I know, I'm sorry, but another 5e3 voltage question...

[stratavox]

Sluckey, your schem of your 5e3 build shows a 330-0-330 power trans. If a 5y3 ups that by a factor of 1.14, shouldn't that produce 376 volts? I'm seeing 340 at "A" in the B+ rail....and I'm old, so please, be gentle...; )

[eleventeen]

First, the "figure factor" of a perfect full wave rectifier is >1.41<, not 1.14. 


You'd get that with a diode rectifier, they are pretty close to perfect, only dropping .7 volts each which is nothing in the realm of 350 volts.


A 5Y3 "loses" considerable volts across the tube. It is among the "lossier" of common rectifier tubes. GZ34's and 5V4's not only lose much less, they have the indirectly heated cathode which delays the onset of full B+ for a bit.


Tube Type   DC mA   PIV   FIL AMPS   Max ACV   DCV   DCV DROP


Diode Rectifier               425   
5AR4 / GZ-34   250   1500   1.9   450   415   10
5V4-GA   175   1400   2   375   400   25
GZ37   350   1000   2.8   450   388   37
5U4-GA   250   1550   3   450   381   44
5U4-G   225   1550   3   450   381   44
5U4-GB   275   1550   3   450   375   50
5Y3-G/GA   125   1400   2   350   365   60
5R4GYB   250   3100   2   900   362   63
5R4G/GY/GYA   250   3100   2   750   358   67

Point being, if you start with 330-0-330 you should have 1.4 * 330 = 462 and lose 60 volts w/your 5Y3 should put you right in the 400 volt zone. Of course, line voltage variation (usually highish) and strength of your 5Y3 can affect things, the line volts more and more often influential. That 400 is easily +/- 20 volts. My experience w/5Y3 which I use a lot because I have a lot of them is that they are bit closer to a 50 volts drop.

[stratavox]

"Point being, if you start with 330-0-330 you should have 1.4 * 330 = 462 and lose 60 volts w/your 5Y3 should put you right in the 400 volt zone."

 OK, I understand, but that is STILL 60 volts more than Sluckey's schem shows at the output of his recto....and with line voltage increases over the years, it should be higher yet, no? I'm just trying to get to voltage MY build can live with...thanks Eleventeen, I appreciate your time...

[labb]

I think that a NOS 5Y3 would put you at about 375. A Sovtek will put you at about 400.

[HotBluePlates]

Sluckey, your schem of your 5e3 build shows a 330-0-330 power trans. If a 5y3 ups that by a factor of 1.14, shouldn't that produce 376 volts? I'm seeing 340 at "A" in the B+ rail....

340v a.c.? Or 340v d.c.?

Did you connect a filter cap to ground after the rectifier?

[sluckey]

If a 5y3 ups that by a factor of 1.14

That's a myth! You cannot say that a 5Y3 will absolutely produce 1.14 more DC than the AC input. There is another factor (actually two more factors) that has just as much effect (in some cases, even more) on the B+ out of a rectifier as the losses of the rectifier itself. That is the internal resistance of the PT itself. If a particular PT puts out 300-0-300VAC but a low current capacity (meaning high internal resistance) then the B+ will be lower for a given load than another 300-0-300VAC PT that has a high current capacity (meaning low internal resistance).

Charts that say that a diode will produce 1.414X, a 5Y3 will produce 1.14X, a 5AR4 will produce 1.2X, a 5U4 will produce 1.3X, etc., are useful ONLY AS A COMPARISON REFERENCE. I.E., for a GIVEN PT and circuit load current, a NOS 5Y3 will produce less B+ than a 5U4.

Bottom line, you cannot determine what the B+ will be by just knowing the voltage out of a transformer. You must also know the current load that will be attached and the internal losses of the PT.

[stratavox]

As always, I continue to learn, and appreciate the time you folks give the rest of us. I feel like there really isn't any place to go any more to learn this technology, except for you guys who share it on the boards...thank you!

[HotBluePlates]

If you want to read all about it, go to the Library of Information, download Radiotron Designer's Handbook, 4th Edition, and turn to the chapter on rectification.

It's a complicated multi-variable problem, enough that the old guys devised a series of charts to aid calculation so you didn't have to do so much math. Filter cap values, circuit current draw, power transformer winding resistance (on the secondary, and reflected from the primary), added series resistance, tube diode internal resistance, etc, all factor in when determining how much rectified voltage you'll wind up having.

[stratavox]

HBP, many thanks. Enjoy the weekend, all...

[PRR]

5Y3 data sheet
bottom page 1

350V AC and 125mA of DC loading gives typical 350V DC output.

Scale that for your actual 330V AC, we'd expect 330V DC.

Simple 1.0 "factor". We don't usually load-up 5Y3 to 125mA, therefore the "1.15 factor" often cited.

OTOH you could have zero DC current. Then the DC would rise to nearly 1.414X or 466V.

So 466V@0mA to 330V@125mA DC, you have to know your DC current.

A 5E3 is typically cathode-bias 2*6V6 and probably sucking 90mA-100mA all total. So a rise from 330V@125mA book-value to 340V observed is reasonable.

Different books and different actual productions vary. Where Tung-Sol shows 350V, a similar-vintage GE sheet shows 360V. A real 5Y3 is a very lame thing. Some makers opted to use better guts; some Russian "5Y3" are reported to give much less drop than older tubes.