Whats going on here?

[DortoH]

OK OK I promise I am getting the hang of PSU's and PSUD2.

Been plugging all sorts of power supplies in PSUD2 to get the hang of it and then I find this one. Don't know what transformer this is but you can see where my two arrows are pointing.

Can someone expalin to me whats going on with the center taps?

http://dortoh.ca/crap/wth.jpg

:?: :?: :?:

[erichayes]

Hi All,

Rod, the big arrow item appears to be a cathode bias network for a directly heated cathode 25 volt filament output tube. Without knowing anything more, that's my best educated guess.

The little arrow guy is a fixed value hum balance network. It gets the heater voltage at close to ground potential without favoring one side of the heaters over the other. Variations of this circuit are a center-tapped heater winding, with the CT connected to ground or the cathodes of the output tube(s) (cathode bias on the output tubes) or a 100Ω 2W pot substituted for the fixed resistors and the wiper connected as mentioned above.

[DortoH]

OK, yeah the big arrow goes to a DHT.

So this is hum control, interesting. I'll have to look into this some more once i get my ST35 done :)

[EWBrown]

Is this PSU from a 2A3 aSE mp? The 2A3 is a directly heated cathode (filament) triode, the 750 ohms (10 Watts) resistor looks about the right value for a "cathode" biased 2A3, connecting the R and C to the 2.5VAC CT would (hopefully) eliminate hum for that stage.

The 2 100 ohm resistors from each leg of the 6.3 VAC filament winding is essentially a virtual center tap, which also is used to eliminate hum from teh 6.3 V filament input/driver stages (this is also done with the ST-35, as the PA774 has no filament CTs).

HTH

/ed B in NH