Single diodes as rectifier in our amps ?

[kagliostro]

Yesterday at a radio amateur flea market I've seen a small HiFi amp build by a guy

he was using a pair of (amazing) PY88 diodes as rectifiers

today I give a look to the datasheet and I've seen that the average anode current is 220mA

http://www.mif.pg.gda.pl/homepages/frank/sheets/010/p/PY88.pdf

Am I corret if I think that using a pair of diodes for a full wave rectify it will be able to handle 440mA ?

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Using diodes with heaters separated from the catode is correct if I suppose I can use it in full bridge configuration ?

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The bad thing is that the heater of the PY88 requires 30v

but there is also all the EY** diodes series to be explored 

K

[AZJimC]

I suppose if you wanted a bridge, with 4 diode tubes, you could power the heaters in series using 120v?

[kagliostro]

you could power the heaters in series

I also think so, but there are many other diodes of the EY** series, that can be connected in parllel to a 6.3v heater winding, that can be experimented
 
Where I'm in doubt is if using a pair of single 100mA diodes for a full wave rectify will give a 200MA rectify

Franco

[sluckey]

... I've seen that the average anode current is 220mA... Am I corret if I think that using a pair of diodes for a full wave rectify it will be able to handle 440mA ?

I don't think so. Only one diode will be conducting at a time, so the max current will still be limited to the current of a single diode. In order to double the current capacity the diodes would need to be connected in a parallel arrangement.

Same is true even if using four diodes in a bridge circuit. Two diodes will be used at a time. One pair handles the positive half cycle and the other pair handles the negative half cycle.  But the conducting pair of diodes are series connected so the same current must flow thru each diode. The PIV would be doubled but the max current will still be limited to that of a single diode.

[kagliostro]

Only one diode will be conducting at a time, so the max current will still be limited to the current of a single diode. In order to double the current capacity the diodes would need to be connected in a parallel arrangement.

      

In the meanwhile, loking to the spec of EY** diodes, I've found this

http://tdsl.duncanamps.com/link.php?target=05259E82
(read the datasheet on the preceding link, where the current for a diode is indicated in 180mA then look to the schematic about the use of a pair for full rectify)



Steve, before to read you, I was convinced I've found a confirm to my supposition

but now I don't know what to think 

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...... using four diodes in a bridge circuit. Two diodes will be used at a time. ............ The PIV would be doubled ......

Also this confuses a bit me, but I think I've understand, the two diodes are in series but with the winding of the PT in the middle, correct ??


Franco

[sluckey]

the two diodes are in series but with the winding of the PT in the middle, correct ??

Yes, correct.

[PRR]

This diode is rated 220mA Average and 550mA peak.

This suggests it will be OK with 440mA half the time.

However at 440mA the diode drop is 27V. 27V*0.44A= 11.88 Watts while conducting. If conduction half the time, 5.94 Watts average dissipation. But this rectifier gives a dissipation limit: 5 Watts.

I would be uncomfortable running over 300 or 350mA per pair.

[kagliostro]

Thank You for your intervention PRR

I think I've understand all what you say

I've only one question

However at 440mA the diode drop is 27V.

How have you done the calculation to establish the 27v voltage drop at 440mA ?

Thanks Again

Franco

[PRR]

> calculation to establish the 27v

Graph page 2 of the datasheet you linked.

[kagliostro]

Many Thanks PRR

Franco