[Amps] HL2K high SWR input

Wed Mar 9 07:25:58 EST 2016

Hi all and thanks for answers,

It seems that the mailing list is not working properly.. I didn't receive
anything during days...

It took me a complete day but i finally made my amplifier work.
As i wrote, the problem was only on 15m and the amplifier worked perfectly
on all other bands.

Of course, did i try another coaxial length between transceiver and
amplifier, etc...

I tried to measure the input with my VNA (amp being off and putting a 56
Ohm from cathodes to ground)  and came to the conclusion that something was
wrong with these input circuits... I didn't have a good match and had some
strange parasitic reflections.
But it is hard to tell where the problem is...
I also noticed that replacing the 56 Ohm with a small pot, i could get a
good match, but at a different input impedance (close to 85 Ohm).

I calculated a PI filter for a Q=2 and input 50 OHm , output 60 Ohms (what
the two 3-500Z should give) and found that the original values are
completely different.
I compared to several other commercial amplifiers and NONE of them has the
same values, the differences are HUGE ! Of course, different configuration
can lead to a good result, but i can't explain such BIG differences...
Where is the truth ?

The amplifier being completely disassembled, i inadvertently had the input
circuit on 24 MHz band and the output on 21 MHz, the amplifier worked
perfectly !
So i only removed the 21 MHz input circuit and connected it to the 24 MHz
circuit.  Et voilà !
BTW, some commercial amplifier have a common circuit for 2-3 bands.

Again, i learned a lot..

That said, i would like to hear of someone who has the same amplifier TOKYO
HI-POWER HL2K and his results on 15m input ?
73, Patrick.

2016-03-09 12:44 GMT+01:00 Charles H <k4vud at hotmail.com>:

> 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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> > Amps at contesting.com
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>
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-- 
Patrick Egloff - TK5EP
email : pegloff at gmail.com
Web page : http://www.egloff.eu