| Author: | trobbins (registered user: 916 posts ) |
| Date: | Mon, Feb 20th, 2012 @ 21:03 ( . ) |
Each tube in a PP pair will see 50% of the rms current for that pair. It may be easiest to determine the tube operating current (by 1 ohm sense in cathode) when testing the amp into a resistive load at highest cranked level, and then fit a fuse to suit which has some margin - but use a true rms meter. So maybe fit 1A and then lower it after testing. I put the 1R in series with the fuse in a few builds - at the 0V end so the sense voltage is relative to ground - if you don't see the LED, then the 1R voltage indicates if the fuse has blown (eg. if you extend the 1R sense for external testing, such as from a spare octal valve base). That MOV looks fine with a spec 805V at 1mA - aim is to have some margin above high mains, unloaded B+, so you should determine a value for that first really. Ciao, Tim |
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