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I just had a 5ar4 go red plates on me. Any ideas why that happened? The amp was working fine about 6 months ago and all the circuitry looks good. I decided to fire it up today with that runaway rectifier spoiling my day. TIA, Dak
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Obviously a short downstream. Make sure the amp is fused per spec, or risk losing a transformer.
While the tube itself can be at fault, the most common cause in my experience is a problem in the power supply or such that causes a large amount of extra current to be drawn through the rectifier - which can quickly destroy it. The red in the plates is heat, and higher current = higher heat.
Something is shorted. Probably a power supply cap or the rectifier tube itself.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Thanx Tre, it looks like the amp will need to go to the shop for an overhaul or tune up. cheers, Dak
That's my experience, at least. Last time this happen = bad cap in the PSU.
Thanx guys. I will be checking the caps in the power supply. Besides the meter I also have an LCR meter. I usually don't use a film cap if it measures more than 10% off value. For electrolytics I usually avoid them if they are more than 10 years old. But, in my power supply the caps are all film, except for 2 in the driver/splitter tube power supply. Of which one showed some leakage but, I had previously removed that one prior to the power up so I am not sure about the other caps. regards, primo
Edits: 11/28/15
If I suspect any of the filter caps, in the main PSU, I just replace them. Usually, the first pi-stage's caps get the most abuse and fail the earliest.
Caps in this stage can be far off the rated nominal value and not cause catastrophic damage to the rectifier or fuses to blow. 50% or more from nominal. Now, they prolly won't filter as well as a good tolerance cap. But, they really need to be near short to ground or no conduction at all, to cause major damage to other parts. At least, in my experience.
Only in my case you could hear-em crackling. Also look for charcoaled parts and other visual clues.
But can't you pull the output tubes out and see if the rectifier still turns red to rule the outputs out. Is that a real sentence????
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