Matamp M15Mk1 Build Help...

For those building and repairing amps on their own. Learna and share ideas.

Matamp M15Mk1 Build Help...

Postby ryanuk on Tue Nov 01, 2016 12:51 pm

Hiya

I'm in the middle of a amp build from a kit I purchased from Madamp. The design is based upon 2 el84s in push pull, dual channel, 15w.

I've assembled the amp but am having some issues; the symptoms are;
1. The amp only the expected sound with 1 of the power tubes inserted. With both tubes inserted it goes terribly gated and distorted.
2. Heater voltages are too high at > 7v. I think this is due to it being a kit designed for "EU" voltage at 220-230v, and UK voltage is @ 240v. I measured it at 242v.
3. There is a low level hum, possibly due to heater voltage? Or perhaps lead dress.

I've eliminated the tubes as a problem as I've had some test these in another amp.

The first problem I suspect maybe wiring error at the PT. Im checking and double everything but wondered if anyone had any other ideas for symptom 1?
ryanuk
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Re: Matamp M15Mk1 Build Help...

Postby Simon Wicks on Tue Jan 03, 2017 11:24 pm

Hmmm, that heater voltage sounds high... should be 6.3v. I'd be more worried about the plate voltage though. whats it putting out after the rectifier? A more UK orientated PT might be the best idea unless you want the hassle of trying to drop the B+ and heater voltages (which i dont suggest!).
Simon
Simon Wicks
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