Help! May have dropped 12sn7 in place of 6sn7

scutterflux · 30th November 2008, 03:47 AM

I bought what I thought were Philco branded "Bad boy" 6sn7's off ebay, not labeled 6sn7 or anything at all, and plugged them in my yaqin mc-100b. They lite up just fine, but one had no sound until I tapped it, then she went. Next day sounded like it was shorting out, distorting and such. On the next fire up she went perfect as drivers, but when I put them back into the gain stage the one didn't work, and next thing the other only worked when the amp was powering down and turned off.....weird! The end result was the left channel no longer works with any tubes. I think they may have been 12sn7's or other, because during this I would occasionally place "correct working" tubes to check nothing bad was happening, but of course something bad did happen, any ideas what? Does this sound like what would happen with the wrong tube?

Here's the schematics from DIY http://www.diyaudio.com/forums/attac...mp=1200504582&

Tom Bavis · 30th November 2008, 03:45 PM

12SN7 won't light visibly on 6.3V. And you certainly can't hurt an amp by plugging a 12SN7 into a 6SN7 socket (might hurt your ears with distortion, depending on circuit...). But a SHORTED tube... that COULD zap something, depending on what's shorted and the circuit it's in.

scutterflux · 1st December 2008, 02:47 AM

That could be, but I'm not 100% sure about the 12sn7, it could be anything that resembles a "bad boy" but I'll bet it's just shorted the way the one was acting, the other seemed OK and sounded good. I opened up the amp and didn't notice anything visual out of the ordinary, I'll check the power tubes next all the pre tubes are good ones now. Then attempt a diagnosis.

30th November 2008, 03:47 AM	#1
scutterflux diyAudio Member Join Date: Apr 2008	Help! May have dropped 12sn7 in place of 6sn7 I bought what I thought were Philco branded "Bad boy" 6sn7's off ebay, not labeled 6sn7 or anything at all, and plugged them in my yaqin mc-100b. They lite up just fine, but one had no sound until I tapped it, then she went. Next day sounded like it was shorting out, distorting and such. On the next fire up she went perfect as drivers, but when I put them back into the gain stage the one didn't work, and next thing the other only worked when the amp was powering down and turned off.....weird! The end result was the left channel no longer works with any tubes. I think they may have been 12sn7's or other, because during this I would occasionally place "correct working" tubes to check nothing bad was happening, but of course something bad did happen, any ideas what? Does this sound like what would happen with the wrong tube? Here's the schematics from DIY http://www.diyaudio.com/forums/attac...mp=1200504582&

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
12SN7 vs 7N7 bs 6SN7	jackinnj	Tubes / Valves	7	28th March 2009 07:01 PM
12sn7 heater-cathode voltage	alexg	Tubes / Valves	6	7th May 2008 11:40 AM
Dropped a SIF Ba	exurbia	Tubes / Valves	21	15th April 2008 08:27 PM
2x 2Sk170 in place of 2SK389 and 2x 2SJ74 in place of 2SJ109?	jarthel	Parts	12	26th July 2007 09:08 AM
Best place to place bleeder resistor in a power supply?	G	Tubes / Valves	13	4th August 2004 09:26 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

30th November 2008, 03:45 PM	#2
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	12SN7 won't light visibly on 6.3V. And you certainly can't hurt an amp by plugging a 12SN7 into a 6SN7 socket (might hurt your ears with distortion, depending on circuit...). But a SHORTED tube... that COULD zap something, depending on what's shorted and the circuit it's in.

1st December 2008, 02:47 AM	#3
scutterflux diyAudio Member Join Date: Apr 2008	That could be, but I'm not 100% sure about the 12sn7, it could be anything that resembles a "bad boy" but I'll bet it's just shorted the way the one was acting, the other seemed OK and sounded good. I opened up the amp and didn't notice anything visual out of the ordinary, I'll check the power tubes next all the pre tubes are good ones now. Then attempt a diagnosis.