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Discussion in 'Shock Brother's DIY Amps' started by theprofessor, Dec 28, 2017.
My Hammond 290CAX has a 275v secondary that reads 327v B+ with a JJ 5y3.
Thanks, @jsnwhite619 . Yeah, that's way too low. That's why I didn't understand that Allen suggested that 270V secondary tap for a tweed Deluxe. But the only one I can find with a center tap that is in the ballpark is the Allen (Marvel Electronics) one. I really want it to be at 350V or maybe up to 360V. loaded, no more. Of course I could add a dropping resistor, but I don't want to add any more sag. Why don't more appropriate PT's have center taps!?!?! Argh!
Honestly, I believe you are overthinking this.
I think anything in the 325-0-325 (+/-10) range will be perfect, that includes the Classictone, Hammond, Allen, etc. Plenty of people have weighted in that the Classictone 40-18016 puts them right at the sweet spot. I use the 330-0-330 taps on the 40-18078 and get ~360VDC on the plates. On the higher taps(355-0-355), the 40-18078 gave me 390VDC (closer to my real 1960 Tweed Deluxe), the difference in tone and feel was negligible and I could still bias just fine
Are you talking about the HT or filament secondary? All the PT's you listed have a center-tap on the HT winding. As for the filament, what's wrong with the artificial center tap used by Fender and 95% of high-end boutique and DIY clones?
Yeah, a couple of precision 100 ohm resistors is really better than using the center tap, since the center tap is usually slightly off center.
Voltages listed for the secondaries are misleading because they're at a higher current load than what the amp will idle at, which makes it difficult to predict what the idle B+ will be. I've never built a 5E3, but if I did, I'd probably use the 40-18016 or the 40-18078.
Thanks, @Wyatt and @Phrygian77 . Yeah, I overthink just about everything, and I appreciate your calling me out on that. It's interesting to hear that your 1960 Tweed Deluxe runs at about 390DCV. It's very likely that some of my frustration is at a phantom, in that I may be misunderstanding some of the information I'm processing regarding transformers. Thanks again.
Like the guys above mentioned, all of the PT's will have the high voltage secondary CT. Some of the PT's offer two secondary windings so you can have a choice between a higher or lower plate voltage. The 6.3v filament winding on some of the models may not have a CT, but like Phrygian mentioned, this is a minor thing and can be cured with the 100ohm resistors. These can be attached from pilot light to ground or connected directly to pin 8 on one of the power tubes.
Thank you, dan40!
I'm sure you've read that AC mains voltages back then were much lower than they are now. So, some people may want a PT built to the original specs, and some may want adjusted voltages so that their amp performs like it did back in the day.
Yes, that is indeed one of the "concerns." I am hoping to land around 350-360, and many of the tweed Deluxe transformers that are produced now end up with much higher voltage for the reason you mention. The way I have dropped voltage before is by using zener diodes on the PT high-tension winding's center tap. That is what I was hoping to do if the voltages should be too high for my liking this time. But even if I can't do it that way, I can just add a dropping resistor without worrying overmuch about "sag," since I'll rarely be demanding so much from the power supply to feel such a sag from that resistor (if I could feel it, anyway). I can also use a 5R4 in place of a 5Y3. I have NOS of both sitting around.
Prof, bear with me, I feel like I've missed something here. Hoping you wouldn't need to drop B+ on this, but *if you did* what would make it so you "can't do it that way"?
Y'all are the ones who are bearing with me! My impression was that the Classictone Deluxe Reverb power transformer did not have a center tap on the high-tension winding. That's the way I've dropped B+ in the past: using zeners on that winding. I've got no problem making an artificial center tap on one of the 6V6s. It's just that I didn't want to drop B+ (again, if it were necessary) using a dropping resistor. My thinking was that this would add more sag.
But: (1) I may well be wrong about the Classictone PT being made without a center tap on the high-tension winding. I may be confused by what @muchxs said on this thread (post #8) about a center tap for the heaters.
(2) I'd only (possibly) notice the sag when I'm really lay into the amp and there is more exertion on the power supply. But that won't really happen much, anyway. So that's a false worry.
In sum, I may just be plain wrong about one or both of these things! Just overthinking it probably, as @Wyatt said. Please set me straight, @King Fan!
P.S. I ordered all my parts save the PT from Tube Depot this morning. Tube Depot has a weight limit for their "free shipping" deal, and the Classictone PT would have put me overboard. So I went with the Classictone OT and waited on the PT. Now the only part I don't have to build the amp (including head and speaker and cab!) is the power transformer.
You've got it -- Much was talking about *heater* center taps, which he liked a lot. Don't forget you can see CTs on wiring diagrams -- ClassicTone (and others) link to these as "Specifications." So stop worrying and learn to love the build!
Thanks, King Fan!
Yep, there you go! When I read some of the discussion around center-taps, I did not know of the distinction between a high-tension center tap and a heater center tap. So even though it said "CT" on the spec sheet, I assumed that there was no CT (talk about prejudicial bias!). But here they are.
The first is the spec sheet for the Classictone PT referenced in the OP (40-18106). It has a center-tap on the HT wind (660V CT @ 120mA) but not on the heaters. The second is the for the Classictone 40-18109, which has a center-tap (actually, several) on both the HT wind (e.g., 660V CT @ 100 mA) and on the 6.3V heaters (6.3V CT @ 2.25A).
I should have been more confident in reading the spec sheets myself, but at this stage the game, I'm not all too confident about my abilities to understand all this, so I made a fact into a counter-fact!
Turns out that much of my discussion in the last page or so of this thread could have been avoided if I had a basic understanding of that distinction between high-voltage center taps and heater voltage center taps. As my mother says, "Live and learn; die and forget it all."
LOL. Good on ya!
But you gotta update your terms. ‘Counrerfacts’ are now called ‘alternative facts.’
Right! So that way, I can still be right, even though I'm wrong. It's a fact in an alternate universe...
In my search for 5e3 transformers across the worldwide Interweb, I found this old Tone Quest Report piece on 5e3 output transformers. There's been a lot of water under the bridge since November of 2010, but I think it's still useful. It reviews other new products for vintage 5e3 tone as well.
Using Classic tone
PT 40-18021, OT 40-18038(6k6-4/8ohm deluxe reverb ot) and stock circuit aside from 3x22uf filters and 800pf tone cap, Weber 12a125a
Vac in 122.5
Stock 250r brown devil 6v6 cathode resistor(252r)
With Nos ge5y3
=364@ 6v6 plates (approx 115% no red plate sounds good, a 300r would most likely put this at 98-100%)
=374@ 6v6 plates (101% sounds good but the GE sound beter)
Sounds realy nice but I have nothing to compare it to in person.
Edit.. Added wall voltage
Thanks, D'tar! Those are very helpful data. By the way, do you mean an 800 pF bright capacitor, in place of the stock 500 pF one?
Tone cap professor.
Sadly, I do not yet own a single coil guitar. Stress the yet! This helped me enough not to revert back to stock value...YMMV