I went ahead and followed the service bulletin. The tick is about 80% gone I would say. Good enough for me to leave it alone. I can only really hear it at 5 or higher which is more than I use anyway.

Also, the static seems to have disappeared. Not sure why - possibly because I've been working my standby switch a lot...I also messed with re-seating the tubes. I'm still getting that "electrical surge" sound upon startup but I think it's just the caps charging. It lasts about a second. I'm calling it done! Thanks again for all of the help

I'm a happy camper! Here is a photo of the amp back in it's cleaned-up cabinet:

IMG_5058.JPG

If you're still getting some "ticking" after performing the modification, try swapping out the oscillator tube with another make. It's weird, but I've had a problem with some JJ 12AX7's exacerbating the problem in this position. In fact I was just working on a Deluxe Reverb this morning that had this problem, and swapping the new JJ out for one the customers old pre's in a different position solved the problem. The new JJ was otherwise quiet and preformed fine in another position within the amp.

That's a fantastic suggestion! Wish I would've thought of that myself. I basically used the NOS preamp tubes that the amp came with. One of them didn't light up so I switched it but none of the tubes in there are new and I haven't done any tube rolling. I'll be giving this a shot.