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-   -   combine filament winding for rectifier (http://www.diyaudio.com/forums/tubes-valves/224363-combine-filament-winding-rectifier.html)

mrneedle 26th November 2012 03:07 PM

combine filament winding for rectifier
 
hi all, i like your ideas/opinions on my poor-man-solution-idea...

i have a PT here with 3 filament windings.

2x 6.3v @ 2a
1x 5v @ 2a

now i like to use a 5u4g but it needs 3A.

can i just lower the voltage with a chunky resistor on one of the 6.3v windings to about 5v and then put it in parallel with the 5v winding?

mctavish 26th November 2012 04:55 PM

NO! The 5v winding is designed for a rectifier tube and in addition to carrying the 5v AC it also carries the rectified high voltage DC. It is insulated differently and sometimes wound differently on the core to account for the H.V. DC it must withstand. The 6.3 volt windings are normally NOT designed for rectifier use. In fact, I dont know of any 6.3v directly heated rectifiers off the top of my head. You may be able to get the 3 amps out of the 2 amp winding without trouble if the rest of the current you are pulling from the transformer is low enough. HTH

Frank Berry 26th November 2012 05:29 PM

Why not change rectifier tubes to something that pulls less filament current?

mrneedle 26th November 2012 07:38 PM

Thanks for your quick and clear answer!

Is it possible to calculate the extra ampere when not fully using the other windings?

I only plan to use it with 3x 6sl7

And frank, i didnt want to buy new stuff but only use parts i have laying around....

kstagger 26th November 2012 07:57 PM

Use a 6X5 one of the 6.3V filament windings. Dirt cheap.

Another option, use a 5AR4, 5V4, or 5Y3 on the 5V filament winding.

mctavish 27th November 2012 01:07 PM

With only 3 6SL7 being used i say go for it and use your 5U4. Your transformer should be just fine. I certainly understand wanting to use what you have on hand.

flatheadmurre 27th November 2012 04:47 PM

If the total VA of the separate windings is less then the rating of the transformer then no problem.

Just add up the separate windings example:rectifier 5V x 3A = 15VA + 6sl7 6.3V x 0.3A x3pcs =5.67VA.

HT current is the trickier part and depends on type of rectification and if you use regulation.

If it adds up to a number less then the transformer rating youŽre safe.

If you overload it a bit and donŽt plan to leave it on around the clock youŽll get away with that to.

mrneedle 28th November 2012 03:51 PM

Quote:

Originally Posted by flatheadmurre (Post 3259291)
If the total VA of the separate windings is less then the rating of the transformer then no problem.

Just add up the separate windings example:rectifier 5V x 3A = 15VA + 6sl7 6.3V x 0.3A x3pcs =5.67VA.

HT current is the trickier part and depends on type of rectification and if you use regulation.

If it adds up to a number less then the transformer rating youŽre safe.

If you overload it a bit and donŽt plan to leave it on around the clock youŽll get away with that to.

also thank you for this explanation.

but all is solved i found a 5Z4 and that tube is within the limits of the transformer...

anyway the transformer is buzzing like mad, even when it's not connected ...

so I'm now try some of the suggestions i found on the forum... we need a good transformer to begin with.....

wa2ise 29th November 2012 02:44 AM

Quote:

Originally Posted by mrneedle (Post 3260982)

anyway the transformer is buzzing like mad, even when it's not connected ...

Maybe it's just the bolts not tight enough to keep the lams from rattling from the 50 or 60Hz magnetic field. Does the transformer get hot? If so, maybe a shorted turn, if not, try tightening the bolts.

AJT 29th November 2012 03:31 AM

just because it says 5volts at 2A does not mean you can not use it for 3amps, the winding does not stop delivering current at 2.1...try it and most likely you can get away with it...


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