help w/all AC amp?

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wayneosdias
Senior tube assistant
Posts: 248
(3/9/04 7:14 pm)
 help w/all AC amp?
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 this guy in my class has this little amp that i cant find any info on. its an old Knox tremtone made in the usa, using a 12au6 for the input another 12au6 for the trem and 50c5 power, a micro OT pushing a 6" noname alinco, NO PT?????. ive never seen this arrangement before, it just takes wall ac voltage w/one end going to the on/off switch before recirculating back into the circuit and the other going to the cap can. the can is 20/40/60u rated a 160v, i see one zener, but that alone couldnt rectify, can this be an all ac circuit? it hums badly and wont play, it has the schematic and is all terminal ptp. any input?

thanks
wayne
 
PHATamps
I only work on tube amps
Posts: 425
(3/9/04 9:10 pm)
 Re: help w/all AC amp?
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 They used to make radios and cheap amps like that with no PT. The filaments are wired in series and the voltage ratings should add up to 110VAC or so.

What you call a zener is probably a regular diode for half-wave B+ rectification.

Problem is, without a PT there's no isolation from the wall, so God help you if you touch your lips to an ungrounded mic while playing through it. YEEOUCH!
 
wayneosdias
Senior tube assistant
Posts: 249
(3/9/04 9:19 pm)
 Re: help w/all AC amp?
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 thanks Paul

the info i got on ampage more or less is what you said. i think your right about the zener acutally being diode and being half wave. consensus is that its a poor/hazardous design, probably advice the guy to toss it.

thanks
wayne
 
Tiny Daddy
I will work on all amps
Posts: 543
(3/9/04 10:46 pm)
 Re: help w/all AC amp?
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 Before you toss it there are some mods including powering from a 12V wall-wart transformer at:
www.jamesaudio.com/faq.html

 
wayneosdias
Senior tube assistant
Posts: 250
(3/10/04 12:07 am)
 Re: help w/all AC amp?
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 thanks TD

good info there, dunno if the guy will be into the cost or if i want to do it.

wayne
 
 
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