This machine will test QBL 5/3500 (or equiv) and TH328/338 tubes.
Tubes are tested with 1000V on the anode, no bias. A good QBL will draw 1A.
The Thompson tubes are tested for
arc-over (most common problem) and emission,
used QBL's are normally fully operational but some have been run down beyond amateur use.
Back to first page