Triode/pentode switch question

Hello,

I have been playing with 2 freshly rebuilt st-70's in a horizontal bi-amp configuration. I plan to go to vertical bi-amp and was wondering if it is safe to operate one channel in triode and the other in pentode. Any issues with this?

Hi All! I'm new here and not new to the stereo gig (50+ years). I built a ST-120 in '12 and I love it. Recently I replaced the stock output tubes with Gold Lion KT88s and I do like them. Last night I turned the amp on and noticed a bit of hiss (white noise) on the left channel so I listened a while and it popped and crackled loudly a couple of times. The amp was in pentode mode so I switched it to triode mode and it hasn't done that since. I'm loath to put it back in pentode mode because the popping was pretty violent and I don't want to damage my new Sonus fabers! All suggestions will be appreciated.

First, try a careful cleaning of the tube pins and sockets. DeOxit products are the best way to accomplish this. Before you replace the tube(s), make sure you retension the sockets. Take a jeweler's screwdriver to each hole and crimp the contact slightly so that each pin fits snugly. My guess is that the contacts on the "bad" tube have become corroded. It's always a good idea to work the tube in and out of the socket on a regular basis.
And every tube batch of every brand may have slightly different diameter pins. Retension and clean often.

My ST120 is a '12 model, so I cleaned the tube sockets with a pipe cleaner and DeOxit, then retentioned the pins. I also cleaned the tube pins with DeOxit, couldn't hurt. Double check the solder connections on the triode/pentode switches...

His Eminence Sir Jim McShane, one of the Expert Tubologists in the country, has repeatedly stated that upwards of 90% of all new tube "problems" are due to these simple maintenance issues. Caveat Tuber. {Beware the Potato???}.

Thank you for the useful advise! What DeOxit product do you folks use?

I found the "DeoxIT Audio/Visual SURVIVAL KIT", which contains three or four cleaner/lube/protectants in various forms (i.e. spray, liquid and drops) plus a plethora of brushes, cloths, and applicators, to cover every possible contingency. It is available from Amazon:

http://www.amazon.com/CAIG-LABORATORIES-SK-AV35-DEOXIT-SURVIVAL/dp/B00DKYPNU0/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1443745365&sr=1-2-catcorr&keywords=deoxit+survival+kit

Much thanks! Just ordered it.

These are handy too ...



(Just gooOOoogle "needle bottle". I got mine from a clock repair dealer when I got some like ... uh ... clock repair stuff.)

I just spray a bit of D5 into one and dribble it here and there as needed. Gets around any overspray issues as you dribble it about, here and there. Doesn't take much either ... just a drop on a pipe cleaner or q-tip will go a long way.

Not a bad idea to follow up with canned air as well. If you do it right, you shouldn't get any cleaner spraying out ... just loose odds and ends that can find their way into the strangest places.

And remember folks ... BEWARE THE POTATO!!

(think I'm gonna get the t-shirt)

sK, good point. Those are the same bottles that are sold at the tobacco VAPE shops; used to refill an electronic cig and should be on the cheap. Dale

Just be sure to label them well ... I don't expect you'll get the intended results if you were to, say ... spray muriatic acid into a tube socket ...

Which brings up another point ... haven't found anything yet the bottles won't stand up to, and I expect in this day and age, they're considered safer than using old syringes found in a back alley somewhere.