|
|
Post by rocknrolla on Aug 2, 2011 23:37:13 GMT -5
Ok, got my bias probe from Bob at Eurotubes and decided to check out my amp while saving up for a new quad of KT88's. I checked all 4 tubes and got alarmingly different readings on all 4.
They biased at 9.5ma, 25.5ma, 12.6ma, and 52ma. What the eff is going on? Do tubes that are approaching death start drawing less current? I moved the one "good" tube to the other three sockets and it stayed the same as did the others so I don't believe it's the amp. So I'm wondering if I've been playing through one good power tube this whole time. Frickin amp still rawks!
Just for reference I popped in 2 JJ EL34L's into the inner sockets on 1/2 power for a second. It sounded absolutely amazing. Now I'm thinking about clipping that extra resistor and ordering a quad of EL34's instead. I could always solder it back on if I feel the KT88 urge I suppose.
|
|
|
|
Post by splawndude on Aug 3, 2011 15:40:26 GMT -5
As you may or may not know I run 2 EL34s in my Quick Rod and love my mid-range growl. I think JJ EL34s would be pretty awesome. I had some Mullards in there before (similar to JJ) and really liked them. Now I have SED Winged C's and like them too. Not sure what I'll go after next for power but it will probably be JJs or maybe NOS Mullards. I'd clip and move forward. As far as you bias being off from tube socket to tube socket I'm not sure what to say. You've got 2 pretty cold, one hot and one decent. How does it sound? (sorry if that is in your OP I didn't re-read) You are getting new tubes so as long as they look close when you install you should be rockin. They will drift to the cool side after several hours of play. Remember, don't play the amp with that probe on there they are not built to take it. Expensive probes I think that may be OK. I'm not an amp tech  |
|
|
|
Post by rocknrolla on Aug 3, 2011 16:57:57 GMT -5
49-52ma is what's recommended. I've never biased an amp since all I owned prior to my Nitro have been Mesa Boogies (fixed bias) so my diagnostic skills suck.
I'm pretty sold on converting to EL34's so I think tonight I'll clip the parallel resistor and throw in my EL34L's and bias on the 1/2 power mode. Down the road I can re-solder it back on if I ever want to go back to the KT88's but for now I like the having the EL34 growl and mid range. Also $60 a quad for EL's vs $160 a quad for KT's will be nice.
|
|
|
|
Post by rocknrolla on Aug 4, 2011 11:04:26 GMT -5
Last night, clipped the resistor, installed 2 JJ EL34L's in inner sockets, set to 1/2 power and 8 ohm load, biased to 34.5ma.
Frikin a!!! ;D
There's my crunch. I've been looking all over for it and it has been hiding in the EL34's this whole time. The KT's are crushing and awesome but very scooped compared to the smaller bottles. The EL34's have a more rich/thick mid range and add a complexity to the tone that wasn't there with the KT's.
The bottom end didn't suffer as much as I thought it would. It's still there but now it has to compete with the mids a bit more. The clean channel is jangly and chimey as ever.
The overall voicing is shifted a little more away from the typical "modern" style and more Marshally. I'm thinking I'll cut a lot better with my band now. I can't wait to get 4 brand new EL34's in there.
|
|
|
|
Post by rocknrolla on Aug 15, 2011 17:41:28 GMT -5
So low bias settings causes noise at idle. I popped 4 new EL34L's in and let them warm up a bit. As soon as I hit the standby the noise returned. I checked the bias and it was down around 20 or so. As soon as I got above 28 it went dead silent. Set her at 34 and have hardly stopped playing since. AMAZING AMP!!!
|
|
|
|
Post by splawndude on Aug 15, 2011 18:10:47 GMT -5
sweet.
glad everything worked out
:cheers:
|
|
