Thread: Fender amp copy
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Old 8th Oct 2019, 3:06 pm   #30
ColinTheAmpMan1
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Join Date: Jan 2012
Location: Wimbledon, London, UK.
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Default Re: Fender amp copy

Quote:
Originally Posted by retailer View Post
He didn't go away and make a cup of tea -seriously though it is impressive.

I delivered the amp only to get a call a few hours later - HT fuse blew. Back on the workbench I found a partial short to ground on the tremelo depth pot, the circuit I used was a modified version which varies the bias voltage to produce tremelo - internet opinion seems to be that it is more reliable and capable of more depth than the neon/ldr setup, the partial short to ground shunted the bias voltage to ground as the tremelo depth control was turned up, both input channels equally affected. Turning the depth control to 4 or 5 reduced the bias from -36V to around -18V, enough to blow the HT fuse.

My son has my Les Paul Custom that I purchased second hand when I first started work back in 1970 and wanted to be a guitar god, cost me 6 weeks pay on lay-by, sadly I had no talent and it ended up shoved under the bed.
I don't much care for the bias-voltage tremolo. It affects both channels as you say and this can be a nuisance if you have a microphone going into the other channel. Tremolo'd voice sounds pretty horrible.
The other objection is that the optimum grid bias on the output valves is being compromised. I tried an experimental hook-up some years ago and I could see the change in current through the output valves varying by noting the red glow fluctuating. I soon re-jigged the circuit. OK, the neon/ldr circuit has its detractors, but I think Fender stayed with it for good reasons.
Colin.
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