[MRCA] GRC-19 power supply

[WA5CAB at cs.com]

PP-1104/G (any model) is in most respects a much better supply than the 
PP-4763, albeit about twice the volume.  The latter has no surge capability 
whereas the former easily handles 100% surge.  And it's CCS rating is 50 Amps 
at 28 VDC or 100 Amps at 14.  So it is much more useful.  Its only 
shortcoming is that you can't use it to test sets set to 6 volts like the Jeep sets, 
SCR-284, SCR-694-C or AN/GRC-9. 

I'll add that floating a 24 volt battery on a PP-4763 is one fix to its 
surge rating shortcomings, but you need to use an adequately rated (read hocky 
puck) float diode.  Two typical size 96 AHr 12V automotive batteries in 
series will hack over 400 A for several seconds.  A set of 6D batteries will 
handle over 1000 A.  Whoever wrote that batteries won't start a T-195 must have 
tried to use an HT battery.  However, as Jeep mentioned, the auto tune 
comment was correct.  Before they were all surplused out, any set that wouldn't 
operate in a vehicle with the engine off would have been turned in for 
repair.  Unfortunately, current owners don't enjoy that service.  :-)

Robert D

In a message dated 10/07/2012 19:17:07 PM Central Daylight Time, 
jeepp at comcast.net writes: 
> On 10/7/2012 6:31 PM, Robert Newberry wrote: 
> >> I'm possibly looking to purchase a GRC-19. I've heard people use two 
>> 12v batteries hooked together.
>> 
>>  Then I read some post on QRZ.com about the batteries do not provide 
>> enough voltage to auto tune and for current in rush in TX.
>> 
>>  What is the groups thoughts? 
>> 
>> 
>> 
>> -
>> 
> Robert,
> Good luck on your GRC-19 project.  Those radio sets can be a nice 
> experience.  A couple of items from my research and direct experience.  If you end 
> up with a non-lettered T-195, one with all dynamotors, the inrush current 
> will be about 70 amps.  Invariably, power supplies like the PP-4763 
> (especially the "A" model) will trip out, every time.  One can replace the 
> fast-acting circuit breaker with SB fuses and it may work better.  That said, if 
> you have a T-195A* or one modified with the high voltage inverter/dynamotor 
> replacement, the inrush current will quite manageable.  The ones I use have 
> all solid-state replacement dynamotors and the operating current is about 
> 31 amps at 29 volts.  If the multi-voltage dynamotor is still there, but 
> with a solid-state high voltage dynamotor replacement the inrush minimal.  
> I'll also add that power relay K2 gets a horrible hit every time its activated 
> owing to the inrush current to the HV dynamotor.  Before I converted the 
> T-195's,  I have had to burnish that item regularly to keep it from burning 
> out.
> 
> Regarding the solid-state dynamotor replacements, they are getting scarce 
> to unobtanium.  They were made by Victoreen and use germanium power 
> transistors and custom toroid transformers.  In essence, Victoreen put 15 lbs of 
> electronics in an 8lb enclosure... so to speak.  What I have helped others 
> do when these HV replacement supplies go bad is to build up an external 
> 1000vdc supply and feed it in via the rear of the cabinet.  K2 provides the 
> "keying" of the supply.  No more HV issues.
> 
> You mentioned the required DC input voltage, and you are correct.  The 
> T-195's, over time, require a bit more voltage to operate the servo circuits, 
> reliably.  One issue is that the matched germanium diodes in the servo 
> discriminator circuits require regular replacement, according to the TM.  If 
> the servo circuits don't work, it will, of course, never tune up!  
> 
> Working through all this, if you get a good one, they are a fine rig and 
> sound excellent if used with a good quality carbon mic.   
> 
> *  Look for the tel-tale yellow painted function switch knob.  However, be 
> sure and look inside to see if the SS dynamotors are there!
> 
> Jeep - K3HVG
> 
> PS:  I have some servo choppers, in stock.
> 

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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