VOX AC30/6 TB

First question back to you is.. is the HT fuse after the rectifier or before it? Or, are you really talking about the AC mains fuse?

If the fuse is really in the AC mains line, then almost all my bets are going to be on a shorted power transformer or a shorted MOV or line bypass capacitor. If the fuse is after the rectifier, then you should pull the rectifier tube, replace the fuse, and see if the fuse blows again. If it blows again, then check to see if maybe one side of the power line is shorted to ground... possibly caused by a shorted MOV or line bypass capacitor. Or a stray piece of wire, or other malady. If the fuse doesn't blow again, then you have a bit of troubleshooting to do. Most likely a shorted B+ filter capacitor or shorted tube. Be sure to keep your eyes peeled for stray wire clippings.

Cheers!!!!

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MOV= metal oxide varistor ? Probably the most diagnostic feature is the 500mA HT fuse, on the DC side of the rectifier tube, is a small gap in the fuse filament with a glob on one broken end, both remnants axially present in the barrel, no staining inside barrel at all. Last gasp rather than catastrophic failure. I'm struggling with sticky needle on my valve tester , again. I know if i poke around in the meter I will totally bugger up the movement , so no use rather than problematic use with a lot of case tapping.

As an aside anyone know when barcodes started appearing on electronic kit or components? for age determination assistance. Mid 1980s is my recollection but googling has not helped

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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the third EL84 tested , started out normally then rapidly accelerated off the scale. I've never had the protection relay on my Avo CT 160 dropping out before. I had to get inside to manually reset it and took the opportunity to sort out the meter needle sticking problem, much easier to get to and into this meter movement than I'd thought.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

The schematics for most of the AC30 derivatives are on the VOX website for free download

Arfa

Why not pull the tubes, put a new fuse in it and see if it blows? Then replace them one by one. I know it ain't a pretty way to diagnose but I've worked on many tube guitar amps and never caused additional damage doing this as long as I was careful. And it did help to have a variable ac supply with a current meter but it can be done using a 100 watt light bulb.

only the older amps

Laney did the same but pulled them from open access a few months ago. I'd managed to download about 2/3 of them, over a few months, before they were all pulled. Just for my personal use at some future date. I would suggest doing the same for any site that has such technical details. I assume some accountant or intelectual property rights lawyer comes along and says "remove that content" from open access that some well meaning technician had put up there.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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or quite likely being removed from site/s because of some health and safety consideration