Portadyne Model Number

[ms660]

230 volts ac in and 46 volts DC out, obviously something wrong there, have you tried Graham's suggestion of measuring the rectifier's heater voltage?

Lawrence.

[Radio Tech]

Hi Lawrence

What I did do as a matter of curiosity is I checked the total heater voltage between chassis and before it went into the rectifier heater pin, that's the bottom of the heater ballast resistor and this measured around 85V, far short of what I estimated it to be which was 134V. It makes me wonder now if the ballast (mains dropper) resistor is at fault here and wondered if there is any way of compensating for the voltage loss by moving the tags which wrap around the resistance wire on the body of the dropper, I have not come across a problem like this so wonder if any other member has.

Ken

I forgot to mention, I did use a silicon diode and with the heater chain of the rectifier linked with a suitable resistor I obtained full HT volts

[Station X]

What's the resistance of the dropper. It'll need to drop about 100V with a current of 200mA

[ms660]

Out of interest I've found:

Heaters...

TX21...21 volts.
VP13...13 volts.
DDT13...13 volts.
PP35...35 volts.
1D5...40 volts.

Lawrence.

[Radio Tech]

Hi Lawrence

The voltages are the same as what I have, I mapped out the heater chain on a sheet of paper and that appears to be ok, and have changed all the paper caps, most being 0.1uF and the resistance of the dropper appears to measure around 820 Ohms which is similar to that of a similar circuit using the same valves. Seems very strange that the rectifier not shoving out what it should though.

Ken

[ms660]

According to a quick calc the heater dropper should be 480 ohms for a 96 volt drop?

Lawrence.

[Station X]

That's what I thought, but back in post #10 the OP talks of 105V being dropped across the dropper resistor, which isn't far out.

With an 820R resistor I'd expect a volt drop of 164V across the dropper.

Something just doesn't add up.

[ms660]

I wonder if the 820 ohms measured is the total dropper resistance including the rectifiers anode feed section?

Lawrence.

[Station X]

Looking at the third picture in post #9, the taps of the dropper presumably go to three tags on the voltage selector. A screw inserted into one of the sockets then presumably makes with a common contact which goes to the rectifier anode?

[ms660]

I'm still trying to spot the rectifier valve or its socket...

Lawrence.

[Station X]

A good point. I'd have expected it to be in the valve holder next to the voltage selector. A bit of reverse engineering is needed.

I can only see four valve holders, so volt drops based on five valves may not be correct?

[ms660]

I'm wondering if the metal rectifier was as originally fitted, I'm looking at the grey wire that runs through it, if you do the sums minus the 1D5 the 820 ohm that was measured is sort of coming into sense if that was the resistance of the whole dropper....On the other hand I could be miles off.

Lawrence.

[Station X]

If it's a four valve set with a valve rectifier, the VP13B doesn't seem to belong in it.

[ms660]

I can see the rectifier's valve holder now, in the first set of pics you can just about make out the holder's socket holes amongst the dust in the 1st pic just below the metal screen, also in the underneath view in the 2nd pic below the left hand orange/brown tag strip...Sorry for the diversion

Lawrence.

[Heatercathodeshort]

The mains dropper fitted is adjustable. There is a screw clamp that can be loosened and reset. If you disconnect everything from the rectifier including the reservoir capacitor you will get a very low reading from the cathode of the rectifier. J.

[Station X]

Originally Posted by ms660

I can see the rectifier's valve holder now, in the first set of pics you can just about make out the holder's socket holes amongst the dust in the 1st pic just below the metal screen, also in the underneath view in the 2nd pic below the left hand orange/brown tag strip...Sorry for the diversion

Lawrence.

Well spotted.

We just need to know the AC voltage across the rectifier's heater, the AC voltage on its anode and the DC voltage on its cathode. I'm assuming those dodgy looking smoothers taped to the side of the chassis have been removed.

[ms660]

Yes, once again apologies for that diversion of mine, only excuse for my lapse is that we had a herd of goats invade the garden today

Lawrence.

[Radio Tech]

hi folks

I did some measurement of voltage, Voltage on anode of 1D5 rectifier is 231V the DC voltage out is 20V after valves have warmed up, Voltage across rectifier heater 24V and the resistance of the dropper Total 1,03 k ohms, used section 896 ohms

Ken

[ms660]

Total series heater string is approx. 122 volts (not taking into account any dial bulbs) so for 230 volts in it would need a dropper of approx. 480 ohms, the dropper you have appears so far to be too high a resistance, I wonder if the dropper that's fitted is not the original one and that a higher value one was fitted when the 1D5 heater pins were shorted out and the metal rectifier was fitted?

Lawrence.

[Station X]

It's been suggested that the "hose clips" be slid along the dropper, but I think they use wire insulated with an oxide coating which will need to be carefully scraped off.

What are the resistances of the individual sections?