Broken mains dropper in Ekco U332

[Dick Glennon]

Hi again, the mains dropper in the Ekco 332 got broken and I was hoping to replace it with a transformer. 110volts I have room for a small one on either the top or bottom of the chassis. Firstly would this be possible to do, and, if so what wattage would I need. Also, would this be able to supply the H.T. As well. I also want to ask about the capacitor that goes from the volume control to pin 1 on v3. It has a centre band which goes to earth. There is a red end on it and a black end as if it were an electrolitic. It reads .018 (.01). Is this just a normal capacitor. Hoping ye will be patient with me. Regards, Dick.

[Ed_Dinning]

Hi Dick, cap with a centre band is often (especially in this circuit position) used to reduce hum.
Yes a transformer could be used on this set in place of the dropper and it would also have an HT tapping.
The smallest possible type would be an auto transformer, but this would not give chassis isolation. A double wound type, to give insulation would be larger and more expensive.

Ed

[Silicon]

The mains dropper is 185 + 185 + 430 Ohms. Which one is faulty?

The simplest option is to replace the faulty dropper with a power resistor on a heatsink.

The total heater voltage when they are wired in series is 126V.

The heaters could be wired with V1 and V2 in series to give 38V.
This combination could be wired in parallel with V3 (50V) and V4 (38V heater).

Transformers with 55V + 55V secondaries are available.
Wire both secondaries in series to get a 110V AC supply for the HT.

Use the 55V tapping for the heaters. Resistors (and 12V bulbs ?) will be needed to drop the 55V down to the 38V and 50V used by the valve heaters.

The HT will be low but it may only affect the maximum volume.

If you replace the valve rectifier with a silicon diode it will raise the HT slightly.

If you have a mains transformer with a single 110V secondary winding you could have enough voltage to feed V1, V2 and V3 heaters in series. They will need 88V. The rectifier would need to be silicon.

[Dick Glennon]

Hi Ed, how much including postage to Ireland would it cost for the transformer. Regards, Dick.

[Ed_Dinning]

Hi Dick, you have a PM.
Is there a prefix to the 332 as I can't find that ref in my circuit collection ?

Failing that what is the valve line up.

I'll try and get a few minutes tomorrow to see if my DAC 90/a autotransformer can easily be adapted for use with sets like this one.

Ed

[Dick Glennon]

Hi Ed, I do not think it would be worth spending that amount of money on the set.I may come on another set with a good dropper. Regards, Dick.

[Cathode Ray]

Hi Dick
What about a capacitor dropper?
https://vintage-radio.com/repair-res...per-calcs.html

just an idea

[Dick Glennon]

Hi cathode ray I could go with a capacitor dropper. My total heater voltage would be 126 volts so I would need to drop at least 114 volts. I would love if somebody would kindly let me know what values I would need to reduce the voltage. Regards, Dick.

[Cathode Ray]

Its fairly simple if you use the excel calculator provided in the link.

But you also need to know the exact current drawn at 126V.

Enter this into the calculator, and it provides the value of Run cap to use, along with surge resistor and don't forget the 100k 1W bleed resistor for safety.

For example,
assuming the current was 300mA.
The C value should be: 5.15 uF so a 5uF should be used.
This is based on 230V mains commonly seen in Ireland.

[ms660]

According to a manual I'm looking at U332) it's 100mA heaters.

Lawrence.

[Cathode Ray]

@ 100mA "our survey says" 1.7uF