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

Tue Jun 24 16:17:08 EDT 2014

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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>
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