time to re tube? - my amps doing strange things.

oooo · #1 01-13-2001, 03:46 PM

I play a VHT pitbull Classic. *The other night during a gig, I started loosing "gain". *It started dropping in volume and then it'd jump back up. *I switched to a pre-amp I keep with me (thank god) and ran it through the clean channel. *It worked great. *I have noticed this several times before but it wasn't as prominant... I would hear it and think I was hearing things. *Only this night it was REALLY noticable! I get it home and tried everything to make it do it again, but nope! seems to work fine. *I've gigged with it several times since, always using it on clean and using my pre-amp (I'm kinda gun shy), and the power section works fine, but I really miss my amp. *Does this sound like a pre-amp tube problem? *If so I'll stick new tubes in it today! *Or does this sound more serious? *I've never had a 12ax7 go out on me before, but I heard they will pop and make noises... none of that here just a sudden drop in gain (by this I mean the amp was suddenly less distorted) and volume that lasted a few seconds then back to normal for a few then back down...etc. *Thanks for any info.

chilln2music · #2 01-13-2001, 05:23 PM

i cant really help you out but i did have a real similar problem...it was my power amp though that was dopping in volume then going back to normal...i could never figure out what it was...it was brand new...tubes, fuse...everything was good...i even replaced the new tubes with brand new ones...i wound up going back to the store and getting another power amp that worked fine...but just a few weeks ago i had the drop in volume...i dont know whats going on...anyone know whats up?

Doink · #3 01-13-2001, 06:43 PM

Sounds to me like it's a preamp tube. Call up some amp shops, I'm sure they can get you a good 12AX7 for under $15. RCA, Svetlana, Sylvania, GE, Amperex, JJ, Tesla, Telefunken and Westing House are good brands. Avoid Groove Tubes, Mesa, Fender, and Sovtek. Fender tubes are sovteks with the fender name on them. Mesa uses cheap Chinese made tubes. Groove Tubes just throws their name on tubes from various manufacturers.

It could also be a bad connection somewhere. Either way, it's good to have some spare tubes on hand. If the problem persists after the new tube is in, I can maybe help you track down the bad connection.

davenit · #4 01-13-2001, 07:44 PM

Doink, if you can find Telefunken (NOS) for under 15 a tube I will take 100. The cheapest I have found is 45 from anyone reputable.

I have 3 sets sitting around. They took my 300 dollar Hafler T3 and made it scream. The greatest investment in tone I have ever made.

0000, check out Telefunkens, they are expensive but they have a life about 10 times longer than the newer tubes. Some have lasted 100,000 hours. Also look into military 12ax7s. RCA, Sylvania and GE has them. Do some searching around the web. There is a lot of info on Military New Old Stock. Some of them are listed as JAN 12ax7s. JAN is for Joint Army Navy. These tubes were used in Radar arrays, radio transmitters and teletype machines.

Telefunkens are my favorites, and everybody elses sorry to say. 12ax7 ecc83 - Make sure they are smooth plate and not ribbed. I hate mentioning it but look on some of the online auction places there are alot on there. Just make sure the person you are buying from is in the tube business. There is a lot of fake stuff out there...

Dave

oooo · #5 01-13-2001, 08:31 PM

thanks for the info... I found a web site http://www.triodeel.com/tubes.htm
they seem to be VERY reasonable. *any body know anything about them? *What do you guys make of this.
(this is a copied section from there web site)

"Tesla/JJ 12AX7/ECC83 These are near exact copies of exotic and rare Telefunken ECC803s.( not the flat-plate ECC83..the really rare frame-grid style which cost $100's of dollars if you can find any).
Get close to real Telefunken sound at a fraction of NOS prices! 7.50 each"

My amp came with Tesla's from VHT (its an older model) and I just love the tone... are Teslas reliable?
I really appreciate the info so far.

davenit · #6 01-13-2001, 10:09 PM

http://www.thetubestore.com/tesla12ax7.html

On their site:

"From our review of this tube (Tesla): "This tube sports a different plate design than found in most 12AX7's. When you look at them you can't help but think that they must be rugged and good for the musician on the road. The compact plate structure does nothing to dampen their sound or dynamic response. I find them to be well balanced. While not as harmonically rich as others I tested, they do provide high gain without the usual noise and microphonic problems you would expect. This is great sound for your dollar. If you're using a combo amp and find the Philips a little rich sounding, the Tesla / JJ ECC83 may be your solution."

On other sites I have read that EI tubes are a good replica of the Telefunken. Two problems. They have quality issues, one might be good, one might be bad. The second is that there not made anymore, or there is a ban on exporting them....

Dave