[R-390] OT: HP-410B Tubes

[Barry]

It wasn't too hard to do.  If you remove the switches, pots, and panel lamp from the front panel, it all comes apart pretty readily.  In order to replace the bypass caps on V2, I had to remove the screws that hold the resistor board and move it out of the way as much as possible.  After that. it's not too bad.

Mine had the monolithic-style 1uF Sangamo filter cap.  I used the existing mounting screw holes to mount two old-style solder posts and the new filter cap fit right between them.  I had to splice one wire to get it to stretch to one of the posts (I didn't want to clip all the lacing just to get some slack in that wire).

One of those Black Beauties was leaking both physically and electrically (it made a pretty nice 82k-ohm resistor...).  I didn't replace them as the newer models didn't include them anyway.

It was suggested to me to remove the 50uF cap across the meter (it isn't on later models); however, I opted to replace it (with a 47uF) as I like the extra damping it gives to the movement.

Good luck with it.

Barry - N4BUQ


 On Fri 04/03/11  9:33 PM , Steve Byan stevebyan at verizon.net sent:
> 
> On Mar 1, 2011, at 9:51 PM, Barry wrote:
> 
> > I have an HP-410B that I have cleaned, recapped and
> trying to get working properly again.  
> Thanks for the report on your HP-410B experiences. It's motivated me to get
> mine off the shelf and on to the bench.
> One question - how the heck did you get in there to recap it? I've removed
> the chassis screws and desoldered the AC line input connection to the front
> panel switch, but the cable harness is still to tight to let me into the
> innards. Did you have to unsolder much of the wiring?
> Mine's an old one too, pre-PC board. I did manage to get in to clip out the
> 0.01 uF Black Beauty caps across the AC line - it's scary to think what
> those things must be leaking to the chassis ground!
> Best regards,
> -Steve
> 
> -- 
> Steve Byan stevebyan at me
> .com>Littleton, MA 01460
> 
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