Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: NSFY on June 23, 2010, 08:56:05 am
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I was ready to try some typical mods for the AB763 super reverb. I wanted to disconnect the tremolo but didn't remember until I had pulled out the chassis that this is PCB which makes it difficult to figure out where on the physical layout to try to do this in a reversible (ideally) way.
Was wondering if anyone had any experience working on the PCB version and any suggestions for the best/easiest way to take out the tremolo. There's lots of ribbon cables and terminal headers. Looks like between P23A-2 and P23B-2 is the place to make break but not sure where or how on the physical layout that might best be accomplished. Thanks in advance for any assistance. btw installing a turreted AB763 board is not an option.
http://support.fender.com/schematics/guitar_amplifiers/65_Super_Reverb_Schematic.pdf (http://support.fender.com/schematics/guitar_amplifiers/65_Super_Reverb_Schematic.pdf)
NSFY
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You want to remove the intensity pot from the circuit. It looks like the speed/intensity knobs are on their own board, so it should be easy to just pull that board and use a soldering iron iron to burn through the trace (carefully) going to the input lug on the intensity pot.
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Thanks for the suggestion Tommy - I'll take a look at that when I get home. My recollection of the pot configuration was that they were all on a single PCB strip that prevented easy access to the backs of the pots or even identification of the traces but I will take a closer look tonight.
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Burning thru a PC board trace? :undecided:
I think I'd prefer looking for P-23A1 or P23A-2 and cutting either of those wires.
By the way, would you consider $700 for a clean used '65 Super Reissue a good buy price? There's around here for that. Seems like an attractive price......for an end user, which would not be me in this case.
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This pic is for a TRRI but I bet the front panel pcb looks very similar (if not exact) in the vicinity of the Intensity pot. Just use a razor utility knife or exacto knife to make a clean cut across the pcb trace. Dont burn! You can easily repair by scraping some of the green paint off the cut trace, then lap solder a short piece of small wire (a tinned resistor lead is perfect for this) across the cut.
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That's the ticket, right there.
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Thanks Geezer! It looks the same. I'll check it out when I get home.
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I looked at the schematic and PCB board again in better light and decided to make the break at the ribbon connector for the pot PCB. I thought It would be easy to pop the appropriate wires out of the connector and also easy to reverse. :rolleyes:
It was relatively easy to pop out the wires but the way they are connected is by some kind of crimped insulation displacement socket so it doesn't look like the wires will go back in without some kind of repair using solder and jumper wires or a new connector.
I think that I only needed to disconnect P23A-2, but to physically get at it I also took off P23A-1 which is the connection from the photoresistor to the wiper of the intensity pot. It didn't look like disconnecting P23A-1 would hurt anything but if someone could confirm that...
So far I like the increased gain that seems to result from pulling V1, and disconnecting the tremolo. I had also disconnected two of the speakers and put a 12AX7 in the PI so I've lost track of which changes may have had the most effect. Thinking about adding a switch to enable/disable tremolo - I originally wanted to use a switched pot but that was before I saw the PCB.
Thanks for everyone's help!
NSFY