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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 13th May 2017, 3:21 pm   #1
prajan
Tetrode
 
Join Date: Jul 2006
Location: Bangalore, India
Posts: 85
Default Mullard 12 band radio set MAS231

Dear forum members

1. During the restoration of the above set initially the LW,MW and SW3 bands were found working but SW2 was not working.On checking it was found that the oscillator coil S34 was open. Repaired the coil and the SW2 band started working. My question is, in the main schematic the capacitor C43 is shown connected across the total winding S33 + S100. whereas in the radio set it is actually connected across only S100. In the schematic part where they have shown the individual bands connections foe SW2 band C43 has been shown connected across S100. I do not know which is correct? All The connections to the coil S33/S100/S43 are original and no alteration has been carried out.

2. All the Band -Spread bands were not working. On further checking I found that the core of the coil S107/S108 was missing and only the brass screw part was present.Since I did not have the spare dust core I removed the core from the 11m oscillator coil and fitted into the S107/S108 coil as both are identical.With the adjustment of the core the 31m band started coming. Still the other bands were not coming. Somebody had used valve 6K8 valve in place of one of the ECH35. I replaced it with a good ECH35. Now all the bands have started coming. I am yet to carry out the complete alignment of the set. My question is that as per the alignment instructions first the coil S107/S108 is to be set. With the band switch in position 8 and the pointer set to 6.1Mhz position on the dial when a signal of 3Mhz is applied to G1 of valve B2 no tone is heard. The tone comes at 2.85Mhz position of the signal generator. I am unable to shift it to 3Mhz position by adjusting S107/S108. If I keep the signal generator at 3Mhz position and move the pointer to the left then the tone comes at 5.95Mhz. On the dial there is a considerable distance between 6.1Mhz and 5.95Mhz ( approx. 50mm ). I checked the capacitor C116 which is connected across S108 and the value is correct 920pf. Why I am not able to get the tone at 6.1Mhz position of the Dial when a signal of 3Mhz is applied.

I would be thankful if members can guide me in the regard.

Regards
P.Rajan
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