Built a 5F2A Princeton clone!

[scott_s]

I recently bragged about this on the TDP, but thought you guys might be interested too.

It's a clone of a late-1950's Fender Princeton amp, built (mostly) from a Weber kit. ~5 watts from a 12AX7, 6V6, and 5Y3 into a 10" alnico speaker. Features include Volume and Tone controls. I was so eager to hear this amp, I got it done in about four days!



I love to use old stuff where possible -- Sprague signal caps, carbon comp resistors from a local radio supply store I'm trying to keep in business , Mallory filter caps, cloth-covered wire from a 1958 Baldwin organ, a smooth-cone alnico speaker that I got (cheap!) from an antique store in Nebraska, and of course, used tubes far older than myself. Dad got the smoked-glass "AC Delco" branded 6V6GT out of a radio from a '49 Plymouth, and since it was too leaky for his standards, he let me have it. Seems to behave in my amp...





The whole thing together:



Oh, and here's the variac I used to form the caps. My process was to use the Weber Copper Cap for B+, but leave out the signal tubes, to save wear and tear on their heaters. I worked up the caps to their voltage limits over the course of two hours, and since none of them popped, I'll consider that much a success.



All in all, it's a good-sounding amp. It can get a little bright with the tone knob most of the way up, but that may be my fearsome speaker with its 7/8" voice coil. The cleans are a little wooly over "3" on the volume, and I'm loving it. Perfect for some grungy tones without annoying housemates or neighbors!

For anyone thinking about building one of these, I highly recommend using the lower-voltage taps on the power transformer. The unit Weber supplies with the kit is the same as used in the BF Champ and Princeton, which puts a lot more voltage on the tubes than is really *correct" for a tweed. Even using the lower-voltage taps, the 6V6 in my amp has about 350-360V on the plate, and dissipates about 12-13 W.

Speaking of BF Champs, here it is, chilling with my friend's '66 Champ. I'm really happy with the larger cabinet and speaker of the 5F2A -- it truly sounds better.



Thanks for looking.

- Scott

[BlueAngel]

Very nice job!

I had an original '58 5F2 Princeton a while ago in absolutely terrible condition - no tweed left, painted grille cloth, changed speaker (10" like this one) - which sounded incredible, better and a lot louder than my near-perfect '59 5F1 Champ. I can't remember why I sold it now, but I shouldn't have done .

I wouldn't worry too much about the voltages on the 6V6 - old-production GTAs will happily take 420V on the plate and dissipate 16W without any problem at all - as they do in later BF and all SF Champs, after Fender replaced the PT with a BF Princeton type to increase the output power to 6W. (They also forgot to increase the value of the cathode resistor, so the tube runs unnecessarily hot and clips really asymetrically at the forward end - which is why BF/SF Champs sound so farty when really cranked up and aren't as loud or have as much headroom as you'd expect for 6W. You can fix this by changing the resistor to 820 ohms or even 1K and increasing the cathode cap voltage rating to 50V.)

The only thing I might have done differently is to use wirewound or metal-oxide resistors for the 10K in the B+ chain and possibly the cathode resistor - if the tube fails by a screen short (fairly common for 6V6s, especially newer ones) these can catch fire before the fuse blows if you're unlucky. The carbon-comps don't have any effect on the tone in these positions.

It looks like you could get a 12" in that cabinet too, as long as the magnet isn't too big...

[ken_j]

Looks like this was a fun and useful project.

[doctorwho]

Noce job, Scott!

[soundmasterg]

Nice job, though I can't see the pics until I get home. (Stupid comsifter!)

Did you use NOS filter caps, or new filter caps? You don't need to form new caps, as long as they haven't sat on the shelf for very long, and going with old filter caps that have been reformed is not going to be as good as just using new filter caps. There isn't a tonal difference with filter caps as long as the values used are the same as original.

Greg

[scott_s]

Greg, I dunno if the color could help you date them, but I used a medium-blue 20uF for the input capacitor (instead of the 2x16uF in the original) and the light blue 8uFs where you'd expect them. They're not ancient NOS, but who knows how long they'd been in the drawer, so I figured it would be cheap insurance to form them before use. Plus, it's fun!

BlueAngel, good point on the resistors. I had the molded carbon-comps on hand, but I can see the wisdom of upgrading to something more robust before too long.

BTW, if my Internet reading is correct, the Deluxe used a cabinet this size until 1956, so it would definitely accomodate a 12" speaker!

- Scott