clintrubber wrote: ↑30 Mar 2018, 14:43
Hi,
Curious if you managed to find that non-standard dual pot for the saturation-position?
Have a 'non-Plus' Backstage upcoming which uses the same pot, and it seems to be scratchy...
Thanks
Actually no, I really tried my hardest to find a replacement 10k/1k dual-gang pot but unfortunately I couldn't find one anywhere, so I ended up replacing the stock one with a single-gang 10k pot, as far as I can remember I only needed to make a very minor mod to the circuit to make the single-gang 10k pot work virtually the same as the original 10k/1k dual-gang pot, I need to refresh my memory by examining exactly what I did to make a 10k single-gang pot work in the circuit.
It seems to me like Peavey were very notorious for using non-standard dual-gang pots in these old 80's (I'm assuming that's when my Backstage Plus amp was made) guitar amps, whether it was on purpose or not, I don't really know for sure, but it sure makes servicing these things a bit harder than necessary, especially when Peavey no longer manufacture them.
Update:
I just figured-out how I did the very minor mod to my Backstage Plus amp so that a standard 10k 24mm single-gang pot will work perfectly well as a replacement pot for the original 10k/1k dual-gang pot, so here's a short write-up of how to do the mod:
Components/Parts needed:
X1 10k Lin 24mm Pot (I used a 10kB 24mm pot I bought from my local Jaycar Electronics store, seems to work perfectly well).
X1 1k/1% Metal Film 1/2W resistor (This replaces the missing 1k half of the original pot).
X7 Replacement knobs with grub-screws to fit all the pots.
X1 Small roll of tinned copper wire.
Here's what you do.....
Step 1....Remove the amp's circuit board from the chassis, after first making sure that there's no power going to the amp.
Step 2...Desolder the original 10k/1k dual-gang pot.
Step 3....On the copper-foil side of the circuit-board locate the solder-pads where the 1k half of the original 10k/1k dual-gang pot was soldered to the circuit board, and solder the 1k/1% metal-film resistor in place so that one end of the resistor is soldered to the pad that connects to C7 (22uF/25V), and the other end is soldered to the pad that connects to the two clipper diodes (CR5 and CR6), make sure you link the centre pad to this pad as well by using some of the 1k/1% resistor's lead as a wire-link.
Step 4...Cut the 10kB single-gang pot's shaft to length so that you can fit the new knob to it.
Step 5...Cut three 50mm pieces of tinned copper wire and solder each of these to their respective terminals on the new replacement 10kB pot, making sure you don't overheat the terminals or the pot.
Step 6...Solder the new 10kB pot in place on the circuit board, making sure that you allow enough tinned-copper wire length for the new pot to sit flush against the chassis where it pokes through the mounting hole.
Step 7....And finally re-install the circuit board back in the chassis before installing the new knobs on all the pots, once the amp is put back-together again give the amp a test-out, you should notice that the Saturation control should work virtually identically as it used to with the original pot.
Here's a tip, Peavey seem to really like using the JRC4558D dual Op Amp IC in these amps, the JRC4558D tends to be a bit noisy and hissy, fortunately there's a good low-noise, pin-for-pin compatible replacement for these, the TLO72CP, I replaced all the JRC4558D ICs in my Peavey Backstage Plus amp with TLO72CP ICs, but I soldered-in IC sockets to make them easily replaceable if I ever need to, works a treat to make the amp nice and quiet, so quiet that when I first turned it on I thought I had damaged something on the circuit-board, but when I plugged-in my guitar, turned up the volume, plucked a string, i was pleasantly surprised.
Hope that helps.......
I'm attaching a PDF of the Peavey Backstage Plus just in case anyone else needs to do service work on one of these, it includes the circuit board layout too, also attaching a pic of my Peavey Backstage Plus.
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.