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Model 18 Scope Troubleshooting

Yes, the voltages conform to specifications.
I have not cleaned the switch, I'll cleaned tomorrow and I'll do a test...

This problem is similar to the tuning meter problems centering on the model 2245,
which can adjust by acting on L501.
I tried to adjust L501 slightly on the model 18, without effect.
 
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if one replaces the scope tube, is the rubber strap around the insuloid pedastal prone to cracking? it looks like the rubber might be old / brittle from age and heat. any tips?

also, how easily does the black tube socket separate from the tube pins? any tips on how to work it away from the tube pins if stuck?
 
monkboughtlunch said:
if one replaces the scope tube, is the rubber strap around the insuloid pedastal prone to cracking? it looks like the rubber might be old / brittle from age and heat. any tips?

also, how easily does the black tube socket separate from the tube pins? any tips on how to work it away from the tube pins if stuck?
Click to expand...

You can use an oring or a rubber ring from a pinball machine...

Just gently pull it off, it will move...
 
The tube socket pulls off easily. Do that first then carefully try to slide tube out from under the rubber ring. Do not lose or damage the tuner string black rubber shield that is found on the tube under the dial string.I didn't want to risk having the rubber strap breaking so I ended up just sliding the tube out that way.
 
I have replaced 3 tubes over the past 3 years, never had one break yet, the rubber bands are pretty tough. Socket just pulls off.
 
bktheking said:
I don't think a scope meter works the same as an analog though.
Click to expand...

... Yet the vertical deviation can be considered as the Signal Strength and the horizontal deviation as FM tuning center.

I have cleaned the Audio display switch, no effect.
 
I will have to pull mine out at some point and poke around, it's been over 2 years since i've worked on one so....will be next week when I have time. Yes I guess so if you combine the two on a scope, in that sense.
 
Has anyone changed their P-Channel fets (Q1201,Q1204)? Some have used 2N5114's. Is this the best option or is there a more robust component that is recommended? Are the specs of the original component known?
 
Brown wire comes up to the audio switch, assuming from the limiter. When I measure mine in tuning mode "centered" it's 0V, when I move the tuning dial the voltage goes either negative or positive depending on the position of the line. I suspect this isn't happening on your sick unit.
 
In tuning mode "centered" I got 0V too, in 12C on the scope board.
when I move the tuning dial the voltage is -150mV to the extreme left,
and +450mV to the extreme right.
I got -350mV to +350mV with my other 18.
It's this deviation in the positive voltage wich made my signal is mostly right.
This signal come from MPX OSC, not Limiter.
Limiter provides the vertical signal (signal strenght), approximately -500mV when the signal is low
to -60mV when the signal is high, dependent of the set station
But I don't understand why there is this deviation from the MPX OSC...

Your Tannoy Arden are wonderful. I want the same!
 
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Disclaimer: I hven't worked on a Model 18 (yet!) and didn't look at a schematic.

It could be that the discriminator needs adjusted which is why a center tune meter will act unbalanced like you're observing.
 
I pulled out my old muting resistor lamp combo and replaced with turbos suggestion. The old resistor was open. Muting now works.
 
I found the way for balanced horizontal signal: Secondary Trim C408 on Detector assembly.
After signal scope is centered via C408, adjust horizontal gain via R505 for using the entire surface
of the scope when tuning. Work perfect now!
Finally it's the same that 2245 when we adjust L501 on Detector assembly for adjust FM tuning.

I just bought Celestion Ditton 66 SM, and I like it, but Tannoy Arden will probably my next speaker.
Is Arden sound good with a Model 18?
 
Hi bktheking,

If your unit is open, would you be happy to post an image of your selector switch? Curious if your's is wired different as it doesn't pop when turned to FM as observed in 3 late 6000 and early 7000 serial units.
 
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Pic of the original photo resistor setup. I reused the metal shield to cover the new install, no heat shrink required.

2l8b7o1.jpg


Here is the switch. If you are referring to that miniscule "click" sound when rotating the input knob I'm far from worried about that, to me it's not a pop that moves my speaker cones violently.

33jsmzr.jpg
 
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