Noob, did I hurt my new amp?

[SteveO]

Hello all! New member here. First post though I have lurked for quite some time!
I would first of all like to thank all of you as I have spent many hours over several months reading your very informative posts and decided I should join in. I am just a hobbyist but I have taken a couple of electronics classes several years ago though but I am a huge tube fan and have several guitar and hifi tube amps. I have always done my own biasing and did a cap job once on my 65 Vox Berkley amp.
Anyway,I recently bought a new Fender Blues Deluxe amp and I decided I would like to experiment with some tube rolling so I replaced all of the tubes in the amp and proceeded to adjust the bias on the output tubes. I set the bias at 68mv both tubes combined and was just about ready to finish up and decided to check the plate voltage. I got my reading on the first output tube and then when I tried to get the second tube reading my probe slipped off of pin 3 on the 6L6GC and touched pin 2. This caused an arc of the 2 pins and of course it stunned me for a second but I reached up and flipped the power switch off. Arrgggg! So I let the amp sit there for a few minutes and after spouting off a few choice words I flipped the power switch back on in standby. Then after a couple minutes and no smoke yet flipped the switch on. The amp made kind of a soft high pitched squeak and then seemed to stabilize itself. Still no smoke so I plugged in my guitar and it sounded fine so I rechecked the bias and it was good to go also. I have since played through the amp for maybe 5 or 6 hours and it sounds great. The output tubes are not red plating. So my question is, did I dodge a bullet or will I have problems down the road with it? Any advice will be greatly appreciated and hopefully will ease my mind about it. Thanks in advance! Sorry for the long first post but I wanted to introduce myself!

[stokes]

Sounds like you "dodged a bullet".What you did put a couple of hundred volts onto your filament circuit.If the filament circuit on this amp has the 100 ohm artificial CT it is possible you could have burnt those.Check each side of the heaters,pin 2 and pin 7 on the 6L6 for resistance to ground.Unless your heater winding has a CT,you should read about 50ohms from each side to ground.If you see very low or zero ohms you have a CT,and all should be okay,if it reads open you have a burnt resistor,find it or them and replace.

[SteveO]

Hi Stokes. Thanks much for your reply! I have been looking at the schematic and I see it shows a pair of 47ohm resistors at the end of the heater leg that are tied to ground. Could these be the resistors you are referring to? They are R80 and R81 1/2watt resistors. I will not have a chance to check these on the amp itself until Saturday but I will take the resistance readings then and let you know what I find out. Do you think I could have damaged the power tube at all?
They are new and matched =C= 6L6GCs'. Should I consider putting the original tubes back in? Thanks again for your help! Steve

[Twist]

Don't feel bad about the slip of your probe. I've been working on amps for nearly 25 years and to this day I still slip and throw sparks. Solid state amps aren't quite as forgiving as tube amps though. In a fraction of a second you can destroy a solid state amp with one little spark. Sounds like your amp is ok.

[SteveO]

Hi Twist, thanks! It's something (working on amps) I have a great deal of respect for! What is your take on my tubes? Do you think I should replace them?
The amp really does sound great especially for the price one pays for them these days (not to mention what's happened to mine). So I'm hoping for the best!

[Twist]

I would bet they're ok. I would follow Stokes advice and check those 47 ohm resistors. You might also pull one output tube out and check the idle current of the other one. Then do the same with the other. If both tubes idle around 25 to 35 ma each (millivolts across the check point) then your ok. This will also tell how closely matched your tubes are. Also you may find one tube is drawing the full 68 ma and the other is dead. But that's unlikely since you said the amp sounds good. While your at it, reflow all the solder on the tube sockets.

[SteveO]

Thanks again Twist! Will do. Also I just found a BDR schematic. I was using the orignal 90s' schematic and I found that those resistors Stokes is talking about are in fact 100 ohm resistors on the heater circuit and not 47 ohm as on the older models so I will check those out on Saturday! Thanks again guys!

[SteveO]

I measured pins 2 and 7 on both of the 6L6 tubes and got 22.4 Ohms on all pins except V5 pin 7 but got 22.1 on that one, with respect to ground. I inspected the resistors R80 and R81 and they look fine. No burn marks at all. I got the same 22 Ohms on the resistors also when measuring those to ground.
I have never soldered on a pcb before so I am a little apprehensive to replace those resistors myself! I cleaned the pins on V4 where the spark was and it looks like the trace is exposed about a 16th of an inch. I am going to reflow the solder on that pin and hope for the best. Also, I will take bias readings with one of the 6L6s' removed and see what I get. Any thoughts or advise is greatly appreciated! Thanks guys!
Steve

[stokes]

I wouldnt be too quick to re-flow any solder traces unless you are sure it is problematic.If those resistors I referred to are okay,you likely dodged a bullet.If the fillament in the tube that the spark occured on was bad,the tube wouldnt operate and the amp would sound bad.If the ground reference resistors on the heater circuit were blown,the amp would still work but you would get more hum from the amp.

[SteveO]

Thanks Stokes for getting back to me! Well, I measured the bias voltage on each 6L6 tube one installed at time and the tube where the sparking was had 2mv less than the other tube. V4 is the tube in question and it had about 34mv. The other tube had about 36mv which surprised me. I thought V4 would have the higher reading. After I put the tubes back in together I biased the amp to 67mv. When I did a listening test it sounded great. I don't notice any additional hum but I don't turn the amp up very far ( 2 at the most ) on the volume. I will try a higher volume setting tonight and see if it hums that much more. I know these amps hum more the more you turn them up but if it's not unusually high, it should be OK. Since the resistors on the heater circuit are not open as far as I can tell, I will probably leave them in for a while and just play the amp and see what happens. I am wondering if when the spark happened it could have caused a tube mismatch in any way? They were bought from a reputable dealer and should be matched. Is 2mv difference a substantial difference? How important is it to have matched tubes in these amps?
Thanks for all your help guys! Steve