Hi. I leant my Burman 501 combo to an impoverished but talented nephew and, a few years later, have been rewarded with a dead amp. He says it was working one minute, not the next. He took it to someone to get it fixed (whose abilities I know nothing of) who claims the output transformer is goosed (he has also nicked all the valves from it!).
It shows no signs of burning. The transformer certainly doesn't look like it's got hot and still looks fine in its red varnish. Measuring resistance across the primaries I get around 83ohms across the coil and 43 and 38 measuring from one end to the centre tap, which seems okay. Measuring from the primaries to ground shows open circuit.
However, measuring from the secondaries to ground I get 0.1, 0.2, 0.3 and 0.4ohms, depending on which tapping I connect too. All of the above are with the transformer still in circuit, no valves fitted and no speaker connected (although connecting one makes no odds).
When I power it up like this (with no valves) the onboard fuse blows after a few seconds (there's only one slow blow, 3amp fuse on it and no standby switch).
Any ideas on how to start tracking down the fault? The next time I attempt to power it up I'll use a light bulb current limiter.
Comments
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
When! You get it all running sweetly, do consider changing that crap "TV" open pre set in the bias circuit!
I say "TV" because I saw a lot of them there and they have a habit of going "gappy" NOT what you want for bias adjustment!
Fit an enclosed type or, my fave, a multiturn jobbie.
Dave.
Someone suggested disconnecting the B+ top the OT's primary and seeing whether it still blows fuses then. Well it does. I guess the good news is that that means it's not the OT that's causing the problem?
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein