Chapman S5E/FM tuner

[djrm]

   
I got this tuner this week, amazed it is working, it looks like a quality unit.
It reminds me of the old Jason tuner we used t have but this is huge in comparison.

It is full of dodgy caps but is receiving fm radio stations.
I'd better check it out before trusting too much.

Not had anything with a magic-eye since the old family tape recorder back in the 60s
I'm playing it through the KT66s valve amp into the Lowther Acousta PM6 for the full retro experience.

[djrm]

I've run it for a bit this afternoon and the mains transformer seems to be getting unusually hot. Not a good sign. HT and heater voltages seem ok though.

[djrm]

I was thinking that the transformer had shorted turns or something causing it to overheat. Today I was looking for a replacement mains transformer and wanted to measure the HT AC voltage to get something equivalent. During the measurement I noticed an unusual amout of heat coming from near one of the panel lights. It turns out that the insulation is breaking down in the bulbholder between the 6.3 VAC and chassis. I've pulled the lampholder away from the chassis and now everything is ok, the mains transformer just gets a bit warm and not hot any more. Photo is the faulty part, I may be able to rebuild it

   
The full system now working with the Parmeko KT66 amp and Lowther Acousta PM6 in my new office after house move.
   

It had been running for an hour now and the transformer is very warm, it may be faulty. 
The amp transformer is just warm.
Is it usual for transformers to run hot?

[Murphyv310]

They can run quite warm, it depends on many factors like the design of the circuitry and the load on the transformer, even an open circuit on one half of the HT rectifier can make the transformer run too warm.
Can you measure the actual temperature after an hours running?

[djrm]

They can run quite warm, it depends on many factors like the design of the circuitry and the load on the transformer, even an open circuit on one half of the HT rectifier can make the transformer run too warm.
Can you measure the actual temperature after an hours running?

Hi Trevor,
Finally got to spend an hour in the office listening to the radio. The tuner transformer temperature is now 38 C, ambient is 16 C
Seems reasonable but not low.

The amplifier transformer is at 31  C, I think most of the heat there is by radiation from the KT66s

I'll 'scope the HT ripple to check both halves of the rectifier are working.

Kind regards, David.

[Crackle]

Hi
You have not said if you have changed the "dodgy caps", if they are paper dialectic ones they will all be leaking. Hunts "mould seals", wax covered caps (waxies) , and even some metal caps (Metalmite) are all known to be leaky. It is not just the smoothing capacitors which can overload the rectifier and mains transformer. The combined DC current passed by all the leaking paper caps can add up to the point where it starts to overload things.

Mike

[Kalee20]

Seems reasonable.

There is little virtue in designing a transformer to have a super-low temperature rise, unless the utmost efficiency is a key requirement. Doing so would make it bigger, heavier, and expensiver.

Good show on finding the original faulty lampholder (before cooking the transformer!). And yes, verifying that both halves of the waveform are contributing to the HT is a very worthwhile task,

[Old Sparky]

I've not come across the word 'expensiver' before, Kalee!

[Crackle]

There are lots of different dialects in the UK.
Mike

[Kalee20]

It just seemed a more appropriate word at the time than 'costlier'. More money without the added value-for-money.