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Old 29th April 2009, 01:24 PM   #1
JandG is offline JandG  United States
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Default Diodes to protest OT's..

Can someone show on a schematic how to wire diodes up for SE & PP amps for OT protection, & what value & type of diodes should be used..?
Thanks Joe
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Old 29th April 2009, 01:43 PM   #2
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What are you protecting it from?
cheers,
Douglas
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Old 30th April 2009, 01:00 AM   #3
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Are you thinking of diodes to clamp the secondary voltage if operated into an open circuit?
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Old 30th April 2009, 01:06 AM   #4
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Common as dirt on guitar amps.

Most are wired diode cathode to plate, diode anode to ground. One diode for SE, one on each side for PP.

Use a fast recovery type rated at LEAST twice the supply voltage and preferably four times. 3A is a good current (larger diode area is more forgiving).

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Old 30th April 2009, 01:36 AM   #5
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For SE a diode can't help. Rather a bridge with powerful Zener in secondary.
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Old 30th April 2009, 02:14 AM   #6
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Quote:
Originally posted by Wavebourn
For SE a diode can't help. Rather a bridge with powerful Zener in secondary.

Dummy me for not catching that one

He's right... it'll cutoff part of your waveform.

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Old 30th April 2009, 02:47 AM   #7
JandG is offline JandG  United States
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Sorry for slow responce.
I am wanting to protect my OT's from whatever happens when a output tube goes bad, runaway, blowup, melts internaly, etc..Rectifier going to the bad, me hitting something I should not when probing hot, etc. If I could see a schematic for decent protection for voltage spikes , shorting , to much current, etc. for PP amps, & SE amps, with eather fixed or cathode bias. I would implement them in all my amps. I do have bad luck with output tubes & allways feel lucky when the OT's still work after words. I have read that fuses are not the answer & can be actually worse. I do not know as I am not at the level of knowing if true or not. I just can't imagine everyone with rarer than heck vintage OT or spendy new iron, not protecting them. I never see circuits implementing such protection. Maybe it is all for not & nothing to be conserned about..?
Joe
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Old 30th April 2009, 05:41 AM   #8
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Oh... you don't want a rectifier, you want a cathode fuse
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Old 30th April 2009, 05:54 AM   #9
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...or a microcontroller with sensors of everything out of regime...
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