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Topic: Princeton Reverb project for Forum Member All done!! |
Ken Fox
From:
Nashville GA USA
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Posted 2 Oct 2012 10:29 am |
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Got this amp in pieces delivered to the shop. Chassis was cut out for a larger transformer but work was never completed. Everything was out of the chassis. I used a supplied Bandmaster Reverb/Super reverb power transformer, choke and a Twin reverb output transformer and built it up as a 2 x 6L6GC amp with the 5U4 rectifier. After getting it up and running it would only produce 10 watts RMS clean. The inverter in the Princeton uses a single 1/2 of a 12AX7 and drives the power tubes from the plate for one phase and the cathode for the other phase.
Had to eliminate the tremolo to free up the other half of the 12AX7 tube position. Changed the inverter to Super Reverb type and got a clean 45 watts RMS now. Next will be covering the cabinet, a new baffle for a 12" JBL and final assembly.
Had the amp been un-modified I would never have made such changes (goes against my love for vintage amps!). But the damage was already done. Here are the parts I used new:
1- set of 6 Fender knobs, cream
4 -preamp sockets and tube covers
3 -octal tube sockets and clamps
hardware to mount tube sockets (stainless steel and locknuts)
4 - RCA female chassis mount
1- new AC power cord
1- AC power cord strain relief
1- fuse holder
1 -50uf at 50 volt cap
1- on/switch (for standy by)
3 - 22uf caps at 500v
2-80uf caps at 450 volt
1- leather handle
4- 10-32 t nuts and stainless steel screws
1- ac convenience outlet
1- faceplate
1- corners
1- feet
4- back panel screws and washers
1- tolex and glue
1- custom baffle baord
4- baffle board screws and washers
1- lot of pot and jack nuts, lock washers
Wil post a few pictures when it is all done.
Last edited by Ken Fox on 24 Oct 2012 3:48 pm; edited 3 times in total |
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Ken Fox
From:
Nashville GA USA
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Posted 2 Oct 2012 10:31 am
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Here is the layout after the changes were made.
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Marc Jenkins
From:
Victoria, British Columbia, Canada
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Posted 2 Oct 2012 7:24 pm
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| Neat idea, was thinking of trying to build something like that from scratch just the other day. |
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 2 Oct 2012 8:08 pm
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Basically what Randall Smith was doing 30yrs ago... a la pre-Mesa Boogie. Franken-Prince!
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Too much junk to list... always getting more. |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Oct 2012 4:10 am
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I was thinking that was the case, Steve. It should be a little monster amp when done.
I was thinking about a version like that but with a true effects loop (like Mojotone has as a kit), a multitap output transformer with rotary selector (liek a Marshall has). That would be a versitle little amp for sure. |
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Steve Hinson
From:
Hendersonville Tn USA
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Posted 3 Oct 2012 12:10 pm
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| Ken,would it clean it up and tighten up the bottom end if a solid state rectifier was used? |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Oct 2012 12:35 pm
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| I would get way to much B+, as I used a Super Reverb power transformer. If I had used a Bassman power transformer I would have indeed used a solid state rectifier. |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Oct 2012 12:36 pm
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| I could use a Weber copper cap, but it would have dropping resistors and still cause the 5U4 sag. |
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Rich Hlaves
From:
Wildomar, California, USA
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Posted 3 Oct 2012 12:39 pm
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Nice job Ken. Thanks for sharing the layout. Very helpfull for a scratch build I have in mind!
I hope the JBL fits with that TR OT in there.
Did you supply the cap board and cover? I missed it on your parts list. I'd hate to see you not get paid for the parts!
How about a gut shot(pic)?
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On man....let the smoke out of another one. |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Oct 2012 12:57 pm
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| I actually hand built a cap board to fit under a small cap can! I do need to add that |
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Tim Marcus
From:
San Francisco, CA
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Posted 3 Oct 2012 2:14 pm
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I notice there is no grid stopper to the PI - are you going to add that?
It can make the difference from the amp sounding like a Princeton or a buzz saw 
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Milkmansound.com |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Oct 2012 2:22 pm
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Tim, I don't follow you on that. The input to the PI tube is the same as a Super Reverb. There are 1500 ohm grid stoppers on the power tube grids.
Sound is clean as a pistol and 45 watts clean on the scope with a 4 ohm dummy load. |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Oct 2012 3:30 pm
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Tim Marcus
From:
San Francisco, CA
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Posted 3 Oct 2012 5:41 pm
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http://www.valvewizard.co.uk/cathodyne.html
the input to the PI is very different to a super reverb - a Princeton has a Cathodyne inverter! The super reverb has a long tail PI
I usually use a 330k-1M resistor to pin 7 of the PI triode to prevent that nasty nipple distortion, which is a very real thing
might be clean where you are right now - but give it time for tolerances to settle in, and you might get some harsh distortion. The big grid stopper is insurance that this will not happen
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Milkmansound.com |
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Tim Marcus
From:
San Francisco, CA
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Posted 3 Oct 2012 5:43 pm
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oh wait nevermind - looks like you do have a long tail PI in there
I did not notice the 12AT7
gotta go cathodyne if you want it to sound like a Princeton!
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Milkmansound.com |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Oct 2012 5:56 pm
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As I stated earlier you can't use the orginal PI and get the power. As I stated earlier it can't drive the power 6l6gc tubes to more than 10 watts clean. Will sound more like a Vibroverb or Super Reverb now. Lots of iron with the Twin OT (ala Stevie Ray's Vibroverbs)
Even the Paul C mod, which I tried would not get it above 10 watts clean. I can see now why a Deluxe Reverb has 22 watts and a Princwton has only around 12 watts. Yet both have the same power tubes.
The idea is to use this amp for his steel guitar and clean power in a small package is what he is after. This does just that.
I am going to build a Blackface Princeton myself very soon. I do love that tone  |
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Bud Angelotti
From:
Larryville, NJ, USA
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Posted 3 Oct 2012 8:06 pm
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Ken & Tim -
I know next to nothing about electronics & amps & such but I gotta tell you fellas, it's so interesting reading your posts. I'll never build an amp, but watching you guys is just so cool. And you just share it. Thanks, really!
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Just 'cause I look stupid, don't mean I'm not. |
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Steve Hinson
From:
Hendersonville Tn USA
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Posted 4 Oct 2012 3:29 am
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| You said you used a Bassman PT in your original post...you got 45 watts @ohms with a dummy load...but with a 12"JBL you will have 8ohms,correct? |
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Ken Fox
From:
Nashville GA USA
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Posted 4 Oct 2012 6:39 am
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A twin Reverb O.T. is rated at 4 ohms for 2 x 6L6GC or 8 ohms with 2X6L6GC. We have 2x 6L6GC so we have an 8 ohm setup with this transformer.
The Bandmaster Reverb/Super Reverb power transfornmer is designed to handle 2 x 6L6GC power as well as designed for use with a 5U4GB rectifier tube. I could ghave used a GZ34, but the voltages would have been more than I wanted in the amp.
If, said Bassman earlier, I stand corrected there and will fix that. |
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Ken Fox
From:
Nashville GA USA
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Posted 4 Oct 2012 6:42 am
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| Well the JBL, K120 came in today. We will have to have a custom cabonet built that is 3" taller to accomidate it. It just fits now with 1/2" distance from the O.T. frame to the speaker paper. Too close for comfort! |
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Tim Marcus
From:
San Francisco, CA
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Posted 4 Oct 2012 7:39 am
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I tried the longtail in my MIlkman guitar amp - but it was too loud
its amazing what a difference that one piece of the circuit can make
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Milkmansound.com |
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Ken Fox
From:
Nashville GA USA
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Posted 4 Oct 2012 8:05 am
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I agree, Tim. Huge difference in headroom from one inverter to the other.
By the way, some beautiful work in your amps!!! |
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Tim Marcus
From:
San Francisco, CA
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Posted 4 Oct 2012 10:34 am
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thanks Ken that means a great deal coming from you!
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Milkmansound.com |
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Ken Fox
From:
Nashville GA USA
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Posted 24 Oct 2012 3:53 pm
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Well almost. 16" fender tilt legs are on the way.
Got a little work on the top off the grill cloth (straighten it up a bit more). Rick Johnson did the cab build and Tolex . I did the grill cloth from NOS Fender cloth that Bob sent.
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Rich Hlaves
From:
Wildomar, California, USA
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Posted 25 Oct 2012 7:46 am
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The amp really looks great. The additional height adds some real class. I've always been a fan of blonde tolex with oxblood grillcloth, pinstripe or not.
Call her "Long Tall Sally".
Classy build Ken.
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On man....let the smoke out of another one. |
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