Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Blind Lemon on October 15, 2014, 01:08:32 pm
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Not a popping of the SB switch being thrown more of a inrush start up sound after the SB switch is engaged. Amps have it to a certain extent but this 5F6-A has a noisier that way than normal.
Any suggestions?
TIA
BL
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Might have something to do with how you have the e-caps distributed relative to the stdby switch.
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I have them like the schematic, after the SB switch.
BL
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Go look at a Bandmaster AB763 or pretty much any blackface Fender amp. You'll see that the highest B+ cap is on the "hot" side of the stdby switch and thus always gets charged. The 20-20-20 uf's for the preamp are on the cold side of the stdby switch.
AS you've described your circuit, with the stdby switch turning on EVERY e-cap, I would imagine one heckuva surge blasting through the output tubes, starting with a no-load overvoltage condition, a big droop as the caps get their first charge, including the negative feedback, and whatever the preamp tubes decide to do (probably minor) but it wouldn't surprise me to find you have a huge glitch when you flip the switch of doom. All those tubes are lit up so they are ready to conduct right away, so you get a big surge sound when you flip the switch. Ergo, I would try moving the biggest B+ cap to the hot side of the stdby switch.
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+1 with eleventeen - switch the OT CT.
--pete
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I'll give it a try.
Thanx
BL
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Put a 220K/1watt resistor across the standby switch. Simple. When the amp is turned on a slight amount of current gets through as well as a reduced voltage and softly charges the caps before the switch is thrown. When the switch gets turned on, the resistor gets shorted out as if it's not there. This will limit your inrush current before the standby switch is turned on and also help save the tube rectifier from the hard effects of effectively shorting until the caps charge by what you're describing.