portadyne: U56; Portadyne Table Model: PSU

Detail of PSU under chassis

1: Wire to top of dropper from mains "live"
2: Wire from first tap on Dropper (about Mains - 10V), feeds both Anodes via 2 x 100 Ohms
12: Wire to the two dial lamps/bulbs  in series across points 1 & 2
3: Wire from 210, 230 or 250 taps at bottom of dropper to start of series heater chain.
4: Neutral wire of mains to on/off switch
5: wire to Chassis from on/off switch
6. On/Off switch on rear of volume control. It's wired like this to minimise hum pickup on Audio preamp (1M pot, 10M grid resistor and high impedance detector)
7: Mains cable.

Large TCC is 8uF between chassis and 25Z6G (or 25Y5G) cathodes.
The pair of 100 Ohms feeding anodes of 25Z6G are using pin 6 (no connect) as a tag for wire to dropper and dial lamps.

Chain of 4 resistors is large green dropper vertical on top of chassis. Three bottom taps are likely 210, 230 and 250V

10V between 1 & 2
135V between  2 & top NC
21V between NC & 3
Mains is about 235V here.

Second resistor must be 450 and not 400, I wrote it down some hours after measuring and obviously remembered wrong. 300mA Series heater current.

Adding the heater voltages in data gives 68.9V. Measurement at the point (3) gives 66.5V, which is reasonable.

So assuming 2 x 6.3V 300mA dial bulbs:
There is a measured 10V, so real lamp current about 238mA.
The top section of dropper measured 110 Ohm (I unscrewed a bulb). So 91 + 238 = 329mA
The heaters are supposed to be 68.9@300mA but measure 66.5mA gives about 290mA (likely a bit more as the heaters are not linear).

This gives a possible HT current of about 39mA. We could measure the cathode current by volts on the 470 Ohms which would give g2 + anode current. Likely the g2 current is a few mA.
 

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Measuring the cathode after warm up is just under 15V. The resistor is 470 Ohms, so current is about 31mA.

This is g2 + anode. But is a little higher than I would have expected as this about 3W dissipation. However the resistor may not be really 470 Ohms. I replaced the "bodge" 470uF 63V part with a more likely 22uF 35V (original possibly between 15uF to 25uF).

 

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