Author Topic: RM KLV350.....NOT!  (Read 148 times)

26AM081

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RM KLV350.....NOT!
« on: October 03, 2021, 10:42:58 am »
I was very kindly donated an RM KLV200 valve linear amplifier some weeks ago from a station not far from me. Sadly they didn't work, which wasn't a major issue, as there so simple inside. The EL519 output pentode had gone pop. Valves don't usually go pop as-such. There's many stages of failure, most typically being weak emissions. However this did go out with a spectacular light show. The Anode and cathode had an internal short-circuit, which is another common fault along with open filaments. I was in company with Pete 26CT3855 at the time when we power up the amp on the bench for testing. I can honestly say it made us both jump back.

Picture below of front panel.

302-0

You may have already noted from reading the post title and looking at the image, the amp is indeed labelled as the KLV350. Obviously RM reused the front panel from that particular version. Looking for information on the internet revels that the KLV350 was discontinued not long after released.

Picture below of rear panel.

304-1

The rear panel has the basic minimum connections for wiring the amplifier inline. Notice how the RTX and ANT labelling runs as one continuous word. I can't help to think perhaps some people wiring this up backwards.(yes it's common, I hear it on the bands a lot.)

Picture of internal view.

306-2

As you can see from the photo, these amplifiers are incredibly simple inside, theres also a sticker label on the transformer confirming the true model number of the unit. If it had been the KLV350, there would be 2x EL519's in parallel configuration.

So why did it fail, well thats probably one of 3 possible reasons.

1st being the plate output loading not being correctly set, this in-time will have a massive effect on longevity, as the valve has more-than-likely been "Red Plating" due to the massive mis-match on it's output.

2nd being the valve has been subject to many hours of standby "without use". This is another contributing aspect to premature failure, as the cathode emission surface will just evaporate, rendering the valve useless and likely to have internal shorts.

3rd and finally is the valve may had an undetected fault which was destine to fail at somepoint after a few hours or thermal cycling. Another contributing factor is excessive shock during transit from supplier to customer. This could have also happened to the valve in place as the whole unit was subject to excessive shock treatment.

Final conclusion

The amplifier now works absolutely fine, and has done ever since I replaced the EL519. I do remember noting that the original owner commented on the relay "Chattering" whilst in transmit. First of all this in not a relay fault. if you look closely at the anode PCB on the final picture, your see there is a very poor attempt as making a "Meander" or "PCB Track Inductor" for the APC or "Anti Parasitic Choke". Those who have spent many years working with valve equipment like myself for just over 30 years, will instantly recognize this problem. You can either replace the valve that has a slightly different spec on performance, or simply add a 6 turn 9mm dia APC inductor in series with a 2 watt 10 ohm carbon resister to stop this issue.

« Last Edit: December 17, 2021, 02:49:00 pm by 26AM081 »

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