Richard Hawley

I just bought a WEM dominator 111 off ebay great price for a 70's valve amp. It sounds great apart from a sub bass background hum. It's not an earth issue and it is there even if the guitar is not plugged in. Talking to some people they say it is normal for an old amp but it is picked up by my mic when recording. I recall my old marshall I had in the 70's had a hum but can't recall if it was as loud as this. Anyone got any experience with old valve amps and the hum issue?

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You could as a first port of call change the valves, even my new Fender Pro junior had hum until i change the pre-amp tubes for a Harma ECC83/7025 which reduced hum considerably. well worth getting new tubes in it.

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''Rocka-Jazza-Blues-A-Billy''
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yeah was thinking about that - it still has the old mullards in it

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After the valves, you might want to try changing the big Electrolytic Capacitors in the power supply (they smooth out the H.T Voltage). Looking at the Schematic here
http://www.schematicheaven.com/bargainb ... _mkIII.pdf

it looks like they're 50uf, you could change them for 47uf (dunno what the Voltage is, you'd have to measure it on the existing ones). It's worth replacing them on an old amp anyroad as they dry out and could blow up if the amp hasn't been used for a while.

If you're not too confident doing it (or can't follow my rubbish directions), you might want to take it to a tech to do it, it's gonna be upwards of 400 volts around there.

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Passive smoking is theft.

Thanks for that. Reckon I'll take it to a tech, it's definitely not my speciality area. I want to get a scaling circuit put in any way.

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