Date: Tue, 22 Oct 2013 15:00:28 -0700 (PDT)
From: Dennis OConnor <ad4hk2004@yahoo.com>
To: "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] 200-ohm tank and "un-un" in HF amp design?
### Some of these folks oughta go back to whatever university they spent huge
$$$ to attend,
and ask for their $$ back ! Ditto with RF consultants. Strap the
bandswitch correctly as per
my previous post. DON’T use braided wire for the various taps, use silver
plated cu strap.
Install a 100 pf NPO cap between chassis and cathode. Install correct sized
coil between plate
block caps and C1 tune cap. Presto, eff on 10m skyrockets. That HF-2500E
..with the 3 tubes
is supposed to do 3500w out. 1200w out on 10m sucks.
Install the above tricks....and you will almost triple the PO on 10m. Heck,
even the 11m folks have
this all figured out..its all old news. You also need bigger ga wire for the
10m coil on the tuned input,
and don’t get the tuned input Q too high on 10m either. If you actually
measure the PO of the
PI tuned input with too high a Q.... you will see that the PO is way down vs
the power applied to
the input of the tuned input. I had that problem on my hb 3CX-3000A7 amp on
15m. With
200 w into the tuned input... I measured just 160W on the output side..into a
dummy load...
using calibrated wattmeters on each side of the tuned input. The fix was to
increase the
uh a tiny bit.... by tapping the coil by an extra one quarter of a turn on 15M.
This was
a manually tuned..tuned input..with a tapped 4 uh coil, used on all bands.
Coil was made
from 6 ga wire. PO rose to 195 watts on 15M. Ok, now way more drive to the
cathode,
more grid current, more plate current..and more PO. A 17 turn coil with a
1.5 inch ID was used
to make the 4uh coil. Two broadcast caps used for the C1 + C2 caps.
Jim VE7RF
Roger - Palstar is no longer in the amp business.
I have the first HF2500E he built. I flew down there a few times to watch the
build.
I flew there to pick it up on a Friday afternoon when they told me they had a
'small problem' with uneven power output.? He did demonstrate that on 20 meters
the amp would make his dummy load beg for mercy.
Said he had a call in to a big name amplifier designer (commercial stuff) to
discuss it Monday morning and I should call him on Monday afternoon.
Called on Monday and they had given up, didn't know what to do.The consultant
said it should produce power and he could not see a problem on the schematic.
What's the problem - I asked - because you are sitting on thousands of dollars
of my money and I have burned a bunch of avgas and I still don't have an amp
and I'm getting annoyed?
So, then he told me that it would not tune much above the bottom of the ten
meter band without losing power - would only make about 1200 watts at the top
of the band.
Oh that - I said - why the hell didn't you say so in the first place, sheeesh.
So, I told him how to fix it and I would be down on Friday afternoon to pick up
my amplifier for CQWW the following weekend.
I'll let the list figure out what it was just from my sketchy description and
how I had them fix it. - most of you should be able to do so.
Anyway, Bill lost money on the redesign (super good design job, too) and wasn't
selling enough amps to cover the payments to Commander for the rights so he
returned the rights to Commander.
Anyway, it is a great desk top amp. Pumps out power quietly.
?
denny / k8do
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