RedBear MKX 50 Power Transformer

[The Dude]

Most searches for rectifier types list half wave, full wave, and bridge (separately), indicating that most folks don't correlate bridge rectifiers with full wave rectifiers, although they technically are. I tend to think of rectifier circuits in terms of how many diodes are involved (not counting series diodes). A typical half wave rectifier is one, full wave is 2, bridge is 4. There isn't a half wave bridge rectifier, so I think it's quite unnecessary to say "full wave bridge rectifer".

[J M Fahey]

Names come from decades old (in fact the better part of a Century) historical usage, so in **layman terms** we have "half wave rectifier" with one diode,full wave rectifier with two, bridge rectifier with four. Period.
That in other fields such as Physics other names are used, fine, but "here" those are the standing ones.

As of this particular PT I wouldn't overthink it.
For NOMINAL 430V +B (this is not Quantum Physics but Geetar amps) you need a PT for a 50W amp, very much doubt a 100W rated one fits in available space, definitely not in available cutout, and about 430*.707=single 304V secondary, say up to 310V to account for small losses and idle consumption.
That single secondary may be center tapped or not, center tap only helps equalize series filter capacitor voltages, does not "feed" anything, if not available you can use a resistive divider, say a 47k 2W resistor across each cap.

We are NOT talking , say,

315/0/315 windings to 380/0/380; and others using 175/0/175

or anything like that,those descriptions apply to full wave rectifiers, you have a bridge here.

Forget PSU designer, apply 50-70 y.o. experience instead.

[Delta362]

As of this particular PT I wouldn't overthink it.
For NOMINAL 430V +B (this is not Quantum Physics but Geetar amps) you need a PT for a 50W amp, very much doubt a 100W rated one fits in available space, definitely not in available cutout, and about 430*.707=single 304V secondary, say up to 310V to account for small losses and idle consumption.
That single secondary may be center tapped or not, center tap only helps equalize series filter capacitor voltages, does not "feed" anything, if not available you can use a resistive divider, say a 47k 2W resistor across each cap.

Would something like a Blues Deluxe or Hot Rod Deluxe PT be better suited?

[Helmholtz]

A two-phase rectifier needs 2 opposite phase transformer windings.

It is actually made up of 2 separate half-wave rectifier circuits with their outputs wired in parallel, each using one half of the secondary.
The opposite phase AC voltages make sure only one of them delivers current at a time and the 180° phase shift between the currents results in fullwave output.

The secondary can be seen as made up of 2 windings having opposite winding directions being connected at the CT.
Only one of the windings is used at a time.

From this it gets clear that the peak output voltage is given by 1.41 (sqrt of 2) times the RMS voltage of only one secondary half.


A bridge rectifier is powered from a single phase winding or voltage, so it's not a two-phase rectifier.

[loudthud]

I'd like to make a curious point about people who write books. Almost everyone agrees that Gerald Weber is full of it. I met the guy, he's not such a bad guy in person, but you'll never find him on a board like this one where there would be too much disagreement with his opinions. He's kind of arrogant on what he thinks makes good tone.

Kevin O'Connor has written several books and most of what is written is accurate and certainly you must admire the sheer volume of his work. That being said, there are a couple of technical points where he falls short of expectations. Like on this forum where he didn't understand that plate Voltage on a push pull power amp can swing negative.

Merlin is a interesting case, he seems to know tube circuits pretty well, but I found a post of his on a solid state forum where he was asking about analog feedback around a CMOS inverter. It kind of revealed to me that he doesn't have a strong technical background.

Teemuk is another interesting case. I found an old post of his where he was asking about what some people call mixed mode feedback, where some feedback comes from a small resistor in series with a speaker. Now, he's an expert. His book digs into just about every variation you can find in solid state guitar amplifiers. I like his style and didn't really find anything I would disagree with.

My point is this: when you write a book, especially without a knowledgeable editor, you are putting yourself out there and if you don't have experience in a particular area, you could be wrong on some minor technical points. Don't take it personally, it's not that you're a bad person.

[Helmholtz]

Merlin is a interesting case, he seems to know tube circuits pretty well, but I found a post of his on a solid state forum where he was asking about analog feedback around a CMOS inverter. It kind of revealed to me that he doesn't have a strong technical background.
.

Intelligent persons ask questions, that's how they learn.
Asking questions is not a sign of ignorance or weakness.- often quite the contrary.
And that question might have had many reasons.

No doubt your conclusion about Merlin's background is completely wrong.
Just read his books and articles in Tube CAD Journal.

[Enzo]

I think the point is, the nature of the questions asked reveal somewhat the level of the asker's experience.

[Helmholtz]

I think the point is, the nature of the questions asked reveal somewhat the level of the asker's experience.

Sometimes yes, sometimes no.
E.g., a seemingly naive question might be part of a clever strategy to find out about the others competence.
Or it might just show some interest in a special application one is not familiar with.
Has nothing to do with technical knowledge.

It takes far more than a few questions to find out about someone's background.

I generally prefer people who do ask.

[Delta362]

Getting back to my last question, would something like the Hot Rod Deville or Hot Rod Deluxe PT be better suited for this amp (both size-wise and ratings)?

Specs on the Hot Rod Deville PT is here {though it's a standup version)
https://www.tubesandmore.com/product...ot-rod-deville

Edit: Here's the Hot Rod Deluxe PT, with a lower rating 200mA than the Deville
https://www.tubesandmore.com/product...hot-rod-deluxe {end edit}

Those amps are marketed as 40W. They have similar HT circuitry, use the same two 6L6 output tubes, but 3 preamp tubes instead of 4. The secondary voltage of their transformers is around 330-340VAC and a 270mA rating, with an approximate 40V winding for the bias voltage supply, and a 6.3V 3.75A heater. Overall, they look like a better fit, but my concern is the 40W rating of the Fenders vs the 50W rating of the RedBear. Do you feel that would be a problem? Thanks!

[uneumann]

Or it might just show some interest in a special application one is not familiar with.
Has nothing to do with technical knowledge.
It takes far more than a few questions to find out about someone's background.
I generally prefer people who do ask.

^^^^^ This discussion about rating people is kind of weird... how many "experts" here are proficient in everything? Please raise your hands. I'd like to know.
Everyone has strengths and weaknesses in the knowledge, background, and experience.
There's no problem as long as you know your limitations and you don't bluster about stuff you're really just guessing at.
You can run into trouble at that front too... sometimes we don't know what we don't know.
LT makes a valid point about writing books (or papers or websites). The words are persistent and over time they can reveal misunderstandings or simply a poor phrasing that leads to confusion - or even an oversight or mistake. Even Einstein had bad days and didn't get everything right.

[Helmholtz]

It is common (or at leasr good) practice with scientific or reputable technical literature to publish an Errata list after a while.

[g1]

https://www.tubesandmore.com/product...hot-rod-deluxe {end edit}

Those amps are marketed as 40W. They have similar HT circuitry, use the same two 6L6 output tubes, but 3 preamp tubes instead of 4. The secondary voltage of their transformers is around 330-340VAC and a 270mA rating, with an approximate 40V winding for the bias voltage supply, and a 6.3V 3.75A heater. Overall, they look like a better fit, but my concern is the 40W rating of the Fenders vs the 50W rating of the RedBear. Do you feel that would be a problem? Thanks!

I don't think it will be a problem. Any power reduction will be slight if even noticeable. I don't think many people playing these kind of amps are looking for max.clean power anyway, more often they want earlier breakup and may even be using a power attenuator already..

All that said, I think the power out spec difference is either incorrect or due to the OT differences. The HR Deluxe has about the same B+ as the RedBear, and the current capability is sufficient. So if all else is equal, both amps should give the same output power as far as I can see.

[Helmholtz]

The Hot Rod Deluxe PT specs look good.
Expect 45W to 50W before the OT, depending on tubes.
The OT typically eats around 10% power, so output will be between 40W and 45W.

[Delta362]

Thank you for your help and discussion! I was able to change my order to the Hot Rod Deluxe version instead. I'll let you know how it goes after I get it installed.

[Helmholtz]

PSUD2 is a very useful tool.

If you like to play with it you can use the following parameters to simulate the behaviour of the Hot Rod Deluxe PT:

Change PT (no-load) voltage to 350V/150 Ohm, C1 = 50µF and change load resistor to constant current source.