[Amps] HL2K high SWR input

[Charles H]

Patrick,
If you have your TS850, which I think is a transceiver, RF output going to the input of your amplifier, your transceiver will not tune your amplifier;  that has to be done with the tank controls in the amp RF output circuits.

Using an antenna tuner on the transceiver/driver to load into an amplifier is not at all a good idea and when doing that, usually it will cause a problem with the amp or the driver.  Of course, thousands of hams do use their driver antenna tuner to get a match into their amp, but even tho it sometimes "works," it is a poor substitute for a near 50 ohm input on the amp.

For example, the MLA-2500 original had such a poor input set of impedances (varying by band) that the MLA-2500B was released with a near 50 ohm input (adding input tuned circuits for each band), giving the driver an accurate 50 ohm impedance load....... and no need for the driver's antenna tuner. 

You did not need disassemble anything except to try to address the need for a near 50 ohm load from the amp to present to the driver, and do repair.

On the tank side of the amp, the final output components exist to resonate that circuit and in some cases such adjustment will allow continued amp output even into a high SWR, BUT IT DOES NOT REDUCE THE SWR appearing at the output of the amp.   That can be addressed by a real antenna tuner, like the Nye model MB-VA, and/or changing the antenna so it presents a load more close to 50 ohm.

The Nye antenna tuner, then, is hooked by coax from the output of the amplifier and then on the TUNER'S output... on to the antenna.

Good luck, Charly

> Date: Sat, 5 Mar 2016 07:41:21 +0100
> From: pegloff at gmail.com
> To: Amps at contesting.com
> Subject: [Amps] HL2K high SWR input
> 
> Hi all,
> 
> I have a HL2K amplifier (pair of 3-500Z) for several years now (got it
> second hand) and it always had a high input SWR on 21 MHz. I matched it
> with my TS850 antenna tuner, so it was OK.
> 
> During last contest i had a problem on 40m (500pF/2kV in output tank
> shorted). So i had to open the amplifier and while being there i wanted to
> see what's wrong with this SWR.
> 
> I couldn't reduce the SWR in adjusting the capacitor.
> 
> I removed all components used in the input tank and checked them. They are
> all perfect.
> Coil is 0.34uH and caps are as marked and on diagram.. Input C = 150 pF and
> output adjustable up to 200 pF.
> 
> So now, i'm stucked....
> 
> On all other bands, the input SWR is just fine, so i suppose there is no
> problem with the tubes or anything else in the amp. I have full power and
> everything is stable.
> 
> Does anyone have a HL2K and can confirm that it is OK (or not) on 15m ?
> 
> Any idea on what could be wrong ?
> 
> 73, Patrick
> 
> -- 
> Patrick Egloff - TK5EP
> email : pegloff at gmail.com
> Web page : http://www.egloff.eu
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