KT 66'S IN 67' BFSR

[muzacman02]

HELLO, to everyone. Im new to this forum. I was wandering if its safe to Run KT66's in my 67' BlackFace Super Reverb.  I understand the 66's are a similar form of 6L6's? and  I do also understand they draw more Heater Current? How do I measure this or check this to know I wont damage my Transformer. I actually tried them set the Bias at 31ma and they sound Fantastic but my main concern is not killing my All Original amp. Thanks for any help or suggestions given, Jamie

[HotBluePlates]

Clip your meter leads to pins 7 and 2 of your output tube sockets (the ones with the green heater wires).

Normally, you might measure 6.3vac between these pins +/-10% given rising wall voltages. As long as the heater voltage hasn't sagged below 10% below nominal (or 6.3v - .63v = 5.67v), then your PT heater winding is holding up fine.

I've used the modern versions of the KT66 in a number of Fender-style amps without heater issues. Sometimes, though, the KT66 wants to ring and oscillate, in which case a bigger grid stopper (say 5-10k instead of 1.5kΩ) and/or a bigger screen resistor (1kΩ instead of 470Ω) generally does the trick.

[muzacman02]

THANKS SO MUCH !! FOR THE INFO, I WILL TRY TO test that this evening. Jamie

[muzacman02]

I FINALLY checked the heater voltage it was 6.3 VAC on both tubes. I hope this is good, The amp sounds FABULOUS. thanks so much for the input.

[HotBluePlates]

6.3vac is exactly where it should be. Glad you're enjoying the amp!