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Sunn Musical Equipment => Q & A => Topic started by: cosmic erosion on January 31, 2018, 05:55:24 pm

Title: '69 sunn solarus issues (warning: long post)
Post by: cosmic erosion on January 31, 2018, 05:55:24 pm
Hello and good day! First, this post will take some time to read as I will give as much info as possible.

So, to start I have a '69 Sunn Solarus (2xel34) that I adore. I've owned a lot of sunns, ampegs, vintage fenders, etc etc. Never have I had this problem. So 2 shows ago, the handle decided to give out on the head and it fell maybe mid calf (i'm 5'8") and hit the ground as I picked it up from the ground. So not far and not too quick. Amp fired up afterwards and I thought nothing of it. 

A week later, it starts making this insane voltage sound (almost like the proton packs in the first ghostbusters movie), almost like a speaker is bad, and cuts out a bit soundwise. It over takes at least 75% of the sound. It starts right away when the amp is fired up. I usually run it at 6 on the volume into a sunn 4x12 loaded with wgs vet30s and et65s, 8 ohm cab. I assumed I had a voice coil rub or something like that, so I call my tech. I also should state that I tested this head into my 1x15 bass cab (8 ohm) and my traynor head into my sunn 4x12. No issues either way.

First, let me say that my tech has worked on numerous amps of mine, buddies of mine, and people I've sent to him. Been a tech forever, etc etc. I explained to him what happened. He has it a few days and says the 7199 tube needs replaced and he cleaned up some pots inside. Replace the 7199 with a nos ge. 

Take the amp to practice, it's better but still not right. We have a show in like 2 days so I just run the amp as is until I can take it back over. I explain a bit better what it's doing and he has me bring my entire rig over to troubleshoot. This is where, if you're still reading, it really starts to make our brains hurt. 

So I plug everything in and show him the sound. So again back to testing to see if it does it on other cabs and/or other heads into my cab. So 2 different heads into my 4x12. No crazy sound. Sounds just the way they should, even dimed they are fine. Ok. So my solarus into his 16ohm 1x12 cab, no crazy sound, amp and cab sound great. I should mention I ran into the 16 ohm cab from the 16 ohm tap on the head. Next up is the solarus into his 2x12, 8 ohm. No issues there. ok......

So back to the solarus into my sunn 4x12. Bam! There's the funky sound again. Which would lead me to believe there is a short somewhere in the cab or something funky with a speaker. I've blown alot of speakers, would not surprise me. Well, maybe in this case since the sunn before this into the cab was a 4xkt88 coliesum pa which I ran at 9. Anyway, cab measures just fine ohm wise at an even 7 ohms. ok..... so I leave the head with him and await his call. 

He hardwires the output tranny taps to the head, explained to me why. Cleaned jacks, replaced the amperex 12ax7 with a jj, reconnects the negative feedback loop in the amp, and calls me back. Says he thinks it's the 8 ohm tap on the head is going out. Explains that the wiring in the transformer ages and will break down and maybe the fall caused a short in it. Makes sense to me, but I know it's a rarity that transformers go out. So I head back over and we fire everything back up. We get the volume to 7 before it makes the bad sound. Which is doable since I run it at 6 usually. We disconnect it all and hook up all the heads to my 4x12 and and the solarus to his cabs to test. It still only does it with my head and cab. He lets me know that he thinks it's the output transformer and to do some soul searching if I want to replace that or move on. I didn't pay much for the amp from a buddy, who bought it nonworking and this tech brought it back to life. 

Fast forward to yesterday at practice. Head fires up, no sign of sound. Drummer and I are baffled. I dime the solarus, no wacky sound. Again, what?!? We practice for maybe 2 hours before it starts to do the sound, barely this time tho at volume level 6. I put it down to 5 on the volume, no crazy sound. Swapped heads at our spot (sovtek mig, my traynor) and try other cabs. You've read the above, same story on that. No wackiness.

So, long story short, here's some thoughts on my end. 

1.) If a transformer is bad, why wouldn't it make this sound in all cabs and at both 8 and 16 ohms? He did crack open the transformer and tried to clean it out a bit and see. He said the 16 ohm tap looked brand new, could I just respeaker my 4x12 to be 16 ohm and be fine? As it only does it on the 8 ohm tap. Do the windings for the different ohms affect each other inside? Say if the 8 ohm tap is bad and goes out, would the 16 ohm tap (and unused 4 ohm tap) be fine and run at full power?

2.) Bad rectifier tube? Maybe it's got a small leak in it and once it warms up, starts to misbehave? Or bad caps? It takes a 4 stage cap he explained. It tested fine, but again, who knows? 

3.) Or anything that jumps out at people? I've had caps, speakers, tubes, etc etc go out, this sound is driving me bonkers.

I just kinda want a 2nd opinion on what it could be. I paid very little for the amp and as I started amp shopping this past week, realized that I'd spend more buying another than just fixing this one. I mean, if a pickup in your guitar went out, you wouldn't just buy a new guitar would you? is kinda where I'm leaning. I would just buy another solarus anyway. The combo of solarus and my jazzmaster is the tone I've been hunting for, and we all know how expensive and time consuming trying to nail THAT sound is. I found it, now how do I fix it?

Title: Re: '69 sunn solarus issues (warning: long post)
Post by: _peter on February 01, 2018, 07:55:51 am

if the problem depends on the cab but the cab itself is fine, I would suggest to disconnect the negative feedback wire for testing purposes.

It is coming from the output transformers secondary and sends a part of the output signal back into the preamp.

If the weird sound disappears, it might be an oscillation that only occurs when the amp is paired with the complex impedance response of your cab.

So that may help to isolate the bug.

Title: Re: '69 sunn solarus issues (warning: long post)
Post by: Isaac on February 01, 2018, 10:29:03 am
No, you can't rewire an 8 ohm 4x12" for 16 ohms. 2, 8 and 32 are your only choices.

You could try using the 16 ohm jack. Tube amps are very forgiving that way.
Title: Re: '69 sunn solarus issues (warning: long post)
Post by: cosmic erosion on February 01, 2018, 12:13:27 pm
Thanks for the replies guys. Much appreciated. So my thoughts:

1.) I know the 8 ohm cab can only run at 8, or if rewired, the ohms Isaac said. My question is, if I respeaker it all to 16 ohm speakers and make the cab 16 ohms and run out of the 16 ohm tap on the head, will this noise continue to be a problem and cascade over into the 16 ohm tap down the line? A hard what if, but i'm trying to understand the problem that's making the sound and how to fix it. Obviously, respeakering the cab or buying a new cab would be my easiest solution (if that is the solution).

2.) This problem just started within the last 3 weeks or so. I've ran this head and cab combo for a little over 4 years together (I've had the cab with said speakers now almost 10 years, used it with a studio pa, coliseum pa, sceptre, 2 v4s, a beta bass, and 2 traynor yba1s) with no issues. The sound was also worse with the negative feedback wire disconnected (it originally was) and just reconnected the last time my tech had it.
Title: Re: '69 sunn solarus issues (warning: long post)
Post by: Isaac on February 02, 2018, 09:56:33 am
1.) Not knowing what is causing the problem, I have no opinion on whether or not it will cascade over to the 16 ohm winding.

2.) I have a 200S with a switch to cut out the feedback. I agree, the sound is worse.
Title: Re: '69 sunn solarus issues (warning: long post)
Post by: Soundmasterg on February 02, 2018, 12:12:00 pm
Does the amp/cabinet combination make the noise if the amp head is NOT on the cabinet or only when it is on the top of the speaker cabinet? It could be a vibration induced noise. I repaired one years ago that would make a strange noise like that but only when it was on top of the cabinet and vibrating. It was a loose/bad solder joint in the PCB on that amp for a cap. It seems really strange to me that the tech is saying the problem is with one of the taps...OT's very rarely fail like that. I could see thinking it if the amp was in a barn exposed to moisture and rats or something but I think it is more likely something got knocked loose in the fall such as a solder joint or perhaps a part that looks ok on the outside is bad now and you can't find it because it isn't obvious.

Title: Re: '69 sunn solarus issues (warning: long post)
Post by: cosmic erosion on February 02, 2018, 01:39:07 pm
Greg, i appreciate the well thought out answer. I haven't tested the head off the cab. Such an obvious thing yet i didn't think of that!
Title: Re: '69 sunn solarus issues (warning: long post)
Post by: GrannyGremlin on February 05, 2018, 11:03:16 am
Is the weird noise all the time (e.g. when you're not playing) or only when you strum a note?

Title: Re: '69 sunn solarus issues (warning: long post)
Post by: cosmic erosion on February 05, 2018, 01:58:32 pm
Only when notes are being played. Ordered all new tubes and caps. Just waiting on them to arrive and when they're installed, go through everything that's been suggested on this site and the gear page.
Title: Re: '69 sunn solarus issues (warning: long post)
Post by: GrannyGremlin on February 06, 2018, 01:03:39 pm
If it's only when you hit a note then I don't think it's tubes or caps.  The issue is probably incorrect (insufficient) voltage to one or more of the tubes. Similar thing happenned to me and my tech also missed it, I don't recall if I made a thread here or not... yeah - see my posts in this thread:,134.msg35654.html#msg35654

Basically it could be a voltage drop resistor in the power section (doubt it; but seen that issue in a lot of fenders, and once in a Solarus 6550) or the screen resistors intermittently opening  like my issue in that linked thread.  A bump could do that; the screen resistors are carbon (vs wirewound like plate etc in these amps) because in a UL amp like this they act as a safety fuse.  Trouble is between the heat and age, they get cooked and brittle, so a drop could crack it luike mine.  The leads are rather thick (they don;t make em like dat no mo) and act like a spring to force the 2 haves together making contact, but hitting a norte creates a momentary open as they vibrate.

Note also that the circuit boards and terminal strips are rivetted to the chasis.  These rivets work themselves loose over time so any ground connection relying on that chassis contact becomes unreliable.  I have found this to create some noise as well (makesw the trem act weird - it starts modulating the background noise not the signal.  The bad grounds are easy to check for and fix;  if you find one, drill out the rivet and replace with a screw lock washer and nut (locktite recomended).