WA2WHV AM
With the BTA-500R
It has MOVED as of 12/16/2002
The NEW OWNER of the BTA-500R
IS Neal Newman KA2CAF

Other Equipment

REMOTE CONTROL:
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

"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!

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

Preliminaries

• 8 ft grounding rod was obtained from a local hardware store and pounded into the ground outside the garage. The BTA-500R manual calls for a 4" wide copper strap. I happened to have a roll of 1" wide copper strap which I used to ground the frame to the rod. This seems to suffice.
• Purchased a 1500W 50 ohm Oil Cooled "Paint Can" dummy load for testing. Do not use wirewound resistors, they are inductive and therefore, present a reactive load to the output.
• Had continual problems with overload shutdown making it impossible to test. Added a pair of parallelled 45 ohm 150 watt resistors in series with the primary of the plate transformer to cut down the plate voltage. This got rid of the wild behavior so I could deal with the transmitter more easily.
• Finally discovered that most of my problems were with the 5763 driver section. In checking the drive level on the front panel it was far too low. Since the final is grid leak biased, lack of drive caused the tubes to conduct higher currents, tripping the overload. The driver printed circuit board, consisting of the octal crystal sockets, crystal switching relays, 6AK5 crystal oscillator tube and 5763 buffer is a weak spot in this transmitter. The 4K 10W plate resistor of the 5763 was found open. I ultimately found it best to replace it with a 25W resistor mounted on the relay frame of this board. In examining the board, I had noticed a considerable amount of resoldering had been done indicating that this section was not well designed. If you are working on this or it's BTA-1R big brother and are having lots of problems, this board is suspect. Examine it carefully for all values and bad solder reworks. I also had problems with an intermittent solder bridge short on this board.

New Crystal Installation

Conversion of PA Tuning section

OUTPUT RETUNING

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.)

BUFFER RETUNING

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.

MODULATION TEST

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

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.

FIRST CQ

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:

• 1815 KHZ
• 1885 KHZ
• 1900 KHZ
• 1945 KHZ
• 1985 KHZ

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%.

NEW OWNER Neal Newman KA2CAF!

SUMMARY

PRELIMINARIES

• Clean up unit and transformers
• Replace all transformers
• Install Copper Strap Ground. Bought 8' grounding rod from local hardware store and pounded it into the ground just outside the garage.
• Install 220V Test filaments and blower
• Get 1KW dummy load to test with

SUMMARY OF TRANSMITTER CHANGES

• Remove second tank coil and second harmonic suppression coil to make room for variable tuning caps. Leave fixed caps in for trimming. The coil with the tuning slug (controlled from the front of the transmitter) remains and, in fact can be used for tuning later on.
• Managed to find 1815 KHZ crystal at hamfest, but ultimately found it easier to order necessary crystals.
• Bought a dual 450pf variable cap for loading and 100 pf variable cap for tuning from hamfest for $10.00 each and installed them fastening them from the top grill. No holes were drilled. Some porcelain standoffs were necessary for the loading cap for spacing.
• Set tap on PI network tank coil to turn #20.
• Set tap on 6146 Driver coil to tap # 7.
• Bought some old Atwater Kent tuning knobs for $2.00 each and mounted them on top for tuning and loading (also bought a couple right angle gear assemblies for eventual front access).
• Purchased 1500W "Paint Can" dummy load for testing to prevent interference with other hams.
• Replaced 4K 10W plate resistor of 5763 stage with 4K 25W and mounted it on the side of the crystal relay box to prevent further "cooking" of the PC board. The original resistor was open, hence, there was no drive from the 6146 to the final.
• Installed 160 meter dipole using RG 8/U coax for testing RF. Use the antenna of your choice here. Inverted 'V' seems to be most popular for 160 M. I had the room for a 240' dipole.
• Audio input for broadcast transmitters is usually a 600 ohm balanced line. This unit allows for either 600 ohm balanced or 150 ohm, unbalanced. For initial audio tests, I simply bought a 12V filament transformer from Radio Shack and connected the 12V side to the speaker terminals of a solid state amplifier I happened to have. The 110V side was connected to the 600 ohm input.
• Ultiimately, I bought a professional broadcast Altec 1592B line mixer which has a 600 ohm balanced output and 5 inputs. I purchased for $250.00 through an ad in Radio World. I have seen them at Ham Fests. One fellow had one for sale for $225.00. I honestly thought I had only $223.00 in my pocket and the guy refused to come down $2.00. After leaving the fest, I discovered a few extra dollar bills, but I decided never to do business with the guy again if I saw him. Moral: If you're a vendor at a fest, don't haggle over a couple bucks out of a couple hundred if the buyer doesn't have it. If you're already selling at your bottom price, add on to the price. (Sorry for the aside, but I just had to stick this gripe in here.)
• On testing the modulation, it was distorted and modulation of more than 30% was impossible. Modulator currents were driving high and pushing the plates very bright orange. This is not normal. The plates should be a moderate red at full modulation. Replacing the modulation transformer cured the final problem with this transmitter. The modulation transformer was purchased from Peter Dahl, but you may opt to find one second hand to save money. It's a personal choice and judgement. One way to test a modulation transformer is to apply 110 V and see if all voltages are proper, given the turns ratio and making sure that center tapped windings have equal voltages on either side of Center. This test, however, checked out OK and did not reveal the problem, which was HV breakdown. In this case, in order to test the transformer, it would have required using voltages typical of the actual transformer operation, a load resistor and some way to measure currents. On this transformer, the winding impedances were marked on the transformer. To obtain the turns ratio, take the square root of the radio of the winding impedances.
• Installed Moseley limiter unit to prevent modulation peaks from knocking transmitter off the air.

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