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/schematics/leslie/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?
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/schematics/leslie/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?
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.
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.
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.
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 ......
Here is one a built a few months ago and sounds pretty good .....
Very high gain ......
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.
Then with the proceeds you can buy parts more in line with a guitar amp.
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.
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.
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
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
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. 🙂
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.
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.
If you're offering up parts to help me build, then i'll happily accept.
To your point about the bugatti... i realize leslie stuff goes for some money, but i assure you... this was out of a Leslie 225 ( i would have left it alone if it was the 125, but it was it's ugly stepsister ), possibly the LEAST desireable leslie speaker cabinet ever...because 1) it was ugly 2) it was huge 3) it only had a single 12" rotor, and no treble rotor 4) it was only 20 watts. I took the speaker itself and chopped the cabinet into a smaller, portable box, and will run it off a guitar head ( which, as you can see, i'm in no short supply of ). The amp itself had no place in the project, and i wanted to build something else out of it...20 watts just won't cut it in live environments.
That sounds exactly like what i'm talking about. I've been looking at this amp, and it does seem to have a pretty tiny power and output tranny. How does one know what their iron is rated for? I've been googling around for the numbers stamped on these, and they aren't turning up anything.
Alright...i think i've got my project. Weber has a project called the "Smoking Joe 2" that is a PP EL84 based amp. Only 4 tubes...solid state rectified... and sub 20-watt, which the OT can handle.
Does anyone have any objections as to why this wouldn't work for my purposes?
https://taweber.powweb.com/store/smokeII_schem.jpg
Does anyone have any objections as to why this wouldn't work for my purposes?
https://taweber.powweb.com/store/smokeII_schem.jpg
Why bother when you've already got 90% of an amp? - you just need a simple preamp for it - you could use the V1a/b part of that circuit for the purpose, you just need one extra double-triode.
IT does seem like i've got most of an amp here, so i do hate swapping stuff out, but at the same time, i've never rolled my own...so just modifying schematics isn't really in my realm of expertise.
But, i've gone ahead and tried it. Can you comment on this? Tell me if it looks funky and i'll make changes. I was confused at the resistors grounding out the pin 3/8 on the PI...i don't know if all that is needed.
Thanks for your help.
Attachments
Sorry, just does not work that way.You can not just take the one input to the Long Tail Pair inverter and hook it up to the voltage divider of the Paraphase phase inverter. The LTP is expecting to see an AC ground and the input to that tube comes from the voltage developed across the shared cathode resistor with the other triode. You either use the PI circuit as shown in the Smokin Joe or you use the Paraphase inverter you have.
So you can see why i'm ripping it up to follow a documented schematic / layout rather than just cobbling together my own. I have no idea what i'm doing. I can follow directions, and that's about it.
A year ago I did not know much about tube circuits but I read a lot and did some experimenting on my own. Even so I have no problem using a well worn design.
May I suggest using the Weber schematic up to the volume control and graft it onto where your current volume control is. I would also suggest a 75k resistor in between the volume control wiper and the input to the 12AU7. This would smooth out the distortion a bit when you overdrive the amp. Also the 12AU7 is not a very high gain tube, later on you might be inclined to swapping it out for another tube in the 12A*7 family.
OK. Firstly, thanks for the advice. I think i've gone ahead and made the changes per your suggestions. Please see the attached schematic.
I added in that Tone pot, so i hope that was cool. Also, i added in a standby switch that was not on the original schematic. Is it in the correct place? also, 12AU7 is now a 12AX7...that shouldn't change any needed voltages, right? My one concern is the plate voltage shown on the (formerly) 12AU7 is only 155V - isn't that pretty low?
Thanks for the help.
I added in that Tone pot, so i hope that was cool. Also, i added in a standby switch that was not on the original schematic. Is it in the correct place? also, 12AU7 is now a 12AX7...that shouldn't change any needed voltages, right? My one concern is the plate voltage shown on the (formerly) 12AU7 is only 155V - isn't that pretty low?
Thanks for the help.
