View Full Version : Lightning 15 watt to 30 watt
10-19-2011, 03:07 AM
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.
10-19-2011, 05:24 PM
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.
10-20-2011, 01:24 AM
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???
10-20-2011, 03:35 PM
Sounds like you might just as well do a new build.
10-20-2011, 04:57 PM
I know. I tried to encourage that but he insisted on this route. Any thoughts on the value of the cathode resistor?
10-20-2011, 05:25 PM
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.
10-20-2011, 05:30 PM
Thanks. I have a 68 ohms @ 25 watts, i'll try that.
02-20-2012, 01:11 AM
I did this mod to 30 watts and added an EF86 channel, turned out great. Thanks for the tips.
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