Problem with my Sunn 2000S

[Math_HC]

I bought recently a 1972 Sunn 2000S and I played for about 45 minutes cranked up and it started to do weird sounds. (wind and pop and cracking) I touch both transformer, One was normal temperature and the other was Hot (like putting my hand more then 10 seconds and it will burn a lot)

I Started playing with the head for about 30 seconds and the sound just drop for about 70-80% and never got higher then that since.

I know the tubes are old (Black/silver stain on the tubes)

Could someone tell me what is going on. Thank you very much!

[Amp Kat]

I would recommend changing those power tubes out would be a good place to start as those symptoms sound like bad tubes. There is also either a 7199 or 6AN8 which is a Pentode/triode in one tube and it could also be the problem. The replacements you'll find for those are usually Sovteks which are the cheapest type and can be a little noisier than say a NOS tube. The Sovteks are about $12 and the NOS can go anywhere from $30 up but may be worth the expense if you plan on keeping it for awhile. Try the two power tubes first though.

[mykey]

Could someone tell me what is going on. Thank you very much![/QUOTE]

burned up screen grid resistors on output tube socket, or
burned sockets on output tubes
have a tech check all this out before installing new tubes.
re-bias new tubes before using amp.
caution high voltage inside.

[Iplayloud]

Would it be possible to try the amp only with the inside pair of power tubes, and then with the outside pair, just to see if it's the power tubes or screen grid resistor before spending the money on this. Thanks (I'm a friend of the original poster)

[Enzo]

Well, you will have to determine if the problem is the tubes, or damage they did to the amp, or both, or none of the above. Might not be as simple as removong half the tubes.

[mykey]

Would it be possible to try the amp only with the inside pair of power tubes, and then with the outside pair, just to see if it's the power tubes or screen grid resistor before spending the money on this. Thanks (I'm a friend of the original poster)

i would take the amp out of the box and have a look at the tube sockets, see if
anything is burned first. look for charcoaled resistors. if it all looks ok then
yes you can try it with inside pair and outside pair.
if it is a bad power tube you can swap them around till you find the good pair.
look for burn marks on the sockets and if its burned, don't play the amp until all that stuff is replaced.
and yes that's right i have seen the 7199 die and cause this type of volume drop out, that is positively correct. i think you can get a new 7199 these days, but not as good as the old ones were.
that would not be a bad idea to change all the tubes, but don't do that until you make sure nothing inside has flamed. after all it's an old amp and it won't hurt to inspect the inside.
SAFETY DISCLAIMER:
and as usual, remember the amp stores a charge when its unplugged. it can shock you (that's how my hair got curled) this is no shit. ( can i say shit in this newsgroup?) it can really give you a jolt. if it does need repair, and you do not know how to discharge the power supply, you may seek a person who does know how. if you have never felt 500 volts before, you won't forget it quickly, and that ain't no lie.

[mykey]

Well, you will have to determine if the problem is the tubes, or damage they did to the amp, or both, or none of the above. Might not be as simple as removong half the tubes.

yes he's right. thats why i would encourage you to look inside first.