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Saturday, 16 April 2016

Pye T19D radio from 1949, repairs and renovations.

A fine fellow called Derek called...

"I've got this Pye radio I've bought, and it doesn't work, it's totally dead.. Can you take a look at it?"

Why not ....

It's a very nice looking Pye T 19 D....

A cursory inspection shows a very clean chassis, but the usual rake of the dreaded Hunts capacitors, both wax type and electrolytics. Nothing to stop it powering up though...



.... so we power it up. Nothing. Not a sausage.

A quick check round with the meter show the mains switch is open circuit. The mains switch is unusual; it's mounted on the tone control/ mode switch. This switch is multi-funtion, and switches the set on, and provides a switched tone control, and selection of the "gram" input, for connection to your external gramophone...

Removal and inspection of the switch show it's stuck in the off position. It's a bit of a tin-pot affair, being paxolin construction and pressed together in a steel case. I managed to get it apart, and un-stick it, but it's not reliable and starts arcing over. Drat. A solution will need to be found....








The tone control/ mode switch without the mains switch sat on the end...














In the meantime, I hook up the main smoothing electrolytic capacitor to the Dreadnaught MK87 capacitor reformer, in the vain hope of it being OK...












...it is nicely dated APR 1949, but I don't hold much hope, the poor thing has been in there for 67 years....










 I start to re-cap the chassis, evicting the evil Hunts...

There was also some Sprague 1000v caps that read leaky; they had to go too to ensure reliable operation...















... and when this is complete, I check out the mains smoothing electrolytic, which has been gently reforming for a couple of days. It's OK! I'm amazed. 67 years in, and it's giving acceptable leakage, a reasonable ESR, and capacitance! ... I short out the mains switch and gently apply some power via the variac... and the set crackles into life! It's quickly apparent that's something's amiss with the tuning drive, which slips badly ... perhaps a re-string of the tuning drive is required? ....

Nope, the tuning capacitor is moving on it's rubber mounts as I move the tuning control...

I slacken off the bearings and give them a little lubrication.. Bingo! Smooth tuning and no sign of slippage on the drive string.. Good news!








The volume control appears to be open circuit for most of it's travel. It works at about 90%, but nothing below...

So, to re-cap (pun intended)... the remaining faults are:

An unserviceable on/off switch and volume control...

The volume control is a 1 megohm log pot. No problem there. These are easily available.
The mains switch? Made from purest unobtainium., no chance...

So what about getting a 1 meg log pot, with a switch, and have the on/ off switch on the pot? Seems a reasonable compromise.... but 1 meg LOG pots with switches are also unobtainium...

I go to the local Maplin, who stock a 1 meg linear pot with on/off switch.. and fit it. It's horrible as a volume control... the control is all "up one end" , as you'd expect.









Now a "log" pot isn't really a log at all, but an approximation of log, by damping one end of it with a resistor; so, after a bit of experimentation, I end up with a 47K resistor at the earthy end of the pot. It works well.

I did contemplate mounting the pot on the end of the tone/mode switch, and not bothering with the pot bit, but the mechanical resistance in the pot made the switch unusable, and worse, prone to arcing if it hadn't exactly sat in it's ident.

So this set now has a volume/on/off control. Not ideal, but it works nicely...

Here's the completed set in action...


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