Tuning & Loading Meter Circuit - Revision history

Gordonp at 20:17, 6 July 2020

2020-07-06T20:17:38Z

← Older revision		Revision as of 20:17, 6 July 2020
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	Satisfied that the circuit is now generally functional, I continue to tune by watching Screen Current, hitting 0mA at whatever power-level I use.		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!!!)
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Gordonp at 20:08, 6 July 2020

2020-07-06T20:08:24Z

← Older revision		Revision as of 20:08, 6 July 2020
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	In operation, I could not obtain a useful meter-reading from the TUNING & LOADING meter position.		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.		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.		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.		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, ~~and~~ the elevated screen-supply, 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.

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

Gordonp: Created page with "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 co..."

2020-07-06T19:57:04Z

Created page with "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 co..."

New page

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.

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.

With the change to a 4CX1500B tube, and the elevated screen-supply, 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.

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