Vox AC30 idle current

[Swampy]

Hi everyone,

The AC30 I have on the bench is drawing 480 mA on standby, and just over over an amp in play mode. It's got a fresh set of EL84's, and their cathodes are sitting at approximately 10 volts. It seems to be playing ok, is the current draw flowing through the filaments?

Chur

[Enzo]

480ma WHERE? The mains? The B+?

If mains, is that 120VAC or 240VAC?

480ma at 120v is less that 60 watts.

I don't know which AC 30 you have, but a quad of EL84, a GZ34 and three 12AX7s, heaters alone will use about 35 watts. Throw in a few watts here and there, like the dropping resistor to the zeners, transformer losses, tube currents. Certainly th quad of output tubes idling in Class A will suck up some watts.

If in doubt, does the PT get real hot? You could disconnect all the PT secondary wires and applu power to its primary - it ought to draw VERY little current that way - is that the case?

[Chuck H]

Where and how are ou measuring the current?

To check bias you should only be checking the current on the HV secondary of the PT.

[imaradiostar]

Or...alternately, you could measure the voltage from ground to cathode at the output tubes. If it's 10 volts across a 50 ohm resistor you've got .200 amps or 200ma. Remember that V=IR where V is volts, I is amps and R is resistance in ohms.

Jamie

[Swampy]

I measuring the current through the PT primary at the wall outlet with a power meter, apologies for my lack of details.

Cathode voltage reads fine relative to the schem (10 v) but calculating the static plate dissapation with these values (10 v / 82 r = 120 mA, 120mA / 4 tubes = 30mA per tube * 365 V (anode to cathode voltage) = 10.95 W, and the EL84 datasheet states the tubes max plate dissapation is 12W ?

I'm just running a power saturation test now to see how she goes, at this stage seems ok, with an 250 hz sine wave input signal dissapating around 35 watts over an 8 ohm load .

[imaradiostar]

Sounds like it's running just fine!

The real question is how does it sound?

jamie

[Steve Conner]

It would be running fine if the wall voltage was 120V.

If it were 240, maybe not so hot.