Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on June 07, 2012, 12:04:17 am
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When I go from standby to play it has about a second or two of static type pops. Never had this problem with a standby on any of my other amps, so I would like to get it corrected. I'm thinking I need to start maybe with a switch replacement and if the problem still persist, go from there. Should I try a cap on the existing standby switch to see if that helps? I am attaching two pixs and a power supply schematic scan. The middle switch with the two red wires is the standby. Platefire
BTW-on the power supply scan, the 680 resistor is connected to the 30uf/500V filer cap + just behind the standby switch--the line on the scan faded out and apprears un-connected.
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Yeah, just replace the switch and all will be good.
I never understood what the real purpose of all those 680 ohm resistors in series was all about. I seems just one big one would do the same thing. Yes?
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Hi LooseChange
Yeah I was kind of set back with all the 680 resistors too! Like to know the reasoning behind that. Never seen anything like it except in some of the crazy stuff I've seen in old Gibson amps.
I think I've got a standby on hand for another project I can rob and pay back later. I've got some radio shack SPST's but I don't trust them for main B+, AC power OK. Platefire
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Changed the standby switch out and have tested it for about 30 minuets switching it to and from standby. So far no more static poping when bringing it off standby to play as before. There is a slight pop when it is engaged now that I don't recall it doing before but I'm testing it with the chassis on a wooden stand on top of the cab--there is a couple of normal ground connections disconnected to sheilding on the cab. Don't know if that would make any difference or not. There is a ground lug screw that goes through the bottom of chassis, through th board and ties into the sheilding attached to the top of the cab. You have to back that screw off a bit to pull the chassis and then going back with the chassis into cab, screw it back to make contact with the sheilding again. Never seen that before.
Got a question??? Please view attached pix of the bundled wire going to the switches. You got line level AC, B+ to standby switch and heater wires all bundled together running parellel. I personally would never have done this and would of had all these wires seperated. Is this Kosher??
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You got line level AC, B+ to standby switch and heater wires all bundled together running parellel..... Is this Kosher??
Yes
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OK! Thanks. Hopefully the standby issue is now corrected on this amp.