Rewiring a Leslie 125 amp into what?

[Magnetmaz]

Hey, guys. I haven't posted to this site in 10 years or so! Good to be back!

So, i'm looking for advice, both opinion and technical...

I have a Leslie 125 amplifier that's not in use. I'd like to make my first guitar amp project out of it. ( i've rebuilt / repaired a dozen amps at this point, so i'm not a total newb ). I'm bouncing around between what it would turn readily into, that's worth building. I'm thinking something like a Fender Tweed Deluxe or Bassman.

Here's the schematic of the amp http://www.hammondb3organ.net/schema...ie/125/125.gif

It's supposedly 20 watts, but what i don't get is why it's only 20 watts, when it seems like it could do more based on the components. Don't 2x 6L6GC amps put out 45-60 watts, depending on how they are wired? I've read that this amp makes a nice tweed deluxe, but the Tweed Deluxe uses 2x 6V6, and this amp seems capable of more... but i don't want to burn out the transformers by turning it into a tweed bassman when it's not capable of it.

Also, the leslie is solid state rectified, and the old tweeds were all tube rectified ( and i see no 5v taps on the trafo, so i guess i'll be sticking with SS).

Any opinions?

[Nigel Goodwin]

It's just a power amp, all you need to do is build a guitar preamp to feed it.

It's less power because it's higher quality, guitar amps sacrifice quality for power, because you don't want quality in a valve guitar amp.

If the transformers are big enough, reducing the value of R11 and replacing R12 with a suitable choke, should increase it's power capabilities.

[Magnetmaz]

Good stuff, Nigel. Is there a guitar amp circuit you prefer that i could work off of? I'm not at a "roll my own" level at this point.

[Minion]

Well , there are Lots of Guitar Tube preamps out there and most of them are fairly simular ......

Here is one a built a few months ago and sounds pretty good .....



Very high gain ......

[simon7000]

I'd eBay it as folks are always looking for Leslie repair parts. There are even folks building new replacements!

Then with the proceeds you can buy parts more in line with a guitar amp.

[Nigel Goodwin]

Originally Posted by Minion

Well , there are Lots of Guitar Tube preamps out there and most of them are fairly simular ......

Here is one a built a few months ago and sounds pretty good .....



Very high gain ......

Yes, I'd suggest you could easily leave out one of the stages.

[Magnetmaz]

Originally Posted by simon7000

I'd eBay it as folks are always looking for Leslie repair parts. There are even folks building new replacements!

Then with the proceeds you can buy parts more in line with a guitar amp.

But...i WANT to turn it into a guitar amp! That's the whole challenge...whether or not i can build an amp ( 20w or otherwise ) with the parts.

I've got a lot of amps anyways... '68 Fender Super Reverb, '68 Vibro Champ, '67 Silvertone 1484, '65 Danelectro DM25, '73 Ampeg VT40, '78 Ampeg B15N, '71 Plush 1060C (bassman 100).....

I'm not doing this because i need a guitar amp so much as i want to do it because it's a fun project.

[Minion]

The Leslie looks like it uses half of a 12au7 as a Phaze splitter but the other half is un-used , You could wire up the other half of the 12au7 as a gain stage , it wouldn"t have a whole lot of gain but if you changed the 12au7 to a 12ax7 you would get a bit more gain out of it .....

You could also just leave the 12au7 as it is and wire in a seperate 12ax7 and get a lot more gain and add a tone stack between the 2 12ax7 stages , the only problem I could forsee is maybe not having enough Heater current for the 12ax7 .....


Cheers

[simon7000]

Originally Posted by Magnetmaz

But...i WANT to turn it into a guitar amp! That's the whole challenge...whether or not i can build an amp ( 20w or otherwise ) with the parts.

I've got a lot of amps anyways... '68 Fender Super Reverb, '68 Vibro Champ, '67 Silvertone 1484, '65 Danelectro DM25, '73 Ampeg VT40, '78 Ampeg B15N, '71 Plush 1060C (bassman 100).....

I'm not doing this because i need a guitar amp so much as i want to do it because it's a fun project.

Then I will be glad to trade you for even more fun parts. A couple of brand new chassis punched for tube amplifier chassis, undersized amplifier output transformers, and even a power transformer or two. Then you really can build something creative.

Of course there are those that would turn a restored 1937 Bugatti 57 into a planter! They would then have the only one.

[Printer2]

You don't have a 57 Bassman, shame on you. Not that I am suggesting anything.


I would add two 9 pin sockets and redo the phase inverter as a LTP. Leave the cathode bias for now and convert it after you get the rest up and running.

http://ampwares.com/schematics/bassman_5f6a.pdf

The low wattage using 6L6's is probably due to the selection of the output and maybe even the power transformers. I have a Bogan amp with 6L6's that is also rated at 20W. The power transformer is big enough for a higher power amp but the OP transformer is the limiting factor.