sctvguy1 wrote:
On Wed, 04 Nov 2015 20:10:35 -0800, Jeff Liebermann wrote:

On Thu, 5 Nov 2015 02:28:05 -0000 (UTC), sctvguy1
wrote:

I have an old boatanchor, a Lafayette HE-10,

https://www.google.com/search?tbm=isch&q=lafayette+he-10
http://www.radiomuseum.org/r/lafayette_he_10he1.html
https://www.youtube.com/watch?v=Lk1dmQEsoIk
Made by Kenwood/Trio for Lafayette.

that takes a single wire antenna and a ground. I would like to make a
simple trimmer to optimize the 75 feet of random coated wire. The wire
is copper, Radio Shack.

I can't tell what it uses for an antenna input (50 ohms, 75 ohms, 300
ohms, broadband, narroband, tracking filters, whatever) so I can't offer
an antenna tuner design. Any idea what's behind the antenna connector?

It is just a simple old screw, made for a copper wire antenna, the radio
was made in the late 50's. I used to have one that I made out of a
variable capacitor and just tuned the knob to trim the antenna. I am now
64 and that was when I was in junior high school? Can I get a variable
capacitor for an old radio and connect the two ends?

Oops! I didn't realize what you meant by trimming an antenna.

Irv VE6BP

On Thu, 5 Nov 2015 10:55:37 -0800, (Dave
Platt) wrote:

In article ,
Jeff Liebermann wrote:

It is just a simple old screw, made for a copper wire antenna, the radio
was made in the late 50's. I used to have one that I made out of a
variable capacitor and just tuned the knob to trim the antenna. I am now
64 and that was when I was in junior high school? Can I get a variable
capacitor for an old radio and connect the two ends?

I'm 67 and know the feeling. The lab that I patiently built up over
the last 40 years is now considered a test equipment museum.

Yes. Just a small 365pf(??) or lower value variable capacitor should
work. I wanted to see the circuitry so I could provide a better guess
at the capacitor value. Something like these:
http://www.ebay.com/sch/i.html?_nkw=365+pf+variable
Any old tube or xsistor radio should have one. Dig around at thrift
shops or ham flea markets for old radios and junk boxes.

Good luck and I'm amazed that such an old radio still works.

There's a manual and schematic for the HE-10 (apparently a
Globe-Trotter 9R-4J) at the BAMA.EDEBRIS.COM site.

Thanks:
http://bama.edebris.com/download/lafayett/he10/he10.pdf
http://bama.edebris.com/download/lafayett/he10/KT-200%20HE-10%209A-4J.pdf
The latter link shows their recommended antennas on Pg 4. If
connected between A1 and A2, a 1/4 wave dipole should work, which I
would guess would be about 75 ohms input impedance. The other
connects A2 to E(earth) and produces an inverted L or Zep. I can't
squeeze anything useful out the schematic on Pg 7.

It looks as if you can use either an unbalanced random-wire or zep
antenna (connect to A1, jumper A2 to E, and connect E to a good
ground), or a balanced doublet (remove the jumper, connect antenna to
A1 and A2).

Yup. If the wire is too short, add series inductance. If to long,
add series capacitance. With a low impedance input to the receiver,
an antenna tuner might be better, but hardly worth the effort.

In either case, A1 and A2 feed into the front-end preselector, which
has a 2P4T switch (one position per band) connected to four sets of
tuned transformer couplers. The signal goes into the primary of one
transformer, out through the (tuned-per-band?) secondary, and then
goes to the grid of the first tube via a 250 pF cap. One of the
tuning-capacitor gangs is connected to the secondary/gate feed as
well.

Yep. I can't guess(tm) the bandwidth of the front end filters without
knowing the turns ratios and approximate inductances. Offhand, it
looks like an equal number of primary and secondary turns, which makes
it a rather low Q affair. Probably needs to be that low to cover the
entire band without a tracking filter.

Gorgeous wiring diagram on Pg 9 and Pg 10. It's even drawn in
perspective. I haven't seen anything that nice if many years.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558