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TJ meshplate 2.5V 300B and Paraglows - mods to avoid arcing

Based on some recent experiences with my Paraglows I would recommend that anyone using the TJ 2.5V meshplate 300bs install a standby switch for the B+. This is pretty easy to do. Basically you break the connection of terminal 1T on the PGP 8.1 to ground, and insert a SPST switch. When you open the switch you will effectively remove the current path for high voltage back to the power trans. Use a switch with a decent voltage rating. RS has a mini switch that does the trick pretty well, don't recall the exact model but it's rated 250VAC. It's pretty easy to put a small switch near the left rear corner of the power trans

The start up sequence becomes -

make sure standby switch is open
throw main power switch and let filament and heater warm up for about 20-30 seconds
throw standby switch to the closed position.

At shutdown you can throw the standby switch open, then throw the main power switch, and you are ready for the next startup sequence.

Without this setup you may experience some arcing of the TJs when they get hit with the B+ before the plate voltage of the driver stage, and hence the direct coupled 300B's grid bias, settles down.

This does not seem to be an issue with the Chinese 2A3s, nor is it an issue with the Parabees, but it could also help with AVVT meshplates.

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Topic - TJ meshplate 2.5V 300B and Paraglows - mods to avoid arcing - Doc B. 12:54:43 06/04/02 (1)

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