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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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18th Jul 2020, 9:11 pm | #1 |
Hexode
Join Date: Aug 2010
Location: nr. Hannover, Germany
Posts: 372
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UY85 Heater voltage
Good evening all,
according to the data sheet the UY85 has a heater voltage of 38V @100mA. For a home brew project I have a transformer that supplies 35,6V off load and 34,5V when connected to the valve. Is it bad practice to under-run the rectifier like this?
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Eddie BVWS Member. Friend of the BVWTM |
18th Jul 2020, 9:33 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,081
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Re: UY85 Heater voltage
Heater voltages are generally best kept within 5% of nominal. This is low by slightly more. But unless you are pulling near the maximum current, I'd say don't worry.
For maximum life, slightly under is better than slightly over. |
18th Jul 2020, 10:12 pm | #3 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,129
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Re: UY85 Heater voltage
What was the mains voltage at the time of the test ?
If on the low side, then that should be fine since any subsequent variation should be upwards and therefore towards running the heater at nominal voltage, or closer thereto. If however the mains voltage was on the high side, then that is of greater concern since future fluctuations are likely to be downwards, and thus running the heater further below the design voltage. |
19th Jul 2020, 9:31 am | #4 |
Hexode
Join Date: Aug 2010
Location: nr. Hannover, Germany
Posts: 372
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Re: UY85 Heater voltage
Guys, thanks for your replies. I fed the Transformer from a variac at the nominal 230V. There will not be a great deal of demand on the rectifier, so I think I'll go ahead with the idea. The mains voltage around here is quite stable and normally hovers around 234-236V which I suppose is good.
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Eddie BVWS Member. Friend of the BVWTM Last edited by eddie_ce; 19th Jul 2020 at 9:33 am. Reason: additional information |
19th Jul 2020, 10:05 am | #5 |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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Re: UY85 Heater voltage
It will be fine. These are designed for series operation normally, so in real use would see different voltages for the spec depending on the mains voltage, other valves in the chain and so on. Slightly lower is better as kalee says...
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24th Jul 2020, 1:39 am | #6 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,199
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Re: UY85 Heater voltage
Since the heater voltage is not the tightly controlled parameter in 100mA valves, you should check the current in the actual circuit. If it's within 5% the valve will be perfectly fine. Even if the voltage is 10% out from nominal, the current might still be within tolerance depending on production tolerances of the valve.
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