Hello everyone!
I got a lot of request for designing a Fender Princeton PCB. I got some time this weekend to design one, and I've already jotted down a layout with it. I've used Rob Robinette layouts as a starting point and the more "modern" version from Ceriatone (with standby switch, HT fuse, etc.)
Plan is to incorporate the filter caps and the bias circuit in the board itself (with the trimmer mod included). Would love to hear your thoughts on this and whether there are additional things that you'd think might be put on the board for mods/expansions.
Size of the board is currently 320x63mm.
Cheers from London,
Andrea
My build is coming along. The board is unique vs. the stock Fender boards. One niggle I had was the possibility of removing/lifting the PC board without a lot of work should something fail someday, or a part might need to be changed. I'm not sure what others might do here, but the easy solution was to add a bus bar to the back of the pots - even though the design does not use it for a grounding path. This way, as with the PC board Marshalls of the '70s, you can pull the knobs, undo the pot nuts, remove the pots from the chassis as a unit, and lift the board upward toward the tubes. Carefully.
Alright, back to work.
Most people stall out when fixing a mistake that they've made. Why?
I found almost all components easily swappable from the top of the PCB--thru hole plated and nice big solder pads. Should prevent the need to ever lift the board!
I build and repair tube amps. http://amps.monkeymatic.com
xtian, 'Mr. you're a better man than I' is playing in the background as I respond... (May the Great Mr. Beck rest in peace!)
I do respect the PCB quality that Andrea has produced here but I have spent too many hours with studio consoles (and perhaps too many Russian mics, not to mention a Sovtek amp or two in for repair) I guess to do things any other way. But I can see that, as you say, your method could work without a hitch. In fact, I modified the power supply to accept two radial caps in series rather than the single axil caps on either side of the choke (just because I wanted to), and I can tell you, his copper ground plate under the power caps is SUPER DELUXE QUALITY, quite beyond anything I have ever seen in audio gear. I actually had to use a Dremel tool to 'grind' away two spots of the bonded copper to clear things up for the two midpoint eyelets. Haha, it almost made me regret my decision to do this. Almost.
Most people stall out when fixing a mistake that they've made. Why?
I'm all wired up at this point, ready to start connecting the many leads. I confess, the multi-colored wire that Andrea presents in his build diagram might make this last part a bit easier. However, yellow wire was on hand...
A couple of things I'm doing diff from the stock AA1164 is to add a Band-Master choke (109 ohms) and adding 470 ohm screen resistors to the pwr tubes. I also modified the power supply to accept two 68uf/250V radial caps in series before and after the choke. This gives me 32uf in each spot and I've bridged a 220K 1W resistor over each cap to assure voltage drain at turn off. Iron is ClassicTone 40-18037 OT, Hammond choke, and a MM FBFPP-M PT. This PT has 150mA secondary, 5A filament tap, and a 4A rectifier tap. It's a great tranny give me a few options like trying 6L6s and a GZ34 (stock AA1164 is a 5U4). The OT is fairly robust (easily the size of a BFBM OT) with 4-8-16 ohm taps for the stock 6V6s. Swapping to 6L6s I'll just use an 8 ohm speaker into the 16 ohm tap, and a 4 ohm speaker into the 8 ohm tap. I'm having a 15" speaker combo cab built and I have a 4 ohm K130 in the wings.
Back to the AAE board, if you've ever worked on/repaired/modified a Fender BJr, then you're familiar with removing the knobs and circuit board screws (and a few other things) to lift the board up from the knob side at an almost 90 degree angle to get to the solder joints. In this build I've added a (unused for grounding purposes because of this particular PC circuit design) bus bar to the back of the pots so that I can do the same thing here. Pretty much like the '73 on PC board Marshall amps. Xtian, BTW, had a diff approach here, and he may indeed have the easier build approach, so check out his AAE PC board DR build in another post here. He built a great sounding DR, no doubt about that (!!). I went the way I did here because it seemed to relate to my experiences with various PC board amps and other PC circuit boards I've worked on.
IMG_6088.jpg
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Most people stall out when fixing a mistake that they've made. Why?
Update on the playtest. Changed the screen resistors to 1K and still find the screens hotter than the plates, around 3-4 volts hotter. Looking at the Marshall 18W circuit and looking at the Marshall OT (that this OT is a copy of), I see that the screen (choke) resistor is 8.2K. This was something I hadn't considered. So, with the 1Ks installed, the amp is definitely more playable. However, I just ordered two 1.5K wire wound resistors that I'll install. I may have to go 2K but I'll start with 1.5K. It might be simpler to add a 2K or 4.7K wire wound resistor in series with the Hammond choke? Maybe.
The AC on the PT secondary leads is 325, using a GZ34, my 6V6 plates are 392VDC, screens 395-6VDC. All other voltages are actually very close to the Fender stock AA1164 schematic, bias voltage at -34/19.1 mA, and the tremolo is much improved by swapping out the 470 ohm screen resistors.
More to come.
Most people stall out when fixing a mistake that they've made. Why?
Update. I will keep the 1K resistors on the tube sockets but after running through a few resistor options (in series with the choke) it turns out that with this particular ClassicTone OT (if I was set on using a choke) I should have initially started with the a vintage AC30 choke (the Hammond 194E choke with 519 ohms resistance). This would've served me better. So, for now, I have added a 390 ohm 5W wire wound in series with the Fender Band-Master choke, and I'll hang with this. Screens 391V, Plates 392V, bias still at 19.1/-34VDC.
Two niggles. If you're building this board, I would suggest using a shielded cable for the reverb return wire (going to V3/pin 7) for an even more noise-free verb experience. I ended up rerouting this wire and using a 1.5K grid stop resistor, but I will replace this with a shielded cable soon. Verb is a big deal for me though, you might not want to pursue this idea. FWIW, if you look at the original Fender layout, you will see how different the two boards are from each other on this subject. Not criticizing either party, just noting a difference. Also, if you are using a 3M (reverse taper) Speed potentiometer that measures 3M, you will want to change the .01 cap that follows the initial .02 cap to a .02 as well. Using a 3M pot, I can maybe turn to 5 before things are oscillating so fast there's no point in going any further.
Building the AAE board was a unique experience, very far removed from creating your own eyelet boards and basically cloning a Fender or Marshall board (with maybe a few different twists and turns). I would urge anyone who's been doing this to try one of Andreas' PC boards. Your brain will thank you (I suspect), rearranging the grey matter is always good. The results here are awesome, Andreas' work is brilliant, and the amp sounds fantastic. I'm very glad I pursued this.
I'll post some sound samples and maybe a video in a day or so. Still waiting for the case.
(Haha, when I said here that the "amp sounds fantastic" I was a bit premature. When I wrote this, I was still having a noise issue with the reverb that I was trying to accept as 'OK'. Eventually I sorted this (3 days later) and passed the info on to Andrea. By the time you read this he will (I hope) have updated his printable PDF layout so your build will sound the same. And the sound sample is in the next post via Dropbox. I think the amp does sound fantastic, but you be the judge.)
Last edited by rooster on Fri Jan 20, 2023 11:22 pm, edited 2 times in total.
Most people stall out when fixing a mistake that they've made. Why?
I've sorted the reverb problems I was having with AAE PC board build. Yep, it had some serious reverb grounding noise that stalled the sound sample process, very strange vs. what I've experienced with a trad built PR. Even what seemed like voltage on the chassis via the reverb return. Basically, because of the reverb, it was an unusable PR for me, although the clean side of things was always great. Andrea was trying to assist but I don't think he is an amp builder, per se. He sent me his circuit board tracing pics but they weren't much help.
Anyway, I tried different ways to sort things, focusing on the RCA jacks grounding layout that Andrea presented, the V1 and V6 wire routing to V3, and the reverb transformer wires. I passed this along to Andrea so I think he will update his PR layout PDF. If you've ever wanted to build a PR, this is the one to build.
rooster wrote: ↑Tue Jan 17, 2023 1:45 am
Building the AAE board was a unique experience, very far removed from creating your own eyelet boards and basically cloning a Fender or Marshall board (with maybe a few different twists and turns). I would urge anyone who's been doing this to try one of Andreas' PC boards. Your brain will thank you (I suspect), rearranging the grey matter is always good. The results here are awesome, Andreas' work is brilliant, and the amp sounds fantastic. I'm very glad I pursued this.
Just reading this - thanks for the kind words, it means a lot
Andrea
