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EDISON ONE/ EDISON 24 TUBE AMPS

Subchannel

Subchannel

Active Member
Hello!
I just bougth an Edison One preamp and two Edison 24 mono amps for $100.Still waiting to receive them, but from the pics it looks like they have been tampered with by a child. But it would be nice to have them playing again. I emailed Erik Andersson about schematics but the answer was NO!
Anyone here experienced with these and/ or have schematics?
Thanks in advance.
 

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they don't look terribly complicated so it should be possible to reverse engineer one.

The power amps look like they were once stereo amps, but now converted to mono use? Guessing that based on the layout and the extra holes that seem to match the output transformer and speaker jacks. There are a couple of ways to make that happen, and I'm sort of curious what they did here. In stock form, my guess is these are basically a Mullard style front end. One triode as a voltage amp, a pair for a long-tail pair inverter, then the output tubes. These look like 6BQ5 / EL84 types. One plate of each tube to the transformer, no funny business.

It looks to me that the two plates on each side are jumped together to form a parallel set of outputs. That has to mean the front end was re-worked. If you just jumped a pair of plates together on a push-pull set, the signals would cancel and you'd get a fat lot of nothing for output. The grids would also have to be paralleled to get the same signal. Just looking at the component layout here, what I think they must have done is pulled one coupling cap from each inverter, so each side has a working LTP, but only one output on each is used. There must be a jumper underneath tying the grids together on each side so this functions. IMO this is an inefficient way of doing it, but its probably the least invasive way of doing it with a circuit board.

The trick here is that parallel output tubes want half the transformer load. Typical EL84/6bq5 load is about 8k plate to plate. Parallel wants about 4k. If these output transformers have a 16 and an 8 ohm tap, no problem. Connect an 8 ohm load to the 16 ohm tap, you get 4k of load at the plates. If its just an 8 ohm tap though, you're still working into an 8k load so those parallel outputs are honestly not going to do much for you. Maybe it will deliver marginally more power but probably not enough to justify the work to get it.

Not sure whats up with the rat nest in the preamp. Volume control is missing and wires are hanging. Have to trace that out to figure out where its even supposed to go.
 
No, these where mono from producer, but the same enclosure was used for the 18 stereo version and the integrated amp as well. So original mono amps.
Output is four EL84 PP, input tubes on amp is ECC88 I read somehwere.
One power amp seems untampered with (at least not as extensive as the other). After cleaning and checking/ measuring, I can try it on the variac.
The preamp don´t look too good, but it´s based on a passiv output, it´s only the phono pre that´s the activ element (just a guess).
 
No, these are original switches for source and tape, there are no resistors there. The volume pot is removed, but it looks like the design from Audio Innovation Series 300, that also has a volume pot right after the source switch (Erik andersson designed that as well).
 
thats fairly typical, input to the switch, output of the switch to both tape out and tape monitor switch, output of the tape monitor switch to the volume control, output of the volume to the electronics. Shouldn't be terribly difficult to figure out what goes where. Curious if it actually has any active gain in here for anything but the phono preamp. 3 twin triodes would be just right for an RIAA stage with a cathode follower for each side. Output that to the selector, the rest of it could just be straight through the selector to volume to output jacks.


so factory mono. Still suspect I'm not far off about how they made that work. That board looks very much like it started life as a stereo amplifier
 
You´re probably right Gadget73, it looks like two mirrored channels.
I know this is a 24W amp, hence the name. The 18 stereo version I guess is around 18w? From my experience two EL84 in PP is usually around 14-15W? Then again, I´m not a tube expert by far.
 
Edison 12 I now see would be the stereo version. Thanks for the tip on the other thread Zack, there is at least schematics for the pre there, and maybe it´s possible to use the Edison 12 schematics for the Edison 24 in some way?

And fron the Edison One schematics, it looks like there´s an active preamp, one tube after input/ phono pre.
 
Nice. Those look like a straightforward project, and I bet they're going to sound amazing once they're fixed up. I don't think I've met an EL84 amp which sounds bad!
 
Me neither. I have a set og Eico HF30 which I use every day, and an Eico HF-14 for restoration. I emailed Heyboer who made the original transformers and asked if they could make new ones for 240V (EU), and they made me two. That´s nice. Same design, same everything, 60 years later!
I have way tooo many tube projects now, but hope to learn, with some books I bought, more about the construction of tube amp´s. One have to love the sound.
 
I think what would really make those look like new, is to remove the boards and clean them in an ultrasonic cleaner, and then dry them really well. I've been doing that lately with great results. The transformers you can clean up with a wire brush just get the rust off and a wet rag to get them clean. The chassis would be best washed with dish soap and a rag, and then dried. It will look great when you're done, there's tons of potential here. The EDISON logo is tacky and speaks of low volume production, but it is what it is, and I've definitely seen worse. The missing knob (or something close) probably can be procured from Mouser or RS if you're in Europe. New electrolytic capacitors would probably be a good idea. Obviously the sockets should be cleaned too. The usual stuff. You won't go too far wrong with a 100k Alps volume control - just don't buy it on eBay or you may get a fake.
 
That is my intention yes! The cap´s I will replace with something better.
I have bad experience buying components from ebay as well. I only buy from safe sources, Mouser mostly. And hificollective for the more exotic parts.
Now it´s summer vacation a couple of weeks, but will post more when they arrive and I have had the chance to look at them.
Thanks so far!
 
Was that an ebay find ? for 100 bucks I'd have bought that stack too. Its certainly got at least that much value in parts. I've occasionally come across interesting deals on there, usually on somewhat messed-with equipment that most people don't want anything to do with.
 
I bought it on the Norwegian Finn.no (Finn= find). As you say Gadget73, most people steer away from items in this shape.

Not a very polite answer from Erik Andersson, but he is retired now, and my guess is he gets a lot of emails regarding old tube amps.

He started Edison, then was designing for Audio Innovation, then Edison again and then Audion.

By the way: how do one pic up or get notified on new threads? I’m quite new here, but would like to help out wherever possible.
 
The guy that designed my preamp passed on I think, or he fell off the face of the earth which is functionally the same thing. No support, can't even get a schematic for it. The one that exists isn't for my specific version, and its barely readable. Its not exactly an enticement to buy one. I've been meaning to re-draw the one that exists, then modify it to match my preamp but its a case of mine isn't currently broken and nobody else seems to need one either. I brought this one home as a repair job for someone, liked it, and bought it from the guy I was fixing it for. I realize most people wouldn't want to work on such a thing, which makes owning it awful difficult for someone who isn't willing or able to fix things for themselves. I'm difficult to live with, and so are a lot of the things I own so I guess it works out.

Subchannel said:
By the way: how do one pic up or get notified on new threads? I’m quite new here, but would like to help out wherever possible.
Click to expand...

click "watch thread", at the top on the right side just above the first post.
 
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