Powertransformer for 5f1 amp?

[Oddvar]

Hi.

Could this transformer be used in a 5f1 build?

Best Oddvar.

[eleventeen]

Massive overkill...the low voltage 5v and 6.3 windings are of course fine. But the HV winding is going to cause you problems with how high the B+ voltage will turn out. You are looking to make let's say 320 volts after rectifier and filter for your highest B+ to feed to the 6V6 plate through the OT. I guess you could use blue/red to red/white (less than half the secondary winding) and a half wave SS diode to produce about 1.4 * ((540 - 22.5)/2) = 362 volts and you'd have to de-rate the secondary current in half to 25 mils. Maybe have to throw a 2K (or other value) resistor at least 3 watts in series. That would work. A bit ugly. If the series resistor needs to be higher value, that series resistor has to go to 5 watt and it would better to go right away to 10 watt.

[drgonzonm]

IMO, transformer is too light on ma, per your drawing 50ma.  Hammond standard is 81ma,to B rail.

6v6 data sheet says tube will draw about 35ma at 315 volts.   but you still to account for the losses on the resistors found on the B rail, and through the o/t.   

[kagliostro]

Eleventeen I don't know if I misunderstand you, but to me, using the wires blue/red and red/wite you obtain ~347V not 362V

540v / 2 = 270v

45v / 2 = 22.5v

270v - 22.5v = 247.5

247.5v x 1.4 = 346.5v

also the current, the transformer has a 150mA winding also halving it you have 75mA not 25mA

Franco

[PRR]

> per your drawing 50ma

150mA

The center-tap is not clearly indicated. IIRC Weber has a crate of PTs where the windings were misconnected, _NO_ CT rectifier is practical, and he has been trying to clear them out at slight discount from a good PT.

A Champ only needs 1A of 6V, so this 5A winding (and the 150mA HV rating) suggests it is WAY oversize for what you want.

[eleventeen]

Aha, I missed the "1" on the current rating which is under the vertical line. 150 ma it is, divided by 2 = 75 mils = fine.


There is no practical difference between 349 volts and 362 volts in tubeland. One who wished to get 320 volts final B+ after filtering would have to be prepared to fiddle with a dropping resistor if they cared. But yes, your math is closer.


My math: The entire red/white winding is 540 volts. There is no center tap at the center (eg; no "0" volts)


Thus half the 540 winding is 270 volts and we would subtract half of the 45 volt low winding. Thus the final AC between red/white and blue/red would be 1/2 of 540 = 270 minus 1/2 of 45 = 22.5, thus 270 - 22.5 = 247.5. Times 1.4 = 346.5. Maybe no resistor or only 1K needed.

[kagliostro]

I think we were both wrong

I'm near sure that if you measure voltage between blue/red and red/wite you have 230v (no 252.5v)

540 / 2 = 275

275v - 45v (NOT 22.5v as we assumed wrongly) = 230v

and so

230v x 1.4 = 322v

Ciao

Franco

p.s.: BTW red/yel IS the CT

[Ed_Chambley]

Yes, you can use it.  Sure, it is more than needed, but it will work if it is the only one you have on-hand.  I would not buy it for a champ, but if I had it I might use it.

[Oddvar]

I was just wondering, I have it lying around, thought maybe.  But I'll buy a more useful one then...Thanks.

[drgonzonm]

I missed that 150 ma,

sorry for the bad recommendation.

[shooter]

fwiw I have 2 of those PTs, use them in the early stages to *nail down* B+.  I've used about every combination of wires.  Can't find it handy but it seems like Weber states in the docs that any combination wire at the 150mA, which I *call* 100mA for MY average-normal.
That said, I have never used it with fixed bias, OR tube Rectifier.

[sluckey]

Could this transformer be used in a 5f1 build?

Yes, absolutely. I would use the red/white wires. The red/yellow is the center tap. The red/blue is a bias tap that you don't need.

It is bigger than what is actually needed for a 5F1 and it may not fit the cutout on a 5F1 chassis. But if I was gonna build a 5F1 in a blank chassis and already had that PT, I'd definitely use it.