KL503HD

[B C]

I just purchased a RM Italy KL503HD (high drive) amplifier. The instruction
book says it can handle 1 to 35 watts input from AM, FM, SSB, CW. I need to know if they are referring to dead key wattage or PEP. On their smaller amps they refer to dead key wattage, but on this one I'm not sure what they mean.
Do any of you know the answer to this, I don't want to release the factory smoke if I can help it.

B C

[MDYoungblood]

Wow, I didn't know they made a HD. I looked it up and the thing that I see is the maximum bypass wattage is 50w, that in itself is telling me there isn't much of a difference between it an the regular 503. I'm curious to know what they are using now a days for the final transistors.

3's

Greg

[Deleted User 30222]

Can't tell off the diagram that came with mine. But did some research, and it looks like there using the RM3 MOSFET.

[295 antenna]

I've always taken it to mean dead key. I have the new high drive 503 and I needed atleast 25 watt input to to get it to key up

[B C]

Hey guys, I have been studying this KL503HD, it is driven by a single RM3, it drives 8 RM3 mosfets. The variance in power (6 levels) is controlled by limiting the input to the RM3 driver. At present I'm driving the amp with my Galaxy 2547, with its power turned down to 1.25 watts the amp. develops 7 watts dead key on level 4, on level 6 it makes 25 watts. Below level 4 it makes 3 watts on level 3, 2 watts on level 2 and less than 1 watt on level 1. I hope they do mean dead key for the input wattage, my Galaxy's (all 3) and my Connex all kick up close to 60 watts PEP and I don't want to ventilate my new toy. I have sent a message to Mr. Lee at 88 to see if they have any definitive answers about input limitations, if any of you have any more info. or pointers in the care and feeding of this new pet of mine it would be greatly appreciated.

B C

[MDYoungblood]

I did a little research on the RM3 mosfets, the specs look like the 13n10 mosfet, so driving it low would save you from letting the smoke out of the amp. The 13n10's (the real ones) are a tad bit more robust than the mrf520's but still have the same SWR change characteristic problem (popping). I installed a 8 fet board in my 2995DX using 13n10's and was 400w PEP (had a Meanwell 45a SPS inside as well), ran for 7 years before a fet decided to smoke.

Treat it right and it should last.

3's

Greg

[NLToontje]

Hey guys, I have been studying this KL503HD, it is driven by a single RM3, it drives 8 RM3 mosfets.

Just double checking, but do you really have the HD (High Drive) version?
I own a non-HD-KL503 and that is 1 driving 8. This amp can only handle 5W input (because of the 1 FET driver).
A friend of mine has the HD version. His is just 8 FETs and can handle at least 30W input.
Another friend just bought the KL703 which is a straight 16 FET amp and I'm surprised to read that it can only handle 30-35W input (according the manual).

[NLToontje]

I need to correct my previous post.
The HD version is not a 'straight 8', but also a 1 driving 8 (like the non-HD version).

Just watched a recent review on YT:

YOUTUBE_ADMIN

YOUTUBE_ADMIN

[Sparky1]

On my 503 HD I run 3-watts on am (dead key) and swing up to 20w and get 300w output. I wouldn't dead key any more than 5w. Hope this helps. 170 Mike central Maine