Vitreous Enamel vs Wirewound Resistor

[Valverine]

Greetings,

I'm gathering parts for my first tube project and most of them will be ordered from digikey.com.

In the spec that I have there is a high-power wirewound resistor for the output tube cathode. But I could only find "vitreous enamel" type with the suitable resistance/wattage value.

Are there any reasons not to use one or it can be freely substituted for a wirewound resistor?

Thanks!

[fdegrove]

Hi,

Are there any reasons not to use one or it can be freely substituted for a wirewound resistor?

What's the wattage we're looking at?

I'd only use WW types in that position if they're of the non-inductive type.

Vitreous enamel ones are often magnetic, steel endcaps and leadout wires.

Cheers,

[Valverine]

Thanks!

Nominal wattage will be 9-12W, depending on how hot I'll run the tube (6AS7G). I guess I need to overrate the resistor to keep the temperature reasonable, don't I?

[EC8010]

"Vitreous enamel" refers to the protective coating over the (wirewound) resistor...

[fdegrove]

Hi,

Vitreous enamel" refers to the protective coating over the (wirewound) resistor...

Yep. These are often the smaller wattage ones whereas the higher wattage ones are often clad in aluminium housings and need cooling from the metal chassis for best operation.

Cheers,

[Valverine]

Greetings,

Thanks for the explanations!

In a supplier catalog I've also found "T220 Style Thick Film Power Resistors" and "Aluminum Housed Wirewound Resistors"- both with high tolerance and in the suitable wattage.

Are there any preferences for one over another?

[jackinnj]

Originally posted by Valverine
Greetings,

I'm gathering parts for my first tube project and most of them will be ordered from digikey.com.Thanks!

Vitreous enamel is what they use to make toilets, in Europe, Japan, the Unites States even that bung-hole New Jersey!.

"What Trenton makes, the world takes" -- the old NJ cr*pper

[Sch3mat1c]

Yup, they wind resistance wire on pottery and fire it to a nice kiln glaze. Works great, doesn't it? Especially when you can run them red hot for much longer than any other type...

Tim

[Valverine]

It's good that they don't make wirewound toilets in New Jersey ...

Anyway, picked up some nice 25W wirewounds in aluminum housing today in a local electronics surplus store.

Thanks, guys!

[AV8R]

It's a pity that Americans are somewhat ignorant about these devices from the other side of the pond!

WELWYN have been making these since time immorial. they cover wattage ratings fron 21/2 to 14 watt. Because of their construction are very quiet and low noise. Are relatively non magnetic (since no metal is absolutely non magnetic in absolute terms). Their reliability is very good and the inductance is low i.e, similar to other wire wounds. The purpose of the vitreous enamel was to protect the wire from oxidizing at elevated temperatures. they are rated to a maximum of 350 deg C.

Values from 0R1 to 100K depending on wattage. have a loook at the Farnell cataloge at www.farnell.com/uk

The TO220 style power resistors are thick film types and do not handle short term overloads well and are noisy. Vishey this and Vishey that come on. Just very expensive thats all.

Aluminium clad need heatsiking to realize their wattage rattings and the voltage rating between resistive element and case is only good for 160 volt AC. so no good on tube HT circuits.

Go forget about toilet humour.