EL34 SE in 430V?

[zxx123]

I've found an old stereo amp, which
works with a pair of EL34s.

The B+ of EL34's plate is measured 430V.
Wow, I have never seen before. The working data in Duncan's
only show SE in low voltage, SE triad in HV, or PP in HV.

No, the amp is not triad-connected.
Can you guess its real power rate? (8 ohm)

 

[Burnedfingers]

Care to share a schematic of the amplifier?

 

[zxx123]

....

Unfortunately, I don't have it.

 

[alejo]

Cathode resistor value?

Valve rectifier type?

You measured with valves in your socket or without them?

 

[zxx123]

values are

470ohm is used.
30V is measured.

Thanks.

 

[kevinkr]

You mean not triode connected?
What type of rectifier is used?
Is the screen connected to a tap on the output transformer, i.e. ultra-linear operation or is it pentode connected? (Screen to somewhere in the power supply?)

Idle current is about 64mA and the effective plate voltage is 400V (plate to cathode.) Plate dissipation is right around 25W or about the tube's maximum dissipation rating.

Output power might be as high as 10Wrms..

Kevin

 

[Tom Bavis]

They're pushing those tubes... 25 Watts total plate/screen dissipation. This may not be as linear an operating point as at a lower voltage, but it probably gives more power, and feedback was probably used to lower distortion.