[Milsurplus] R388 reform school

[J. Forster]

Although we differ a bit on the details, I substantially agree with you on the
essence of what you posted.

Using the set's own tube rectifier is a mstake. The external PS is a better
approach. Be patient and raise the voltage in roughly 10 % steps. If there are
VR tubes, be careful about overvoltaging circuits downstream of them.  I usually
test the tubes, and put them into the circuit before reforming. They are
essentially open circuits with no filament applied.

Sometimes reforming can take a week. Note that either way, cathode bypass caps
will not get reformed by B+ and no filament. You need another PS and clip leads.
Also, take the set out of it's case, so you can see stuff burning or leaking
easily.  MAKE SURE the reforming current is limited. Big caps can pop (explode)
if they get too hot internally. This is dangerous.

The light bulb in the power line is a good idea for line powered units. If you
are working on a set with a dyno, remember to pull the HV brushes before
applying the HV to the circuit or otherwise disconnect the HV output.

FWIW,
-John



Unserviceable but Repairable wrote:

> Heartening to see "bring it yp slow on the variac" becomming conjectural.
>
> For a long time I've railed agin' it saying dusies like "it's safer
> to store it with 2 BigMacs for a week and plug it in."
>
> Pull all the tubes.  Next, if applicable, pull mech. filters, & replace
> primary connections w. 22k resistors
>
> Then comes stunt 1.  Take a power xfrmr with HV winding seriesed w. 20K
> 10W wire-wound* then a 1N4007.  Connect same to B+ line w/o any AC power.
> Then let B+ across system rise as reformation process sees fit.
> IE, come back in a few hours
>
> You CAN do this at home.
>
> After B+ rise plateaus, check for coupling cap leakage.  Like to 1st
> audio, screen IF bypasses, AVC amp couplers, etc.  Also can apply B+ to
> AVC line & look there for leakers.
>
> Next put 60w bulb in series w. power xfrm's primary & try it & make sure
> no shorts.  Reason you pulled all the tubes.
>
> Replace discovered problem-cap.s & tubes, plug in, & listen to hollerin'
> missionaries on 49m
>
> Or send it to Rick Mish
>
> Or replace every bypass/coupler & get a few installs wrong - then
> return to prior suggestion
>
> Now to spin up my J4 for 3885 Sunday Morning Coffee club.  Bet
> "Dennis topic" will prevail down here in Magnoleum Land.  Love to work
> some of ya.
>
>   'rm
>
> *that's the current-limiter that bypasses need for constant current
>  monitoring and/or educated wrist rotation
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net