Thread: Moreton Cheyney
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Old 23rd Nov 2019, 11:27 am   #98
allan
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Join Date: Oct 2005
Location: South coast near Ringwood/Christchurch, Dorset, UK.
Posts: 230
Default Re: Moreton Cheyney

Synchrodyne & PJL
It is puzzling that the push-pull amplifier would be driven by totally different audio signals especially one via an 0.001uF in series with 240Kohm, although I guess the frequency response of the capacitor would be swamped somewhat by the resistor and might be used to provide a sort of loudness effect. It's an area in which I have no experience.
The two capacitors C81/C74 at the anodes of V12/V13 are exactly the same and a bit unusual so this tends to imply they were used for the same purpose and C81 at V12 should not therefore be grounded, but connected to C74.


The double gang pot shaft isn't off-line or if it is, within manufacturing tolerances. The wiring around the two pots looks a bit scruffy as does wiring in other areas. I suspect the last owner may have been chasing a problem and we're looking at the end results... failure!
Understandable, because faced with a misbehaving receiver and the lack of a circuit diagram the last user may have got into a real mess.

Thinking laterally.. there seems now to be not one but two 6B8 valves. One position was certainly occupied by a KTZ63 and this would cause no end of trouble. I also noted that KTZ63 and KTW63 valves were in the wrong positions. A fixed u valve in a position wired for a variable u valve would pose a problem.. maybe even severe distortion from overloading?
If the guy tackled the audio stages rather than RF stages he may have ended up in a muddle and of course a KTZ63 without the diodes would also result in audio problems. The resulting audio may have been developed not by 6B8 diodes, but by anode bend detection in the audio amplifier?

The plan is to work out the most likely original circuit.
The possibility is that there were three individuals. The original purchaser.
The guy that swapped to a pair of KT66s and swapped to some RS parts, and the guy that messed up the equipment when it started to go wrong.

I've begun to get the receiver going. I've determined the IF is almost certainly 465KHz and the Sprague condensers are in excellent shape.
It's going to take ages because I keep getting interupted by customers demanding my attention.. the usual stuff.. "there's a 93 year old stuck on the 3rd floor because the lift isn't working.. it's just a few bad relays" and "here's 3 faulty drive units.. please make one good one from the three"
I should retire and concentrate on important stuff.. my hobbies.
Allan G3PIY
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