[Collins] [CCAECollins] Questions about a 51S-1

[Jim Whartenby]

JacquesSee Nick England's site: http://navy-radio.com/rcvrs/r388.htmAlthough this article is about the R-388 receiver, the first paragraph may help explain the out of sequence issues you have raised.
I am not a member of the other groups you have sent this email to so you might want to forward this to them for more comments.
On the subject of capacitor replacement, I use to use the shotgun approach and replace all.  I have changed my mind when working on high end commercial and military radios.  Now I only apply close to the rated B+ which is current limited to perhaps 10 or 20 milliamps but no tube heater power.  
I use the low tech approach by using large value power resistors instead of a regulated power supply to limit current.  I let things cook for a few hours while I do other things and then check with a voltmeter to see if the electrolytics have reformed and if other coupling or bypass capacitors are leaking.  Pretty easy to compare power supply open circuit voltage with closed circuit voltage to calculate leakage current.  This procedure is less time consuming then shotgunning.  If a capacitor is indeed bad, no harm is done since the current limiting prevents any damage to the set from high voltage.  If enough capacitors fail this test, I then replace all; it is a judgement call.
If everything checks out then I apply AC power and again monitor B+ for normal values.  I do the above for a receiver I have had on the shelf for a long time just for a sanity check.  If the B+ settles down in an hour or so, all is well.Jim I wonder why people argue over the 10% of their differences and ignore the 90% they agree on?

      From: Jacques Fortin <jacques.f at videotron.ca>
 To: CCAE-Collins at groups.io; 'Heinz Breuer' <hbreuer at debitel.net> 
Cc: collins at mailman.qth.net; collins_radios at yahoogroups.com
 Sent: Wednesday, November 28, 2018 11:30 AM
 Subject: Re: [Collins] [CCAECollins] Questions about a 51S-1
   
Hello Heinz,

Thank you for your answers.
I cannot tell if the front panel was changed/swapped with another unit, but
if it is so, it was done following the Collins standards.
All the screw threads are sealed with the same bluish lacquer, so all the
assembly looks original to me.
Reading more of what is available about the 51S-1, it seems that they were
made by "batches" and some kept in semi-assembled state until an order came.
The unit was then "finished" and sent to the buyer.
That can explain why it was made in 1967 but have a "transition period"
front panel.

But this is not the problem I have with that unit for now.
It is obvious that only the first schematic revision change (the capacitors
around the filters) is applied to it, but not the ones that followed.
The BFO stage is completely different from the manual rev. 11 schematic,
same for the calibration oscillator.
There is a 200µF, 30V capacitor connected at the junction of R52, 54, 55, 56
to GND that does not appear in the latest schematic (and this one is
defective, BTW).

If somebody can provide me with the earlier version of the schematic (which
was the one used for the 1967 production ?) it will be a great help.
What did you recommend ? Updating the circuit to the latest schematic or
leave it as-is ?
All the electrolytics need to be changed within anyways !

For the tuning tool, it is made of white nylon but I cannot tell if it is an
original or not.

What did you mean with " not the ex-Israel military metal scrap" ?
Did you mean that there is Collins-made 51S-1s and cheap "copies" ??
I've seen a 51S-1 on the web with different knobs than the genuine Collins:
is that an Israel military one ?

73, Jacques, VE2JFE

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