Tube rectifier B+ differences

[tubedood]

I'm trying to learn I thought there was a formula to figure the voltage drop. My GE 5Y3 data sheet I am trying to decipher. I really don't want to ask you guys silly questions that are simple to you. Here is the datasheet I have what is my B+ at 290-0--290 and at 315-0-315.

[ric]

I'm trying to learn...I really don't want to ask you guys silly questions that are simple to you...

Wouldn't be much of a forum if nobody asked any questions.

For every bunch of people that know about the subject already and are discussing the question at hand there are always more folks (like me) that are learning the answer along with you.

The answer's always simple if you already know it.

[mozz]

There is not a set voltage drop, depends on the current draw.

[tubedood]

I know mozz just asking about a guideline. I thought I saw a posting about the voltage differences with different rectifier tubes.
No biggie thanks for everyone's input, it really is appreciated.
Dale

[Merlinb]

Great folks thanks! I was hoping there were some basic guideline to what kind of B+ to expect with the various tube rectifiers.

I depends on the load current, because tube rectos have internal resistance.

With SS diodes you get 1.4 times the transformer voltage at no load, down to about 1.35 times the transformer voltage at full load. So basically we can call it 1.35 times and don't sweat it.

But with tube rectos it's more like 1.4 times the transformer voltage at no load, down to maybe 1.1 times the transformer voltage at full load, and that also varies with the tube type. So how close does your circuit get to full load? There is no universal answer.

Also, notice I said "transformer voltage". Remember, the transformer voltage will ALSO sag between no load and full load, by perhaps 15% (transformer regulation)!

[Pedro Vecino]

If the problem is to choose a power transformer for its voltage associated with a rectifier tube, for me it´s best to know the power stage (tubes, configuration...) and the orientation of the design. And another important factor in many cases (dependent on the orientation of the amplifier): the dynamic aspect. Related to the intensity of the guitarist's pulse. This can also make a difference to determine the final voltage.
On the other hand, a useful resource (because the result of previous calculations are not always ideal) is to have different rectifier tubes to adjust the voltage in the most appropriate way.
I always have at least GZ34, American and Russian 5Y3, 5V4 and 5U4 at hand.
I don´t know well if this is exportable but this is the formula (where intuition and previous references play a role) that I use.

[mikepukmel]

Before I started building my first amp last year, I spent a ton of time looking for this kind of thing as well.

Starting from zero knowledge, I ended up with the graphs from a bunch of tube data sheets. There are only a few rectifier tubes used anyway, that Ive seen. The next question I had was: are these old tube data sheets really applicable to new tubes? The newer tubes didn't have nearly as complete data sheets as the old ones did.

[ric]

I depends on the load current, because tube rectos have internal resistance.

With SS diodes you get 1.4 times the transformer voltage at no load, down to about 1.35 times the transformer voltage at full load. So basically we can call it 1.35 times and don't sweat it.

But with tube rectos it's more like 1.4 times the transformer voltage at no load, down to maybe 1.1 times the transformer voltage at full load, and that also varies with the tube type. So how close does your circuit get to full load? There is no universal answer.

Also, notice I said "transformer voltage". Remember, the transformer voltage will ALSO sag between no load and full load, by perhaps 15% (transformer regulation)!

Good to see you posting here again, Merlin.

Appreciate you putting excerpts from your books up online as well. They're clear and understandable for people like me with no technical background.

Hope to hear you chiming in often.

[pdf64]

I depends on the load current, because tube rectos have internal resistance...

I think that it may be worth noting that this 'resistance' isn't a regular linear thing; rather it seems to follow a characteristic whereby the equivalent resistive value reduces as current increases (or at least that was my finding when tinkering with a vintage GZ34 in a Fender BF type 2x6L6 amp, and comparing it with silicon rectifier diodes and various sag resistor values).

Hence a formula to derive at Vdc at a particular load may be rather complex, and it's probably best left to the Duncan calculator, or 'suck it and see'.

[Helmholtz]

I'm trying to learn I thought there was a formula to figure the voltage drop. My GE 5Y3 data sheet I am trying to decipher. I really don't want to ask you guys silly questions that are simple to you. Here is the datasheet I have what is my B+ at 290-0--290 and at 315-0-315.

Maybe it helps to analyze an example from the datasheet above (5Y3).

If you look at the values for capacitor input (page 2, Characteristics and typical Operation, left column), you find that for a transformer voltage per plate of 350VRMS the DC output at the cap will be (only) 360V.

Under no-load condition the DC output voltage will correspond to the peak value of the AC input of 350*1.414= 495V. This means that with 125mA DC (load) current the DC drops by 135V! Far more than the specified tube voltage drop of 50V.
The reason for this huge difference is mainly due to the "Total Plate-Supply Resistance per Plate", in other words the equivalent series resistance of the transformer winding of 50 Ohms per side, which causes the AC input voltage to drop/sag with increasing load current. Unfortunately, as the AC currents are non-sinusoidal, the actual AC input voltage under load cannot be simply calculated from the resistance value - the actual sag is considerably higher than Irms*50Ohms".

Tube rectifiers always require a minimum series resistance to avoid excessive peak currents.

Now if you look at the lower chart "Operation Characteristics" for capacitor input on page 4, you will find the curve (5) corresponding to 350VRMS input. It starts from around 495V DC output at no load and ends at 360VDC for 125mA (point E). Along this curve you can find the respective DC output voltages for any lower currents.

The ratio of DC to AC varies from 1.414 to 1.03 with increasing load current. And the specified tube voltage drop (50V@125mA) isn't of much help either. It may be used to estimate the voltage difference between tubes, though.

DC output under load will increase somewhat with higher cap values, but it is not recommended to significantly exceed the manufacturer's recommendation.

[tubedood]

Thanks to everyone for helping to clear this up for me! Every day I pick up on something new in this forum. You all are great.

Dale

[Helmholtz]

I think that it may be worth noting that this 'resistance' isn't a regular linear thing; rather it seems to follow a characteristic whereby the equivalent resistive value reduces as current increases (or at least that was my finding when tinkering with a vintage GZ34 in a Fender BF type 2x6L6 amp, and comparing it with silicon rectifier diodes and various sag resistor values).

The V-I characteristic of each of the tube diodes looks just like the output curve of a triode at zero grid voltage (see page 5 of the 5Y3-GT datasheet above). It's the same physics.
Not really much curvature=non-linearity in the interesting region.

[loudthud]

In this thread: http://music-electronics-forum.com/s...ad.php?t=39620

I posted plots of instantaneous Voltage drop verses current of various rectifier tubes. Not exactly what the OP needs but interesting just the same.

[eschertron]

In this thread: http://music-electronics-forum.com/s...ad.php?t=39620

I posted plots of instantaneous Voltage drop verses current of various rectifier tubes. Not exactly what the OP needs but interesting just the same.

Took another look. Very interesting thread, even after (or maybe because of?) the passage of time.

[mozz]

Is this what you are looking for? It's the first page to come up on google. http://www.300guitars.com/articles/r...ge-drop-chart/
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

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