12-04-2022, 12:55 PM
A Radio Rentals 66AC, Bakelite, E40 valves, AC only.
Has a damaged case but it will repair, maybe needing to be painted.
Chassis is clean and untouched, I can find no previous repairs.
EZ40 rectifier valve had gone to air, a replacement restored operation.
As usual I replaced the grid coupling cap C25, the original was leaky.
Set then worked quite well on both wavebands but at the high end of the medium wave all stations were surrounded by birdie whistles.
The smoothing caps reformed quite well. C23 IF suppression was blameless.
I replaced C27, output anode to ground to be sure any residual IF oscillations were suppressed from feedback with a 3n3 and 4n7 ceramic in series to ensure that there could not be a short which would destroy the output transformer.
Still got a flock of starlings.
A quick valve swopping session revealed the EF41 IF amp to be responsible. The birds have flown.
The mains input is on a 2 pin plug arrangement, an alternative pin giving voltage selection with a rotating shutter selecting which pins the free socket fitted on.
I don't have the socket so I insulated the 3 pins with heatshrink, and rotated the shutter so there is no access to any of the pins.
Fitting a strain relief and fixed mains cable through the hole where the voltage indication was ensured that the shutter cannot be rotated back again.
I like the Rentals sets, so easy to work on with the deliberate design feature of easy chassis removal.
Has a damaged case but it will repair, maybe needing to be painted.
Chassis is clean and untouched, I can find no previous repairs.
EZ40 rectifier valve had gone to air, a replacement restored operation.
As usual I replaced the grid coupling cap C25, the original was leaky.
Set then worked quite well on both wavebands but at the high end of the medium wave all stations were surrounded by birdie whistles.
The smoothing caps reformed quite well. C23 IF suppression was blameless.
I replaced C27, output anode to ground to be sure any residual IF oscillations were suppressed from feedback with a 3n3 and 4n7 ceramic in series to ensure that there could not be a short which would destroy the output transformer.
Still got a flock of starlings.
A quick valve swopping session revealed the EF41 IF amp to be responsible. The birds have flown.
The mains input is on a 2 pin plug arrangement, an alternative pin giving voltage selection with a rotating shutter selecting which pins the free socket fitted on.
I don't have the socket so I insulated the 3 pins with heatshrink, and rotated the shutter so there is no access to any of the pins.
Fitting a strain relief and fixed mains cable through the hole where the voltage indication was ensured that the shutter cannot be rotated back again.
I like the Rentals sets, so easy to work on with the deliberate design feature of easy chassis removal.
Boater Sam.
