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Old 22nd February 2011, 11:58 AM   #21
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Originally Posted by chris661 View Post
Nigel, that's certainly an impressive resumé. I'm also in a band, with another guitarist, drummer, singer and no bassist. My last amp died trying to fill in the bottom end of a song, but that's beside the point.
Another 'group' Melissa intended was run by the Police for young offenders, which they opened up to non-offenders - she met some interesting characters there

While she went mostly to learn to drum, she also played bass while there (only a limited number of drum kits and rooms) - and one day the bass combo she was playing through poured out loads of smoke!!. As a result, I was asked to look at it - and I was assured that the amp was still working while smoking, which I didn't believe

It was a Carlsbro 60W combo - and true enough, it was working and smoking.

I toook it to pieces, and found the Zobel resistor was smoking - something I'd never seen before - but the capacitor in series with it was an electrolytic, again something I'd never seen before.

Usually for an 8 ohm amp the zobel network would be 8.2 ohms and 0.1uF in series, so I fitted those, and it worked perfectly, and was stable as far as I could tell on a scope.

However, as Carlsbro are (were!) a local company I rang them - and spoke to the service manager - he asked me the serial number, as apparently they used different values on different production. He then told me the modification for it was to fit 8.2 ohms and 0.1uF - which I had already done.

So be aware, amps CAN smoke and work!.
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Old 22nd February 2011, 06:14 PM   #22
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though I'm not sure about it, I have a suspicion that some professional rock guitarist's use i-tune, but I dont know
I think that should have been auto-tune
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Old 22nd February 2011, 10:58 PM   #23
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Nigel, before it's death, mine smelt for over an hour during rehearsals.

On my multi-effects, low turned all the way up. Then on the amplifier, bass turned all the way up. Feeding a 4ohm set of speakers, volume at 8 or 9 out of 10.
As we moved things from the side room to the stage, during practice on-stage, volume was suddenly lost (maybe 6dB). As I was playing with distortion, I hadn't realised the bias had shot off in one direction, putting a severe amount of DC on the output (output transformer stopped this getting through). So, I turned the mid control up on my amp and the volume came back. Notice it's still smelling pretty bad at this point.
So, after another 5-10 minutes of one output transistor being stuck to supply voltage, it desoldered the wire connecting the speaker to the board. Despite all this, the 2A fuse on the output didn't bother to blow. Fixed it when I got it home, turned it all the way up and the fuse went pop on the first chord. Grrrr....

Chris

PS - in a moment of temporary insanity, I bought a battered old bass guitar for £50. Sounds lovely, but those strings are a nightmare compared to the super-easy-to-press guitar strings I love so very much.
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Old 23rd February 2011, 07:00 AM   #24
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So be aware, amps CAN smoke and work!.
Musicians too !!! ;-)

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Old 23rd February 2011, 08:42 PM   #25
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I'm too young to smoke, but can't see the appeal, myself.

Chris
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Old 24th February 2011, 10:06 AM   #26
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I'm too young to smoke, but can't see the appeal, myself.

Chris
It's always struck me as an incredibly stupid thing to do!.
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Old 24th February 2011, 10:08 AM   #27
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Originally Posted by chris661 View Post
Nigel, before it's death, mine smelt for over an hour during rehearsals.

On my multi-effects, low turned all the way up. Then on the amplifier, bass turned all the way up. Feeding a 4ohm set of speakers, volume at 8 or 9 out of 10.
As we moved things from the side room to the stage, during practice on-stage, volume was suddenly lost (maybe 6dB). As I was playing with distortion, I hadn't realised the bias had shot off in one direction, putting a severe amount of DC on the output (output transformer stopped this getting through).
What sort of transistor amp has an output transformer?.

The only ones I've ever seen are 100V line output types, for announcement type PA - not really very suitable for musical use.
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Old 24th February 2011, 10:54 AM   #28
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Back in the sixties you could encounter transformer-coupled transistor amps every now and then. Some radio receivers for instance had two tiny little audio transfomers in them. They were actually using old-fashioned PP circuits like the ones used with tubes.

Back to topic: SS amps by Peavey for instance use output transformers IIRC when they are of the tube-sound-emulating type. Or do they just emulate the transformer behaviour ? Maybe I'll have to check back.

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Old 24th February 2011, 12:42 PM   #29
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Back in the sixties you could encounter transformer-coupled transistor amps every now and then. Some radio receivers for instance had two tiny little audio transfomers in them. They were actually using old-fashioned PP circuits like the ones used with tubes.
Yes, low quality, low power, hardly PA amps

One of the transformer types was an LT44 if I remember correctly?.

Quote:

Back to topic: SS amps by Peavey for instance use output transformers IIRC when they are of the tube-sound-emulating type. Or do they just emulate the transformer behaviour ? Maybe I'll have to check back.
Seems a LOT of expense for little 'gain'? - but I can't say I've ever heard of one?.

A quick google finds a Peavy amplifier series called 'transformer', but they don't appear to use an output transformer, it refers to the tube/valve emulation.
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Old 24th February 2011, 12:48 PM   #30
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H. Peavey mentions in a paper that the output transformer contributes quite a lot to the sound of tube guitar amps. He even mentions that the most expensive mistake would be to use a beefy high-quality output transformer - that is made for HiFi tube amplifiers - for a guitar amp.

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