Rectifier efficiency?

[Cliff Schecht]

The correct multiplier is 1.414, not 1.3. For 440V, you need a 310-0-310 and for 450V you need about a 320-0-320. FYI the 1.414 comes from the square root of 2, it's not some random made up number!

Also keep in mind that some transformers are rated under load, others are rated unloaded. I know Hammond specifies their transformers at load but I don't know about other guys..

[ToneMerc]

I've been considering a PT swap to get the voltages down to 440v 450v.

So. I should be looking for 340v x 1.3 = 442v, if I understand this thread correctly. Do I have this about right?

Anyone with experience in the 5F6-A type build? Please let me know how yours turned out. Thank You.

If you uing an adequately rated power transformer and a good vintage brand GZ34 tube rectifier then that is close enough. At 120v using a 345-350 tranny will get you just shy or sitting on 450 volts on the plates. If the wall voltage is typically a few volts greater than 120, then a 340 will keep you closer to 440.

TM

[Mars Hall]

The correct multiplier is 1.414, not 1.3.

I thought the multiplier was 1.3 for a 5AR4 rectifier and 1.414 with a SS rectifier.

[M Fowler]

0.707 for full wave rectifiers with CT

1.414 for bridge and half wave rectifiers.

diode is 1.414 conversion
5Y3 is 1.13 conversion
GZ34 is 1.3 conversion
5U4 is 1.2 conversion

Mark

[Andy Le Blanc]

those are peak figures too.

the average V dc is .45 with a full wave and .9 with a bridge

The I dc is 1 full wave and .62 for a bridge, full wave is better for current
bridge is better for volts.

Isn't a forward voltage loss in with the tube data

like with a 5y3 the ac applied is 700 the dc out is 390 (vs the 497 the math shows) plate imp. is 50 ohms and the full current load drops the v to 360.

Use the operation characteristic graph for the tube type.

Strict math will give you "ideal" figures, not always "practical" figures.

[David Root]

One rule of thumb calculation I got here a few years ago is:

Take the desired quiescent plate voltage eg 450V

Add the voltage drop of the chosen rectifier tube, if using one, eg 5AR4 20V,

So, 450+20=470V

Divide by 0.90, = 522V

Multiply by 1.4 = 730 V

Divide by 2 = 365V ie you need a 365-0-365 PT secondary.

With SS rectification, you only need 350-0-350.

I have found this to be pretty accurate for most designs and only comes in low if you have lots of preamp tubes and/or run your tubes real hot ie class A.

[Cliff Schecht]

You guys I'm sure are right about the different multipliers for different rectifier types. I've always used SS though so I wasn't even thinking about the fact that tube rectifiers are less efficient!

[Rick]

You never see these in tube guitar amps, (I do use them where thought to be needed or useful) MLR to the tube recto. Older tube manuals will often list them. Some say all tube rectifiers should have them. Tube rectifiers can only deliver so much current, the limiting resistor keeps it from being swamped for current, it will also lower the voltage by ohms law. I'm not sure why no one uses them on guitar amps (besides me that is), but they will extend rectifier tube life and give voltage dropping that can be useful. They will get hot and need big ratings and installed where the heat will not destroy things, maybe that is why they are often eliminated or ignored, still, they can be very helpful in dropping an excess 10 or 15 volts or more and the rectifier tube will love you for it.