jrok
Well-known member
Hey all,
Well I have this perfect Orion TV tube ( A48ACB32X ) complete with yoke that is also perfectly converged. Unfortunately I need to replace the tube from a WG4901 which had two very dead guns that even witchcraft could not bring back to life.
The WG4901 stock runs with a higher impedance yoke, this one measures 32ohm vertical. So the only way to get this going is modify the chassis to support the lower impedance. The replacement yoke measured at 10ohm vertical, 4 ohm horiz.
There's nothing technically that stop this from being possible. So it's just a question of how. BUT, and perhaps much more importantly, "how" without turning the chassis into a firey ball of G08 style goodness.
It'd be nice if there were some more apps notes and details on the HA11423 vertical stage drivers but there's enough to work with.
The overall change is to alter the feedback to the HA11433 vertical drive amp, size adjustment for the vertical oscillator and finally increase the current available to drive the Vertical yoke deflection.
In order:
Power resistor R313 was replaced with a 180ohm 25W, the 25W was chosen because it what I had to hand.
Current through the resistor increased from 0.0707A to 0.120A so it needs to upgraded to a 15W (at the least!) to deal with the increased current. Voltage drop across the resistor reduces from 33V stock to 25v.
I'll note that even with an unmodified chassis that resistor freaking COOKS. If my math is correct, with stock voltage/current then that thing is dealing with up to 6.5 Watts !
Q302 voltages measured are C=105v, B=48v, E=48v, stock gave C=93v B=44, E=44, so even with the mod it's still within the specs for the transistor.
Q303 C=48v B=0.56 E=0 ( stock was 44,0.56,0 ) so not a big difference from stock measurements.
I'll note in the manual Q302 shows Collector voltage being 79v, my own notes say around 90v (!) Anyone else like to comment on this ? Granted I've only had 2 other chassis like this
Next, R310/R309 changed for the vertical amp, and R318 for the vertical size adjustment.
Final summary of component changed:
R310 = 56K ohm 1/4W Stock = 39K with 220k in parallel ( so 33.1k )
R309 = 18K ohm 1/4W Stock = 22K ( this can be left the same but I think the 18k improves the vertical linearity )
R318 = 270 ohm 1/4W Stock = 560 ohm
R313 = 180 ohm 15W Stock = 470 ohm 7W
( although a nice heat-sinked TO-220 cased non-inductive power resistor would really rock )
The monitor's been running burn in on for about 24 hours total on-time now without incident and nothing measured was really out of whack.
So, I'm pretty happy with the results.
Anyone free to jump in and say "you've forgotten about X".
- James
: edited for grammar & typos
Well I have this perfect Orion TV tube ( A48ACB32X ) complete with yoke that is also perfectly converged. Unfortunately I need to replace the tube from a WG4901 which had two very dead guns that even witchcraft could not bring back to life.
The WG4901 stock runs with a higher impedance yoke, this one measures 32ohm vertical. So the only way to get this going is modify the chassis to support the lower impedance. The replacement yoke measured at 10ohm vertical, 4 ohm horiz.
There's nothing technically that stop this from being possible. So it's just a question of how. BUT, and perhaps much more importantly, "how" without turning the chassis into a firey ball of G08 style goodness.
It'd be nice if there were some more apps notes and details on the HA11423 vertical stage drivers but there's enough to work with.
The overall change is to alter the feedback to the HA11433 vertical drive amp, size adjustment for the vertical oscillator and finally increase the current available to drive the Vertical yoke deflection.
In order:
Power resistor R313 was replaced with a 180ohm 25W, the 25W was chosen because it what I had to hand.
Current through the resistor increased from 0.0707A to 0.120A so it needs to upgraded to a 15W (at the least!) to deal with the increased current. Voltage drop across the resistor reduces from 33V stock to 25v.
I'll note that even with an unmodified chassis that resistor freaking COOKS. If my math is correct, with stock voltage/current then that thing is dealing with up to 6.5 Watts !
Q302 voltages measured are C=105v, B=48v, E=48v, stock gave C=93v B=44, E=44, so even with the mod it's still within the specs for the transistor.
Q303 C=48v B=0.56 E=0 ( stock was 44,0.56,0 ) so not a big difference from stock measurements.
I'll note in the manual Q302 shows Collector voltage being 79v, my own notes say around 90v (!) Anyone else like to comment on this ? Granted I've only had 2 other chassis like this
Next, R310/R309 changed for the vertical amp, and R318 for the vertical size adjustment.
Final summary of component changed:
R310 = 56K ohm 1/4W Stock = 39K with 220k in parallel ( so 33.1k )
R309 = 18K ohm 1/4W Stock = 22K ( this can be left the same but I think the 18k improves the vertical linearity )
R318 = 270 ohm 1/4W Stock = 560 ohm
R313 = 180 ohm 15W Stock = 470 ohm 7W
( although a nice heat-sinked TO-220 cased non-inductive power resistor would really rock )
The monitor's been running burn in on for about 24 hours total on-time now without incident and nothing measured was really out of whack.
So, I'm pretty happy with the results.
Anyone free to jump in and say "you've forgotten about X".
- James
: edited for grammar & typos
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