[TenTec] Ten-Tech Matchbox 229 vs 238 series.

[Edward Mccann]

Thank you to those who replied.

Yes, I mixed up the nomenclature.
Was trying to suss out improvements/changes from the 229 to the newer 238 KW series. 

Senior moment, caught by all.

Great answers from several of you.

I include below a snip of a response from another extremely knowledgeable source addressing a related question on another great web site, since there may be others reading without specific Ten-Tec Matchbox experience.

FYI:

“Balanced Matchboxes:  
Technically, there is no reason for the T to have a broader matching range than the L.
Mechanically there is.
The L has a couple of challenges.
First, it must have its variable capacitor switchable from input to output.
Second, it sometimes requires A LOT MORE CAPACITANCE, which is impossible to obtain with a variable capacitor that fits inside of a desktop box.
The simple solution is switched caps.
 
There are/(was) those who understand this and know how to deal with it. 
For about 30 years, TEN-TEC built a “Model 238” ( then 238A, 238B, 238C).
They even built similar before that but I’ll begin with what they did their last 30 years.
 
The 238 has a roller inductor and a single 500pF capacitor.
In addition, it has 4 fixed capacitors, each 440 pF (if my memory serves me correctly), that can be switched in, in parallel to the 500 pF.
That totals 2260 pF.
However, especially when matching openwire fed antennas, even that is sometimes not enough.
So Ten-Tec provisioned for adding an external high voltage capacitor on the rear panel of the matchbox.
They even included a 1000 pF disc ceramic capacitor with the matchbox.
This enabled 3260 pF!
 
In practice, after 25 years of owning these matchboxes, I have used the external capacitor twice.

·       Once was on my short 80m vertical dipole in Oklahoma.  See Pics:  www.dj0ip.de/my-station/oklahoma-2010/
·       The second time was here at this QTH when I first put up my 160m antenna in a November snow storm.  I had to match it with the matchbox and needed an external cap for that too.   In the springtime I was able to tune the antenna an match it at the feedpoint and then I didn’t need any matchbox anymore.  But this external cap feature enabled me to participate in CQWW DX CW on 160m back in November.
 
BTW, I did not use the 238’s built-in 4:1 voltage balun with the 80m Vert. Dipole.  That balun is rubbish!
NEVER USE ANY 4:1 BALUN AS YOUR MAIN TUNER BALUN.
ONLY USE A 1:1 GUANELLA!
(If needed, you may also use a 4:1 transformer in front of it, but ONLY if it is absolutely necessary).”
 
73,
Ed McCann
AG6CX


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