Welcome to TheFret, Michael.
I agree you should check the preamp tubes to start with........even new ones can be microphonic occasionally.
Your photography is stunning, btw, esp. the wildlife.
Welcome to TheFret, Michael.
I agree you should check the preamp tubes to start with........even new ones can be microphonic occasionally.
Your photography is stunning, btw, esp. the wildlife.
Guitars
Wilburn Versatare, '52 FrankenTele(Fender licensed parts), Fender USA Roadhouse Strat, Fender USA Standard B-bender Telecaster, Agile AL 3000 w/ WCR pickups, Ibanez MIJ V300 Acoustic, Squier Precision Bass,
Amps
Ceriatone Overtone Special, Musicman 212 Sixty-Five, Fender Blues Jr., Peavey Classic 30, Fender Super Reverb, Traynor YCV-40 WR Anniversary w/ matching 1x12 ext. cab, Epiphone SoCal 50w head w/ matching 4x12 cab (Lady Luck speakers), Avatar 2x12 semi-open back cab w/ Celestion speakers
Pedals
Digitech Bad Monkey, Digitech Jamman, DVM's ZYS, Goodrich volume pedal
Thanks for the replies guys! Extra thanks to oldguy for checkin' out my pics. I'm glad you like 'em.
So, I just tap on the tubes and listen for strange sounds, eh? I guess that sounds easy enough. Even for me.
In fact, I'll go give that a try right now.
See my photos at: micknewton.smugmug.com
A microphonic tube will be obvious, kind'a the dental hygenist hitting the exposed nerve.Originally Posted by Mick
I pick a moon dog.
Well, I removed all of the metal shields (vibration dampers?) from the preamp tubes and let the amp warm up. Then I tapped each tube several times, including the power tubes. All I heard was a tiny bit of noise that sounded like small vibrations coming from the springs in the reverb tank. And they all sounded the same. I did the test several times, with the reverb dial set higher each time. None of the tubes had any obvious difference. Oddly enough, this time I was able to turn the reverb dial up to 8 without getting the feedback. But if I turn it any higher the feedback starts right up.Originally Posted by tot_Ou_tard
Is it possible that I have the bias set too hot? Can that cause feedback? The bias setting instructions on Eurotubes.com says "Super's and Twin's have a higher plate voltage so with the JJ 6L6GC's we see them come out of crossover distortion at about 34mA but we typically like to bias them between 38 to 44mA and most players like them best at 38 to 40mA." I set the bias on this amp to 39mA.
What should I try next?
See my photos at: micknewton.smugmug.com
What should I try next?[/QUOTE]
I would swap out the tubes one at a time until the feedback goes away.
Okay, I'll try that...Originally Posted by Moshe
But what if the problem is actually a combination of two or three bad tubes? This amp has a total of 12 tubes (seven 12AX7's, one 12AT7, and four 6L6GC's) and any of them might be microphonic, right? I could be swapping tubes in different combinations until hell freezes over!
When I was a kid they used to have vacuum tube testing machines at the store. I remember my dad taking tubes from our TV in for testing. Why don't they have something like that nowadays?
See my photos at: micknewton.smugmug.com
So that people can charge you extra for doing the testing for you. But really, without the cynicism, a tube tester like that won't pick up a microphonic tube. For that you need an audio amplifier like, say, a guitar amp. Get two new 12AX7s and a new 12AT7 and swap each one with the new ones. If you swap one out and there's no difference you can say that's a good one. The problem won't be in the power section so you can save yourself the cost of the 6L6s and a bias adjustment straight away. And when you've found the bad one and thrown it away, you'll still have a spare or two for when the next one goes bad :Originally Posted by Mick
Electric: Fat strat > Korg PB > TS7 > DS1 > DD-20 > Cube 60 (Fender model)
Acoustic: Guitar > microphone > audience