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I have been aiming to start a new amp build for a while now. I put a lot of time into trying to decide which amp I would get a lot of use out of and not just build for the sake of building it. A low powered tweed is something that I don't own, so it seemed like a good idea to go that route. I was initially going for a 5F1 Champ but figured the addition of the tone control on the Princeton would come in handy for me. I also found somewhere that will make a cab with a 10" speaker instead of the original 8". I have a Jensen P10R on hand that needs a recone, so I figure I'll do that and put it to use. So far I have a chassis and a few other odds and ends. I went with Mojo for the chassis because it is chromed steel like the originals, versus the polished stainless of some other brands. I also like that it is welded instead of bolted together. I have a couple old 6V6GTs to pick from and a few rectifiers. I need to get ahold of a couple old 12AX7s to try in it. I was let down when I heard that Classictone transformers were no more. I had no idea. Now I think I'll be going with a Hammonds for this. Probably a 290CAX for the PT with it's 275v taps. I ordered a 5F2-A eyelet board from Mojotone as well but they sent me a generic board instead. I messaged them but haven't heard back yet. Hopefully the quickly take care of that. I have eyelets and board onhand but I'd rather spend the few bucks rather than the time. I can't wait to accumulate all the parts and get it up and running!

For transformers, you should maybe give Edcor a chance.

tribi9 wrote: ↑

Fri Apr 01, 2022 4:34 pm

For transformers, you should maybe give Edcor a chance.

I actually have checked them out. Their lead time is pretty intense and I didn't find any in stock at any of my usual places. The specs on paper look good though. If I found one of their PTs in stock for a similar price to the Hammond, I'd have no qualms about using it. I think I am going to use a Heyboer for the OT. I found one with 4 and 8 ohm taps for a little extra versatility in the future should I need it.

Hammond is a good shout for the power transformer. They're quality, they're affordable enough, and that's about all I'd ask for. I've ceased putting too much stock in "magical mojo" power transformers.

Edcor is also fine, but sometimes you have to wait awhile if you want something specific. Hammond stuff tends to be off-the-shelf in a pretty wide range.

For the output transformer, Heyboer is the right move. They're really good. Probably considerably better than the other company that's no longer in business.

øøøøøøø wrote: ↑

Fri Apr 01, 2022 5:50 pm

Hammond is a good shout for the power transformer. They're quality, they're affordable enough, and that's about all I'd ask for. I've ceased putting too much stock in "magical mojo" power transformers.

Edcor is also fine, but sometimes you have to wait awhile if you want something specific. Hammond stuff tends to be off-the-shelf in a pretty wide range.

For the output transformer, it might be worth plunking down for a Heyboer. They're really good. And that's a place where a really good quality part really can make a difference. If budget is a concern, maybe find a way to save elsewhere?

EDIT: I see you're already doing the thing

I found the Heyboer OT that I am going to go with. I'm going to put in the order later tonight. It's a 7k primary with 4 and 8 Ohm outputs. It looks real nice and is paper wound too.

As far as a PT goes, do you have an preference for artificial center taps verses a real one? Hammond makes two similar transformers where that is the biggest difference. I understand how to work with either type, just doesn't seem like there is a real advantage one way or the other as long as it's done right. The one without the CT is cheaper. Both have 275v options for the secondary which is how I'd like to go.

Subscribed! I've been contemplating a 5F2-A kit for my first amp build. I'm looking forward to watching this progress.

I've used Hammond 290's on the last two PT swaps I've done on my Blackface Fenders and I really rate them. The holes line up perfectly, the wire seems good and they're labelled well. They also look the part which helps.

Both swaps have been easy and painless and they run nice and cool. Would recommend and will use again.

Funnily enough I've been trying to work out if I can combine a 5F2 with the tremolo circuit from a 5F11 somehow for my next build. Something like a Tweed Vibrochamp/Princeton crossover.


*EDIT: in fact, I've just had a thought, see your PMs

i love sharin foo wrote: ↑

Fri Apr 01, 2022 5:56 pm

As far as a PT goes, do you have an preference for artificial center taps verses a real one? Hammond makes two similar transformers where that is the biggest difference.

For the 6.3v filament winding it doesn’t matter at all from a functional perspective, if that’s what you’re asking about. That said, I’d pay a few more dollars for one with the CT just because it’s a bit more elegant from a construction point of view (a bit easier to connect a single wire to the desired ground point than it is to find a way to get two resistors there). If this doesn’t bother you (or if it’s substantially cheaper) then there’s no functional disadvantage

If the high voltage winding lacks a center tap, you’ll want to choose a different transformer

øøøøøøø wrote: ↑

Sat Apr 02, 2022 5:47 am

i love sharin foo wrote: ↑

Fri Apr 01, 2022 5:56 pm

As far as a PT goes, do you have an preference for artificial center taps verses a real one? Hammond makes two similar transformers where that is the biggest difference.

For the 6.3v filament winding it doesn’t matter at all from a functional perspective, if that’s what you’re asking about. That said, I’d pay a few more dollars for one with the CT just because it’s a bit more elegant from a construction point of view (a bit easier to connect a single wire to the desired ground point than it is to find a way to get two resistors there). If this doesn’t bother you (or if it’s substantially cheaper) then there’s no functional disadvantage

If the high voltage winding lacks a center tap, you’ll want to choose a different transformer

I just noticed that I didn’t specify but I was referring to the 6.3v. Thanks for the insight!

I have nothing useful to say about OTs for this build, but did want to chime in to say that I’ll be watching this closely to live vicariously through you. I LOVE amp build threads! Enjoy the journey and please give us loads of pics if you can!

wproffitt wrote: ↑

Sun Apr 03, 2022 6:15 am

I have nothing useful to say about OTs for this build, but did want to chime in to say that I’ll be watching this closely to live vicariously through you. I LOVE amp build threads! Enjoy the journey and please give us loads of pics if you can!

Thanks!

I'll be sure to document everything as soon as it actually gets underway . I watching build threads too! I only have a chassis, tubes and a few other odds and ends right now. I have an output transformer ordered and johnnysomersett is very graciously sending a power transformer my way (THANKS again!!).


And for anybody reading along, I have been poring over images of the blackface Champ/ Vibro Champ PTs... from the factory, it appears that they all had a center tapped 6.3v secondary for the heaters. But they did not use the center tap, they grounded one of the heaters and ran the other as a single line to the sockets. By grounding the one and running the other, it was effectively a 6/0 secondary rather than 3/3 or more accurately 3/0/3. I never really thought about that before or noticed it. It seems kind of weird but it worked. I however plan on running both 3.15v taps and grounding the center tap instead. This transformer should probably be about 315v, too which is more than I initially was looking for, so the plan is to use some Zener diodes to drop some voltage down to where I was initially shooting for. I am stoked to start wiring it up!

Next stop is the accumulate the caps and resistors. I plan on doing either F&T or Spragues for the electrolytics. I'm not sure what I want to use for the film caps yet. There's only a couple in the circuit.

Yeah if you have a center-tapped filament secondary, it'd be silly to run unbalanced heaters.

If you don't have a center-tapped filament secondary, I'd recommend creating an artificial center tap with two 150 ohm resistors to ground.

With a tight, uniform twist on the filament wires (and with filaments kept in-phase throughout the amp... pin 9 goes to pin 9 on all preamp tubes, etc) you'll radiate much less interference and have a quieter amp.

øøøøøøø wrote: ↑

Sun Apr 03, 2022 9:04 pm

If you don't have a center-tapped filament secondary, I'd recommend creating an artificial center tap with two 150 ohm resistors to ground.

With a tight, uniform twist on the filament wires (and with filaments kept in-phase throughout the amp... pin 9 goes to pin 9 on all preamp tubes, etc) you'll radiate much less interference and have a quieter amp.

I had to do this on my recent (first) amp build and it worked perfectly - although it seemed an oversight to not supply a PT with a center-tap when the amp design required it - and had it on the layout . Fortunately for Justin the old Fender PT I'm sending has one.

I mentioned up top that Mojotone accidentally sent me the wrong eyelet board. They replied first thing this morning and are sending out the correct one today. Thumbs up to them. Their customer service is as good as I remember. It’s been over a decade since I last purchased from them.

Last night I bought all the caps I needed. Mostly F&T for the electrolytics (two Sprague Atoms for the 25uF) and a few Mallory 150s for the others. I was looking at the Zoso blue molded caps but I don’t really think the 10x price is going to be justified by any difference in sound. Not that my ears can perceive at least. I went slightly higher in value on the filter caps for hopefully a bit less noise, maybe a little more lowend capability, and less costly. I also bought some other odds and ends. It shouldn’t be long before the build officially starts. I still need to find a decent 12ax7 though.

sounds like you’re on the right track. for my tweed champ, I built an oversized 10” cab but ended up really liking a hemp eminence 8” in there. baffle can change to a 10 later if needed. I also added 5f2 tone control, and negative feedback mod. the f&t caps I used for the power section did help with hum. i started my amp journey with mallory 150, i’ve done a few now with sozo and jupiter there is no appreciable difference worth the money to me; i’ve even swapped them in the same circuit.

edcor xformers are great, I’m using them whenever possible but lead times are much longer after classic tone disappeares. i built a tweed harvard recently with Heyboer I believe, and the b+ with NOS rectifier was right where it needed to be.