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Mullard EL37/6L6GC Tube Rolling Question

Does anyone have any ideas why my Ampsandsound Forge amp, which is designed to take 6L6GC, EL34, and 6550 family of tubes and run in triode mode, will not run NOS Mullard EL37 tubes? I bought a matched pair and they do not even light up even though the 6SL7 input tube lights up normally. According to my past experience with EL37s in speaker amps they ran successfully in place of 6L6GC tubes but not in the Forge, even if they have the same pinout according to online sources. When I try other 6L6GC variants such as the GEC KT66 and new production Tung-Sol 6L6GC-STR tubes before and after trying the EL37, they run normally but the EL37s never even light up. The EL37 seller says he tested the tubes fully prior to sending but I guess I will have to send them back. Any ideas, anyone? Thanks.

rlawry
3 responses Add your response
jasonbourne71's avatar
jasonbourne71
1,392 posts
 

If the heaters won't light up the tubes are dead. Send them back for a refund/replacement.

noromance's avatar
noromance
10,143 posts
 

Can you switch to pentode mode and retest?

rlawry OP
486 posts
 

No, unfortunately, the Forge amp only straps beam tetrodes and pentodes in triode mode so there is no way to run them in pentode mode.

BTW, I sent the EL37s back to the seller who tested them successfully in his tester so the problem is not with the tubes.  The amp designer says the EL37 should run in the amp although the Forge has somewhat excessive plate voltage of 380-450 volts for the EL37 whose specs call out a 360 volt maximum.  That said, the amp should at least light up the heaters and any problem would be either a shorter lifetime and/or red plating in the amp due to overvoltage.  Every other 6L6GC, EL34, and 6550 family tube has run successfully but for some reason my amp is allergic to the EL37.

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