Lightning 15 watt to 30 watt

[echidna]

I made a Matchless Lightning style amp based on a couple of drawings last year, it's 15 watts and i used AC 15 transformers i had. A friend begged me for it and i let him have it, but he wants more headroom and has asked me if i can swap the trannies for AC30's, which i have in my spares.

I know i will need to add 2 x EL84 sockets and choke, but what else might i have to do? Uprate the filter caps. The drawings i used were from Tr1nity and Ceri@tone.

Thanks

[Prattacaster]

Wire, screen resistors, grid resistors, and a new cathode resistor. You shouldnt necessarily need different filter caps, Use the AC30 power supply.
Usually a 2xEL84 uses a 120ohm cathode resistor. For a 4xEL84 you would use around half that value but DOUBLE the power rating. I think a 10w resistor will do.

[echidna]

Got all that, except would that cathode resistor need to come down to around 60 ohms @ 10 watts, or 2 x 120 ohms like in a TW Liverpool, so the 60 for all four 120 for each couple of EL84's???

[TimmyP]

Sounds like you might just as well do a new build.

[echidna]

I know. I tried to encourage that but he insisted on this route. Any thoughts on the value of the cathode resistor?

[Prattacaster]

so then 60 for all four, 120 for each couple of EL84's???

This is a true statement. The end value will depend upon your plate and screen voltages, but these are good ballpark figures. I think the original used a 50 ohm but that seemed to bias too hot.

[echidna]

Thanks. I have a 68 ohms @ 25 watts, i'll try that.

[echidna]

I did this mod to 30 watts and added an EF86 channel, turned out great. Thanks for the tips.