Err Innovine. Did you ever re-bias your amp with new tubes?
Dt25 Tube Upgrade: Quick Review Of Jj's Tube Upgrade
Posted 24 February 2014 - 11:41 PM
Well.. If bias is too hot (that means underbiased: Current way too up), it can cause all kinda trouble and real damage to amp. Usually that comes with recognizeable (120Hz. Googled it ) hum. But but...
Opinion alert!: Tubes are more magical things, than spawn of pure engineering That's why almost everything can happen with them. However we're talking about same type of tubes here and it's not very common to get tubes with this big differences. Maybe, if old, normally coldish tubes were biased a bit on hot side and these new ones were... Takes lots of fruitless guessing really.
Of course - with bad luck - lots of things can go wrong, when changing tubes. For example if a tube socket happens to be loosely soldered (these days everything is made in bulks, so 100% quaity is practically a distant dream), even slightest move - like pulling out old tube - may get it loose and that can cause bigger problems. It's amazing, how you can one day drop a tube amp from a moving car without damaging it at all and the next day you sneeze next to your buddy's amp causing it to burst in flames.
If you have possibility to get those new tubes tested, it helps a lot. So far we really can't know, if it is the tubes or the amp, which failed. Amp by having bias miles away i mean.
Posted 25 February 2014 - 12:14 AM
I will return both. I think it's unlikely that there's a problem with the socket since I put my old tubes back in and they are working fine. The tubes were tested and matched very closely in the store, I have a print out of that test result somewhere. The bias for my old tubes was 25mV and 26mV. There was no hum or noise, in fact I thought the JJs had a MUCH lower noise floor (couldn't tell the amp was on just by listening, until I touched the guitar, then it was loud as hell).
I'm just gonna return the pair, purchase new ones, and get store credit if the returned pair show up as defective.
Posted 25 February 2014 - 08:57 AM
There is no need (or ability) to rebias the 12AX7 tube, so you only have to replace the tube. Make sure your amp has been off for some time (I did mine in the morning after the amp had been off all night and the power tuned off at the mains). Make sure you don't touch anything other than the tube.
Remove the stock and insert the new tube using a clean soft cloth so you don't get finger marks on the glass.
Hope this helps.
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