[quote="marinblues] Do you think that I could change them out myself or should I go to a tech. The stuff regarding the phantom currents in the final stage sounds scary...
Also, I guess the final stage would require rebiasing? Correct?
Thanks Marin
Since you have a suspect output tube, the one that sparks, replace it now before something gets fried. The amp will perform best with the bias set optimally but a consumer amp that hasn't been tweaked by someone to have the tubes near frying should work reasonably well as is. There are plenty of fixed bias amps out there. The factory set point is adjusted to be safe. There are "techs" out there who will set the bias so that the tube is on the hairy edge of melting to get the "best sound" from it. In fact there is a "tube amp" book out there that avocates this practice. It is true that an amp biased too "cold" can lose some of the life and magic it could have. So at your earliest convience, take it to a tech and have the bias checked and reset if necessary.
While it could be possible with metallic fingernails to touch the pins on the output tube while it is going into the socket and get the B+ voltage, it would take some effort and ingenuity. Tubes have long been considered "user servicable parts". In the 60's Most grocery stores had a tube tester, with a bunch of GE or RCA tubes in the base, sitting where the ATM machines are now. You went down there with a bag of tubes from your radio, amp, or whatever wasn't working, looked up which socket to use and the settings for a couple of knobs, stuck the tube in there and pushed a button. A meter with green, yellow and red sections told you if you needed to buy an new one. That was the extent of the mystical nature of tubes. My dad, who repaired electrical contraptions for a living, thought nothing of sending his 10 year old kid down to the store to check the tubes out of his amp or the TV.
The preamp tubes should be easy to change and the amp won't need any adjustment there. Just make sure you have the key on the output tubes and the missing pin on the preamp tubes lined up right when you stick them in the sockets. I have seen 6L6's with the key busted off, stuck back in amps before, and the pins on preamp tubes can get bent if you try to force them in wrong.
Welcome to the wonderful world of glass. I'm sure there are some purists out there who will say that you need to use only 30 year old NOS tubes with the filimants hand wound by Hungarian virgins. And then have Howard Dumble himself adjust the bias. I hear more expressive range of tone in one bar of your playing than there is between the variations in good tubes.[/quote]
In the end I got some Electro Harmonix 12AX7EH and 6L6EH's (6L&GC's). My regular shop ran out of JJ's and if I understand well, the 12AX7EH is a selected 12AX7LPS. I should be warmer than the the Sovtek WBs but not as warms as the JJ ECC83. It seemed like a good compromise, changing too many things all once can be counterproductive.
Also, Robben uses the 12AX7EH's!
The amps at the guitar tech shop and should be back in a few days.
In the meantime, the Banzai arrived and I had the amp working for 10 minutes or so (before the noise reappeared) to say - WOW!
Congrats! Should work well. The EH is not a hand picked LPS btw. The EH is a short plate. The LPS is long. Different design. I like the EH a lot more!
Scott
Good to know. There is a lot of contradicting opinions regarding the EH tubes. The most common opinion is 12AX7EH = Sovtek LPS and 6L6EH = Sovtek 6L6 WTX.
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