Hello!
?? I was at the local Electronics Flea Market yesterday and scored a well-used HP 410B - complete with the RF probe! - for $20.
It had a piece of masking tape on it that said "Needs Work".??? It was festooned with stickers proclaiming ownership by "Philco Ford", and announcing that it was due for calibration in 1974.
? There was also an added panel light with a sticker that said "Calibration void when lit".??? And a clockwork mechanism that turns a screw that moves a pointer...and apparently at 1900 hours, the lamp is turned on.
? I popped it open, cleaned all the switch wafers and pots with DeOxit and DeOxit Fader.? Then slowly brought it up on a variac.? Wonder of wonders, it seems to work.? Just needs calibration.? Well, the power supply electrolytic is leaky.? New one on order.? It's only leaking .3mA at 350V, but I'd rather not trust it.? New caps are small;? I was able to slip the cardboard outer insulator off the existing cap, and I'll put the new one inside it.
?? Even the RF probe works.? Interestingly, there was a sticker "Not calibrated above 10MHz".? And indeed, above 10MHz, the response fell off considerably.? Turns out that the filament voltage to the RF probe was low.? Instead of 5VAC ( rms ) it was more like 4VAC.? I cranked it up to 5.0, and the frequency response went up past how high I could go with my Wavetek 3000 ( 550MHz ).? I wonder if they set the filaments low on purpose, to extend the life of that very expensive tube?
? Those little diodes are indeed expensive.? $50-$150 on Ebay.? I wonder if I should get one anyway, to have a spare?
? The leather strap is not in good shape.? Might be an excuse to get into leatherworking.
