[ADXA] DX on a budget isn't all it is "cracked up" to be!

[Dennis Schaefer]

Great story, Randy!  We lived through it with you!

I could afford a better amp also, but we need some occasional excitement.
I have two AL-811 amps, which have three 811A tubes.  I get 500 watts out
and can usually prevail on CW and SSB.  The conventional wisdom is that
these amps are not suitable for digital modes.  They certainly weren’t
designed for continuous duty, even though the MFJ marketing department
implied you could put a brick on the key.  I never tried using one on RTTY
or other digital modes.

It occurred to me that a little power would come in handy on 80 and 160,
though.  I had previously added padder capacitors to the tank circuit for
80 and 160 on one amp, and that increased efficiency at the low end of 80.
I tried tuning several different ways and determined that I could run cool
at 400 watts out with 50 watts drive.  At lower outputs, 200, 300 watts,
etc, efficiency suffered and tube dissipation was much worse, exceeding the
195 watt limit.  At 400 watts, we broke into the right part of the curve,
and dissipation was safely under specs at about 140 watts.   RTTY
transmissions or 15 second sequences don’t trouble it.

It seems to be running fine.  I’ve had some things take up my BIC time, but
I think this will work.  However, in the back of my mind is how startling a
plate-to-grid short would be!   That happens with 811A tubes that are
misused.   I have made the mods that supposedly protect the rig from ill
effects in that case and I have 11 spare 811A’s.

A solid state amp would be nice, and a couple of clicks and the brown truck
would deliver it.  But - we must live just a little dangerously to feel
alive.

See everybody at the hamfest!

73,
Dennis/RZ



On Thu, Feb 27, 2025 at 11:44 AM Randell Curtis, W5ZJ via ADXA <
adxa at mailman.qth.net> wrote:

> While in hot pursuit of getting #50 confirmed on 160, I have run into a
> slight issue. With the rig running in the shack last night, I noticed from
> the house that I was seeing Sardinia at at decent snr, and that he also had
> recently uploaded to LOTW, so I decided to run out to the shack to give him
> a call.
>
> PD (puppy dog) and I hurridly ran out to the shack about 9:30 pm, and were
> immediately disappointed due to not having enough horsepower for Sardinia
> to hear me.  Being a forever optomist, I kept thinking propagation would be
> better in 30 minutes...then the next 30 minutes....and so on, until about
> 12:30am. It was then that I decided to redeem my time, jump over to 40 and
> work some "gravy" DX just for fun.  Little did I know this thought would be
> the beginning of the end.
>
> I turned the amp off, jumped over to 40, tuned the inv L, switched the amp
> on, hit send and POW!  After peeling PD and me off the ceiling, I stood
> there in shell shock as the smell of death wafted up from the inside of my
> dear Jethrine. While sleepy and in a hurry, it seems that I had failed to
> band switch the amp. At this point, I was struck with the realization that
> auto bandswitching and swr protection  are probably some very nice features
> to have in a solid state amp.
>
> In the light of morning, I tended to Jethrine, and realized, that even
> though she looked rough and tough, she did need TLC, and attention.  Even
> though wounded, with a little care and $$$, she should be back on her feet
> in no time.
>
> In other news, Mouser is now adding a tariff charge to the replacement
> mrf300's I just purchased. Oddly enough the tariff charge on the 300an is
> almost $4 more than the tariff charge on the 300bn. Don't that beat all?
>
> Here are my final thoughts...
> 1. Cheaper is not always better...but cheaper can sometimes provide a
> bigger thrill.
> 2. PD hates ft8 and would be nervous in the shack...now she won't come in
> the shack at all.
> 3. If you have an amp, cherish it. If you don't have an amp, be thankful
> that you aren't paying a tariff on the parts you bought today.
> 4. A mosfet letting go at 12:30 am is not the same as a mosfet letting go
> at 12:30 pm. I'll give you 2 choices to pick which is the more surprising.
> 5. 50 countries on 160 for 1/2 dxcc is near impossible to get. If you have
> exceeded this at anytime in your life, I suspect you are superhuman...and
> never owned an amp made by me.
>
> Have a great day. Don't forget to give your amp a big hug today.
>
> Randy/W5ZJ
>
>
>
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