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February 17, 2020, 02:59:31 PM

Author Topic: EML 45s  (Read 883 times)

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Offline jake111

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EML 45s
« on: February 13, 2017, 06:53:52 PM »
These tubes require a plate voltage of 250v and filament voltage 2.5v
Is A2 and C2 where you measure  plate voltage?
Are the filaments measured between A1-A4 and C1-C4?
Thanks, Jess

Offline Paul Birkeland

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Re: EML 45s
« Reply #1 on: February 14, 2017, 02:53:43 PM »
A1-A4 and C1-C4 are indeed the filaments. 

To measure plate voltage, you need to measure the DC voltage between A2 and the center lug of the hum pot.  In practice, we tend to do this by measuring the DC voltage from the hum pot to ground, then the DC voltage at pin 2 on the socket, and the difference between those is your plate voltage.

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline jake111

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Re: EML 45s
« Reply #2 on: February 15, 2017, 03:39:08 PM »
Ok. So A2 to hum pot is 288v and hum pot to ground is 55v. That gives me 233v plate voltage. Right?
Am I correct in thinking that as long as the plate voltage isn't over 250v there shouldn't be any ill effects to the tube?
Thanks, Jess

Online Paul Joppa

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Re: EML 45s
« Reply #3 on: February 15, 2017, 06:20:36 PM »
"Ok. So A2 to hum pot is 288v and hum pot to ground is 55v"

A2 to hum pot is the plate to cathode voltage. A2 to ground must be 343v, i.e. the plate to hum pot plus hum pot to ground. The EML specification is for a maximum plate to cathode voltage of 300v, so 288v is within spec. http://www.emissionlabs.com/datasheets/EML45.htm

Old-stock 45s did not explicitly specify a maximum voltage, but the published operating points don't exceed 275v, so I regard that as the maximum - thus an old-stock RCA (for example) would exceed the spec, but only by a tiny amount, well within the usual 10% tolerance.

I am assuming you have followed the manual for the conversion, and also the correction for plate choke wires (blue to A2 and C2, black taped off, and red to high voltage.)
Paul Joppa

Offline jake111

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Re: EML 45s
« Reply #4 on: February 15, 2017, 07:24:50 PM »
Yes, on the conversion. Thanks Paul.
Jess