EF86 build

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Jdandry8383
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EF86 build

Post by Jdandry8383 »

I need some help with a new build, basically a 18w lite with a EF86 V1. Main issue is that the amp has too much signal off the EF86, not so much little headroom but the volume on the 500k audio volume pot comes up very fast, I’d like to smooth it out better if that makes sense. First I tried getting the voltages in line with what I read was optimal.
My supply voltage is about 335v, .0056 cap off the plate into the Volume control with 18w term channel tone control values. Originally I was using a 1M/220k screen/plate combo and was getting very little difference in the screen and plate voltages, about 118v on the plate and 113v on the screen. I tried using a 2.2M/330k combo and it put the tube more in line with what I’ve read to be an optimal screen/plate voltage ratio, 120v plate and 70v screen, that didn’t help, but maybe opened the amp up a bit.
I’m thinking about trying to lower the 470k grid leak resistors on the EL84s down to 330k, but I don’t think that would help the real issue. I’d like to be able to tune the output drive of the EF86, I think that’s where all the voltage gain is coming from. Voltage divider, RT.66 tone stack to knock down the signal? I am correct that changing the volume pot to a 1M would increase the output? Also thinking about decoupling the EF86 supply from the PI supply so I could lower the EF86 supply voltage..Thanks for any suggestions !
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JMPGuitars
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Re: EF86 build

Post by JMPGuitars »

What schematic did you follow? We have a couple options you could look at for reference.

This is the classic EF86 Lite: files/JMPGuitars_18_Watt_EF86_Lite_Schematic.pdf

This is my tweaked version with what I think is a better implementation of the EF86, called the EF86 Lite 2P: files/JMPGuitars_18W_EF86_Lite_2P_Schematic.pdf

More docs can be found here: viewtopic.php?t=24429

Thanks,
Josh
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Jdandry8383
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Re: EF86 build

Post by Jdandry8383 »

I used the Classic Lite. Would the lite 2P values help with my issue you think?
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JMPGuitars
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Re: EF86 build

Post by JMPGuitars »

Jdandry8383 wrote:
Sun 02/05/23 12:08 pm
I used the Classic Lite. Would the lite 2P values help with my issue you think?
Use this voltage chart, take your voltages, and share them here: files/JMPGuitars_18_Watt_EF86_Voltage_Test_Chart.pdf

I like the way the Lite 2P works/sounds better, but that doesn't mean it has anything to do with the issues you're experiencing.
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