Max plate voltage on 45 tubes?

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svante
Posts: 11
Joined: Wed Feb 24, 2021 6:17 pm
Location: Sweden

Max plate voltage on 45 tubes?

Post by svante »

Hello blue glow members & Mark

I’m building an SET 45 tub amp, it’s almost done now, I will post some progress-picture in share your latest project map when completed. I’m using the Yamamoto 08 diagram, but not the Kit, it’s a completely other physical layout in metal chassis. However, I am a bit worried about the proposed Plate voltage 339 / 352 V (there is two version of the wiring diagram, one with AC heater and one with DC, therefor two levels). The RCA handbook states max 275 volt on the plate. will not 300+ V age the tubes fast?, or is it only the heat dissipation that causes this. Right now I have the 45 tubes on 340 V and 33 mA with the 1,5k Katode resistor that is proposed in the diagram.

Br Svante

Link to diagram:

https://www.google.com/search?q=yamamot ... -vA3nxnPFM
svante
Posts: 11
Joined: Wed Feb 24, 2021 6:17 pm
Location: Sweden

Re: Max plate voltage on 45 tubes?

Post by svante »

Hi, maybe the max 270v is referenced to Katode, and not chassis ground? seems reasonably, I must check what voltage I have there.
Can someone confirm?
Br Svante
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Tom_S
Posts: 90
Joined: Thu Feb 25, 2021 2:29 am

Re: Max plate voltage on 45 tubes?

Post by Tom_S »

I built a couple of simple 45 amps many years ago based on a popular JE Labs design. They were around 325v B+ with 55v at the cathode. 340v might be a little high, but you are still below the max 10w plate dissipation. The old broadcast engineers I used to work with once told me if you are within 10% of the specs, you'll be fine with most tubes.
svante
Posts: 11
Joined: Wed Feb 24, 2021 6:17 pm
Location: Sweden

Re: Max plate voltage on 45 tubes?

Post by svante »

Hi Tom. Thanks. then I stay with the current voltage level, still missing some parts to get the driver (717A) tube in to correct boundaries, so its a week or two before I know what that "special" 45 sounds is like.

Br Svante
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