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Very often, all that is necessary is to run a bizness card between the contacts. A card with a particularly-rough finish is great, but don't use a card with an epoxied smooth or glossy finish on one side. If you do, then try to stick a sheet of ordinary notebook paper to that side of the card so it doesn't contact the relay contacts. The epoxy or gloss may rub off onto the relay contact and make the problem even worse.

When you run a bizness card thruogh the contacts and examine it, you will notice gray or black residue is left on the card. However, the card will not clean up a burned or pitted contact very well.

73,

Steve K0XP

There are burnishing tools for exactly this purpose.? Using finger nail files and files for this purpose is risky, as the potential damage of removing too much contact material is high.

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I have one of these:

Here are two more:

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Burnishing tools have very fine almost invisible teeth.? Using a burnishing tool is a safe method for cleaning relay contacts.? Every radio amateur that works on equipment with open frame relays should have one in his tool kit.

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73,

Dave, w6de

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From: [email protected] <[email protected]> On Behalf Of Louis Parascondola via groups.io
Sent: 30 November, 2023 22:56
To: [email protected]
Subject: Re: [ham-amplifiers] Need Help with Amp Supply LK500ZC

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John, you just might have a worn out contact that switches bias on the antenna relay. ?If the contacts are severely pitted they might not make up too good sometimes and other times ok. ?You need to inspect the that set of contacts in particular. ?If you carefully remove the rear spring on the relay you can lift the armature off and inspect all the contacts. ?The contacts that switch the RF can be cleaned gently, the contacts on the bias may be in bad shape, there may be a tiny point on the armature contact and a tiny depression on the body contact. A gentle filing to remove the “pit” and a cleaning should restore reliable contact. ?It’s not unusual at all to see the bias contact hood bad with the age of thst amp especially being used on CW a lot. ?Seen it quit often and by doctoring up the bias?contact that problem went away. ?Lou

Sent from the all new AOL app for iOS

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On Thursday, November 30, 2023, 3:58 PM, John Roland <johnroland51@...> wrote:

Lou, Mike, Jim, Adrian and all,
I removed the tubes one at a time.? I let the amp idle (no drive) for 10 minutes with each tube in place individually.?? No signs of anything overheating.? I then replaced both tubes and let it set another 10 minutes, still no sign of overheating.?? I then applied about 20 watts of drive in RTTY mode and was getting around 200 watts out.? (I'm still using my Heathkit watt meter circa 1978)? Attached is a photo of my grid and plate current with that 20 watt drive.? The meter shows 2900 volts when idling and drops to about 2600 when transmitting.?? (I'm operating 240 volts on about a 20 foot length of 12 AWG from the panel.)?
The pictures below are 1.? the front tube at 10 minutes.? 2. the rear tube at 10 minutes? 3. Both tubes back in place after 10 minutes.? 4.? A picture from yesterday of both tubes just after switching off the power (light) which looks to me like both tubes are overheated. 5.? A picture of my meters with 20 watts RTTY drive applied.? The Plate volt meter does return to 0 when switched off.
So it now looks like I may have some kind of an intermittent ??
Thanks again
/John?
W7SWB