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Old 5th Jul 2020, 6:07 pm   #1
Vishnu Mohan
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Smile Telerad vintage radio. Valve over heating.

Dear all,
Greetings for the day....

Recently I tried to restore my TELERAD RT-302 (made in India) radio. It has EM84, EBC81, EL84, EZ80, EF89 and ECH81. Among these the ECH81 is just getting hot instead of glowing. Is it because of a faulty tube or any other problem in the circuit?.. Unfortunately I don't have a schematic of the same. Please help
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Old 5th Jul 2020, 6:16 pm   #2
paulsherwin
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Default Re: Telerad vintage radio valve over heating

A lot of valves don't produce an obvious glow when working normally. If it's getting warm then it must be working at some level. Look at it in a dark room.
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Old 5th Jul 2020, 6:55 pm   #3
Ed_Dinning
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Default Re: Telerad vintage radio valve over heating

I would imagine the ECH81 should run a bit cooler than the EL84 or EZ80 as it is a lower power valve

Ed
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Old 5th Jul 2020, 7:07 pm   #4
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Default Re: Telerad vintage radio valve over heating

The only valves that would run very hot (too hot to touch) would be the EL84 and EZ80, the others should be warm or very warm but not too hot to touch.

You don't say if the radio is actually working?
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Old 5th Jul 2020, 7:20 pm   #5
turretslug
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Default Re: Telerad vintage radio valve over heating

Hi Vishnu, sometimes it can be surprisingly difficult to see the heater glow in a valve, especially if it has a dark or shiny coating around the top of the glass, but if it feels warm, that suggests that the cathode is being heated. As the others say, it shouldn't be very hot- the EZ80 and EL84 will probably burn your fingertips after just a few minutes running but the others won't normally get hot, just rather warm,

Colin
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Old 6th Jul 2020, 9:29 am   #6
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Default Re: Telerad vintage radio valve over heating

if a valve loses its vacuum it won't glow but will get hotter than usual.
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Old 6th Jul 2020, 12:55 pm   #7
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Default Re: Telerad vintage radio. Valve over heating.

Measure the DC voltages to calculate the power input to the grid and anode structure.
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Old 7th Jul 2020, 4:16 pm   #8
Chris55000
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Default Re: Telerad vintage radio. Valve over heating.

Hi!

This is just a standard 5 valve AM superhet with an added EM84 tuning indicator!

First thing, do you have two green bars showing in the front of the indicator valve? If the front indicator is not showing two green bars, then there is a h.t. (high–tension) power supply fault, which will cause the set to fail to operate!

If the front indicator is alight and showing two green bars, turn the volume control up to maximum and place your ear to the speaker –you should almost certainly get some background hum, hiss, crackles or pops, etc., if the i.f. and audio stages are working.

If you hear some noises in the loudspeaker when you operate the front controls, there's either a h.t. feed missing to one of the earlier valves or the local oscillator isn't operating.

Do you have a good D.M.M. to check voltage readings with?

Chris Williams
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Last edited by Chris55000; 7th Jul 2020 at 4:24 pm.
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