[Milsurplus] Bathtubs redux

[wf2u at ws19ops.com]

Well, Marty,

There is something to be said for selectively recapping tubs...
I wasn't going to do all of them, only the non-capacitating ones!

Case in point:
I just fixed my SX-73 which had been sitting on a shelf unused since  
we moved to this QTH 7 years ago.
"Variacing" it up slowly resulted in a live radio but doverloaded and  
distorted with strong signals, AVC/manual gain switch didn't make any  
difference.
Of all the caps, it was only the bias supply filter cap - a bathtub! -  
which was shorted out to ground (50 V rated, but the bias supply  
voltage doesn't exceed -24 VDC). Nothing went bad as there is a  
resistor network in the gain control circuit and the current is very  
small.
Disconnected the ground side of the tub and connected a small  
electrolytic to between the "hot" side of the tub and the nearest  
ground lug, and hid it under the tub for now - the receiver is working  
great now!
All the other caps in the SX-73 were OK. What's nice is that the plate  
voltage in that receiver is only 160V, so it's nice and gentle on the  
components.

So in the RCH receiver I have to check out 12 or so tubs, some of them  
triple cap, some others double cap. Hopefully some of them will check  
good!

73, Meir WF2U


Quoting Marty Reynolds <cosmoline at aa4rm.ba-watch.org>:

>
> Why has everyone piled in with the bathtub condemnation mob?
>
> It's getting like the command set cap-bucket group-think
> hip-shot
>
> Bathtubs are oil-impregnated paper jobbies & are almost permantent
> capacitors as long as they don't leak
>
> Apply, say, 400v in series w. 20k ww to B+ line in a '342 & patrol
> around w. vt/fet vom checking for drag-downs.  If none, power same set up
> & listen to radio,  If so, one or two assidously place mylars ought
> to get u listening to CHU-Canada again
>
> It's better to work smart than hard.  And also, the angst-ridden
> process of re-doing bathtubs, etc. just wards folks off the hobby
>
>    signed
>
>          anonymous
>
>
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