200s amp, help!

[Soundmasterg]

That should be 65% of the max dissipation for the KT88, which is 42 watts. So that works out to .65 times 42 = 27.3 watts. So you should measure the plate voltage, measure the cathode current, and multiply them together to see where it shakes out in relation to that. If you readjust the bias, the plate voltage will have changed, and so will the cathode current, so you will have to measure both again and multiply again to get the wattage. Do you have a way to measure the cathode current?

[ian]

I have a bias tool (the kind that plugs inbetween the socket and the tube) and my ohm/amp meter.  I'm planning on messin with it, one of these days. After some minor repairs the amp is sounding great, I had a tech work on it and someone dropped it, bending up a tranformer and scratching the face plate, It also appears they swapped out my knobs, I have pictures to prove it. NBS electronics is, not so good.  I should have listened to your suggestion of taking it to Mission Electronics.  It's just made me study up and remember some amp basics to do it myself, what i can do anyway.  I think the previous tech has it touch under biased. But i have some pretty mismatched tubes in now. Your info will help me get it figured out! (w=vXc, I remember this from Electronics school 16 years ago!)
Hey, you wouldn't happen to know what the safe operating voltage level for the sovtek 6l6wxt+ is? I can't seem to find any real testing out there.  One web site suggested 680 volts. sovtek.com hasen't gotten back to me yet, i'm sure they will. I want to use them in my music man HD 150 that runs em at 700v. thanks again, -ian

[Soundmasterg]

Sovtek.com is the same as New Sensor, which is the company that owns the Sovtek, Electro-Harmonix, Tung-Sol, Mullard, and other brand names. Their owner is Mike Matthews, who started the EH company back in the late 60's and made (and still makes) all the cool EH pedals. He owns the factory in Russia that makes the Sovtek and EH and (new) Tung-Sol tubes. They are not very forthcoming about sharing the tube data on their products and never have been. That said, the Sovtek 5881/6L6WXT is a very strong tube and is well made and reliable. It is not a true 6L6GC or 5881 type, and is actually some Russian designation that is close but not quite the same thing. It works fine in 6L6 circuits, but sounds kind of bland compared to some other types. I think your Musicman may run the plates close to 700 v but it probably runs the screens down around 300v or so, and that particular Sovtek tube is a strong one so it would probably handle it. This guy at this site I listed built an amp for himself that uses the Sovtek 5881 and he runs them at very high voltages with no problems, so you should be ok. Take a look at his site and read about his amp...pretty interesting.

http://www.ken-gilbert.com/tubestuff.html

You should be ok with your bias tool...just be careful when you measure the plate voltage in the amp. When the bias is set correctly, the plate voltage will probably be somewhere around 560v, and that is enough to kill you. Exercise caution. Sorry to hear the place you took your amp was incompetent and stole things from you. You should call them on it so they can either pay you for damages or show their true colors. At least then you might be able to file charges and stop them from doing the same to someone else.

[ian]

ya, they showed true colors...BROWN... I emailed my pictures to them but it's my word against theres, funny, 'NBS', they say stands for NO BULLSHIT SERVICE, which clearly has turned out to but the opposite.  Ya every time I look at the knobs I think about small claims......Any way, I'll put my Sovs back into my MUSICMAN. 
 
One more thing about my 200s, I let my chick friend practice guitar with it and set everything on 10, with both boost switches on into a fender 15. She uses an old les paul copy with a crappy dan electro pedal.  I just wanted to see it be the workhorse it is. After that, I beat it with bass for a couple practises, into my sunn 18 and inspected the insides. I replaced the 680 ohm resistor, which started sweating and once it was out it, the old one measured 750 ohms. Replacing that bad one cleaned up my amp allot, as well as the cap of the prevous repair. It dosen't distort like it used to.  I also was thinking about replacing the rest of the carbon resistors in my 200s, Any reason I shouldn't?

[Soundmasterg]

You could replace them. They probably have drifted like the 680 ohm did. But keep in mind that most resistors today don't have long leads like they used to and will not reach across the phase inverter socket area unless you use a higher wattage resistor than what is in there. I had to use 2 watt NTE metal films in mine. The metal films that Ted Weber sells (www.tedweber.com) would be long enough in a 1 watt version though. They weren't available when I rebuilt mine. You won't find any carbon comps or carbon films with long enough leads to fit in there, and metal films are quieter anyway. The stock coupling caps in the amp aren't very good sounding or good quality ones, and you could change to Orange Drop 225P, 716P or PS series, or Mallory 150, or any other good quality modern plastic cap and they will improve the sound more than replacing the old resistors will. Its a bit of work though.

[ian]

got it. i have a pic of the usuall spot to park the caps but i dont know how to post it here. Sunn is good!
this is a link that will get you to a myspace pic, i think it will, anyway thanks for all the help!!
-ian
http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=70995905&imageID=1489987861

[Soundmasterg]

The pic looks good. You're welcome....glad to hear its working well.

[made by hand]

now..if you could only find a 200s cab to hook up to your 200s head....you will die and go to musical heaven...those two componets were made for each other.....i hope you read what just said.....the cab made the amp sound like it was ten feet tall....start looking.....throw that fender cab away......