70 solarus head with a problem or two

[Anonymous]

Hey all,
      I'm new here and would like to say that THIS SITE IS AMAZING!!!  

but to the question:

I recently found a Solarus Head amongst my father's old gear (of which he has a lot).  I never knew he had it or I would have been after it sooner. There's nothing like that vintage Sunn sound.
The fuse goes as soon as I turn it off Standby. I've tried it without the tubes in but it still blows.  Any suggestion for what to check and how to do it?
A repair shop would be ideal, I know, but I just finished college today (for good, woohoo!)and I'm as broke as it's humanly possible to be. I am semi-learned in the field of electronics (like how not to get killed or blow something up:x) and I figure if I'm gonna use it, I might as well know how it works and how to fix it(just the way I am).
Also, the preamp tube is a 12dw7, which I think was only used in Ampegs.  He bought it new and has never changed the tubes(so he says). Should I be concerned about that? I don't think the wiring is compatible for a 12dw7 and a 12ax7 is it?  The driver tubes are 6550's, it has a gz34 rectifier tube, a 12au7 for the reverb, and a 6an8.
Any help would be fantastic.  
Thanks all.
 
Mike J.

[Greg Z]

The 12dw7 is similar to the 12ax7 'cept
one section has lower gain. (twin triode)
 should work ok,probably put in to increase headroom. the 6an8a is the driver,the 6550's output tubes.
Fuse blows coming off standby. one of three
possibly things.(most likely)
1. Shorted power supply caps
2. shorted power tubes
3. low or no bias.

Pull the power tubes 6550's if fuse blows
it's #1
If fuse doesn't its #2 or #3

[sunnamps]

your best bet would to go to a site http://www.classamp.com.
the guy is a really good amp tech he might be able to tell you what your problem is.
i have the exact same head 1970 sunn solarus they have great tone.

[sunngri-la]

the fuse is still blowing without the 6550's and still blows without any of the tubes in.  Could it be the power transformer?(got a little rust on it) and how could I check to see if it were that or the filter caps?
Thanks,
mj

[Greg Z]

Caps

[sunngri-la]

so i've done a little work and now the fuse doesn't blow coming off Standby when there is no gz34 in, however, when I put it back in the fuse blew...now I'm out of 3amp fuses   anyway, could it be anything other than the caps? and does anyone have suggestions for acceptable replacements for the filter caps?--since i'm gonna change them anyway.
once again,
eternally grateful,
mike

[JoeArthur]

Just stay as close to the stock values as you can... you can go over-voltage ratings but I wouldn't go over capacitance ratings on a tube amp.

BTW... having no rectifier tube in the amp kinda makes the standby switch redundant - your B+ supply is still open to the caps.

Your problem is definitely caps!

[sunngri-la]

Thanks, once again.  Good information is as good as gold.  Any suggestions for where to get some caps?  Retailers and such that is.
Sorry that I have a million questions.  I'm just quite passionate about wanting this amp to work.

[JoeArthur]

http://store.yahoo.com/triodeel/elcap300to60.html would be a good place to start looking.  

[sunngri-la]

OK, much appreciation thus far.  I've found  all the replacements except for the 20-20-20-30uf 525v can.  I know it's hard to get and I don't have any problems with using four seperate caps to replace it but I'm not quite sure about what to use.  Now the question:  Is 500v enough, or should I get the (much) more expensive and probably much too large (to fit four of them in there) 600v cap? I'm not sure what the dc current is at that particular stage. Also, my rectifier tube gets hot as hell (hot enough to burn me) and gets this crazy blue-lightning thing inside when the fuse blows.  Is that normal?  
Once again, many thanks.
mike

[Bill Matthews]

Forget Triode... go to http://www.fliptops.com.  They have a 40/40/40 @ 525VDC.  This will allow you to keep the can capacitor look and only have to bury one axial cap under the chassis.  Good luck!!

[JoeArthur]

Sunngri-la... you have a short through the caps on the secondary side of the transformer.  The rectifier tube and the standby switch are "in series" to the short.  Taking either one or the other "out" of the circuit prevents the short.

Your saving grace is the fuse.  You are lucky that it blows before excessive current draw takes out the transformer... if you are really lucky, maybe the rectifier tube will go belly up before the transformer.  

Tubes are supposed to be hot.  That is how they work, that is part of their nature.  Hottness of a tube should not be judged by your hand unless you are fond of burns.  Tubes operating under normal conditions can burn you quite quickly and easily.  Excessive current draw through the rectifier can make the plates glow red hot, assuming the fuse doesn't rescue them first.

Until the caps are replaced and the short eliminated, there is no "normal" for the amp.  Excessive current draw is not a normal situation.  Whatever happens in a non-normal situation cannot have a normal aspect to it.  I don't know what your "crazy blue lightning thing" is... but I wouldn't worry about it now.

Unless your intention is to destroy it, I suggest that you stop playing the roulette game with your amp.  

[sunngri-la]

Okay,
     new filter caps.  We're up and running.  I only played with it for about 5 minutes (hard to resist that sweet sweet tube Sunn sound).  Suggestions for things to check out before I play some more? How should I go about biasing and the reverb is doing that "old-worn-out-Sunn-reverb crackly poppy thingy".  I just want to be sure that nothing is going to get damaged by my relentless thirst to play with this bad-boy.  Thanks for everything, guys.  I couldn't have gotten this far without your help.  
Eternally grateful,
mike

[JoeArthur]

Hey!!  Progress!!  That's great!

Let's see... I gave my biasing recommedations somewhere else... yep, here it is, and I still stand by them.
 http://www.sunnamplifiers.com/phpBB/viewtopic.php?topic=927&forum=1

If your amp hasn't blown itself up in five minutes set the bias.

The quickest way to get an indicator on the general health of an amp, is to measure all of the B+ voltages against what is listed on the schematic.  But be careful as this can kill you.  You don't need an exact match as there will be some tolerance variations but it should be less than 5%.  Your are really looking for unusually high or low readings.

As for the reverb, it sounds like a dirty control.  Sunn uses a transistor for the reverb recovery and runs DC through the control that also acts as the collector load resistor - not one of their best designs.  

Clean the control first with some control/contact/tuner cleaner and run it back and forth several times.  Should take care of the problem.  If it doesn't, then the control probably needs replacement.