I'm picking up 3 PA amps tomorrow; a Davis 201A (20 watts), a Bogen Challenger CHB-35A (35 watt), and a Precision Electronics 60PA.
I've found schematics online for the former two but can't find them for the latter. Does anyone happen to have them? I can get a service manual off of e-bay for $10, which I'll do if I can't find them otherwise, but was hoping to spare myself the expense.
I've found schematics online for the former two but can't find them for the latter. Does anyone happen to have them? I can get a service manual off of e-bay for $10, which I'll do if I can't find them otherwise, but was hoping to spare myself the expense.
I have looked for PE schematics and they seem to be "unobtanium" for free. I have a couple of PE amps and haven't found any for free. They did make amps for others and re-branded like Burnstein-Aplelebee, Grommes and others. If you can find those, maybe you have a chance. Here's one for $8.49, free shipping. 1959 Precision 60PA Tube Amplifier Amp *service Manual PhotoFact Schematic Fix | eBay
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Oh, I won't buy it until I need it, but I'm just curious about the design. I get the amps at 7:00am tomorrow.
I could draw out the schematic myself, and that may be easy enough to do. We'll see. If it is, I'll do it myself. For my little Ace Tone, it was a nightmare because it was two-sided PCB that wasn't terribly transparent, so it was a real pain to match parts and connectors on one side to traces on the back side. It didn't help that the layout wasn't squared at all. The traces were all curved, like someone hand-drew them out.
But I suspect the PE is point-to-point, so that might be a little easier to sketch out.
I could draw out the schematic myself, and that may be easy enough to do. We'll see. If it is, I'll do it myself. For my little Ace Tone, it was a nightmare because it was two-sided PCB that wasn't terribly transparent, so it was a real pain to match parts and connectors on one side to traces on the back side. It didn't help that the layout wasn't squared at all. The traces were all curved, like someone hand-drew them out.
But I suspect the PE is point-to-point, so that might be a little easier to sketch out.
Yes, that PE is point to point. All of those old PA amps were back then.
That Hammond L100 is nice. Laid out just like an old Fender on a board unless that guy tore into it. It really lends itself nicely to mods/rebuild, no need to gut it. Also, watch your voltages on this one. The L100 organ had two smaller amps up by the keyboard, so it used to power 5 or 6 more 12a_7 tubes, so your B+ will be higher. I found a 5Y3 works well instead of the 5U4 that was in it. Also, if you do use the reverb, that 12BH7 can be substituted with a 12AU7 if you don't have the 12BH7.
That Hammond L100 is nice. Laid out just like an old Fender on a board unless that guy tore into it. It really lends itself nicely to mods/rebuild, no need to gut it. Also, watch your voltages on this one. The L100 organ had two smaller amps up by the keyboard, so it used to power 5 or 6 more 12a_7 tubes, so your B+ will be higher. I found a 5Y3 works well instead of the 5U4 that was in it. Also, if you do use the reverb, that 12BH7 can be substituted with a 12AU7 if you don't have the 12BH7.
It looks like it's an L101 (not much difference). I'm still not 100% sure on what parts I'm getting. I know I'm getting the reverb & power amp sections and the reverb tank. He also said something about the other two "preamps" which I assume are the vibrato and percussion amps.
The L101 actually has all the tubes. It doesn't look like the PAs do. I've got several 12A_7s (several each of T, U, V and X). I just won a lot of 80 tubes on e-bay earlier today. Don't remember if there are any 12BH7s in it, though. Where I'm going to come up short is power tubes for the PAs.
The Precision Electronics, for example, needs 2 EL34s and I don't have any of those (of course. I have EL84s, 6V6s, 6L6s, 5881s, but no EL34s).
The Bogen uses 7868s, which I had never heard of. I suspect I'll just replace it with 6L6s. I've seen plate voltages ranging from 415-490V, depending on the schematic I look at, so I'm not even sure I can put the 5881s in there.
The Bogen and the Davis use 6EU7, which I think I might be getting some in that lot of 80 tubes, but if not, I can just rewire the sockets for 12AX7s.
There's actually a guitar conversion amp from a Bogen CHB-35A (the model I'm getting) on e-bay right now for $230. I'll be curious to see if it sells. I suspect it won't. For one thing, no demo tracks. I'd never buy an amp I didn't hear first.
I'll still need to come up with a few odd tubes. My wife's uncle has boxes and boxes of tubes, so I'll probably hit him up the next time we head down his way. He'll hand me a pail and tell me to go take whatever I want.
Love uncles like that.
I'm surprised you don't think I should gut the Hammond. It's got so much stuff going on and the reverb stuff is all kind of tied into the power amp. I guess I'll have a better idea once I pop it open. If it's clean and easy to follow, then I may leave it together (I had a recommendation from someone else to gut it).
I like Hammond's schematic. They have each section broken down with the gain. Most of them say, GAIN __X @ 130C/S (for example, GAIN 40X @ 130C/S). Is the C/S cycles/sec? So it'd be the gain at 130Hz?
The L101 actually has all the tubes. It doesn't look like the PAs do. I've got several 12A_7s (several each of T, U, V and X). I just won a lot of 80 tubes on e-bay earlier today. Don't remember if there are any 12BH7s in it, though. Where I'm going to come up short is power tubes for the PAs.
The Precision Electronics, for example, needs 2 EL34s and I don't have any of those (of course. I have EL84s, 6V6s, 6L6s, 5881s, but no EL34s).
The Bogen uses 7868s, which I had never heard of. I suspect I'll just replace it with 6L6s. I've seen plate voltages ranging from 415-490V, depending on the schematic I look at, so I'm not even sure I can put the 5881s in there.
The Bogen and the Davis use 6EU7, which I think I might be getting some in that lot of 80 tubes, but if not, I can just rewire the sockets for 12AX7s.
There's actually a guitar conversion amp from a Bogen CHB-35A (the model I'm getting) on e-bay right now for $230. I'll be curious to see if it sells. I suspect it won't. For one thing, no demo tracks. I'd never buy an amp I didn't hear first.
I'll still need to come up with a few odd tubes. My wife's uncle has boxes and boxes of tubes, so I'll probably hit him up the next time we head down his way. He'll hand me a pail and tell me to go take whatever I want.
Love uncles like that.I'm surprised you don't think I should gut the Hammond. It's got so much stuff going on and the reverb stuff is all kind of tied into the power amp. I guess I'll have a better idea once I pop it open. If it's clean and easy to follow, then I may leave it together (I had a recommendation from someone else to gut it).
I like Hammond's schematic. They have each section broken down with the gain. Most of them say, GAIN __X @ 130C/S (for example, GAIN 40X @ 130C/S). Is the C/S cycles/sec? So it'd be the gain at 130Hz?
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Just got off the phone with the guy. I'm meeting him at 6:00am in the morning. This actually was really fortuitous. He lives in NE Oklahoma and I live in NW Arkansas and he and his wife happen to be driving to Missouri tomorrow and they'll be passing right by my office (which is about 20 mins away) so I don't even have to drive out there to pick the stuff up.
He said the Davis and the Hammond both have tubes. So I just need tubes for the Bogen and Precision Electronics.
So I'm looking at the davis schematic and there are 3 Mic inputs. Mic inputs 1 and 2 come into the two halves of V1 and Mic input 3 goes into half of V2 and then the other half of V2 is the second stage for all 3 tubes. It looks like the half of V1 used for Mic 1 and the half of V2 used for the second stage don't have B+ to the plates. Do you think they missed a connection to the line between R12 and R15? Surely that's it, since there'd be no point in having R12 AND R15 in series like that and given that R12, R13, R14, and R15 are all the same value...
He said the Davis and the Hammond both have tubes. So I just need tubes for the Bogen and Precision Electronics.
So I'm looking at the davis schematic and there are 3 Mic inputs. Mic inputs 1 and 2 come into the two halves of V1 and Mic input 3 goes into half of V2 and then the other half of V2 is the second stage for all 3 tubes. It looks like the half of V1 used for Mic 1 and the half of V2 used for the second stage don't have B+ to the plates. Do you think they missed a connection to the line between R12 and R15? Surely that's it, since there'd be no point in having R12 AND R15 in series like that and given that R12, R13, R14, and R15 are all the same value...
It's 7:00am and I'm the proud owner of 3 PAs and a Hammond L101 amp + 2 preamps. He must have been confused. The Davis doesn't have tubes, but the Bogen does. Given the price of 6EU7s, I'll probably just rewire the sockets in the Bogen for 12AX7s.
The Bogen and the Davis are in really fantastic shape. A little dust and, well, the cases are old and stained, but no real rust to speak of. With a little scrubbing, they'll look pretty good, I think.
The Hammond is really dusty and dirty and though the cardboard-ish casing on the can cap looks like it's rotted from moisture, there's barely any rust.
The Precision Electronics is in the roughest shape. I haven't looked inside at the wiring, but are bits of rust all over the chassis and case. I'll probably scrub it pretty good with a brillo pad and paint it.
Unfortunately, my wife picked today to have a massive garage sale, so no playing with amps for me today :-( Finally have everything I need to hopefully power up my Ace Tone tomorrow and see how it's working with all the work I've done on it (recap, replace speaker & OPT, and replace reverb). Happy days...
The Bogen and the Davis are in really fantastic shape. A little dust and, well, the cases are old and stained, but no real rust to speak of. With a little scrubbing, they'll look pretty good, I think.
The Hammond is really dusty and dirty and though the cardboard-ish casing on the can cap looks like it's rotted from moisture, there's barely any rust.
The Precision Electronics is in the roughest shape. I haven't looked inside at the wiring, but are bits of rust all over the chassis and case. I'll probably scrub it pretty good with a brillo pad and paint it.
Unfortunately, my wife picked today to have a massive garage sale, so no playing with amps for me today :-( Finally have everything I need to hopefully power up my Ace Tone tomorrow and see how it's working with all the work I've done on it (recap, replace speaker & OPT, and replace reverb). Happy days...
I have a few of thoughts.
1. For the PE amp, if it is cathode bias, sub in 5881 tubes and replace the cathode bias resistor if need be.They have close to the same wattage output. You just need to check about OT pri impedance. At lower B+ voltages, they could be close.
2. For the Bogen, 7591s are the same tube as the 7868, just a different base and pinout. Just replace sockets and rewire. No worries about OT or anything else. They are structurally the same tube. Your trannies might not handle the 6L6s. If you want to try 6L6s, then you have the correct base for them.
3. The reverb is not tied to the output section for the Hammond. Is this the one you said the guy started working on? If he did, it might be best to start over. You don't know what he did with it. I only added volume controls and changed a few resistor and cap values to get the sound I wanted. I also got rid of the places they killed all the preamp signal. It sounds as good as any 18 watt amp I have heard and this includes Marshalls too. This amp sounds so good, I haven't even put in a tone control yet. I just use the controls on my guitar. Less signal loss this way. And it cleans up really nice for those sounds, too. Just use the vol on the guitar.
1. For the PE amp, if it is cathode bias, sub in 5881 tubes and replace the cathode bias resistor if need be.They have close to the same wattage output. You just need to check about OT pri impedance. At lower B+ voltages, they could be close.
2. For the Bogen, 7591s are the same tube as the 7868, just a different base and pinout. Just replace sockets and rewire. No worries about OT or anything else. They are structurally the same tube. Your trannies might not handle the 6L6s. If you want to try 6L6s, then you have the correct base for them.
3. The reverb is not tied to the output section for the Hammond. Is this the one you said the guy started working on? If he did, it might be best to start over. You don't know what he did with it. I only added volume controls and changed a few resistor and cap values to get the sound I wanted. I also got rid of the places they killed all the preamp signal. It sounds as good as any 18 watt amp I have heard and this includes Marshalls too. This amp sounds so good, I haven't even put in a tone control yet. I just use the controls on my guitar. Less signal loss this way. And it cleans up really nice for those sounds, too. Just use the vol on the guitar.
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1: He had mentioned that the PE had a replacement xformer on it (he purchased it that way) and I just read the little label on it. 6600ohm (to 4, 8, 16) but only 35 watts. So that got me curious and I cracked open the bottom to look inside. A couple of wires have been cut (and have the helpful labels, "1", "2", and "3" on them and they're just dangling free with their strands happily waving about). So I'm thinking that maybe the PE wants to be a different amp... A 60 watt replacement OPT won't be cheap (with shipping, probably $90 from Edcor) I'm not sure what the B+ currently is, but I'll have to measure the transformer at some point to see what it's putting out and then I can start thinking about what kinds of power tubes would make a good replacement. I'm in no rush on that. Got plenty of other stuff to do first.
2: I didn't realize the 7591s were going to be so much less expensive (should have checked). That's an excellent solution. I could buy adapters ($20 each), but I'm pretty cheap, so I'll probably rewire the sockets.
3: He didn't want to sell the Hammond he had started working on (though he initially put it on the list of what he was willing to sell, but that's cool. He was a super nice guy and I got an awesome deal, so no complaints). This is a pull from an L101 he had, separately. I haven't cracked it open, but looking at the schematic (Page 32 of 78 in the PDF. The ones on 33, 34, and 35 appear to be more or less the same. Maybe some minor component changes) for the L100, it looks like the input comes from the percussion amp, goes into a 67X 12AX7 gain stage, then into a 12BH7 reverb driver, reverb transformer, reverb tank, then on to a 40X 12AX7 reverb return gain stage, a 17X 12AX7 gain stage, then a 12AX7 PI, and then EL34s.
It looks like there's a bypass for the reverb (to the right of the reverb return gain stage and I believe the bypass signal runs below on the line labeled ".14VAC"). He gave me the percussion and vibrato amps as well. I might turn one of those into a tremolo circuit and hook it into the main amp.
2: I didn't realize the 7591s were going to be so much less expensive (should have checked). That's an excellent solution. I could buy adapters ($20 each), but I'm pretty cheap, so I'll probably rewire the sockets.
3: He didn't want to sell the Hammond he had started working on (though he initially put it on the list of what he was willing to sell, but that's cool. He was a super nice guy and I got an awesome deal, so no complaints). This is a pull from an L101 he had, separately. I haven't cracked it open, but looking at the schematic (Page 32 of 78 in the PDF. The ones on 33, 34, and 35 appear to be more or less the same. Maybe some minor component changes) for the L100, it looks like the input comes from the percussion amp, goes into a 67X 12AX7 gain stage, then into a 12BH7 reverb driver, reverb transformer, reverb tank, then on to a 40X 12AX7 reverb return gain stage, a 17X 12AX7 gain stage, then a 12AX7 PI, and then EL34s.
It looks like there's a bypass for the reverb (to the right of the reverb return gain stage and I believe the bypass signal runs below on the line labeled ".14VAC"). He gave me the percussion and vibrato amps as well. I might turn one of those into a tremolo circuit and hook it into the main amp.
This schemo might serve you better,I put the power supply in the lower left because there was nothing there of concern. The input is the RCA jack marked WH. The reverb send is RED and return is GY. I redid the Red as the input jack and the WH as the reverb send. This way both reverb jacks are next to each other. You can sub a 12AU7 for the 12BH7 if you don't have one. Must be a typo but the output tubes are EL84s.
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Very cool (I've seen his Hammonator and several other projects, but haven't looked at this one before). I could build it into an amp and get the 190V tap off an existing transformer and then I'd just need to buy an OPT. Edcor has a $17 one that should do the trick.
Ooh, and I can do the Liquidator with the Vibrato amp! I need a chorus anyway.
So maybe just put the Hammond and those two units all in 1 case, since I know the Hammond power transformer can handle all that.
Ooh, and I can do the Liquidator with the Vibrato amp! I need a chorus anyway.
So maybe just put the Hammond and those two units all in 1 case, since I know the Hammond power transformer can handle all that.
Some photos for anyone interested:
Precision Electronics 60PA (in the roughest shape of the bunch):
The Hammond (very dusty and the cardboard covering on a cap is rotted away a bit, and a little surface rust, but otherwise in good shape):
The Davis 201-A:
And the Bogen Challenger CHB35A:
Precision Electronics 60PA (in the roughest shape of the bunch):
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The Hammond (very dusty and the cardboard covering on a cap is rotted away a bit, and a little surface rust, but otherwise in good shape):
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The Davis 201-A:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
And the Bogen Challenger CHB35A:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
There's a screwdriver pot on the back of the amp labeled "gain". Is that the "Factory Volume Adjustment" shown on the schematic?
Just to confirm, the OPT is 8 ohm secondary, correct?
I cleaned it up. The 50uF cap between the 12BH7 and the reverb has been gnawed on by mice, it looks like (from the pix, I thought it was rotted). Some of the external wiring was eaten too, but the internal wiring is all clean as a whistle. I'll probably replace the PS filter caps too. They're metal, so no mouse damage, but old... Do you think I should replace any of the caps on the tagboard or should I just give them a try?
I also need to replace the power cable. Other than that, it may be just about good to go.
Did you rebias the preamp stages at all or just leave them as-is?
Just to confirm, the OPT is 8 ohm secondary, correct?
I cleaned it up. The 50uF cap between the 12BH7 and the reverb has been gnawed on by mice, it looks like (from the pix, I thought it was rotted). Some of the external wiring was eaten too, but the internal wiring is all clean as a whistle. I'll probably replace the PS filter caps too. They're metal, so no mouse damage, but old... Do you think I should replace any of the caps on the tagboard or should I just give them a try?
I also need to replace the power cable. Other than that, it may be just about good to go.
Did you rebias the preamp stages at all or just leave them as-is?
Yes, the gain knob is Factory Vol. Adjustment. NFB loop.
Yes, 8 ohm secondary.
You know, I have built two of these and brought them up with a variac and haven't replaced any filter caps, just those cheap disc coupling caps. My amps were in much better shape, were stored better so no corrosion or other things. I have very little 60 cycle hum.
The changes I made are to numerous to get into on the forum. Changed resistor and cap values, added preamp and master vol, boost switches, reverb, etc. I left the tubes biased the same in one and changed one in the other.
One thing for sure is the power to that cap the mice chewed on. If you don't use the reverb, disconnect the power to that circuit. The circuit with the 12BH7 is essentially a Class A single-ended power amp with that small transformer mounted next to the cap as the OT. Or I suppose you could just pull the tube.
Yes, 8 ohm secondary.
You know, I have built two of these and brought them up with a variac and haven't replaced any filter caps, just those cheap disc coupling caps. My amps were in much better shape, were stored better so no corrosion or other things. I have very little 60 cycle hum.
The changes I made are to numerous to get into on the forum. Changed resistor and cap values, added preamp and master vol, boost switches, reverb, etc. I left the tubes biased the same in one and changed one in the other.
One thing for sure is the power to that cap the mice chewed on. If you don't use the reverb, disconnect the power to that circuit. The circuit with the 12BH7 is essentially a Class A single-ended power amp with that small transformer mounted next to the cap as the OT. Or I suppose you could just pull the tube.
It's actually not in as bad shape as the pictures would suggest. I took it out to the shed last night and gave it a good scrub down and it cleaned up nicely. There's a bit of rust on the outside of the chassis and the power xformer. Everything else was just dirt (like the tops of those two filter caps and the other xformers)
I'll order some new caps to replace the disc caps. I have a pretty limited collection of high voltage caps.
He gave me the reverb tank and I love me some reverb, so I'll just replace that cap too. I've got a handful of 47uFs that I was going to use in the amp I'm building, but I'm giving the Hammond priority right now, since it's the closest to a done deal.
I'm going to replace all the big caps. I'm a bit gun-shy with electrolytics. A couple months ago I had a small one (like 25-35v, 22uF or so) on a breadboard, hooked in backwards, of course, and my arm happened to be stretched out across it when it blew and it popped me good on the inside of my upper arm. It was like getting shot with a BB gun and that was just a tiny little cap... So I don't want to be in the same room when a big one goes...
I guess I'll just keep everything close to stock for now and then we'll see what it sounds like after I get it up and running. If it sounds good, I'll just leave it as-is. If I don't like it that way, I can start re-biasing stuff.
I will add in volume & gain and stuff, of course.
I'll order some new caps to replace the disc caps. I have a pretty limited collection of high voltage caps.
He gave me the reverb tank and I love me some reverb, so I'll just replace that cap too. I've got a handful of 47uFs that I was going to use in the amp I'm building, but I'm giving the Hammond priority right now, since it's the closest to a done deal.
I'm going to replace all the big caps. I'm a bit gun-shy with electrolytics. A couple months ago I had a small one (like 25-35v, 22uF or so) on a breadboard, hooked in backwards, of course, and my arm happened to be stretched out across it when it blew and it popped me good on the inside of my upper arm. It was like getting shot with a BB gun and that was just a tiny little cap... So I don't want to be in the same room when a big one goes...
I guess I'll just keep everything close to stock for now and then we'll see what it sounds like after I get it up and running. If it sounds good, I'll just leave it as-is. If I don't like it that way, I can start re-biasing stuff.
I will add in volume & gain and stuff, of course.
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