15-04-2017, 07:10 PM
One more post.
The mystery is solved. I have worked out the circuit this afternoon.
The mains transformer is straight on the mains, no switch, no earth.
HT winding is tapped at "12". So this is an adjustment for current, regulation must be quite poor.
Top end of this winding feeds the rectifier main part of 8 fins. into the choke which is a wrongun, someone has fitted an RF choke!
Usual pi smoothing with 4uf either side of the choke. This is the 150v hole.
Then there are 2 chains of dropper resistors, first is 33k to 80v, 20k to 60v, 33k to negative line and hole with 2uf across it.
Other chain is 15k to 90v, 18k to 75v, 15k to 50v then 2uf to negative. Regulation on this chain is anyone's guess!
The top 2 pin plug is in the HT negative line after the wander plug which is the selector for 12/18mA.
The bottom plug is for LT, in the centre tap line from another winding on the transformer, as was thought by some.
Top and bottom of this winding each go to a pair of paralleled diodes in the other part of the metal rectifier to be the LT+. No idea what the voltage is but there is no regulation at all, just full wave rectification. I assume it will be 2v but do I risk my rare valves on it?
So its quite crude but should work. the transformer has continuity, the 4 electrolytics will be dead, it needs a proper choke, all the resistors are at the top end of their tolerance, a Clik 2 pin plug is missing. Running round the rectifier all the diodes are OK but it may be well down.
I'll cook and test the transformer before deciding if its a goer or not.
The mystery is solved. I have worked out the circuit this afternoon.
The mains transformer is straight on the mains, no switch, no earth.
HT winding is tapped at "12". So this is an adjustment for current, regulation must be quite poor.
Top end of this winding feeds the rectifier main part of 8 fins. into the choke which is a wrongun, someone has fitted an RF choke!
Usual pi smoothing with 4uf either side of the choke. This is the 150v hole.
Then there are 2 chains of dropper resistors, first is 33k to 80v, 20k to 60v, 33k to negative line and hole with 2uf across it.
Other chain is 15k to 90v, 18k to 75v, 15k to 50v then 2uf to negative. Regulation on this chain is anyone's guess!
The top 2 pin plug is in the HT negative line after the wander plug which is the selector for 12/18mA.
The bottom plug is for LT, in the centre tap line from another winding on the transformer, as was thought by some.
Top and bottom of this winding each go to a pair of paralleled diodes in the other part of the metal rectifier to be the LT+. No idea what the voltage is but there is no regulation at all, just full wave rectification. I assume it will be 2v but do I risk my rare valves on it?
So its quite crude but should work. the transformer has continuity, the 4 electrolytics will be dead, it needs a proper choke, all the resistors are at the top end of their tolerance, a Clik 2 pin plug is missing. Running round the rectifier all the diodes are OK but it may be well down.
I'll cook and test the transformer before deciding if its a goer or not.
Boater Sam.
