[Collins] FW: AN/VRC-24 UHF radio
Marco
marcocasagrande2407 at hotmail.com
Wed Jun 25 05:53:43 EDT 2014
They are definitely the two rf power tubes: Maybe they left in tx for days ... with the antenna in short!I mounted a 6263A in place of 6442 and in these conditions is able to get a couple of RF watt (14-15 rf volt) that decreasing during the seconds... 4x150 to! But works with a few of negative modulation, speaking into the carbon mike!Now a little bit of quiet for me to waiting the 7554 spare and close the screens for the cooling, hopes in a very cheep rf power replacement line-up to proceeding vs next step.I've found more infos about SRC-20 and URC-9 including traineer guide and schematics !Thank you again, I let you knowmarco
> Date: Tue, 24 Jun 2014 13:41:15 -0700
> From: antqradio at sbcglobal.net
> To: collins at mailman.qth.net
> Subject: Re: [Collins] FW: AN/VRC-24 UHF radio
>
> 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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