Correct Frank
I did mention "old" but don't know how old. This could be a problem if technology has improved somewhat. So it may be updated. The print I have also doesn't specify anything about their power resistors either, so that is why I was asking.
I did mention "old" but don't know how old. This could be a problem if technology has improved somewhat. So it may be updated. The print I have also doesn't specify anything about their power resistors either, so that is why I was asking.
Anyone got any recommendation on a good wirewound(Looks like a white coffin type)?
I will use it on the b+ of my diy pre amp.
Cheers
Kenneth
I will use it on the b+ of my diy pre amp.
Cheers
Kenneth
Does anyone think it would not be ok to put a small heatshrink sleeve over the steel endcaps of these Welwyn resistors if they are run at a small fraction of their rated dissipation,for example,7 watt units dissipating less than I watt?
Heatshrinking wont be a problem.
I've played around a bit with power resistors b/c most are more inductive and magnetic than MFs and CCs. In my prototype OTL guitaramp I've paralleled a 0.5W 20ohm carboncomp with a 3W 10ohm wirewound. Yes that's pushing it for cathoderesistor on a 6AS7 but it's for experimentation. The wirewound has blown up twice while slamming on the guitarstrings, while the little CCs have hold their ground. The second time it happened, the CC grew like a marsmellow in the microwave and it's resistance increased to about 50ohms, but it didn't fail completely.
Wirewounds obviously can't handle pulses too well. Makes sense since the wire is really thin. Of course wirewounds are also made noninductive and pulse capable, but they are never in stock at any vendor. Digikey has some WWs made for audio, can't remember make, and they are nonind and nonmagnetic.
I usually use two 3W WWs and one CC in parallel as cathoderesistor.
In my HiFi amps I only use CCs (paralleled many).
For use in the cathode circuit their so called noise is not an issue.
I've played around a bit with power resistors b/c most are more inductive and magnetic than MFs and CCs. In my prototype OTL guitaramp I've paralleled a 0.5W 20ohm carboncomp with a 3W 10ohm wirewound. Yes that's pushing it for cathoderesistor on a 6AS7 but it's for experimentation. The wirewound has blown up twice while slamming on the guitarstrings, while the little CCs have hold their ground. The second time it happened, the CC grew like a marsmellow in the microwave and it's resistance increased to about 50ohms, but it didn't fail completely.
Wirewounds obviously can't handle pulses too well. Makes sense since the wire is really thin. Of course wirewounds are also made noninductive and pulse capable, but they are never in stock at any vendor. Digikey has some WWs made for audio, can't remember make, and they are nonind and nonmagnetic.
I usually use two 3W WWs and one CC in parallel as cathoderesistor.
In my HiFi amps I only use CCs (paralleled many).
For use in the cathode circuit their so called noise is not an issue.
I have used wire wounds such the welwyn types with a 20 times power
overload for several seconds at a time, The 350 degree rating is due to the fact that the vitrious enamal like glass becomes conductive, even the ceramic
materials on the box shapes whitish coulor types sufer the same effect.
But if you are applying only 1 watt to a 7 watt type then the temperature is
going to be less than about 50 degree above ambient. No heatsink needed.
The Welwyn series I have used in noise critical paths such as Tape Head
amplifiers as being superior to any other, Also, I used a 22K 7 watt
as plate resistors with no failures or noise problems on product that I have made over 30 years.
If ECC8010 wishes to have the last word and as a moderator he should moderate not inteject with put downs. Then I will no longer bother
to input any comments. We are all so superior to little old me and my near 50 years in this industry. Thank you.
overload for several seconds at a time, The 350 degree rating is due to the fact that the vitrious enamal like glass becomes conductive, even the ceramic
materials on the box shapes whitish coulor types sufer the same effect.
But if you are applying only 1 watt to a 7 watt type then the temperature is
going to be less than about 50 degree above ambient. No heatsink needed.
The Welwyn series I have used in noise critical paths such as Tape Head
amplifiers as being superior to any other, Also, I used a 22K 7 watt
as plate resistors with no failures or noise problems on product that I have made over 30 years.
If ECC8010 wishes to have the last word and as a moderator he should moderate not inteject with put downs. Then I will no longer bother
to input any comments. We are all so superior to little old me and my near 50 years in this industry. Thank you.
Sorry AV8R, it was about heatshrink to insulate the steel endcaps not a heatsink that I was enquiring! However,many thanks as you have answered my question completely anyway. The heatshrink I am using has a maximum operating temperature of 135 degrees so your helpful information about temperature rise gives me complete confidence. My only reservation about these Welwyn resistors is the steel endcaps; once I had a smoothing choke with a bent(as supplied!) fixing lug work slightly loose and move during transport and this steel endcap contacted the choke body. Have you ever seen this vitreous enamel totally melted? Fortunately this 1k resistor acted as a fuse and prevented damage to the electromagnetic components. Thank you again,Regards, N.A.
Caddock makes film resistors in transistor cases. I like them. They can be bolted to conventional heatsinks.
First: I don't see where ECC8010 put u down.
Second: don't stop giving us your knowhow, it is appreciated!
Third: in my case the WWs were Vishays, I have not tried a Welvyn. The pulse that blew them up was perhaps some 600mA, and it was a cool effect with sparks, smoke, and a bang louder than the noise from the speakercab.
I had a similar problem with Dale wirewounds. I thought they were covered by some black cement, but it was a flammable paint.
This is an example of the type I use, The vitrious emamel is as the name implies a glass like coating that makes it difficult to contact any point but the end wires. They weld the resistance wire to the ends, so no contact noise.
I know the are other examples out there. Such as these which are very quiet
and at 100K serve as extremely good plate resistors. The inductance is so negligible that it perfomes well to 100 MHz. Not cheap though. Not designed to handle high power. but at half watt more then adequate for a few milliamps.
RHOPOINT|5G10D 100K|RESISTOR, 0.2W 0.1% 100K | Farnell United Kingdom
WELWYN|W23 22K JI|RESISTOR, WW 10W 5% 22K | Farnell United Kingdom
I know the are other examples out there. Such as these which are very quiet
and at 100K serve as extremely good plate resistors. The inductance is so negligible that it perfomes well to 100 MHz. Not cheap though. Not designed to handle high power. but at half watt more then adequate for a few milliamps.
RHOPOINT|5G10D 100K|RESISTOR, 0.2W 0.1% 100K | Farnell United Kingdom
WELWYN|W23 22K JI|RESISTOR, WW 10W 5% 22K | Farnell United Kingdom
- Status
- Not open for further replies.