"Equal Opportunity" MM Pre

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#241
Recommended Practice?

Being new to tubes, do you guys leave the power on all the time, or turn it off when not in use? I'm curious because I had a Tungsram tube fail in about 3 months. Because it was a NOS part with unknown history, it is likely that it was just an issue with the individual tube, but I have been turning the power on and off.

In case you are curious, it failed rather suddenly and apparently during "power on". The glass was smoked near the top of the tube compared to it's mate which is clear. And no current flowing through the tube. I replaced it with a Matushita and everything works fine.

Thanks in advance.

Jac
 
#242
lehmanhill said:
Being new to tubes, do you guys leave the power on all the time, or turn it off when not in use? I'm curious because I had a Tungsram tube fail in about 3 months. Because it was a NOS part with unknown history, it is likely that it was just an issue with the individual tube, but I have been turning the power on and off.

In case you are curious, it failed rather suddenly and apparently during "power on". The glass was smoked near the top of the tube compared to it's mate which is clear. And no current flowing through the tube. I replaced it with a Matushita and everything works fine.

Thanks in advance.

Jac
Click to expand...

Many far more expert than me, but Amphenol Thermonetics (was GE Thermonetics) make inrush current limiters which cost about $1.50 from Mouser etc. NTC thermistors have high initial resistance which drops as they heat. You have to size the thermistor for the app using the formula on the datasheet. http://amphenol-sensors.com/en/products/temperature/inrush-current-limiting/858-siweb-pl329

lehmanhill said:
Here in Michigan, we have two peninsula connected by a bridge. So all of us that live in the lower peninsula are called trolls because we live under the bridge. 🙂 Of course, we don't make quality transformers.

Jac
Click to expand...

I worked with a Yooper. He was so tight that he'd unplug the TV before he went to work.
 
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#243
jackinnj said:
Many far more expert than me, but Amphenol Thermonetics (was GE Thermonetics) make inrush current limiters which cost about $1.50 from Mouser etc. NTC thermistors have high initial resistance which drops as they heat. You have to size the thermistor for the app using the formula on the datasheet. Inrush Current Limiters

I worked with a Yooper. He was so tight that he'd unplug the TV before he went to work.
Click to expand...

I'm a troll, not a Yooper, but I've still been known to turn off a light when leaving the room. Maybe I can blame that on my partially Scottish heritage.

I'm familiar with NTC thermistors on Pass amps. But that is so you don't cause a brown out in the neighborhood with the current surge "required" on a good Class A power supply. Are you suggesting this approach for B+ and B- supplies? As far as I could tell, the heater still worked. I am assuming the failure was in the signal part.

Jac
 
#246
The L|A articles regarding the Equal Opportunty don't go into great detail regarding the heater supply, beyond suggesting the use of the heater supply as outlined in the His Master's Noise blog post. I thought it would be prudent to have that (freely available) heater supply schematic reposted in this thread. So here it is:

fig7-large.png


I'm very anxious to begin this build. In fact, part of the delay is due to the fact I have yet to complete my Lenco turntable build. Still need a couple more parts for that one...
 
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#247
Furiously collecting parts for my build, I have the advantage of a preamp that has balanced inputs for it's single analog input. This is kind of a no-brainer choice, especially as I'm a big fan of the AT150MLX.
 
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