EL84 voltage question on pins 7 and 9

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StevenEsq
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EL84 voltage question on pins 7 and 9

Post by StevenEsq »

I checked my new build against the voltage chart. Besides generally being a bit on the hot side, my voltage on pins 7 and 9 of the EL84s don't look right:

Pin 7 = 347
Pin 9 = 343

Pin 9 should be lower by about 15 volts, no? (I've got 11.4 on pin 3)

Did I screw something up? Does this matter? Thank you.
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zaphod_phil
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Post by zaphod_phil »

The voltages between different amps can vary quite a lot, and are also affected by your local AC mains voltage. As a safety check, can you measure the AC voltage on your heaters? It needs to be below 7V.
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Newt
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Re: EL84 voltage question on pins 7 and 9

Post by Newt »

StevenEsq wrote:I checked my new build against the voltage chart. Besides generally being a bit on the hot side, my voltage on pins 7 and 9 of the EL84s don't look right:

Pin 7 = 347
Pin 9 = 343

Pin 9 should be lower by about 15 volts, no? (I've got 11.4 on pin 3)

Did I screw something up? Does this matter? Thank you.
Which version and what OT do you have? If you take a look at your schematic you'll see that, from the first filter cap, where your OT center tap is likely connected, (a) your plate voltage will drop due to the DC resistance of the OT primary, and (b) your screen voltage will be dropped by a dropping resistor leading to the next filter cap on the B+ rail and resistors between the rail and your screens. Your plate and screen voltages could be this close because (1) the OT you are using has a relatively high primary resistance, (2) your plate current is high (3) your screen current is low.

Are the plate and screen voltages the same or very nearly the same on both output tubes? What is your cathode voltage and what cathode resistor are you using?
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