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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Re: Why do my tubes keep blowing? posted by occ on December 8, 2006 at 00:58:30:
Before setting aside the direction I suggested, might I ask you a few questions?Firstly, when the failure first occurred, in the manner you described, I presume there was no red glow on the plate of the output valve that failed; correct so to presume? I would think I am correct to presume this because you wrote the manufacturer could find no fault. If a bias resistor, for example, had been implicated with current draw running away in an auto-biasing circuit, that resistor would indicate failure, and there would be little doubt about it. Again, your description of failure would not suggest bias circuit failure but heater failure. I must ask, also, is the circuit auto-biasing?
With the new unit supplied after return of the first unit, was the problem with the same channel, and if so, in the same tube location? Or, was the problem in another tube location? I know you mention use of a substitute AR power amplifier and the problem with it, and the inference drawn, but I would, nevertheless, like to know.
I appreciate your reply to my first posting in the thread, but I must ask again is the mains transformer rated on the primary 220vAC, 230vAC or 240vAC?
Do you know the voltage being supplied to the heaters of the output valves? (Nominally, the tap on the secondary side would be expected to be 6.3v.) If you do, is that voltage between 5.7v and 6.9v, that is, within the range, 6.3v +9.52/-9.52%? And, if it is, and the voltage varies with input voltage variation, what is the value of heater voltage for the 245v minimum input voltage you mention?
You mention EH tubes, but which type? EL34, 6550, KT88, or KT90? Have you used but the one type/designation, that is, not substituted another set of output tubes of a different designation/type?
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Follow Ups
- Re: Why do my tubes keep blowing? - Seán 07:26:43 12/08/06 (0)
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