With the BTA-500R
It has MOVED as of 12/16/2002
The NEW OWNER of the BTA-500R
IS Neal Newman KA2CAF

Columbo and Me

Door open with
tubes and xtals

Internals from back

Other Equipment

(From WERA) From Top to Bottom:
Moseley TFL-280 Audio Limiter
Moseley TGR-340 Audio Gain Rider
Moseley TRC-15 Remote Control System
Remote Unit
(From WERA)
Moseley TRC-15 Remote Control System
Remote Terminal (transmitter end)
(Separate Purchase)
Altec 1592B Line Mixer/Amplifier.
Has 600 ohm balanced line output.

The transmitter provides terminals to switch the plate voltage on and off, transmitter on and off, raise and lower power, and switch crystals. One way to use these terminals would be to run separate wires to the remote control site, which would be many. The remote control system eliminates this. The receiving unit at the transmitter end is connected to all necessary control wires for a short distance. The remote control unit is connected to the receiving end with one coaxial cable. The remote unit sends a "carrier" or signal to the sending unit. The carrier alone does not perform anything else, but to tell the remote unit that it is present and to light a presence light on the receiving unit panel. On the remote control unit any of 15 channels may be selected and controlled. Depending on what operation is performed. When a channel is selected or other function is selected, the carrier signal is keyed by shifting its frequency. For example, if channel 1 is selected, the carrier is shifted down for one long period followed by one short period. If channel 15 is selected, one long shift is sent followed by 15 short period shifts. The receiving unit responds by first resetting, then switching to the appropriate channel.

Preliminary Cleanup

Bottom of transmitter cabinet before cleaning,
showing tagged transformer and inductor wires.

After cleanup using Softscrub cleaner.

"Be Happy, Go Lucky, It's Lightup Time"

(you have to be old enough to remember that slogan)

It's COOL because it's HOT!

220V connected 7/24/1998. Tube lightup test succeeds.

Initial installation and connection of 220V line completed. The blower, filaments; and associated switches and relays work.


New Crystal Installation

This picture shows that an old standard
crystal holder can be plugged into the octal
sockets between pins 4 and 6 to replace the
oven controlled units. Three crystals can be
installed into CR1, CR2 and the Connelrad
socket on the right. Front panel and remote
control switching is provided for easy QSY,
using crystals. In this picture CR1 is
1885 KHZ, CR2 is 1945 KHZ and the
Connelrad socket has a 1958 KHZ crystal.

The 6AK5 is the crystal oscillator, 5763 is
the first amplifier and driver to the 6146 at
the top.

Conversion of PA Tuning section

Original tuning section configuration.
Consists of two PI networks and 2nd
harmonic trap. Vertically mounted coil
on left is main PI network inductor with
tuning slug, adjustable from front panel.
Note all capacitors are fixed.
New tuning section configuration.
Second PI network and 2nd harmonic trap
coils removed. 100pf tuning cap and dual
section 450pf (900pf) loading cap mounted
from top grill. Loading cap is shunted with
original 1500pf fixed cap and two 100pf
resonance caps. The coil is tapped at turn #20.


I managed to find a 1815 KHZ crystal at a hamfest to replace the broadcast band 1590 KHZ crystal. The output network was modified to use variable caps for easier tuning as shown above. These caps work, but I plan to replace them with larger caps for better tuning range. I picked up the variable caps at a hamfest for $10 each. Threw them in the dishwasher and they came out sparkling clean. (I suggest placing a piece of paper over any labels and taping over them, if you decide to do this. It DOES protect the label on the caps.)


The 6146 buffer output consists of a broadband network with a coil which adjusts by moving a jumper. For 1815, I peaked it on jumper position 7.

Jumper on buffer coil moved to
position 7.


Modulation sounded pretty bad. Above 25-30% it breaks up intermittently and contains a raspy, static-like distortion which got worse with modulation level.

At low a low level of modulation, envelope
looks and sounds fine.

Beyond about 30%, envelope looked like this
before transformer replacement. The ragged
envelope is the appearance of harmonics due
to the fact that the driver stage was pushed to
the limit causing clipping (flat tops). The amplification
factor of the modulator was severely reduced because
of a HV short breakdown in the modulation transformer.
This problem was not evident by conventional 110VAC
tests on the transformer.

I ultimately borrowed a modulation transformer from Tony Dee's BTA-1R which worked beautifully. I decided to order a Pater Dahl Universal 1KW modulation transformer which was installed on 12/12/1998 and marked the completion of the BTA-500R conversion and repair project. Some friends encouraged me to look for a second hand replacement, but I decided to spend the extra money for a brand new replacement to be assured of longer life and flawless operation.

Two views showing original, 110 lb modulation transformer
on the left with the new 40 lb modulation transformer from
Peter Dahl on the right. Transformer technology sure has
improved! The new one works beautifully!


On 11/10/1998 I bought two extension shafts and an 11/16" wood drill bit for my hand drill and managed to drill a hole diagonally through the wall in the corner and through the garage ceiling. I ran a two conductor shielded cable for the audio and a 50' piece of RG-58/U coax for the remote control. After the appropriate amount of messing around I was finally able to turn the transmitter power on and off and key the transmitter from my office. The plate voltage off control in the transmitter did (and still doesn't) work, so I could key it on, but not off. I worked around this by driving an NC relay connected to the remote interlock terminals on the transmitter which results in the same behavior, except that the interlock has to be NC. There was a 30V DC terminal on the back of the control unit which allowed me to drive the relay.

On 11/12 1998 I called CQ for the first time on 1900 KHZ at 1300 UTC. Tha band was not in good condition so I got no answers. I installed 3, switchable crystals on 1885, 1900 and 1985.

I have the a total of 5 crystals for the following 160 meter frequencies:

All but the 1815 crystals were ordered and custom made by Jan Crystals.

JAN Crystals 800-526-9825: 813-936-2397
P.O. Box 06017: 2341 Crystal Drive: Crystals
Ft. Myers, FL 33906-6017

The oscillator schematic was mailed to Jan for optimal crystal design. The modulation leaves something to be desired. The modulation transformer is suspect.

First QSO on 1885 KHZ, 11/12/1998 at 00:13 UTC with W3FJJ, Chuck Hanavin, Conowingo, MD. Signal S9+20.
(This is also my first 160 M QSO ever in my 35 years as a ham.)

12/02/1998 - Tony Dee permitted me to borrow the modulation transformer from his BTA-1R. Upon replacement of the modulation transformer, the transmitter is now fully operational with clean modulation at 100%.

The blue-green Altec Line Mixer and remote
control unit on top of the Viking Valiant are
my connections to the BTA-500R in the Garage.
On the left are 2 SX-28s. The main RX is a JRC
NRD-525. Other equipment is an Icom R7000,
Ten-Tec Omni-D, MFJ electronic keyer, Dual Pentium
133 and 486/DX-100 computers.


Other Broadcast Transmitter Ham Projects W6THW




BACK TO BTA-500R Conversion Page