wharris wrote:I'm with Rick and Spider. Over-biased tubes don't pop and they sure don't billow smoke.
Yes but the heat transferred may have fried a few caps and resistors, purely Nik's suggestion, he knows these amps like the back of his hand.
Here is one of Nik's emails:
If anything you guys are not sure, do ask me first.
Also, this is Oz? You might want to check your wall.
Usually, when this happens to a new amp, the wall in OZ is sometimes at 250V
instead of 240V. We have had this happening (dead tubes)
A 250V into 240V amp means abt 5% diff.
So B+ voltage of abt 470 could easily go 490V, which is enough to cause bias
to be real hot.
For cathode biased amps (like an 18W) or AC30, where the EL84s are already
ran very hot, the tubes will definitely fail very shortly.
But in any case, perhaps indeed something is not right. If you can get your
step dad to open it and take a look (esp power section ie the PS board and
the power tubes area), that'd be good
Send me some pics as well, so I can check too.
Don't worry, this will be covered should there be any need.
Also, when you saw smoke, did the tone of the amp change?
Things to remember:
1) Do not run the amp with just 2 power tubes
2) If you want to change to 1/2 power, best to do it while amp on standby.
3) Other than the usual speaker impedance thing. But , to be safe, check
what your cabinet is, impedance wise.
You can easily do this by measuring across the tip and sleeve, for
resistance.
Although it is rare, a cab could be miswired, or have 1 speaker affected,
causing impedance to be wrong.
Hope this helps, do let me know..
Thanks!
nik
