Crate Blue Voodoo 6212 questions about a Hum

[rythymroach]

Howdy yall, I'm new here and joined this fine place after seeing the amount of qualitiy help you fellers assist others with.

Now my question is this, I just bought a second/third/maybe fourth hand Tube amp, as an addition to all my others. The feller I bought it from off of craigslist said (as they always seem to do) that he had just retubed this amp with mesa boogie 6l6 power tubes, (which actually I doubt he did in truth).
When the amp is on in standby it is silent, when i turn the standby switch on to play the clean channel has a noticeable hum, although it's not deafening, it is something that can be heard, now when I switch to the second channel that hum decreases in volume quite a bit. The amp plays by my standards really well and is loud, I dont turn it up past three actually and it's biting my head off. Can anyone clue me in to what I may need to do to silence this hum somewhat? or is it just tube amp idiosyncrancies?
Also I have no problem taking this to my tech and having the entire thing retubed both power and all 5 of the (I assume 12ax7's) other's.
Any advise would be greatly appreciated, I have no knowledge of these things and appreciate any/all replies! Thanks Greg

[pecorporation]

If the volume doesn't affect the hum level, then it's likely the biasing is off. Many tube amp owners swap output tubes and never adjust the bias to match the new tubes. I'd recommend having your tech check the bias first, should be a quick cheap fix.

[rythymroach]

many thanks

Thank you, I just stopped playing it a few moments ago, is there any chance this thing could be self biasing? because I have noticed the hum now seems to be a lot less noticeable. or am I just getting used to it? LOL
I'll be sure to have my tech take a peek at it asap though just to be on the safe side!! I try to maintain all my equipment to the best of my ability. I sincerely appreciate your time and assitance in this matter!!

[pecorporation]

YW, let me know how it goes.

[rythymroach]

one more question

Um i turned the volume all the way up on the clean channel and the hum did not really increase but there was a scratchy hissing that was really evident? is there anything else you could advise me or the tech to check?? when i turned the master volume on the second channel this hissing sound was also on it, please realize i'll never have them cranked wide open like that in any situation, but I'd like to think there is something that can be corrected to keep that from happening. thanks again for your help!

[pecorporation]

The scratchy hissing is more than likely a noisy preamp tube or sometimes dirty tube socket. Lightly tapping each tube with a plastic stick (or pen) may shed light on the problematic tube. If you have extra preamp tubes, swap them out one at a time to see if that narrows the cause down.

[rythymroach]

Thanks again, will do!! I have noticed in the past a lot of times guys wil change the power tubes but never change the preamp tubes lol!! it would not suprise me if these tubes are original in this amp lol!

[Prairie Dawg]

Thanks again, will do!! I have noticed in the past a lot of times guys wil change the power tubes but never change the preamp tubes lol!! it would not suprise me if these tubes are original in this amp lol!

I've got a TV6212 combo that is similar and has similar issues-lot of background noise and hiss, but mondo power. The first preamp tube is very sensitive. Also there may be a socket for a lone 12AU7 so make sure the right preamp tubes are installed in the right sockets.

I've always thought that Crate 'automatic hands off biasing' was a crock but I'm willing to suspend my disbelief. I'll have to see what it really does with a bias checker.

Of you figure out what works for you let me know.

[rythymroach]

Appreciate both you fellers replies. I spoke with our bands tech tonight on the phone, he is doing some research on this and I will send the amp in sometime in the next month or so for him to go through it and check all the solder joints, etc while he is replacing all the preamp tubes. I did open it up and must say the feller who sold it to me did in fact put some mesa boogie 6l6 tubes in it, so I have to reiterate my assumption that he just said he had replaced the power tubes as a selling tactic. I'm gonna use it in rehearsal a couple times before I send it in, because the small hum aside and the hissing when I maxed out the volumes on both channels (without a guitar attached) this amp has some really good attributes with it's tone. So I really hope that these few problems I mentioned are correctible, I already love this amp and have only owned it for 2 days now. I appreciate the heads up ont the 12au7 tube as opposed to just all 12ax7's in it. I passed on the comments and my concerns to my tech, and wil just cross my fingers and hope this is as easily fixed as he and you feller's have mentioned. Again many thanks for your help, I'm just a guitar picker and songwriter, I have never been to much in the technical department, and have to leave all that stuff to guys like yall!!

[Prairie Dawg]

The other thing i forgot to mention is that if you do not have a schematic it's easy enough to get one by contacting Loud Technologies customer service and giving them the serial number of the amp and attesting you're the owner.

Best of luck. I really like the power mine delivers but it's been through a few owners who just couldn't deal with the background noise level. I'm cooking up an order for Mouser so I'll probably go ahead and replace all the electrolytics as a first step, and shield the inputs.

[rythymroach]

Got the schematics via email earlier

Hey Pdawg, I got the shcematics from Loud a short while ago.
One question I have for anyone to field is this.
a document was attached to the schematics that said " this amp is cathode biased even though the tubes are 6 l 6's"

what does that mean?? (I guess by my questions you guys already realize I'm, like a dork when it comes to this stuff)

I dont know how or why websites like this work the way they do, but I for one sure appreciate the fact that it exists and you folks are willing to spend moments of your valuable time helping some of us out! many thanks and much appreciated!!