Hi
I have a BGW 250D stereo power amp. It comes with banana posts standard, so I wanted to change them to 1/4 inch for both left and right and also for bridged mode.
The instructions for bridged mode say take the hot from the left channel (with the switch in Mono) so after I put in the left and right speaker jacks I wired the bridged output jack with hot from the left channel by taking loops off the new stereo speaker jacks. OK so far?
Somehow this left me with a dead short on the right channel, probably because the cold side of the bridge speaker jack comes from the tip connector on the right channel speaker jack.
Anyway, the right channel no longer works. I see no damage and smell no burning, and I would have expected a well-made amp like this to have open and short circuit protection.
Obviously I've disconnected the bridged speaker jack and although I have no more short circuits I have no audio either.
Any ideas on what might have blown please?
THanks
Phil
I have a BGW 250D stereo power amp. It comes with banana posts standard, so I wanted to change them to 1/4 inch for both left and right and also for bridged mode.
The instructions for bridged mode say take the hot from the left channel (with the switch in Mono) so after I put in the left and right speaker jacks I wired the bridged output jack with hot from the left channel by taking loops off the new stereo speaker jacks. OK so far?
Somehow this left me with a dead short on the right channel, probably because the cold side of the bridge speaker jack comes from the tip connector on the right channel speaker jack.
Anyway, the right channel no longer works. I see no damage and smell no burning, and I would have expected a well-made amp like this to have open and short circuit protection.
Obviously I've disconnected the bridged speaker jack and although I have no more short circuits I have no audio either.
Any ideas on what might have blown please?
THanks
Phil
Obvious one - check for internal fuses. You might be lucky.
Failing that it's almost certainly blown output transistors and possibly more.
Failing that it's almost certainly blown output transistors and possibly more.
1/4" jacks are bad news for amplifiers.
PERIOD.
Even if wired correctly (you can't use one for a mono output, it shorts out one channel), they will short out the amp if the plug gets pulled out while the amp is on.
Typical BGW amplifier, the smaller they are, the fewer the number of outputs.
BGW used a magnetic circuit breaker for the power switch, no B± fuses.
"I would have expected a well-made amp like this to have open and short circuit protection."
After 30 years you expect everything to work as new?
PERIOD.
Even if wired correctly (you can't use one for a mono output, it shorts out one channel), they will short out the amp if the plug gets pulled out while the amp is on.
Typical BGW amplifier, the smaller they are, the fewer the number of outputs.
BGW used a magnetic circuit breaker for the power switch, no B± fuses.
"I would have expected a well-made amp like this to have open and short circuit protection."
After 30 years you expect everything to work as new?
Short-circuit protection
Hi
That power switch is interesting because I noticed that it seemed to be live no matter what the switch position. I don't know how that works.
I would have thought that if the amp were built with open and/or short circuit protection on the outputs that they would still work after 30 years, yes.
So it suggests that it never had them (if those are shown on the plan you sent me, I appreciate that but as a nominee for the Darwin awards I can't read a schematic lke that).
As there was no burning smell, I can hope that something was tripping. As I recall something was, because the power switch kept kicking off until I unplugged the speaker in the shorted side. So maybe the power amp section is ok. Although I suppose if it were ok, I would get some noise out of it.
THanks
Phil
Hi
That power switch is interesting because I noticed that it seemed to be live no matter what the switch position. I don't know how that works.
I would have thought that if the amp were built with open and/or short circuit protection on the outputs that they would still work after 30 years, yes.
So it suggests that it never had them (if those are shown on the plan you sent me, I appreciate that but as a nominee for the Darwin awards I can't read a schematic lke that).
As there was no burning smell, I can hope that something was tripping. As I recall something was, because the power switch kept kicking off until I unplugged the speaker in the shorted side. So maybe the power amp section is ok. Although I suppose if it were ok, I would get some noise out of it.
THanks
Phil
"As I recall something was, because the power switch kept kicking off until I unplugged the speaker in the shorted side."
That's what it's supposed to do with a short.
"That power switch is interesting because I noticed that it seemed to be live no matter what the switch position"
Sounds like the breaker/switch is now failed.
"I would have thought that if the amp were built with open and/or short circuit protection on the outputs that they would still work after 30 years, yes."
I don't think that is reasonable.
Small signal transistors made 30 years ago had gold-plated leads. The gold migrates into the tin of the solder, and the joints become brittle, and fracture.
5% carbon film resistors have the copper plating (which is then tinned) on the steel leads fail and and causes the resistor to appear to go open. (these are called copperweld leads)
On many old amplifiers with gold small-signal transistors they start working when you remove all the old solder and re-solder with 4% silver solder.
If the resistors are starting to go they must be replaced.
I've also had film caps with copperweld leads fail. Carver used mylar input caps (on some models) that had this problem.
This amp may not be ecconomical to repair, I have one that I have wasted so much time on that I would have been better of replacing it.
That's what it's supposed to do with a short.
"That power switch is interesting because I noticed that it seemed to be live no matter what the switch position"
Sounds like the breaker/switch is now failed.
"I would have thought that if the amp were built with open and/or short circuit protection on the outputs that they would still work after 30 years, yes."
I don't think that is reasonable.
Small signal transistors made 30 years ago had gold-plated leads. The gold migrates into the tin of the solder, and the joints become brittle, and fracture.
5% carbon film resistors have the copper plating (which is then tinned) on the steel leads fail and and causes the resistor to appear to go open. (these are called copperweld leads)
On many old amplifiers with gold small-signal transistors they start working when you remove all the old solder and re-solder with 4% silver solder.
If the resistors are starting to go they must be replaced.
I've also had film caps with copperweld leads fail. Carver used mylar input caps (on some models) that had this problem.
This amp may not be ecconomical to repair, I have one that I have wasted so much time on that I would have been better of replacing it.
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