[Milsurplus] Fwd: Re: VRC-12 continued

[Ray Fantini]

The PA cavity was super clean, but I cleaned the tube and socket anyway. This problem surfaced after dragging the mutt up on a car trailer to PA and then driving up and down the mountain at Port Clinton.
Maybe it's just like you say. The radio lives out in the garage and is subject to all type of environments but the thing is the radio itself is sealed or so I thought.
I somehow keep thinking about if this is related to how servo motors seize up when not used for some time. Have always thought that was from issues with the lubricant but maybe it's an electrical problem instead?

Ray F



From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Bruce Gentry
Sent: Monday, December 12, 2016 3:11 PM
To: Milsurplus at mailman.qth.net
Subject: [Milsurplus] Fwd: Re: VRC-12 continued




-------- Forwarded Message --------
Subject:

Re: [Milsurplus] VRC-12 continued

Date:

Mon, 12 Dec 2016 15:07:37 -0500

From:

Bruce Gentry <ka2ivy at verizon.net><mailto:ka2ivy at verizon.net>

To:

Ray Fantini <RAFANTINI at salisbury.edu><mailto:RAFANTINI at salisbury.edu>



Contacts get dirty in many ways. If a connector of any kind is never disturbed, airborne dirt, not corrosion, can get slowly work it's way  between  contact surfaces and cause poor contact. Vibration and temperature excursions cause this to happen quicker. This problem is especially bad with relay and switch contacts that simply touch and don't wipe.  It was a constant problem with circuit boards in elevator door operators and controllers, even when all the contacts were gold plated. Wiping the contact surfaces clean with or without cleaning solvent, then re-seating the boards and connectors gave immediate good results. In the RT-246/524 PA, if the screen ring got cruddy there is no telling what could happen. It's unlikely the band switches or condensors in  the PA were responsible because they are a wiping contact and will make good contact unless terribly cruddy or corroded.   RT-246s are cool to repair and see and hear the servo operating, and they are good performers too.

        Bruce Gentry, KA2IVY



On 12/12/16 2:39 PM, Ray Fantini wrote:
Over the weekend had the opportunity to pull the 6100/6200 power amplifier from the RT-246 and removed the ten thousand little screws that secure the cover over the PA tube and its base. Everything looks very clean and did not see any issues but decided to clean the band switch S6202 and removed the 7843 PA tube but was not able to find any reason for the power dropping off. Did change the orientation of the PA tube being that's easy with those coaxial power tubes and after reassembly the radio puts out full power now. Go figure. Maybe it was a dirty PA band selector but it looked as clean as if it were new. I have had issues with this radio before with the band switch in the receiver front end needing to be disassembled and cleaned so maybe it's just the nature of these contacts that after years of not being used they oxidize or something. Lot like the problems that I have had with DC servo motors in radios like the GRC-106 sticking and needing just that little bit of attention to get them working again. If the problem reoccurs will be changing the PA tube for another and see if that fixes it.

Ray F/KA3EKH






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