Electric Radio 202 2006 Mar.pdf

(7362 KB) Pobierz
$3.85
celebrating a bygone era
ELECTRIC RADIO
Published monthly by Symbolic Publishing Company
PO Box 242, Bailey, Colorado 80421-0242
Periodicals postage paid at Cortez, CO
Printed by Southwest Printing Inc., Cortez, CO
USPS no. 004-611
ISSN 1048-3020
Postmaster send address changes to:
Electric Radio
PO Box 242
Bailey, CO 80421-0242
Copyright 2006 by Symbolic Publishing Company
Material appearing in Electric Radio may not be used in any
method without prior written permission.
Editor
Ray Osterwald, N0DMS
Editor Emeritus
Barry R. Wiseman, N6CSW
Electric Radio is all about the restoration, maintenance, and
continued use of vintage radio equipment. Founded in May of 1989
by Barry Wiseman (N6CSW), the magazine continues publication
for those who appreciate the value of operating vintage equipment
and the rich history of radio.
It
is hoped that the magazine will
provide inspiration and encouragement to collectors, restorers
and builders.
It
is dedicated to the generations of radio amateurs,
experimenters, and engineers who have preceded us, without
whom many features of life, now taken for granted, would not be
possible.
We depend on our readers to supply material for ER. Our pri-
mary interest is in articles that pertain to vintage equipment and
operating with a primary emphasis on AM, but articles on CW,
SSB, and shortwave listening are also needed. Photos of Hams in
their radio shacks are always appreciated. We invite those inter-
ested in writing for ER to write, e-mail, or call.
.
Regular contributors include:
Chuck Teeters (W4MEW), Jim Hanlon (W8KGI), Tom Marcellino (W3BYM), Bruce
Vaughan (NR5Q), Bob Grinder (K7AK), Bill Feldman (N6PY), Dave Gordon-Smith
(G3UUR), Dale Gagnon (KWH), David Kuraner (K2DK), Larry Will (W3LW), Brian
Harris (WA5UEK), John Hruza (KB00KU), Hal Guretzky (K6DPZ)
Editor's Comments
Winter Operating Events
I should be receiving the results of the recent winter Classic Exchange
/ICX/I
event
and from the American Wireless Association's AM QSO Party in the coming weeks;
I will print them in ER when they become available. The AWA AM event probably
had more participation than did the CX, and at times it was hard to find other
stations in the Classic Exchange to work on the bands. I did work Jim Hanlon
(W8KGI) on 80 CW, and Jim had 8 different transmitters running, most of which
either had been or will be the subject of ER articles!
It
sure was great to hear that
many rigs, and the other stations I worked had equally interesting gear, some of
which were from the early 1930s. Unfortunately, other commitments prevented my
participation in the AWA phone contest.
There was a lot of participation in the Electric Radio Heavy Metal Rally last
December. I have only received 3 logs, so I am declaring the three entries equal
winners. The rally is a lot of fun and is popular, but I will probably need to think
about changing the rules for next December.
A Correction
W2FU, Meir, has kindly sent a correction for the photograph on page 44 of the
February 2006 edition of ER:
/I...
The equipmentdepicted in the magazine is not
from the US Navy, but is from a WWII Victory ship (US Maritime Commission)
modelFT-102MF /HF radio console, manufactured by Federal Radio and Telegraph
(later became ITT). The transmitter is the McKay 167-BY. It's a CW-only transmit-
ter, covering 2 to 24 MHz. The output is a pair of 803s, rated output is 125W. The
middle part, where the owner put a modulator, is where originally the receiver was
mounted. According to the manual, the receiver should be either the RMCA AR-
8506 or the Scott SLR-F ...
Thanks, Meir, for sending this valuable information.
The AM Broadcast Transmitter Log
Dave Kuraner's popular series on broadcast transmitters and audio processing
will return in next month's issue. 73, Ray, N0DMS, and Keep the Filaments Lit!
/I
TABLE OF CONTENTS
2 Martha's Breadboard Deluxe: Homebrewing in the 1930s, Part 2
K6GLH
8 Restoring a Hammarlund SP-200LX
W3LW
19 The American VHF-AM Gallery, Part
1:
The Heathkit Pawnee
K7SC
22 High Performance Audio for R-390 AM Reception, Part 1
N6PY
26 Using Component Source Date Codes
K5SEP
28 The Restoration Corner
ER Readers
30 Ham Radio's Twins: Conars Model 500Receiver and 400Transmitter
W4PQW
32 Another 1984 R-390A Has Survived
Paolo Viappiani
43 Vintage Nets
ERReaders
44 Classified
ER Readers
Martha.s Breadboard Deluxe, Part 2
A Modern Version of Homebrewing in the Mid-1930s
By Gary Halverson, K6GLH
503 Jessica Ct.
Mokelumne Hill CA 95245
ghal@ix.netcom.com
only simplified the modulator construc-
tion, but also facilitated audio tailoring
with an outboard audio chain. The 300-
volt DC power supply built on the modu-
lator chassis for the oscillator also pro-
vided enough current to
power the 45s.
The original choice for
the modulator tubes was a
pair of 211s operating in
Class Bwith a new old stock
200-watt Hadley universal
Class Boutput transformer.
However, the bias require-
ment meant adding yet
another power supply, and
since this voltage was nor-
mally supplied by dry bat-
teries in 1935, switching to
the near zero-bias 838
seemed like a logical
choice. But alas, the
Amperex/Collins ZB-120
was designed specifically
for Class B modulator ser-
vice without any bias, and
there just happened to be
several NOS pairs in the tube cupboard.
Bringing the modulator up ushered in
the next set of challenges. The first prob-
lem was insufficient modulation. This
turned out to be a silly miswiring of the
universal modulation transformer sec-
ondary. Correcting this problem produced
more than enough audio which led to the
next problem, flashover in the RF deck
PA plate tuning capacitor plates. Because
the high voltage was on the PA tank
components, anytime flashover occurred,
it put a major strain on the 866 high
voltage rectifiers. Some "cheating" was
clearly in order, so a DC blocking cap was
installed to remove the high voltage from
the tank capacitor. While this minimized
the flashover problem, it still occurred
occasionally on voice peaks. A 200-watt
March 2006
In last month's story I was all excited
about the 1935 re-enactment homebrew
project. By this time, however, the feel-
ing was very different. I've learned a lot,
mostly about things never anticipated.
While the construction was fun and find-
ing vintage-correct parts was challeng-
ing, getting the rig to work has proven to
be a major effort that has left me humbled
by how much I didn't know.
The Modulator
Once the RF section was working, the
modulator was the next step. I decided
not to mess wi th a low-level microphone
preamplifier on the breadboard due to
ground loop and hum pickup possibili-
ties, but rather just go with a line-level
input and use a pair of 45s running Class
A to drive the modulator tubes. This not
2
Electric Radio #202
Schematic of the modulator with line level input.
modulator feeding a 100-watt RF final
just wasn't going to work.
The Power Amplifier
There was no escaping the inevitab iiity
of adding an RF power am-
plifier deck to provide a
more appropriate load for
the modulator. Combined
with the reality of needing
at least 200-watts of carrier
power in today's AM win-
dow for relatively comfort-
able communications, it
made sense to bite the bul-
let and add another deck to
the wooden tower.
A push-pull circuit using
a pair of 203As was selected
from the handbook and a
fourth wooden chassis was
built. The amplifier com-
ponents were laid out for
symmetry. Construction
went smoothly and the
completed unit was stacked
on top of the exciter and
wired into the interconnect
harness. A short twisted
pair feedline connected the
output link on the exciter
to the input link on the
power amplifier. A 4-turn
link on the output was sub-
stituted for the capacitive
coupling on the output tank
coil. Everything checked
out. And that's when the fun started.
First, the coupling link on the exciter
March 2006
3
Martha's backside during construction
of the interconnect wiring harness.
Electric Radio #202

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika:

Zgłoś jeśli naruszono regulamin