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Discussion in 'Shock Brother's DIY Amps' started by James Knox, Jul 29, 2021.
The 5Y3 has a significant voltage drop, Using SS diodes you will get about 50 volts rise. I would say just build it and measure using a dummy resistor load.
The nice reply from @Gijs answers both these questions; as you can see, the 'SS choice' in a voltage drop chart would essentially be the reference value, as in, “Drops 50 volts compared to what?”
A helpful tool to *estimate* B+ is this page. Just an estimate, but I’ve found it pretty useful.
It also estimates current draw. For the 5F1 etc, be sure to click the SE button — and at that point note the SE formula doesn’t require Rload to be entered.
Thank you for that...
If you go from a 5Y3 conventional tube rectifier (uses center tap) to taping off the center tap and using a bridge rectifier you will more than double the output DC voltage. By not using the center tap you double the voltage going to the bridge rectifier and you lose the approximately 60v drop caused by the 5Y3. You also cut the transformer output current rating in half.
What you really want to do is replace the 5Y3 with a solid state conventional rectifier. That's two diodes in a "V" shape, top of the V is AC input, bottom of V is DC out. We usually use two diodes in series on each side of the V (total of 4 1N4007 diodes) for longevity.
My old Magnatone wired on tag strips
@James Knox here is a Two Stroke/Maggie I built a little while ago - happens to use conventional (not bridge) diode rectification, and the same 290AX's 275-0-275 taps. I'd have to get back to my notes for the real number, but B+ is in the neighborhood of 380 here.
@Drew617 I feel like I’m on a trail that you blazed before me, lol.
So, do you like using diodes like on this Maggie build, or the little black square diode pack like on your current 5F2A in a 4x6 Box build better?
Are you “missing” a Tube Rectifier when you play guitar through these SS rectified builds?
What are your findings regarding sag and tactile response on SS Rectified Single Ended Amps?
I’m attempting to find his out for myself right now and I appreciate hearing your thoughts!
I mentioned in another thread that the pre-assembled rectifiers and diodes could be interchangeable, which is only half true. As Rob and others point out here, you can either build a bridge rectifier (for your PT without a HV CT) or a conventional full-wave rectifier (use the CT as you would with a 5Y3) out of four diodes. As far as I know, those pre-built things are only bridge rectifiers. Square/rectangle thing.
I've built bridge rectos out of diodes too, depending on circumstances. The prepackaged rectifiers are sometimes a little more convenient or compact, and fit easily between two rows of tags where I might struggle to fit diodes in the same space without burning them. I suppose individual diodes are a little cheaper, but we're talking about cents, not even whole dollars...
I'd build a single ended amp with a tube rectifier only if 1. it was supposed to be a faithful recreation of something specific or 2. I had a B+ target that wasn't easily achieved otherwise. It's an unnecessary cost, failure point, and heater.
I haven't built or played every last SE amp so I suppose there may be exceptions I don't know about, and theoretically voltage sag can still be induced by preamp. But IME there's no meaningful difference in sound or feel.
I'm not much of a "mojo" guy. I can hear a little difference between some tone and coupling caps but limit my choices to M150s, Xicon MPPs and 715P ODs. Worrying about it beyond that feels silly to me.
PP amps on the other hand... there's not a wrong answer and I prefer SS rectification anyway sometimes. But there is a real difference.
Also IME, beware recto conversations in the forums from non-amp people. There's a ton of solid state GZ34 this, juicy toanz that, standby switch blah blah... by people who are generally not accounting for the +/- 50V B+ changes they are introducing with a swap. May or may not be healthy for the amp, but more than that they're often just describing the sound of a voltage change.
So Rob is right of course, you need to use the center tap plus two diodes. And a dropper (sag?) resistor maybe, suppose you want to drop 50 volts and your amp draws about 50 mA, 50/0.05 = 1000 Ohms resistance. It will disspate 50*0.05 = 2,5 watts, so I would get a 10 watt 1k resistor.
Have a look here: https://robrobinette.com/5e3_Modifications.htm (search for "Simulate Tube Rectifier Voltage Drop and Sag Using a Solid State Rectifier and Sag Resistor") for how to calculate the drop resistor.
I think it was Blencowe going as far as saying there is no good reason for a valve rectifier: a few diodes and (if you want) a sag resistor is all you need.
Thanks Rob - yes, that is what I want to do. I was not understanding The difference between Bridge and Conventional Rectifier. I have now found where you break it down on your site!
Good to know. I am concerned with the 60v difference between a Diode Rectifier and a 5Y3. Trying to ascertain if I will need to use resistor(s) to drop the voltage.
Ahhhh... remembered had read about it once, should have known it was RobRobs site. Thx for the reminder.
“...no good reason for a valve rectifier...” Interesting quote!
If you have a specific B+ target in mind, 60V does obviously matter. If you don't, ~380 B+ (your 275-0-275 secondaries with diode rectification) should be right at home for a lot of Champy type circuits. That's one of the reasons I like the little Weber WRVBPT so much - it's $28 and 260-0-260 but runs a little hot, and produces almost the same.
Just my preference, and my experience is not extensive or expert-level. I've done the sag resistor thing in a PP amp where sag is expected. In a SE amp with 5V taps available, if I really had to knock B+ down 50V, I'd just as soon do that with a tube rectifier outside the chassis.