[Collins] AN/VRC-24 UHF radio
Marco
marcocasagrande2407 at hotmail.com
Wed Jun 25 04:14:46 EDT 2014
Hy Jim, Thank you for prompt reply but I did cheched K-102 inside twoo or three times but is very clean and none oxid is formed up to the strange (it's mirror clear but dark..) strong plating (crome?) little ball contact; The dark plating is very similar to the multi variable caps rotor contact point finishing.So the 6442 adapter caps has burned out the 7554 filament when I did pulled the three sisters (6J4WA) for various voltage tracing :-(The VRC-24 is a very beauty heavy gear from the fabulouse sixties (like me) and I not plan more of what I still make it now, like a flirt! The only flaw is that it was manufactured from Arvin Industries...73' Marco
> Date: Tue, 24 Jun 2014 12:43:51 -0700
> From: antqradio at sbcglobal.net
> Subject: RE: [Collins] AN/VRC-24 UHF radio
> To: marcocasagrande2407 at hotmail.com
>
> Marco
> I would check to see that K-102 armature is also moving when you key the R/T unit. Since both relay coils are in parallel, it is possible to have a good K-101 and a bad K-102. If relays K-101 and K-102 are indeed both switching and the contacts are clean and mating, then my guess would be that the 6442 is suspect.
>
> Now the 6442 has an adapter cap that brings the inside filament connection to the outside so that the socket finger makes contact to the outside of the adapter cap. If that cap is not there then the 6442 has no filament voltage and whatever RF drive voltage leaks through the grid to plate Miller capacitance could be what you see as drive to the 4X150D. Just a guess on my part!
>
> What are your plans for the VRC-24? Your location is Italy?
> Jim
>
> --------------------------------------------
> On Tue, 6/24/14, Marco <marcocasagrande2407 at hotmail.com> wrote:
>
> Subject: RE: [Collins] AN/VRC-24 UHF radio
> To: "antqradio at sbcglobal.net" <antqradio at sbcglobal.net>
> Date: Tuesday, June 24, 2014, 12:34 PM
>
> #yiv0874265138
> #yiv0874265138 --
> .yiv0874265138hmmessage P
> {
> margin:0px;padding:0px;}
> #yiv0874265138 body.yiv0874265138hmmessage
> {
> font-size:12pt;font-family:Calibri;}
> #yiv0874265138 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 RF
> 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
> >
> >
>
> >
>
> >
> >
> ______________________________________________________________
> > Collins mailing list
> >
> Home: http://mailman.qth.net/mailman/listinfo/collins
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:Collins at mailman.qth.net
> >
> > This list hosted
> by: http://www.qsl.net
> > Please help
> support this email list: http://www.qsl.net/donate.html
> >
>
>
More information about the Collins
mailing list