13-04-2015, 09:51 PM
I have lifted the covers off today to reveal a nice clean chassis.
First I spotted that there is a cordless drive on the fine frequency control. When I turned it around I found that the next section of the drive does indeed have a cord.
It has a very nice chassis layout with easy access to all the components and I have even spotted military arrow logos on some of the large capacitors.
It has a lovely 4 gang variable capacitor.
All the valves look like they have got good getters and it looks like it has been powered up at some time perhaps when the two capacitors were changed.
These old capacitors look like they have come from the oscillator section as there are two mustard capacitors in there and also there is an electrolytic capacitor C15 that does not look original. It is in the level stabilizer circuit.
So what if any work needs to be done before I show it some power?
Time for a close visual inspection in conjunction with the service information.
The first issue I spotted was a "zit" on C24 output transformer snubber and the the series resistor on C23 is high on the other half of the output transformer primary. They are Dubillier paper types and are very likely to fail leaky.
There is another large blue paper capacitor like the ones that have already been changed in position C20 output stage phase splitter. If leaky it will drive the single triode phase splitter on so that the output will become distorted at high level due to the valve turning hard on on the peaks of one side of the signal.
The previous owner should have looked at this one as well as the two in the oscillator. Now I will have to have a look for another mustard to match the other two already replaced ones.
There was a spot of wax on the cabinet floor and this was traced to the cathode resistor in the output stage. It does not look like it has been very hot and the transformer measures all right on both halves of the primary.
There are two very large grid coupling capacitors that are the most likely culprit for this and they will drill out for restuffing without issue. These are C21 and C22.
I have also spotted tin whiskers growing on the chassis and they really do show up on camera too. Zoom it up and have a look.
First I spotted that there is a cordless drive on the fine frequency control. When I turned it around I found that the next section of the drive does indeed have a cord.
It has a very nice chassis layout with easy access to all the components and I have even spotted military arrow logos on some of the large capacitors.
It has a lovely 4 gang variable capacitor.
All the valves look like they have got good getters and it looks like it has been powered up at some time perhaps when the two capacitors were changed.
These old capacitors look like they have come from the oscillator section as there are two mustard capacitors in there and also there is an electrolytic capacitor C15 that does not look original. It is in the level stabilizer circuit.
So what if any work needs to be done before I show it some power?
Time for a close visual inspection in conjunction with the service information.
The first issue I spotted was a "zit" on C24 output transformer snubber and the the series resistor on C23 is high on the other half of the output transformer primary. They are Dubillier paper types and are very likely to fail leaky.
There is another large blue paper capacitor like the ones that have already been changed in position C20 output stage phase splitter. If leaky it will drive the single triode phase splitter on so that the output will become distorted at high level due to the valve turning hard on on the peaks of one side of the signal.
The previous owner should have looked at this one as well as the two in the oscillator. Now I will have to have a look for another mustard to match the other two already replaced ones.
There was a spot of wax on the cabinet floor and this was traced to the cathode resistor in the output stage. It does not look like it has been very hot and the transformer measures all right on both halves of the primary.
There are two very large grid coupling capacitors that are the most likely culprit for this and they will drill out for restuffing without issue. These are C21 and C22.
I have also spotted tin whiskers growing on the chassis and they really do show up on camera too. Zoom it up and have a look.
