*This has already been posted in another section, I've copied it here as well on the advice of a fellow member. Mods, please delete if you feel the other section is more appropriate
I have a valve PA amplifier which has been my possession for many years. It was my late grandfathers. I've never seen it working. It's complete but would obviously need a fairly comprehensive overhaul before it could be used. The valve line up is EL34, EL34, ECC81, 6BR7, 6BR7, ECC82. There are 2 EZ81 rectifiers also.
It's an strange old thing which has the option of running from a 12v battery. It has a wierd mains/battery socket on the front. I think it looks pretty cool and would love to use it as a guitar amp and build a little cab for it to sit on top of, finishing both the amp and speaker cab in a matching quilted leatherette similar to the beaten up stuff that's already on the amp casing.
Whatever happens, it stays as it looks now. It won't be cannibalised for parts!
The issue is that I can't find a schematic for it. I've looked many times over the years and come up with nothing.
Searching on Google just brings up old posts on vintage-radio, (one of which was made by myself), another gives some interesting background info on the company who made it. However there's no schematics posted anywhere.
If I had a diagram to follow I'd be able to make better sense of the circuit but as a relative beginner, it's beyond my capabilities to trace out the entire circuit.
So, I'm thinking of just starting from scratch and finding a suitable guitar amp schematic which uses the EL34's and rewire it that way.
I've no use for the 12v circuitry etc...
I'm thinking a good starting point would be to make sure the transformers work, these being the most expensive things to replace.
If anyone can suggest a guitar amp that could be make use of as many of the existing components as possible, let me know.
Any ideas on how to precede will also be welcomed!
Chances are the EL34s are in push-pull for the power stage. IIRC, Marshall uses/used those for their amps. Schematics appear to be available.
Have a look at the datasheet for the smaller valves to figure out what they are and might be used for. Probably just dual triodes used for gain for the mics and tone controls. One of them will likely be a phase splitter for the push-pull output stage.
The usual caveats apply for working on old valve gear: the PSU caps are almost certainly knackered, so replace those. I wouldn't expect the chassis to be at high voltage with this unit, but old radios did have that "feature" and it's certainly one to be aware of.
I'd also remove the octal socket labelled "supply" and replace with an IEC connector, or maybe PowerCon if you want something round. Mains should never be on pins which can be touched.
Chris
Have a look at the datasheet for the smaller valves to figure out what they are and might be used for. Probably just dual triodes used for gain for the mics and tone controls. One of them will likely be a phase splitter for the push-pull output stage.
The usual caveats apply for working on old valve gear: the PSU caps are almost certainly knackered, so replace those. I wouldn't expect the chassis to be at high voltage with this unit, but old radios did have that "feature" and it's certainly one to be aware of.
I'd also remove the octal socket labelled "supply" and replace with an IEC connector, or maybe PowerCon if you want something round. Mains should never be on pins which can be touched.
Chris
