Vox AC30 hum issue

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Reg18
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Vox AC30 hum issue

Post by Reg18 »

Anyone know how the AC30HW works on the inside?
Got a hum when on 30watt setting but it pretty much disappears when on 15watt setting which means it's most likely one side of a Output valve or 2?
It also has a loud hum on start up which comes in when the valves warm up for about a few seconds and then disappears, is that normal?

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Re: Vox AC30 hum issue

Post by sizzlingbadger »

Perhaps it only knows the words on the 15W setting.


I would try some new EL84's first, maybe just borrow some if you can to test it.
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Re: Vox AC30 hum issue

Post by Reg18 »

sizzlingbadger wrote:Perhaps it only knows the words on the 15W setting.


I would try some new EL84's first, maybe just borrow some if you can to test it.
Do you know how the wattage switch works?
I assume it either turns 2 off or lowers the power/volts getting to them or something along those lines.

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Re: Vox AC30 hum issue

Post by TmcB »

Why don't you swap the inside tubes with the outside tubes and see if it's still happens?
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Re: Vox AC30 hum issue

Post by Reg18 »

TmcB wrote:Why don't you swap the inside valves with the outside valves and see if it's still happens?
Thanks for the tip, do you know how the half power switch works?

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Re: Vox AC30 hum issue

Post by sizzlingbadger »

On the AC15 it just a voltage drop in the power section. I haven't seen the schematic for the AC30 so can't be sure.
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Re: Vox AC30 hum issue

Post by TmcB »

Reg18 wrote:
TmcB wrote:Why don't you swap the inside valves with the outside valves and see if it's still happens?
Thanks for the tip, do you know how the half power switch works?
Well, I figure it's going to be either cutting two of tubes out or going from pentode to triode mode - those seem to be the most common ways of halving the wattage straightforwardly.

Moving the inner tubes to the outer space would troubleshoot if it was the former mode, and if there was no change I'd highly suspect it was the latter mode - in that case, it could be worth trying a known good or matched set and see if it still does it.
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