EML 300B-XLS, anyone using them?

[Paul Joppa]

Hi Paul.  I measured the resistances hot (after 48 hours) and cold and got 10.38 ohms cold, 11.68 ohms hot.  This was with the stock EH 300B's.  What do you think sir?

Copper temperature coefficient is 0.004041 per degree Celcius, so I calculate a 31 degree C temperature rise above ambient; let's say a 25C ambient so 56C. The transformer components are designed to tolerate 155 degrees C - doesn't look like temperature is going to be a problem!

I generally design to a target of no more than 100C internal temperature to provide a safety and longevity margin.

[johnsonad]

That's good to know!  I have to say the screws holding the reg unit to the chassis near the tubes get much hotter than the bell housing on the power transformer.  I did try the drop of water test by the way

SO, what's the verdict then, can the Paramounts handle the EML 300B XLS with a 1.4 or 1.5 amp current draw without modification and stay within 4% filament tolerances in your best guess (having not tested it yourself)?  If by chance they strayed outside the 4% tolerance specified by EML, can the Paramount be modified to provide 5v?

Thanks again Paul for your help in this!


Aaron

[Paul Joppa]

Paramount filament voltage depends on the power line voltage, so a tight variation limit might require some line voltage adjustment. Should be something easy to scramble together is it's needed.

[johnsonad]

I've have regulated 120v power right now but if I needed more are you saying it would be easier to put a variac in and adjust it this way vs. modding the circuit? 

Thanks again Paul.

[Paul Joppa]

Yes, that's exactly what I'm saying. The bonus is, if the filament voltage is right then all the other voltages will be right as well - it's not just the easier way, it's also the better way. If you have reliable 120 volts then you should not need any adjustment.

[pro_crip]

Good, I've been sticking my dmm probes in an outlet in my eventual listening room on a regular basis and I've been getting a steady buck twenty, from a low of 119.9 to a high of 120.4. Still plan on getting the soft start shunt upgrade when that comes out.

Rich

[johnsonad]

Great news!  Thanks Paul!