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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 16th Mar 2006, 9:04 pm   #1
Reproman
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Default Thermistors and Brimistors.

Hello Everyone,

I have two M.E.S. thermistors ( CZ2 type) that have crumbled in a radio set. Are replacements available? or can you get around the problem of surge limiting another way,these particular thermistors limit the surge in the heater circuit and the dial lamps ( 12 volt 0.1 amps) I hope you can help me on this one.

Kind Regards
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Old 17th Mar 2006, 3:46 pm   #2
radiohm
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Default Re: Thermistors

Hi Reproman.
this document might help you possibly to find a replacement if you can't get tho originals.

Hope it helps.

Regards.
Mike.
Attached Files
File Type: pdf BRIMISTORS CZ1 - CZ12.pdf (70.4 KB, 1227 views)
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Old 17th Mar 2006, 9:34 pm   #3
Reproman
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Default Re: Thermistors

Hello Radiohm,

Many thanks for your help,does anyone have any suggestions for getting around these pesky components! (ie using resistors?)or do I have to put up with the occasional blown bulb!

Kind regards
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Old 17th Mar 2006, 9:47 pm   #4
paulsherwin
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Default Re: Thermistors

Yes, you don't actually need a thermistor in the heater chain. If you replace it with a resistor there will be a switchon surge, but valves were built to take this (6.3V valves with a transformer will flash with a switchon surge as well). Just recalculate the total dropper resistance required.

You're actually more likely to blow bulbs than anything else, so it may be worthwhile underrunning these (e.g. replace 0.1A bulbs with 0.15). A bit of experimentation may be necessafy.

Good luck, Paul
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Old 22nd Mar 2006, 5:19 pm   #5
Reproman
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Default Re: Thermistors

Hello again,

What would be correct resistor value? to replace the two CZ2 thermistors
this radio uses the following valves...UY 85, UCL83 X2, UCH 81, UBF 89
the Brimistor characteristics chart for thermistor CZ 2 gives several resistance figures which one of these would be correct?

I hope you can clear things up for me

P.S. thanks Paul for your assistance

Kind Regards
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Old 22nd Mar 2006, 10:18 pm   #6
XTC
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Default Re: Thermistors

Bardwells do a couple of types of rod thermistor.

http://www.bardwells.co.uk/subcats.asp?catid=THER01

The rest of the site is worth looking around.

I believe the TH3 is intended for use in .3A heater chains. The CKT one may be closer to the mark. For what they cost, it's worth buying a few to experiment with using a bench PSU and a meter to see if they do what you want.

There are a few suppliers such as Birkett's who have stocks of older components and they may have the part you want.

Pete.
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Old 23rd Mar 2006, 8:08 am   #7
dazzlevision
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Default Re: Thermistors

Hello,

The Bardwells "CKT" thermistor looks like the "two-in-one" type used in GEC/Sobell hybrid single standard colour TVs.

Regards,

Dazzlevision
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Old 23rd Mar 2006, 1:12 pm   #8
paulsherwin
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Default Re: Thermistors

Quote:
Originally Posted by Reproman
What would be correct resistor value? to replace the two CZ2 thermistors
this radio uses the following valves...UY 85, UCL83 X2, UCH 81, UBF 89
the Brimistor characteristics chart for thermistor CZ 2 gives several resistance figures which one of these would be correct?
Paul Stenning's page on dropper calculations has all the info you need: http://www.vintage-radio.com/repair-...per-calcs.html

His spreadsheet does all the hard work for you: http://www.vintage-radio.com/downloa...lculations.zip

In this case the total voltage required by the valves is 38+38+38+19+19 = 152V, so you need a total resistance of 880 ohms to drop the extra 88 volts. The existing dropper will be a bit less than this, so add the difference to replace the thermistor.

You may need to make some special arrangements for the dial lamps. Check the voltage across the valve heaters when you've finished.

Good luck, Paul
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Old 23rd Mar 2006, 1:27 pm   #9
Reproman
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Default Re: Thermistors

Hello everyone,

Many thanks for your input, all information is
of enormous use, it's nice to be in contact with people who know what they are talking about .

Regards
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