Phil here, introducing myself and my plan`

[pjd3]

Hello, nice to meet ya and thank you for stopping by.

After years of good success building my own guitar pedals, condenser mics, high quality preamps, compressors DI's, I really got a heavy drive to build a real nice guitar tube amp. A year as an engineering tech at a high power test lab also taught me great lessons on saftey. We tested fuses rated up to 1500V and 100kA. One wrong move and we could take out a room or kill somebody.

I have a Princeton Reverb chassis and eyelet board for starters. They just got delivered today. But, I don't really want a Princeton reverb. I need to make this into an amp that will serve the application of the kind of gigging I do which is fair amount, say 60-70 gigs a year.

I want this amp to support the use of 6L6GC's and even KT66's. And this amp doesn't have to have the reverb circuit and maybe even not the tremelo circuit. I would like a long tail pair phase inverter so, I think that would call for another preamp tube. I don't think a classic Princeton has a place for the added needed tube stage.

Really I need this amp to be pedal platform that is low to medium power and stays pretty clean through much of its volume range. If it stays fairly clean and doesn't break up too too early, I would like to use a reverb pedal and the end of my chain, and of course, we don't want to be distorting the reverb. I prefer having a few types of verbs, hall, plate, room as opposed to only a spring, which is great in itself, but I like a wide variety of ambiences out of the amp.

So I'm thinking about a 30-40 watt amp, Fenderish cleans but a good platform for many kinds of overdrive, distortion and fuzz pedals, and reverb pedal. So, its got to be a jack-of-a-few-trades, and doesn't have to be a master-of-one. The Princeton chassis and eyelet board is just a platform to make this amp provide a specific application.

Whats nice for me is that I have one of the well known and mentioned vintage tube amp techs in the north of Boston area that lives 5 minutes from me. Stan Day. He's a great guy and seems willing to provide some good guidance for someone like me that is ambitious and likes to listen and learn. I've already got good advice on what to watch out for when shopping for amp parts. Especially about the capacitors! The threads on that topic are just hilarious. Although very informative, they are also just good entertainment.

So, thank you for your patience with me! Long damn winded post from a guy that only has a chassis and an eyelet board, but, I come with the child mind and a large ambition to build a great little useful tone monster.

Thank you for your time, and look forward to reading about your experience and taking you advice on such a great exciting venture.

Best,
Phil Donovan
Reading, Ma
617-470-9821

[Stevem]

That chassis is on the small side to stuff in the needed PT, OT and regular Fender choke for a 30 to 40 watt amp, and even with that level of power the overall cab is too small to really sound good even if you stuff in a 12" driver which can be done by the way!

I would suggest you get a seperate cab with at least one 12" for doing gigs, the amp is small enough to just concider it a head if you ask me!

I did one of these for a guy once and to save myself from trying to enlarge the stock square hole in the chassis for the PT I mounted It on the floor of the amp on a steel plate to reinforce it.

It was the best thing I ever did as that freed up more room on the chassis and the amps idle hum level from having the 60 HZ flux so far away from the preamp section was near zero!

A good PT to start with is the British 45 low power one from mojo tone and this will give you the option of using a recto tube if you care to.
I just used another one of these in a guys 66 Bassman and it put out 40 watts of clean power!

[TUBEDUDE]

I use these chassis all the time and use 5 preamp tubes. You can punch out two extra holes and be fine. It gets crowded with the extra circuitry, but a little creativity will get things right. Using the Princeton chassis with a 12" works well with 10-20 watts. Even with a 12" speaker the cab is very small for 40-50 watts. Perhaps a head and larger cab would be more toneful.

[martin manning]

Sounds like you want something that is pretty bare-bones; clean, no verb, no trem, so you already have more holes than you need in that chassis. What about the controls? You will have extra holes there too, so new faceplates are needed. You could use an upright PT with 50W power to avoid enlarging the cutout. I think I'd want to start with a blank chassis for this. You might want to go over to the Dumble section and search for Small Special. I think that would fill your needs nicely. See here: https://ampgarage.com/forum/viewtopic.php?f=4&t=23609

[pjd3]

What a nice generous set of responses. I'm starting to like this place and I just got here! Thanks!

I should have mentioned that this will be a head. I have a cab and could even use my Bogner Alchemist amp for the 12" Weber C12B that's in there.
I"m absolutely fine with this amp being done in a semi-prototype fashion. If I need to put the bigger PT mounted on the bottom of the head cab then so be it. (or enlarge the holes) already sounds like the advantage of noise/buzz/hum reduction is worth it right there. There's a guy selling unfinished cabs on-line and thats fine. I like doing a little wood finishing, applying stain and things. Its not a big extra investment and I find it fun and rewarding. Even the faceplate I'm not too worried about. I'm good making one myself whether its ground plated exotic wood , brass, whatever it needs to be. The great thing is this head only needs to impress me, and performance trumps everything. Of course, I'll be passing the amp off once or twice to Stan Day in Wilmington to make sure I don't lose $300 in parts when I flip the "on' of "standby" switch. 97% of the things I have built have worked the first time due to my penchant for checking things over 20 times, and then another 10 times to be sure. I'm obsessive and paranoid that way. I hope that will be an advantage here.
And Yes, bare bones it can be. If it can give me a lower power clean but bold straight Americanish sound on its own, while providing an un-obstructive platform for pedals, then I'm in good hands. Should there be any additional mods, I'd rather have something like a "Raw" or "mid" control to bring in some mids or thickness when called for. For instance, my Marshally pedal and Voxish pedal are rather bright, while the Fulltone is very middy and on the dark side. I'd wouldn't mind some frequency variables to make the different pedals fit better EQ wise from song to song.

I got the chassis for 44 bucks on Ebay which I'm usually quite hesitant to do, but all the reviews seemed to reveal a well made and dimensioned chassis that fits standard Princeton reverb amps. If I need to do any wood removal or shimming, thats fine (to a point). And the eyelet board is from Mojotone for the AA1164 circuit.

It seems to be a process now of defining electronically and functionally what the amp is going to be in order to source the right parts and not get painted in a corner which I've been moving to do, researching how to assess and calculate current and voltage requirements based upon what kind of tubes, rectifiers, power and number of tubes that will be present. And to elavorate, I play a great deal of outdoor concerts during the summer. My drummer uses a digital set which means our stage volume doesn't have to compete with and acoustic kit. My desire is to have my amp set up closer up to me, almost as if my amp is also a personal guitar monitor also. I've been using a Bogner Alchemist (American channel only) and its just a bit too much for this band. I wan't to go a bit smaller and closer while improving the base foundation tone quality. (The Alchemist did not have the kind of opulence a good Fender has).

I grew up on sixties amps, loud, clear, dynamic. It would sure be great to get some of that back on the stage.

So absolutely, I'm open ears to the elements of the amp that will define proper choices in parts. Right now, I've been investigating how to determine the minimum current and voltage requirments to choose a Power transformer. And its OK it its bigger that it needs to be. I don't mind playing it safe with things like that. I'd love to try a pair of KT66's, I know they are about 1.3 amps of heater current each and will take some pretty high plate voltages. I'll pay a few extra bucks to meet those things.

Thanks again for your great feedback. Time to go the supermarket and steal all the milk and bread. Word has it we are getting 12-20 inches of snow here in New England starting in a few hours!

Best,
Phil

[martin manning]

Picking transformers for this will be relatively straight-forward, just get 40-50W Fender replacements. You won't be short of heater current for KT66 since you are eliminating several preamp tubes. If you went with 2x KT66 @1.3A and 2x or 3x 12AX7 @0.3A that's only 3.2-3.5A where the typical 50W Fender PT will have 4.5A available. If you get a PT with a 5V rectifier winding you can use that third octal hole if you want. I'd suggest this one, which is an upright-mount: http://www.classictone.net/40-18094.html There are a couple of voltage options, and a 5V winding for a tube rectifier. For the OT, I'd go with Black/Blonde Bassman http://www.classictone.net/40-18001.html That one is for 6L6 with 4k2 primary. KT66 are often run at a higher impedance, but I think you would be ok.

[Tony Bones]

As usual, I'm going to agree with Martin. Without reverb or trem, there should be plenty of room in that chassis and more than enough holes for both tubes and knobs. And, as Martin suggested, a power transformer that mounts upright instead of Fender lay-down, means you won't need to find something that fits in the existing square hole in the chassis. You may or may not want to use the Princeton eyelet board. Doug Hoffman can make a custom eyelet board for not much $$ once you have an idea what circuit you want to build.

My advice is to start by thinking about what existing amps have a sound you like and work from there. 60's Bassmans have an awesome clean sound and can be built with a single channel. Of course Dumble's are the king of clean and he basically modded Fender circuits for that.

[didit]

Allen Amps has some transformers that might make it easier to follow your plans — http://allenamps.com/trans.html. A power transformer Princeton drop-in fit with roughly Vibrolux specs. Also a potentially useful output transformer, with Bassman specs but different mounting. Worth considering.

Best .. Ian

[jeanfrançois]

Bonjour !! Messieurs
I went on Bassman 70, but a lot of modifications made amplified
2 x 70 watts sous 4 ohms UL ot bassman 70

[pjd3]

JeanFrancais! You are the builder I'll never be! Maybe someday. I did dream about a Head with dual/quadruple ganged pots, two independent amps and a cab with 2 spread 12"s , one for each amp output and some nice stereo effects, mic each speaker, pan out full left and right out of the PA system. I'll need to become a genius in order to win a war like that with my wife. I'm going to see first if I can not blow up a simple 30-40 watt single head! Beautiful looking work you've got there.

Thanks everyone again for your informative and direct-full comments. I have been scoping out the Classic Tone offerings in the last week or two and have been looking at the Allen amp transformers for a while now. While the selections for Classic Tone are very wide the Allens selection seems to have something or two that would work for what I'm doing. I may go with the Classic Tone for a little cost savings. See there are even choices for PT input Voltage, output taps and B+ voltage choices. Thats pretty nice. I'll have to decide of its worth the cost to have that kind of flexibility. I don't see my self using anything other than 115-120V in and 8 ohms out but, that my be a lack of foresight on my part, something to bite the ass in the future. I even started printing out "specifications" sheets for the transformers that looked to be contenders from Magnetic Components.

A question or two for you fine builders - has anyone ever noted a sonic difference using Output Transformers with multiple taps vs single tap outs? Just seems like the coupling architecture of a muti-tapped OT would have to be different than a dedicated single. Just curious. I did come upon one or two threads where that topic came up and one or two people felt there was a differnce. Stan Day told me the Classic Tones make for fine transformers as well as Allen and I see that most of the offerings of Classic Tones appear to be multiple tap OT's. I don't think he would have recommended them if there was a compromise there. Probably one of those "splitting hairs" topic.

Another question, if I'm even ready to get it - As long as a Power Transformer has a high enough voltage, is it a straight ahead process to adjust plate voltages? Are we talking simple resistor voltage divider calculations or will it be more involved than that? I'm still in the process of understanding how all the elements in the output section work to achieve a desired power although I've worked day jobs setting up circuits to achieve specified current, power, power factor, phase angle, time constants. I'm hopeing to put that all together soon in my head, have made some headway.

I found a place that sells capacitor kits for various amp circuits, they had that in Orange Drop, Mallory 150's, and Jupiter Vintage. I was going to just order the Mallory 150 signal/tone cap set for Princeton Reverb. Just want to keep the ball rolling and start collecting components that I "probably" or "might" use. I really am attracted to the expensive snake oil reputational ones like Jupiter and Sozo Blues. They look nice. ha. Again, the threads on capacitors are just a gas. Stan told me just get the Mallory 150's, they make for a sonic-ally fine amp. I told him I like the snake oil ones. He said "Phil, I'm just trying to save you some money". I suppose he is, and very convinced I'll be fine with good old Mallory 150's. Whats ya think? Order em up? I'd like to start compiling a selection of relevant components, even if I decide to use another value one day. I'll just buy more.

Thanks for hanging in with me here, it does mean alot. I'm a real greeny, just trying to keep my feet moving a little bit everyday - you've been awesome, helpful and very patient with the likes of me!

Best,

Phil

[xtian]

Adding additional output taps to an OT changes its performance somehow? That's a new one on me.

You need a PT spec'd for the plate voltage you're after. Adjusting B+ is not as easy as adding voltage dividers. You can drop voltage with tube rectifiers, MOSFET B+ reducer on the CT, and other approaches, but noting beats the right windings.

Snake oil caps? Forget it. The more I build, the less I believe in snake oil. You can build great amps with off the shelf components. The only person who will know you used $6 coupling caps is you, because your wallet will be thinner.

[xtian]

Adding additional output taps to an OT changes its performance somehow? That's a new one on me.

You need a PT spec'd for the plate voltage you're after. Adjusting B+ is not as easy as adding voltage dividers. You can drop voltage with tube rectifiers, MOSFET B+ reducer on the CT, and other approaches, but noting beats the right windings.

Snake oil caps? Forget it. The more I build, the less I believe in snake oil. You can build great amps with off the shelf components. The only person who will know you used $6 coupling caps is you, because your wallet will be thinner.

Oh, no. I've become old and cranky, like @Reeltarded and @CBass...

[sluckey]

You are maturing!

There are others of us in that camp too.

[pjd3]

Hey xtian, perhaps its wisdom that is masquerading as crankniness as a result of real experience. I can live with that. Speakers and Tubes are the only thing I could even comment on and thats even questionable. So, all I have to go on are other peoples perspectives. So, crank it out on me. I require it and have got it coming to me.

Thank you!

Phil

[sluckey]

I'm just curious... Why would you buy a PR chassis and board when you clearly want a bigger amp?