[ARC5] SCR-522 Project: Finding Bad Coupling Caps in 10 Mins.

[David Stinson]

SCR-522
Got the dynamotor supply and the "mounting rack:
with its electro-mechanical channel and antenna
switching working.  Rub Goldberg would love this
thing.  Here's a video of channel changing (RX-TX
not installed; just the rack):
https://photos.app.goo.gl/1p5oH4aMpjFDG2H38

Having replaced the eight bad bypass caps in the
BC-624 receiver, began the process of finding bad
grid coupling caps.  The diagram shows nearly
every stage is coupled
Plate-Circuit-to-Grid-Circuit via capacitors.  No
filament, 300 V on the B+ busses and test all tube
grids for DC.  Only one turned-up: the Audio
Output grid was standing at 135V.  Nasty.
Replaced that capacitor.
With bypass and coupling caps corrected, it's time
to see if this old soldier can stand, even if a
bit wobbly.
"First light:"
https://photos.app.goo.gl/rq1MmEiuRP1Bd1Tv7

100.2 MHz.  No alignment done yet (lots more tests
to do before that) Haven't even tested to tubes
yet- need to do that next.  Only the regular
front-end tuners and the crystal oscillator
peaked,  the set is full-quieting at about 160
microvolts.  Spec is about 2 microvolts, so lots
of work yet to do, but "the lights are on" after
75 years.

The control box for this set has had Chan. D
selection disabled and the pilot light for it,
removed.  Haven't traced yet, but I think this one
was used with "Pip-Squeak" and that kept the pilot
from transmitting on the DFing channel and munging
someone's bearings.

Note:  For the one other person on the planet who
might try to get one of these going:
The ground return for the Power On, Channel-Select
switches in the control head goes through the
Transmitter chassis.  So if you're attempting to
test the electro-mechanicals of the mounting rack,
you'll need to open the BC-602 and clip a ground
lead on the switch ground-return buss.  If you
look at the channel switch from the top and to the
rear, there are two sets of contacts
"daisy-chained."  The lower buss is the one you'll
need to ground.

A confession:
For years, y'all know I've kinda "snubbed" the
SCR-522, calling it an "ugly black lump of a
radio."  I won't un-say a word about how it looks,
but I've got to admire how easy it is to service.
Unlike the Western Electric BC-942 / AN/ARC-5 R-28
VHF receivers, which are crammed tight and
four-handed plus a magnifying glass and surgical
instruments to fix, these sets are open and
straight-forward.  Working in the front-end module
is probably going to be challenging but the
remainder of the rig is "pocket knife and a
forked-stick" to fix.  I've found this typical of
U.K. sets designed and/or produced during WWII.  I
admire the engineering forethought that went-into
building a radio one could supply and maintain
while bombs were falling on one's head.  "Good
show," Gentlemen.   

Request:
These are "GE Mazda" or "2F" bulbs used in the
BC-602 Control Head.  Hoping someone has a couple
in their junk box?
https://photos.app.goo.gl/V3tH16LaR8Kja4Sf7

Much more to do, but my Grand-Daughter's 8th
Birthday Party awaits.  

GL OM ES 73 DE Dave AB5S

"Telling the truth won't get you many friends.
 But it will get you the right ones."
                John Lennon