Sunn 200s - multicap can replaced - help needed!

[Tbass]

Thanks to All for the input on the Sunn 200s multicap can etc!  Replaced the can with one from Dynaco rated at 550-600v and 30/20/20/20 mf and the two associated resistors with 33k-1w & 15k-2w metal oxide; and replaced the 2 bias 150v-50mf electrolytics.  Also installed a 3 prong power cord and disconnected the polarity switch and wall power input on back.  
    Originally, this amps problem was boiled down to: blew fuse when powered up on standby & no tubes in place.  Power transformer was suspected and pulled ( though this PT never smoked, stunk, or overheated ) , but couldn't find a problem with it so it went back in. The cap replacement/etc needed done anyway, but now the amp still has the same problem!?!? Blows fuse within 2 seconds of switching power on while on standby with no tubes installed.  Being without my Sunn has become very frustrating since I'm forced to gig with an old solidstate carvin pb900.   Since the same basic problem persists, and the power transformer is the main part in the circuit before the standby switch is closed, I think I have to buy the PT.  Does anyone have any other ideas...  possibilities I could check?  Thanks.

[Soundmasterg]

There is either a wiring problem in the amp, or most likely, the power transformer is bad. The only other check you can make would be to disconnect all of the secondary leads from the power transformer, but leave the primary leads hooked up. Make sure none of the secondary leads are touching anything, or touching each other, and then try to power up the amp again. If the fuse still blows with absolutely nothing connected to the secondaries, then the power transformer is bad for sure.

Greg

[Tbass]

  A wiring problem was suspected in the primary - fuse, polarity sw, power sw, wall power outlet - circuit.  At one point a 3-prong power cord was installed (w- sw, bk- fuse, g- gnd).  We wondered if the polarity sw could cause a short, so the polarity sw and wall power outlet were removed from the circuit.  Also suspect is the .05mf 600v cap from polarity sw to gnd, originally always in the circuit; if damaged or missing could it take out the fuse? Also the IN2070 20ma diode (couldn't source it - installed IN4007) - first in the bias circuit on the red-bk wire.  If damaged, or installed backward could it blow fuses?
    What makes this problem seem so -twilight zone- odd to me is this amp stopped working 5 yrs ago.  No smoke or stink, just blew the fuse every time I turned it on. Couldn't deal with it at the time, so it went in the closet.  Last year I got it out, cleaned it up, and put the tubes back in.  Powered up ok and played thru it for more than an hour - It sounded great!  So I took it to a friends house, put it on standby while getting  ready to play and the fuse popped in about 20 min. - on standby.  It hasn't worked since.
    Greg,  the checks you outlined to isolate the PT make sense.  I'll post results, Thanks!

[Soundmasterg]

  A wiring problem was suspected in the primary - fuse, polarity sw, power sw, wall power outlet - circuit.  At one point a 3-prong power cord was installed (w- sw, bk- fuse, g- gnd).  We wondered if the polarity sw could cause a short, so the polarity sw and wall power outlet were removed from the circuit.  Also suspect is the .05mf 600v cap from polarity sw to gnd, originally always in the circuit; if damaged or missing could it take out the fuse? Also the IN2070 20ma diode (couldn't source it - installed IN4007) - first in the bias circuit on the red-bk wire.  If damaged, or installed backward could it blow fuses?
    What makes this problem seem so -twilight zone- odd to me is this amp stopped working 5 yrs ago.  No smoke or stink, just blew the fuse every time I turned it on. Couldn't deal with it at the time, so it went in the closet.  Last year I got it out, cleaned it up, and put the tubes back in.  Powered up ok and played thru it for more than an hour - It sounded great!  So I took it to a friends house, put it on standby while getting  ready to play and the fuse popped in about 20 min. - on standby.  It hasn't worked since.
    Greg,  the checks you outlined to isolate the PT make sense.  I'll post results, Thanks!

The .05uf 600v cap from polarity switch to ground is also known as the death cap and should be entirely removed from the amp. you don't need the polarity switch any more with the 3 prong power cord. A 1N4007 is just fine in the bias circuit, but it should be installed backwards from the normal setup for a power amp in that location. Since the bias voltage needs to be negative, the diode should be installed the reverse of the way they are installed in the other areas of the power supply....basically install it the same direction the 1N2070 was installed. A backwards diode there could blow fuses because the tubes would not get any bias and they would over heat and burn out, but you would probably have other things happening before that happened....the e-caps in the bias circuit would blow for instance, since they would now be hooked up backwards as compared to the output of the diode.

The failure mode that you describe is strange, but you'll figure it out if you approach it logically and take your time. Make sure you have the primaries hooked up correctly, and if the secondaries are disconnected and you test it and it still blows the fuse, well since nothing is connected except the power transformer then that is your problem. The Sunn power transformers wereoriginally Dynacos, and later Schumachers, and they were both on the ragged edge as far as the current they had to supply, so over time a lot of them have failed because there was no leeway before they would blow. Replacement ones are available from Triode Electronics that are higher rated than the originals so they work better. Of course if it isn't bad, then you don't need to replace it, so that would be preferred. Do the tests and see where you're at.

Greg

[rasaban]

SoundmasterG

      What's upper?  Its your buddy, Ernie .... well I think I was you bud, last time I checked. How are you doing?
    Hope school is going well....... Got that Chassis from watts, its a little big but I think it will work, Might stick a beer cooler in there. Thinking I might get a new larger turret board. and make it look real nice........ etc
   Talk to ya later ,I'll give a call this weekend or so.  This seems like a nice Forum.....  

ErnDog
  BTW I hope this is soundmasterg from Portland..... that I'm making contact with here. it not pardon the intrusion.... 

[Soundmasterg]

SoundmasterG

      What's upper?  Its your buddy, Ernie .... well I think I was you bud, last time I checked. How are you doing?
    Hope school is going well....... Got that Chassis from watts, its a little big but I think it will work, Might stick a beer cooler in there. Thinking I might get a new larger turret board. and make it look real nice........ etc
   Talk to ya later ,I'll give a call this weekend or so.  This seems like a nice Forum.....  

ErnDog
  BTW I hope this is soundmasterg from Portland..... that I'm making contact with here. it not pardon the intrusion.... 

Hi Ernie,

Yah its me. Glad you got your parts. This is a cool forum. It used to be elsewhere and I convinced TBoy (site owner) to pick up the Sunn area from the former site owner, and glad I did because it's found a permanent home.

You can PM me on here if you want, or send messages like this in the forum threads, but email is always best if you want to get a hold of me as I don't often check all the threads. I plan to be at the jam this next week now that finals are done.

Greg

[rasaban]

   Very Cool Greg
       It was nice reading that article on Conrad,    Oh yeah I'll be contacting you by E-mail, Just happen to be surfing and found the forum. Nice stuff here. I think I'll be drilling  on the chassis this weekend.  Yeah I'll at the jam next week.

     Nice forum Here
   Rasaban

[Bim1959]

did you ever find the problem with your amp? If not I have a few suggestions.

First thing is to disconnect the outputs of the transformer and isolate them. Then turn the amp on and see if the problem still exists. If it does then it's definitely the transformer. If not, then I'd replace the multisection can with another one. I hope you took pictures of how everything was attached to begin with so you can trace everything back and make sure you didnt cross something up.

As I was taught years ago, to test the power transformer on a tube amp, unplug ALL the tubes and turn the amp on. If it blows the fuse then the power transformer is suspect.

Another thing to do is unsolder all the leads from the transformer and use a VOM to check continuity.