Make: Bell P/A - Model: Carillon '35'

PRNDL said:

You're on the right track.

Here's a site that has build info on the Fender amps you are thinking about.
http://www.kilback.net/homebrewtweaks/amps/amps.htm

It might be wise to figure out what the power transformer wiring is like before removing it, since there's a lot of wires.

The chassis looks fine and has plenty of room to put in a circuit board. Use a Brillo pad to clean it; then coat it with clear. Leave the transformer heater wiring to the tubes in place, since they don't change.

Another choice would be whether to replace the old capacitor cans or use electrolytics on the circuit board.

I'm currently rewiring an old organ amp into something similar to a Matchless Spitfire.

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Posted by: tablebeast


I have yet to relace a Bell PA but you can pretty much turn any PA amp into a guitar amp. Here is what I would do with that Bell:

1. Forget about that 12AV6. You're going to focus on the 2x 6L6's and 3x 12AX7's

2. Find a guitar amp schematic for an amp that you like that shares the same tube layout. I'd say 60's Blackface Fender or Marshall Plexi would be a good start.

3. Figure out from the stock Bell circuit where each of the wires from the transformers are going and what they are doing. You're only going to reuse the chassis, sockets and transfomers here for sure, though you may be able to recycle some of the wiring and passive parts as well. You will NOT be reusing the Electrolytic Caps or Pots. Even if they work fine now you're setting yourself up for early failure by using old parts there, though reusing the carbon comp resistors and non-lytic caps would be a good idea if possible.

4. Gut the whole thing and rewire it according to your new Fender/Marshall circuit. You can leave stuff that will be the same or similar alone if you want. If it has a circuit board lose that **** and go point to point.

5. For the input you can go 2 channel parallel like the old amps or instead use the first two stages in series (and maybe a footswitch to take the extra stage in and out of the path) ahead of the stack like new amps.

6. You have just enough pot locations already for the classic guitar amp layout of: Gain 1, Gain 2, Hi, Mid, Lo EQ, Master Vol, and Presence Controls. Of course you're also going to have to put 1/4" jacks on the back to replace the screw on mic connectors for the input as well as the weird sockets for the output. Use switching type 1/4" jacks so that when there is a not a cable plugged in it shorts to ground. The input jacks should fit right in the holes that are already there and for the output you should drill out the mounts for the speaker sockets and remove the octal bases. Replace these holes with octal block off plates and drill out a hole for the 1/4" in the center of the plate.

7. Depending on the output taps for the transformer you may have a bunch of taps you don't need. For guitar you're never going to need more than 4, 8, and 16 ohm taps. Most people can get away with only two of these three so decide on how you want the output jacks to work. On amps like this that I relace I like to have one or two output jacks setup in parallel with the hot leg of the jack hooked up to a wire with a open spade end that you run out of the case to the screw on the tag strip. This allows you to select the load with the wire, very simple. A lot of PA amps used this kind of stup already. Any output taps that you don't use should have the wire ends covered with shrink tubing and bundled up, you don't want the end to short out on the case so make sure its sealed up well with the tubing.

8. Replace the ungrounded AC cord with a grounded three prong one and connect the ground wire to a power transformer mounting bolt. If you're output transformer is center tapped (most likely it is) put a switch between the center tap and ground, this will be your standby switch.

9. Its likely that this amp uses a cathode biased setup with little or no negative feedback. Keep this and don't go for any exotic biasing if it doesn't already have a negative bias supply tap on the power transformer.

10. Rock out! These PA heads make great guitar amps and are each unique in their own ways. Because they are using different iron than the circuits you're cloning (or tweaking) of course they will have their own sound. Good luck!

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