[Collins] FW: AN/VRC-24 UHF radio

Tue Jun 24 16:41:15 EDT 2014

Rob and Steve
I just did the math, it was 45 years ago for me.  I worked mostly on UHF when I was stationed at Mactan AB, RPI.  GRA-53, GRA-54, TRC-68 and even ARC-27's which were installed in the MPN-13 RAPCON vans.  About half UHF and HF with the base public address audio system to round thing out when stationed at Zweibruken AB, Germany.  
Seems like yesterday...
Jim
--------------------------------------------
On Tue, 6/24/14, Rob Lee <rob at k7tgu.com> wrote:

 Subject: Re: [Collins] FW:  AN/VRC-24 UHF radio
 To: collins at mailman.qth.net
 Date: Tuesday, June 24, 2014, 3:17 PM

 Like Steve, it has been a long time since working on one of
 these, in my 
 case the URC-9. I recall an intermittent/no power out
 condition that was 
 associated with a poor contact on the main tuning capacitor
 grounding tabs. 
 A small burnishing file took care of this issue.

 Rob K7TGU

 ----- Original Message ----- 
 From: "The Rices" <srice3 at cfl.rr.com>
 To: "Marco" <marcocasagrande2407 at hotmail.com>;
 <collins at mailman.qth.net>
 Sent: Tuesday, June 24, 2014 11:47 AM
 Subject: Re: [Collins] FW: AN/VRC-24 UHF radio

 > Been too long since I worked on them (60's) so I would
 have to claim 
 > ignorance as Jim already had you check the relays and
 the voltages I would 
 > suspect in transmitting. As for the tubes well a 6442
 is nos on ebay at 
 > the moment for 34.00 . Course nos is not new by any
 means. Also the 7554 
 > tube is available but from what I saw on a quick search
 over 100.00.
 > Anyway I will let Jim continue as he seems very
 knowledgeable and has a 
 > manual by the sounds of it or good memory.
 >
 > Let me know how you make out
 > Steve N4YZA
 >
 > -----Original Message----- 
 > From: Marco
 > Sent: Tuesday, June 24, 2014 1:36 PM
 > To: collins at mailman.qth.net
 > Subject: [Collins] FW: AN/VRC-24 UHF radio
 >
 > I've pushed reply... 73' Marco
 >
 > From: marcocasagrande2407 at hotmail.com
 > To: antqradio at sbcglobal.net
 > Subject: RE: [Collins] AN/VRC-24 UHF radio
 > Date: Tue, 24 Jun 2014 19:34:18 +0200
 >
 >
 >
 >
 > Dear jim and Steve,Many thank's for Yr prompt
 replies:I've checked the 
 > K-101 and carefully cleaned the long ball end contact
 of K-102 relays, the 
 > 20 ohm resistor so all the rf connectors and checked
 all low power tubes, 
 > including the three 6j4WA. All tubes exibit more of
 140-150% of 
 > efficiency!! From mine old box 6AK5,2C51 ecc only
 90-95.... ;-) As from 
 > tech serv manual, I've checked all tube sockets dc
 voltages so unworking 
 > status resistance (pulling connectors) and retouched
 the various 
 > oscillators and relative tracking filters obtaining two
 valuable RF 
 > voltages at V-101 tx mixer (about 6-8 V rf up to dc, of
 plate voltage and 
 > 0.8-0.9 RF Volt to the catode)During signal tracing
 (pulling the three 
 > 6J4) have fused the 7554 (aghh!!) the filament is in
 series/parallel to 
 > 6442 and its filament adapter caps was leaking.. but
 now waiting the spare 
 > part, i've mounted a 5876 with similar gain and output
 voltage at 7554 
 > output (about 5 RF Volt to 6442 catode at 399.9 Mhz)
 but only 1 R
 > F Volt is measured to the 4x150 control grid with tube
 pulled and max 
 > retouching of various trimmers (C127-C141). Could be
 out of minimum C 
 > class drive RF voltage limits or... the 6442 is
 Out?I've tried to test the 
 > 6442 on the table at 160 vdc and -15 to -2V grid
 biasing but only 5 mA 
 > at -2V is been measured. UmmmhCiaoMarco
 >
 >> Date: Tue, 24 Jun 2014 08:59:28 -0700
 >> From: antqradio at sbcglobal.net
 >> Subject: Re: [Collins] AN/VRC-24 UHF radio
 >> To: marcocasagrande2407 at hotmail.com
 >>
 >> Marco
 >> I am familiar with the other variations of this UHF
 radio and there are 
 >> many.  The VRC-24 was the first but I worked
 on later versions like the 
 >> GRA-53, GRA-54 and the TRC-68.  There is also
 the Navy version, the 
 >> URC-9. If RX seems to be working and TX isn't, then
 there are only two 
 >> tubes and associated circuits that  could be
 the problem.  V-102, V-103 
 >> and V-104 are used in both RX and TX.  V-105
 is a 6442 and V-105 is the 
 >> 4X150D, the D indicates a 24 volt filament. 
 These two tubes are used in 
 >> TX only.
 >>
 >> First, I would check K-101 and K-102 relay
 contacts.  These two relays do 
 >> the reconfiguration between RX and TX.  You
 should be able to clean the 
 >> relay contacts with alcohol and some paste board
 like a match book cover. 
 >> I would not use a file or any such rough
 material.  If you have a 
 >> burnishing tool, so much the better.  If you
 still don't have TX at this 
 >> point, I would suspect either the 6442 or the
 4X150D or the B+ to these 
 >> two tubes also check the fuses on the front panel.
 >>
 >> Once you get an indication of RF out in TX, then
 let me know.  There is a 
 >> trick to limit the need for tab bending when tuning
 the RF and Power 
 >> Amplifier for max output.
 >> Jim
 >> --------------------------------------------
 >> On Tue, 6/24/14, Marco <marcocasagrande2407 at hotmail.com>
 wrote:
 >>
 >>  Subject: [Collins] AN/VRC-24 UHF radio
 >>  To: "collins at mailman.qth.net"
 <collins at mailman.qth.net>
 >>  Date: Tuesday, June 24, 2014, 8:51 AM
 >>
 >>  Hi guys, I'm a couple weeks that I'm
 >>  going crazy to run this UHF radio in tx mode:
 don't push
 >>  enought driving signal in the rf power amp.
 module (J104)
 >>  but seems" receiving ok (no calibrated sign
 gen.).I bought
 >>  this "anvil to very little money but since it
 is very well
 >>  built, have motor, step actuators relays and
 many gears so I
 >>  would like her to sing her song. Is there
 here any Collins
 >>  wizard who has some additional tricks respect
 to the service
 >>  infos contained in its liberated" manual
 >>  (TM-11-5820-222-35). Thanks and 73 'Marco
 IZ0MFI
 >>
 >>
 >>
 >>
 >> 
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