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i have a v4 master volume issue with a severe buzzing output. the original problem was: amp was running fine then the power went taking the 6amp ext. fuse out. the 6amp was replaced and then when flipping standby switch poof!!! small amount of smoke came from the switch. checked the switch, it read fine. turns out r54 180k (light resistor) was shot. i replaced this and then upon further inspection i realized there was no 10amp fuse in this amp! it was just plain old wire. i soldered in a 10 amp fuse checked for bad connections and now when power switch is engaged the buzzing is very loud.(note i have not yet tried the standby switch in fear of taking something larger out) when testing i originally pulled the power tubes to make sure the standby switch didn't go because of a spike. now when i fire it up without the power tubes, the buzzing persists...any ideas here? thanks.
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Have you checked to see if the rectifier isn't shorted. It sounds like you have a dead crowbar short somewhere causing the power supply transformer to physically vibrate. It could also be filter caps etc. Sounds like the amp got surged. Now you have to find the damage.Originally posted by randomair View Post -
v4 short somewhere..
i did check the rectifier, its fine. im getting 505 across all diodes. i need to address the filter caps next...its always a chase to find the culprit. hoping its something quick. well keep plugging away at it.Comment
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I'm confused here, but heck I'm easily confused.
You are getting a loud buzz from the speaker output of your amp with the power switch on and the standby off, even with the power tubes pulled from their sockets?
Please clarify.Comment
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certainly a buzz with just power switch on...
hey there 52 bill. yeah, standby switch is off, power switch is on, power tubes are pulled and yet there exists a buzz. it sounds like a transformer buzz. one thing i didnt mention is that the power transformer was rewound at some point. this amp is a friends and he brought it to me to repair it for him. he said he played a set one night and suddenly it just died. he realized the external 6 amp fuse had blown, so he changed that out, tried firing it up (turned on power switch, there was the buzz, then he hit standby and poof!!!) smoke came from the standby switch, so he shut it down. there are no visible markings of the smoke inside the chassis, which is odd.
the only thing i found close to the standby switch was the open 180k resistor in series with the standby switch, i got absolutely no reading on that resistor, so i replaced it. i knew replacing that resistor would not stop the buzz, but i did it in good faith. i think i am dealing with more than one problem here. also, he hadnt changed the power tubes since he has owned it (3yrs.) and it has been gigged alot. so i know those need a changin'. would you agree i am dealing with multiple problems? these type of repairs are always headscratchers...wish i could of been there when the problem occurred.Comment
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Did you tighten up all of the hardware on the transformer? It may have loosened up.Originally posted by randomair View Post
It may have been that resistor that smoked, but maybe not. It could have been something on the standby switch contacts vaporizing as well.Originally posted by randomair View Post
Yes, there are multiple things going on here, but don't let that confuse the issue. The transformer may be buzzing because of a circuit fault or because a nut has come loose.Originally posted by randomair View PostComment
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It sounds like you have arcing switch contacts. Smoke from the switch??? Problems in there dude. Don't let your meter fool you. When you start drawing current, anything can happen. Replace the power AND standby switches at the same time, then check it again. I just had a similar situation with a Matchless Chieftain in here for service last week.Comment
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yes there is trouble
after posting this morning i went down to address the issues and found that both the OT and PT were not completely secured. so i tightened them down and fired it up, just the power switch, still buzzing like crazy. i will now address the switches and follow johns lead. im trying to go real slow with this beaut'. i will keep updates coming. thanks for the prompt replies guys. i will post progress throughout the day.Comment
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I am unclear what you mean. To me "transformer buzz" means actual mechanical noise coming directly from the transformer - the transformer is vibrating and thus making sound. Is that what you have? Or is this buzz coming out the speaker?Education is what you're left with after you have forgotten what you have learned.Comment
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sorry for the confusion. the buzzing is coming from the speaker. the transformer itself is not mechanically buzzing. i tightened it down, thinking it was a mechanical buzz, but it turns out the buzz is coming from the speaker. i did find a burn mark near the .047 cap (c16 attached to one side of the rectifierOriginally posted by Enzo View Post
). the burn mark is directly where the PT red wires and the cap meet. i am going to try and replace this capacitor being i dont have a capacitor meter to check it and see if that does the anything for me.Comment
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If you get hum from the speaker on standy then what you have is magnetic coupling between pwr and output xfmrs. I think the xfmrs are at opposite ends of the chassis on those so this would be quite an extreme case and a bit of a stretch. Could be a partial short in the output transformer. I'd pull all tubes and put an ammeter in series with the CT on the output xfmr to see if theres any current drawn. Replace the stby sw first.The farmer takes a wife, the barber takes a pole....Comment
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