HEATHKIT APACHE TX1/SB10 BULLETIN transcribed by Jerry Proc VE3FAB E-mail: jproc@bellglobal.com This document outlines various changes that Heathkit incorporated into the Apache TX1 transmitter and some resolutions for commonly encountered problems. MODIFICATIONS ============= As general policy, the Heath Company does not suggest or recommend any modifications to present equipment other than those made and approved by our engineering department. We realize that modifications to Heath equipment will appear in various magazines, however, we do not have the resources for testing each modification. Such modifications, therefore , must be done at the builder's own discretion. The following official list of modifications have been made in the TX-1 by our Engineering Department an are included in all kits with a manual dated 4-29-60. The date listed are change dates on each modification. MODE SWITCH 9-24-58 -------------------- Changed 63-152 switch to 63-196 to minimize arcing. NEUTRALIZATION 11-3-58 ----------------------- Neutralization was added to reduce detuning of the grid circuit on higher frequencies. The yellow lead to terminal strip CI-2 was removed and reconnected to terminal strip CJ-1 to prevent a negative meter indication in grid position during key up conditions. (Step #10, page 66). TERMINAL STRIPS 11-24-58 ------------------------- Terminal strips JD(T), JS, JW and GC were replaced with new, improved spacing and dielectric strips. FAN INSTALLATION 1-21-59 ------------------------- A fan was installed to increase air flow in the final amplifier compartment. This resulted in much cooler operation of the 6146 tubes. A fan modification kit is available by Model #MK-2. BACKLASH 6-10-59 ----------------- The dial drive mechanism was changed to provide spring tension on the nylon cluster gear to reduce backlash. MODE SWITCH 6-29-59 -------------------- The 63-196 mode switch was modified to disconnect neutralization when operating SSB and reconnect it for AM and CW. It also disconnects the OB2 regulators when operating AM and CW and reconnects them for SSB. Neutralization will affect SSB operation and OB2's may fire on modulation peaks causing downward modulation. The new switch and installation instructions are available at a moderate cost. NPO CAPACITORS 4-29-60 ----------------------- To improve stability, and in some cases eliminate frequency shift, NPO capacitors were installed. FIXES FOR SOME COMMON PROBLEMS ============================== 1) LOW GRID DRIVE (10 Meters) -------------------------- A. Check the 5763 and 6146 tubes, preferably by substitution. B. In the centre of the 10-15 meter driver coil (Part #40-61), spread the windings from 1/4 to 3/8 of an inch or until maximum grid drive can be obtained on the high end of 10 meters. C. Inspect the wiring on the exciter band switch and check voltages at the 5763, 6CL6 and 6146 sockets. D. Low grid drive on 80 meters could be caused by either a shorted 10 mh RFC (#45-16) or an 11 uh RFC (#45-31). 2) INTERMITTENT KEYING (40 meter XTAL) ----------------------------------- A. Replace the 47 uuf coupling capacitor between the 6CL6 and 5763 tubes with a 200 uuf 500 volt mica capacitor. Then, with the receiver tuned to the crystal frequency and with the plate switch off, adjust the 15 meter slug tuned coil (at location BK) alternately. Continue to adjust the coil while sending a series of fast dots until proper keying is obtained. Usually three or four turns will provide proper operation. This should not affect the grid drive on 15 meters. B. Check the wiring in the time sequence circuit (terminal strip FC). C. Check the 6CL6 and try other crystals. D. Check the keying circuit (keyjack, mode switch, etc). Above all, make certain that the transmitter is properly grounded and connected to a properly matched antenna. 3) OSCILLATION AND HUM IN AUDIO AND MODULATOR ------------------------------------------ A. Check operating voltages and tubes. Reheat all connections and tighten all mounting hardware on tube sockets and terminal strips. Shorten all leads and dress them just long enough to reach their intended destinations. B. Dress the Spirashield covering leads from HA-6 and V9-2 as close to centre of terminal #2 of control HJ as possible. In some extreme cases, check the placement of the shielded cable coming from the microphone connector and connecting to strip-pack terminals HA-1 and HA-2 in the cable harness. This could cause oscillation. To fix the problem, replace this cable with a length of 52 ohm coaxial cable and route it away from the harness. C. Hum can be caused by excessive heater-to-cathode leakage in any one or more of speech amplifier or modulator tubes. A substitution check should reveal any defective tubes. D. Re-route the grey lead from breakout #2 along the harness and up and around 46-4 choke and 51-23 driver transformer. Reconnect to the positive terminal the bias rectifier. (This lead supplies AC to the rectifier and in some instances, when routed close to 12AX7 pin #2, will cause hum pickup). E. Be certain the antenna is properly matched and a high SWR is not present. A high SWR could cause hum and/or oscillation. 4) DOWNWARD MODULATION ------------------- A. This condition can be caused by a shorted modulation transformer #51-34, a weak EL34 or insufficient bias. It is also possible that the OB2 voltage regulators are firing on modulation peaks and limiting the 6146 screen voltage. A new mode switch is available, (#63-196) from the Heath Company which will automatically disconnect the OB2's when operating AM and CW and reconnect them for SSB. 5) TELEVISION INTERFERENCE (TVI) ---------------------------- In approximately 90% of cases involving television interference, it was found that the TV receiver was actually at fault and not the amateur transmitter. Several conditions such as misalignment, defective tubes, corroded TV antenna or lead-in, improper adjustment (fine tuning) will favour reception of unwanted signals. The installation of a high pass filter in most cases, will eliminate or at least reduce interference. The cause of the TVI must be determined. Check: - Transmitter for proper adjustment. - That the final amplifier is tuned to resonance. - For sufficient grid drive. - Equipment ground conditions (use several grounds of varying lengths). Next, try loading the transmitter on a dummy antenna such as a 150 watt light bulb connected directly to the output RF connector. This will rule out the possibility of a problem in the antenna system. Vertical or trap type antennas which are not operated on or close to the resonant frequency can cause TVI. With the dummy load connected, if interference exists, check for loose, rosin or cold connections. Re-heat any that look questionable. Tighten all terminal strips as much as possible, especially those that depend on the mounting foot on the ground. Re-dress or reposition the leads in an attempt to eliminate the interference. 6) VFO DRIFT --------- A. Check 6AU6, OA2 and 5V4-G tubes by substitution. Inspect VFO wiring and re-heat the connections. Check the feed-through capacitors for damage and replace if necessary. Check for a loose rear bushing on the differential capacitor. B. In shipments with a manual dated 4-29-60, NPO capacitors were installed to replace the 5% mica capacitors. These capacitors are available from the Heath Company by part #21-84 (24 uuf), #21-85 (56 uuf), #21-86 (75 uuf) and three #21-29 (4.7 uuf N750) at a nominal cost. C. Oxidation on the VFO band switch may cause intermittent contact. Rotate the band-switch through its entire indexing action to bare new metal and provide proper contact. SB10 NEUTRALIZATION =================== If, after following the preceding suggestions, the SB10 still appears to need neutralization, you might try the following method: First, remove the .01 ufd disk ceramic capacitor connected between the ground lug GL1 and the common wire connected to #1 lug of all driver coils. Replace this capacitor with a 330 uuf mica type. Drill a hole adjacent to coil L5. Connect a stiff, insulated wire to lug #1 of L5 and pass the wire through the hole along the chassis. Bend it up so the final 2.5 inches of wire is parallel with, and approximately 0.25 inch from the envelope of the 6BQ5 tube. Remove the plate and screen voltages from the 6BQ5. Apply minimum excitation. Using a grid dip meter in the diode position and, with its coil near the 10 meter coil in the output stage, bend the wire near the 6BQ5 for MINIMUM RF indication. -- EOF --