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Re: for RG: suitable PT?

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5/11/1999 5:33 AM
Roger K.	Re: for RG: suitable PT? >>>I got thise cute little PT from Allied a while back, PN: 6K27VF. It is a 125v @15mA and has a 6.3v winding @600mA. <<< That should power two 12ax7 tubes just fine. I got a couple of trannys just like this from Antique Electronics ~$12 ea. Roger

5/11/1999 6:35 AM

That would be fine for one 12AX7, may be marginal for two.

The 12AX7 filament is 300ma at 6.3V, so two of them eat up the entire 600ma rating of the input transformer. The plates of the tubes need something like 1/2 to 1ma apiece, so you might need 4ma of high voltage, and a diode bridge will cause the RMS current from the transformer to be about 1.8 times the average, so the HV output is using 7.2ma. This reflects to the 6.3 input of the HV transformer as about 20 times the current, or 144ma, so you'll see about a 744 ma load on the incoming transformer's 6.3V winging, a bit of an overload, about 26% more than the design rating.

While this might work, you'll get a fair amount of sag out of the HV.
and might see some overheating.

Maybe, could be, but cautionary.

5/11/1999 8:23 AM

Wait a minute... I misread your note. I was stuck in the two transformers back-to-back.

You have a transformer that does BOTH 6.3Vac AND 125Vac as secondaries? If that's it, it will be just dandy for two 12AX7's. The HV winding there should be able to run as much as 7.5ma DC to the plates, and sometimes these things are rated at the actual DC out after rectification, so maybe the full 15ma.

Sorry - I was sleepy when I read the original.

5/11/1999 11:38 AM
Jim L.	So that Allied transformer will work good? What size is it? Where can I buy one? Thanks, Jim

5/11/1999 3:18 PM

Jim,

>>So that Allied transformer will work good?

Apparently, according to RG Keen, and he is *the Man* when it comes to transformers

>>What size is it?

My paper catalog lists it as 2 X 2 3/8" X 1 3/4" (HxWxD)

>>Where can I buy one?

http://www.allied.avnet.com/

Check with Allied. It is not listed in the new catalog (according to them) but they maybe able to special order it. My paper catalog lists it as $11.54 for quantities of 1-9.

Hope this helps,

Steve

5/11/1999 3:13 PM

RG,

Thanks for the reply. The PT in question does indeed have two windings, an HV and a filament.

Sorry the number I gave was the manufacturers number, not the Allied part #. Here is the Allied part #: 705-0034. In catalog 980 it is $11.54 for quantities of 1-9. There is also another PT that looks promising: 250v@25mA, 6.3v winding @ 1A, part# 705-0001, $13.52 in quantities of 1-9.

You can perform a part# search on Allied's website:

http://www.allied.avnet.com/

Hopes this helps.

Steve

5/22/1999 9:40 PM

RG,

Can I use this power transformer to power 2 12AX7 tubes?

Is 200 volts enough voltage for 12AX7?

Thanks
Jim

quote:
"I got thise cute little PT from Allied a while back, PN: 6K27VF. It is a 125v @15mA and has a 6.3v winding @600mA. Unloaded it puts out about 140v, and with a FWDB it puts out about 198v."

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