Precision Electronics PE-15

Brendan

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My attempt to buy the RCA hi-fi amp fell through, but I did manage to get this in a trade today.
PE15.jpg


The previous owner had already modified it to a Fender circuit last year and was in the process of converting it to a different design when we made the trade. The original tube compliment was 6SJ7, 6SC7, 2x 6v6 and a 5y3. It has two 6SJ7 at the moment. I've been reading up on octal preamps and I think I'll leave those alone. So far I have found two schematics that I may use. The Ampeg J12b and the R12 both use these same tubes. I heard the R12 and it sounds great - very tweedy. I haven't heard a J12b yet, but I did read that it is the tamer of two. Anyone have thoughts on either?

I asked the previous owner if he knew what the output was on the PT. He said 295 which I presume is VAC. It looks like that's in line with Ampeg, but low for some of the Fender schematics I've looked at. The cap can will definitely be going. Going hunting for tube amp books at Powell's tomorrow. :)
 

capnjuan

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Hi Brendan; I'm already liking this better than the RCA SA-3 ... if for no other reason getting to dance away from an RIAA circuit in the preamp. Fender wasn't the only company to use the pentode 6SJ7 as a preamp tube; Gibson used them too ... all over the place (6SJ7: pinouts and tube data.):

Early LP Jr / GA5
Early GA20
Early GA30 and the
Early GA40 Les Paul before they switched to 5789s in the preamp ... also a pentode.

The 6SC7 is a twin triode; same functionality as a 12AX7 but in a different package: pinouts and tube data. Used by both Fender and Gibson as either a preamp gain stage or phase inverter. Aside from the octal sockets, these types can present headaches in their heater wiring; one of the reasons the types were abandoned in favor of the 12A_7 group was the common practice of grounding one side of the heater circuit ... more opportunity to pick up unwanted heater noise.

Anyway, you didn't ask but I strongly suggest you getting as many details from the former owner as possible. Depending on how extensive his cutting and pasting was, you may never figure out what you have there and, with respect, cutting up a Precision Electronics amp into a 5A3 Deluxe doesn't make it a 5A3 Deluxe ... it makes it a Precision Electronics that's been cut up into a 5A3 Deluxe. L. Fender, S. Lover, E. Hull ... all of these people made liberal use of the early post-war RCA Tube Manuals and technical data produced by Western Electric ... a lot of which had been developed for military use but, after peace broke out, RCA particularly needed somebody to buy the tubes they'd formerly been selling to the Government so they released gobs of designs using ... not surprisingly ... RCA tubes.

So ... waddya sayin' Juan? Many of the very early versions of Fenders and Gibsons are barely distinguishable electronically from each other; so ... they're going to be tone (first) cousins and sound a great deal alike ... more alike than different. If you have 300VDC to work with, you're not going to get a screamin' Champ or Deluxe out of it and those octal tubes ... unless you're prepared to drill out the chassis, replace the sockets, and re-wire the heater circuits ... I think they stay and if left on it's own, that amp would be closest to a Gibson GA20 ... and that wouldn't be a bad thing at all.

Chassis shots when you get the chance; congratulations and good luck!
 

Brendan

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Thanks, Capn.

I did do some digging before sealing the deal and was not able to find a schematic anywhere. I did find posts from two folks who had converted theirs to guitar amps and were happy. I found this clip from one that is said to be stock.
http://kilback.net/tunes/pe-15_demo.mp3
I have PM'ed the owner to see if he has a schematic or gut shot. Unfortunately the power and preamp circuits are gone on mine. Only the heaters and rectifier are wired up. I'll get some shots of what I have tonight. I took this on with the approach that I'll have fun making whatever I can from it, so I'm completely open to any schematic that will work with this iron. I have no objections to drilling or any mods for that matter. Here's the one I was studying this morning.
Ampeg1959r-12schematic.jpg

I found this clip of one in action. http://www.youtube.com/watch?v=N9L13TrZyd8

I've listened to some GA20 clips and I love that sound. I'm looking at the schematic now.
 

capnjuan

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Hi Brendan; the link you posted: http://kilback.net/tunes/pe-15_demo.mp3 is none other than LTG's own Valcotone/Sean K who, for a time, was the Admin for the 'Chicago 51 - A Valco Discussion Forum' bb which I think is gone now ... the link no workee. I bought this Jensen P12Q from Sean several years ago:

12inspeakersfinal-1.jpg


The Ampeg R12 is using 6SL7s; pinouts and tube data ... twin-triodes .. like the 6SC7s. The early Gibson GA20s ran on pentode 6SJ7s, the later models on 12AX7 twin-triodes. Without pics it's hard to tell but if there are two 6SJ7s, it suggests that it was originally a two-channel amp; does it have two volume controls?

If you build it back as an R12, the good news is that since the 6SL7s are octal base, you won't have to drill out sockets but the R12 design only uses two tubes; 1/2 preamp, 1/2 tremolo oscillator, and 1 for phase inverter/driver although your chassis has three preamp tube sockets. Anyway, whatever you decide to do, I think you have makings of a fun, good-sounding amp; it's hard to go wrong with 6V6s.
 

Brendan

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Thought I'd give an update. I've been reading a great book by Dave Hunter to assist with mah learnin....

The original octal sockets were a mess, so I found some ceramics locally at an electronics overstock shop. I wasn't shooting for "bling",...gold was all they had in stock. I capped off the canister cap hole and will be using F&T filter caps instead. I'll be using a CTS concentric pot to handle the tremolo adjustments. They don't make a 500K/1M pot, but I'll open up the 500K / 500K unit and swap in a 1M wafer.
chassis2.jpg


The coupling caps I wanted were out of stock, but should be here in a few days. I have all the other parts. I'm using stand-offs on this one and I'm working on the layout now. I'm not sure where the previous owner got the green power cord. I'm wondering if it came from a weedwacker. :shock:
chassis.jpg
 

capnjuan

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Love that bling on the sockets! Coastie has run into that problem with pots; I guess they aren't being made in those values and whatever comes and goes on the market is a function of people finding NOS here and there in wholesalers' warehouses ... same deal with multi-section can caps :(

If you're talking about Hunter's Guitar Amp Handbook, it's the greatest book since Hans' The Guild Guitar Book. The guy turns techno-jabber into ideas and principles a hobbyist can understand and use. I have his 'Guitar Rigs' book; it's probably better than it seems but I was looking for the same illumination I got from the Handbook ... just didn't happen.

Did you decide on a layout; the R12?
 

Brendan

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capnjuan said:
If you're talking about Hunter's Guitar Amp Handbook, it's the greatest book since Hans' The Guild Guitar Book. The guy turns techno-jabber into ideas and principles a hobbyist can understand and use. I have his 'Guitar Rigs' book; it's probably better than it seems but I was looking for the same illumination I got from the Handbook ... just didn't happen.

I admit, the bling is growing on me a bit. :D
Yes, The Guitar Amp Handbook is the one. I'll be reading it again too. I agree, he made it really easy to understand.

capnjuan said:
Did you decide on a layout; the R12?

Yes, I did decide to try the R12. This youtube vid made it very tempting.
http://www.youtube.com/watch?v=N9L13TrZyd8
This will be mounted in a cabinet with a 12" speaker and I'm really looking forward to making that too.
 
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