Need component ideas for Blackface build

[luthierwnc]

Hi all,

I'd usually ask this over at the AmpGarage but that site seems to be compromised. If anyone has news on what's happening there, please share.

I'm building a Princeton Reverb clone (sorta) and wanted to see what current production (or NOS reliably available) caps and resistors are best for replicating the tone. Caps are less of an issue since I've had good luck with the Mojo Dijons. I haven't looked at a Fender build in a long time. Most of the amps I've built in the last 8 years have been Dumble, Marshall or experimental homebrews using largely MilSpec metal film plate resistors and polypropylene bypass caps. Too harsh and exact for the warmth I'm looking for. Same goes for the cathode resistors.

If anyone has some good ideas on alternatives, I'd love to hear them. It's a one-off so cost isn't an issue. I'm trying to avoid reading about third-party secret stashes of NOS Allen Bradleys I might be able to get when the old guy finally dies.

Thanks, Skip

PS What's with the ten thousand Asian singles? Soldering is hard enough on the carpals.

[Chuck H]

I can't say about the Asian singles. Would you believe there are NONE at my place right now!?!

As far as the amp...

I like Mallory 150's for BF builds. OD's are great too if you're after a bigger tone. And I might catch crap for saying that too since the common wisdom here is that all decent film caps are created equal But IMHE polyester does sound different from polypropylene. Mallory 150's won't cost as much as the specialty items and have been popular with Fender cloners for decades. Why spend more? I can personally attest that the amps "I" used them for worked out great. You can use carbon comp resistors for everything but the plate loads. As long as you stay clear of the plate loads, especially the first preamp stages, it doesn't add appreciable noise and it does seem to make a small difference getting "that" sound.

Just one guys opinion and limited experience on the matter.

I can't say about Amp Garage. My browser says the site is unsafe.?. We had some infections here several years back. We lost a lot of files and the site was down for a couple of weeks! I was suffering withdrawal by the time it came back and it was still intermittent for another month due to ongoing maintenance. Big kudos (BTW) to tboy, our site janitor and patron saint of all that is good about the forum. I hope AG doesn't suffer similar circumstances. The greatest collection of knowledge on the TrainWreck amps and circuits could be compromised!

[Enzo]

I'll believe you hear a difference between Mallorys and ODs, but only after you match them for value before the comparison.

[überfuzz]

I'll believe you hear a difference between Mallorys and ODs, but only after you match them for value before the comparison.

True, but faith moves mountains, and hear difference in capacitors.

[luthierwnc]

Now I'm getting a St. Jude's ad so no Chinese fantasy girls today.

I took a risk and opened TAG. There are several threads that don't really explain the warning but it seems to be working fine. The regulars are all still there. If you have faith you can program the browser to ignore specific threat sites. I posted the same basic question there.

Right now I'm leaning towards using carbon film Kiwame or Takmans in the plate and cathode positions. Parts Connexion keeps reliable inventories. It can take a little longer to get things here from Canada but I haven't even had the chassis cut yet. I've still got a lot of MilSpec metal films in the bin but they don't really give it up like carbon resistors. Gotta have them with multiple gain stages but a Princeton is more about simplicity. There are also some spots where you don't get exact 66:1 plate/k ratios.

I've used 150's in the past and they worked fine. The Mojo Dijons work well too. Orange drops were the first mod hot-rod in the 1970's. They can be a little bright in Blackfaces and even more so in cathodyne inverters. I'm going to be pushing an organ-rescue 1962 Jensen P12N. For an alnico speaker, they are fairly precise too -- especially at only 13 watts. It's an original cone so more than that would probably blow it out.

I still have a commercial account with Mojo from when they were in Petaluma 20 years ago. My volume isn't keeping them open but the prices are good and things get here next day since they're only 250 miles away. The laser-cutting CNC shop is only five miles away so I couldn't ask for more than that -- unless it was for lonely Chinese beauties ;-)

[Chuck H]

I like Mallory 150's for BF builds. OD's are great too if you're after a bigger tone. And I might catch crap for saying that too since the common wisdom here is that all decent film caps are created equal But IMHE polyester does sound different from polypropylene.

I'll believe you hear a difference between Mallorys and ODs, but only after you match them for value before the comparison.

True, but faith moves mountains, and hear difference in capacitors.

Told ya.

[Jazz P Bass]

Other than bragging rights on this cap & that resistor, what is the question?

[ric]

According to TAG members that have sophisticated enough firewalls to pick it up, the malware warning on their machines is there sometimes and not others. The latest ( maybe an hour ago) was that one kind of Chrome was still showing an alert but Chrome for android never. I'm on my phone so I'm not worried about it.

Discussing parts choice here is an invitation for ridicule. This place is more about getting help than a DIY community of active builders.

Sounds to me like you're headed in a carbon comp direction, 22 filters instead of 100's, concertina instead of long tail pair, less is more gain stages etc.

Sounds warm and chewy to me.

I thought polypropylene coupling caps sounded smoother with polyester more in the crisp and clear camp, but that's just me. I'm not worried about a following pile on of posts dripping with scorn....cause I gotta get out and get to work.

Best luck with your project, work safe, enjoy.

[luthierwnc]

Well, carbon something rather than MF for the plate resistors. Probably for the cathodes too. The 2-watt Kiwame's have nice noise stats and they are pretty small. I'll build this on a garolite board with splayed lugs and should have plenty of room. Other mods are; a choke, mid control and a GZ34 instead of a 5U4 -- mostly because I might need some extra volts with the PT on the shelf. That could change easily. Either way, the first and second filter nodes will be 40uf and 20uf so a little more regulation than stock. 1m trimmer dwell pot, 1k5 grid resistors and 500R screen resistors, adjustable bias, diode across the intensity control and ...

The one thing I've done with every TMB amp I've made for the last ten years is put a switchable resistor on the bottom of the mid control -- usually a trimmer on a p/p pot set to 70k or so. It's my version of the Dumble preamp boost and for an extra five bucks in parts it is very useful. It does put more emphasis on getting the treble cap right. I've spec-ed a silver mica 250 puff but I'll get a low-end ceramic with the order in case I need to take a little hair off the gain. Might need to cut the first bypass cap down to 10uf too. The full 22uf might get a little woofy.

That's about it. I did an overhaul on one of these years ago. The filters were shot but the board components were mostly good. Some of the plate resistors were baked and way out of spec but the couplers were mostly still within the high end of the 20% tolerance. It was a great sounding little amp when I was done and I suspect that's because it was a great sounding little amp before I got it. Volts were up with modern juice but they are all like that.

Thanks for you input and good luck with your own projects, sh

[Chuck H]

If you can discern a difference between a 22uf and a 10uf cathode bypass cap in a typical guitar amp gain stage then your ears are better than mine. Across a 1.5k cathode resistor a 10uf makes about .15db less gain than a 22uf at 82Hz. (that's not "15", there's a decimal there ) That's a really tiny amount when you consider that any reasonable guitar speaker is also already demonstrating deficiencies at that point. That said... I used 22uf in the last BFish build I did "just cuz". If I already had some 10uf's on hand I would have been tempted to use them though. Unless the guitar used is a seven or eight string (and why would anyone play such a thing through a Princeton?) and the speaker/s are good to lower than average guitar frequencies (and why would anyone put such a speaker in a Princeton?) I don't think the difference between 10uf and 22uf in this circuit is important. So if you have 10uf's on hand, just use 'em.

[Jazz P Bass]

I have 'tweaked' Fender Princeton amps simply by picking the right first stage bypass cap.

Depending on the speaker, the Princeton can sound pretty crappy with a 22uf.

[Chuck H]

I have 'tweaked' Fender Princeton amps simply by picking the right first stage bypass cap.

Depending on the speaker, the Princeton can sound pretty crappy with a 22uf.

Agreed! But I've noticed that the first stage bypass cap is pretty important to setting up the reaction of the tone stack with the BF topology. For the BF topology I usually go with a small value for the second stage bypass cap. There's no clipping at this point in the circuit anyway so as long as some bass gets culled before there is it's all good.

[ric]

Well, carbon something rather than MF for the plate resistors. Probably for the cathodes too. The 2-watt Kiwame's have nice noise stats and they are pretty small. I'll build this on a garolite board with splayed lugs and should have plenty of room. Other mods are; a choke, mid control and a GZ34 instead of a 5U4 -- mostly because I might need some extra volts with the PT on the shelf. That could change easily. Either way, the first and second filter nodes will be 40uf and 20uf so a little more regulation than stock. 1m trimmer dwell pot, 1k5 grid resistors and 500R screen resistors, adjustable bias, diode across the intensity control and ...

The one thing I've done with every TMB amp I've made for the last ten years is put a switchable resistor on the bottom of the mid control -- usually a trimmer on a p/p pot set to 70k or so. It's my version of the Dumble preamp boost and for an extra five bucks in parts it is very useful. It does put more emphasis on getting the treble cap right. I've spec-ed a silver mica 250 puff but I'll get a low-end ceramic with the order in case I need to take a little hair off the gain. Might need to cut the first bypass cap down to 10uf too. The full 22uf might get a little woofy.

That's about it. I did an overhaul on one of these years ago. The filters were shot but the board components were mostly good. Some of the plate resistors were baked and way out of spec but the couplers were mostly still within the high end of the 20% tolerance. It was a great sounding little amp when I was done and I suspect that's because it was a great sounding little amp before I got it. Volts were up with modern juice but they are all like that.

Thanks for you input and good luck with your own projects, sh

The mid "boost" is interesting. I've been thinking of trying a dbl "crunch" (1st gain) pot with a cap bleed wired with it as in up with gain and down with some selected frequencies at the same time. My favorite part of building is trying new ideas.

You mention bypass cap size selection ( and I see others have discussed it); I have done a "voice" circuit where a six way selector has: no bypass,4.7,10,22,50,220 on the first gain stage (figuring that would have the most noticeable effect). Worked for me.

My "boost" circuit on that amp was a switched no bypass/ .068 on the second gain stage. Myself, I like some aspects of an unbypassed stage.

Best-r

[J M Fahey]

FWIW one of our own distinguished Members, John R. Frondelli from DBM Music New York often repairs/maintains U2 stuff when they are in town.

Curious about the Princetons used live and recording and knowing one of them was marked as being THE one, he proceeded to compare it with others side by side.
The only difference he found was that it had a wrong value coupling cap , a .01uF one where a .022uF one was indicated.

Funny thing is this was not a Mod, but Factory original.

When asked about it, a former Fender VP confirmed that it was not unusual, that if some amp batch *had* to be finished and delivered by some very close date and there was no time for missing parts to arrive, an "as close as possible" one could be substituted if they considered it would have little impact on tone or performance and that in a Princeton a smaller than normal coupling cap would not be a big deal.

So now you know it, a slight bass cut enhances distortion quality.

I bet you already knew

[luthierwnc]

Thanks all. Yeah, JM, remember these were designed when civilized players thought "7" was living dangerously. Cranked they distort! Of course, everybody loved them like that but you still have enough hash and enough low end to get muddy. I'm guessing the switch was the coupler coming off V1b -- although there are 5 .022's in there so how you decide where to scrimp would be a strange production decision.

ric: I do the boost different than most Dumble cloners. Mine is a really simple design that doesn't need bleed resistors to keep the caps from popping. On either a push/pull pot or relay you only need a spst switch. The Mid #1 lug goes to the pole and to either a trimmer or resistor that is grounded. The normally closed throw is also grounded. N/C is stock. N/O through between 68k and 180k gives you maybe a 1 to 1.5 (on a ten scale) volume boost but it stays pretty clean. Very useful and stupid cheap. Takes up no real estate on the board either. A 10mm trimmer attached to the switch lugs of a push/pull pot could be done on any TMB stack -- even one with a printed board as long as you are careful to use the same grounding point.

Thanks again all. Think I'll go with the Kiwame's and maybe ARCOL carbon comps on V1. Cheers, Skip