View source for Tuning & Loading Meter Circuit

In operation, I could not obtain a useful meter-reading from the TUNING & LOADING meter position.
Digging further, CR101A (a 1N34 diode) was completely shorted.  Under this condition, the TUNE/LOAD meter gave about a 1/3-scale reading, with only a tiny response to adjusting Tune and Load controls.  I tuned the amplifier for use by observing Screen Current.

[[File:original_tuneload_pcb.jpeg|500px|thumb|center|Original Tune/Load sensing circuit-board]]

I replaced both CR101A and CR101B with 1N5711 Schottky hot-carrier diodes.
Capacitor C112 and resistor R105 both required adjusting (per 1976 mnaual, page 4-2, section 4.5).  To adjust R105 safely, I pushed a foot of cable-jacket onto the shaft, then jammed a medium-length screwdriver into the other end of the cable-jacket - making a flexible adjuster which also kept my fingers out of the compartment.

[[File:1n5711_tuneload_pcb.jpeg|500px|thumb|center|1N5711 diodes installed]]

With the change to a 4CX1500B tube, the elevated screen-supply, change in diode-specifics, and aged surrounding components, I could not quite dial-in a "perfect" 0-reading on the meter, at resonance - there's no adjustment-travel left on either C112 or R105.

Satisfied that the circuit is now generally functional, I continue to tune by watching Screen Current, hitting 0mA at whatever power-level I use.

(Thanks to K5MGR / Mike Langner for his generosity in sending me the diodes!!!)
<br clear=all>

[[Repair|Back to Repair]]