JJ 6V6S putting out >15w in my Victoria 518

[MLG8675]

Just put a JJ 6V6S in my 518. After allowing it to warm up, I felt the urge to crank it up immediately. It sounded awesome but after a few minutes of playing, my speaker (Weber 8" Alnico Signature rated at 15 watts) began to make a "sizzling" noise. I backed off and haven't fully cranked the amp since. It sure sounded like a speaker frying, but could it have been the amp making a funny noise as the tube is burning in? The speaker works fine, but I'm affraid to crank it up now. Is it possible the JJ is putting out over 15 watts, whereas the previous tube EH was under 15 watts? I know these amps are rated at 5 watts, so I'm scratching my head here. Thanks for the help!

Matt

[MLG8675]

Bump

[Blue Strat]

You could put a Million Watt tube in that amp and it will never put out more than the power supply and output transformer will allow. You may be getting 1 to 2 watts more out, maximimum.

[unklmickey]

hi Matt,

sometimes, when carbon resistors begin to fail, they generate an electronic noise that resembles the sound of frying eggs.

i'd suggest disconnecting the speaker from this amp and connecting the speaker to another amp.

if it sounds the same when driven by another amp, you know the problem is with the speaker.

if it sounds okay, then then Vicky likely has a stuffed resistor somewhere.

cheers,

unk

[fullerplast]

Is it possible the JJ is putting out over 15 watts, whereas the previous tube EH was under 15 watts?
Matt

Just working some typical numbers:

Assume the following:
-plate voltage will stay the same for both, say 375V
-cathode resistor is 470 ohms
-EH draws 40ma
-JJ draws 50ma

For the EH, the cathode voltage is then 19V, plate to cathode voltage is 356, and static dissipation is 14W.

For the JJ, cathode voltage is 23.5V, plate to cathode is 351.5V, and the static dissipation is 17.6W.

Much depends on what your actual plate voltage is, but these numbers are not out of the ordinary. It gives you a feel for how much even a 10mA difference between tubes can change things. The cathode biasing "regulates" to a degree, but not enough to keep your power from increasing. If your plate voltage is on the high side, it may not be a bad idea to put in a larger cathode resistor, like 560 or 820 ohms.

[MLG8675]

Thanks for the great info. I just loaned the amp out to a friend for a couple of gigs so we'll see how it is when it gets back. I warned him not to crank it Ronnie Wood style!;)

Matt