Screen Taps for 18 watters?

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sepulchre
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Screen Taps for 18 watters?

Post by sepulchre »

Hello,

I'm building a 2 x EL84 18 - 20 watt box. I will be using an Edcor CXPP25-8K OT. My question is will using the screen taps of the OT be Okay? Or should I have screen resistors off the HT? (PT=550v ON it's taps)

I'm seeing a pretty wide range of of screen resistors and thought maybe just using the OT taps would be best.
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martin manning
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Re: Screen Taps for 18 watters?

Post by martin manning »

No reason you can't try it both ways. Even using the UL taps a small screen resistor can be included. Experiment a bit and see what you like.
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Re: Screen Taps for 18 watters?

Post by Stevem »

Are you running a rectifier tube, or SS?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

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didit
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Re: Screen Taps for 18 watters?

Post by didit »

Magnatone had a family of amps in the mid '60s. Output is a pair of 7189 (high voltage EL84) into UL tapped primary. Their transformer is similar to a Dynaco Z565, with larger core & winding than typical 18W. Different preamp and tone controls from the 18W classic. It's a clean amp, warm jazz to country twang.

Video demo provides a good tone sample ---




As Martin suggests, experiment and see if works for you. Easily made switchable.

Best .. Ian
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sepulchre
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Re: Screen Taps for 18 watters?

Post by sepulchre »

Thanks for the replies; I think a switch might be in order. I definitely want the amp to be overdriven, sometimes a lot. I've used the preamp in another of my designs, the Harlow, and it's got plenty of guts. So after reading up more on UL screen configs I may want to use it to clean up the tone a bit when needed. But mostly not. In fact, I'll leave the leads long enough to use but not hooked up initially. I'm thinking 470R - 1K screen resistors to be kind to the tubes. Then if it's necessary the UL taps can be hooked up to a switch (I'll leave a space on the front panel).

Anyway, thanks again for the replies and advice. As always, this place rules.
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