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Old 12th August 2007, 02:16 AM   #11
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Location: Newark, DE
All my output tubes are EL84, which means they're cheap (about $4 each for the Russian old stock variety). Most of my amps are old and in need of rebuilding, which means they have power transformers designed to run on 115 VAC (and power in my house is more like 125).

As a result, all my amps tend to run around 100% of rated plate dissipation (or sometimes even more). I'm not sure exactly what the rated dissipation is for the 6L6WXT. The plain jane 6L6 seems to be 20.5 watts. The 6L6WGB is listed at 26 watts. Another poster said the 6L6 family was good for 30.

At 35 mA on 367 volt plates, you're only 63% of the 20.5 watt rating. If the limit is 26 watts, then you're still not halfway there. If you believe the 30 watt limit, then your tubes are just loafing along.

Now, don't take any advice from me. I already pointed out that my tubes are nearly disposable. But, if it were me, I'd crank those 6L6WXT until they start to glow, and then turn them back a hair.
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Old 12th August 2007, 03:09 AM   #12
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Regarding the "6L6 family" (RCA ratings):

Metal 6L6 and 6L6G: Max. Pa = 19W, Va = 360V, Vg2 = 270V
6L6GB and 5881: Max. Pa = 23W, Va = Vg2 = 400V
6L6GC: Max. Pa = 30W, Va = 500V, Vg2 = 450V
7581A: Max. Pa = 35W, Va = 500V, Vg2 = 450V
7027: Max. Pa = 35W, Va = 600V, Vg2 = 500V

(Added to above data, is that in case of UL, Vg2 max. can be the same as Va max.)

Then, however: The Russians are quite free with their numbering. The 6L6WXT and 6L6EH is supposed to be same as 6L6GC. Internal construction of NOS GE 6L6GCs shows somewhat more anode radiating area and a larger G1 heat radiator. Beware of 6L6s with innards mounted on a glass tongue but marked 6L6GC. They are not - they are 6L6GBs. One must also remember that Pa ratings suppose open 25 degrees outside temperature.

Thus I would regard the 6L6WXT as more than capable of working up to 500V (I have used them there). Regarding the Pa .... there is not much of a difference; if in doubt (and in Arizona), regard as 25W.

Last indicator: Look out for semi-circular slots in the mica mounting wafers, between the anode mounting pin and the rest - that is proof of a higher voltage rating. If no slots, no 6L6GC etc.
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Old 12th August 2007, 12:11 PM   #13
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Thanks for the information guys. I will put the 5AR4 back in and bias the tube higher and watch if the plates in case they start glowing.

Sal Brisindi
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