reviving a very used solarus head.

[sky pup]

Hey all, I've been reading this board for several years and have finally found a reason to make a post.

Sometime in 2002 I obtained a "1969 Sunn Solarus Head" for ~$200 on eBay. I plugged it in and it sounded like it had a lot of potential, however, it hummed like crazy, had buzzy reverb, flabby tone, etc. Lack of money and other priorities let it sit untouched for several years.

It came loaded with these tubes, all quite old-looking:

-two mismatched, but similar looking 6550s. One RCA, one "Leslie" brand.
-one faded preamp tube I assume to be a 6an8a or equivalent.
-one Garnet brand 12ax7.
-one 12au7A/ECC82, housed within a metal spring-loaded casing, I assume this is the reverb tube. Its only marking reads "GT. BhITAIN".
-an empty tube socket that can fit a 6550, however I would think this is for a rectifier tube.

I am now in need of a real, functioning tube amp so I decided to pull this thing out and give it a look before taking it in to a tech. Keep in mind I'm quite a beginner to electronics so apologies for any ignorant-sounding descriptions.






The first problem I encountered when removing the chassis is the large block on the left, which I assume to be a power transformer. It is bent to the left and makes it very difficult to slide the chassis out smoothly. Is this any kind of damage I should be worried about? Can it be fixed without replacement?






Upon removing the chassis I find that this amp was made in 1970. I can't find schematics for this model anywhere.






Here's an overhead shot of the chassis. I am curious as to what goes in the empty socket on the left there, next to the bent power transformer. The amp seemed to power up and work OK when I had tried it, and I thought I had read that after 1969 Sunn switched over to solid state rectifiers, so I am very confused about this part. Also, what is that big metal shaft sticking out in front?







Here's shots of the front, and of the inside for anyone who's curious. Looks quite clean.




So, here is what I would like to do with this amp. I would appreciate any comments, concerns, or criticism of my plans. After all, I am a mere man among giants here.

1. retube, rebias, fix/replace any caps that need it.
2. turn the 2-prong power cord into 3-prong.
3. obtain a rectifier tube if it is indeed what belongs in that empty socket there.
4. repair that bent power transformer if need be.
5. fix whatever is causing the reverb to create such a loud buzz when turned up.
6. any tweaking/cleaning that is necessary.

Do these seem like realistic goals for this amp? Would it be worth it to take it in or just find a new rig? I really love its sound and would love to bring it into my setup for good.

I enjoy reading & learning from all the good info you guys put out here. Any response would be greatly appreciated. Thank you.



P.S.  I almost forgot, controversial question. I love the overdrive sound but I actually would love less headroom. A master volume mod would be nice, but I understand it would damage the value of this amp and the cosmetics of the front. Is this feasible or am I better off with something like a MXR Micro Amp? Thanks again.

[loudthud]

There isn't a good schematic online anywhere I know of. What you have is basically the same as a 100S with the mid-boost switch like shown in the 1200S. The power supply is somewhere in between with just one 20uF 600V cap.

http://sunn.ampage.org/site/schematics/100s.jpg

http://www.el34world.com/charts/Schematics/Sunn_1200.pdf

You pics show the reverb cables aren't plugged in, is that the source of hum?

The 12AX7 belongs in the socket with the shield, the 12AU7 next to it. The GZ34 rectifier socket has some diodes soldered to it on the inside so plugging in a rectifier tube won't make much difference. It won't be cheap to rehab this amp. Get an estimate.

[sky pup]

There isn't a good schematic online anywhere I know of. What you have is basically the same as a 100S with the mid-boost switch like shown in the 1200S. The power supply is somewhere in between with just one 20uF 600V cap.

http://sunn.ampage.org/site/schematics/100s.jpg

http://www.el34world.com/charts/Schematics/Sunn_1200.pdf

You pics show the reverb cables aren't plugged in, is that the source of hum?

The 12AX7 belongs in the socket with the shield, the 12AU7 next to it. The GZ34 rectifier socket has some diodes soldered to it on the inside so plugging in a rectifier tube won't make much difference. It won't be cheap to rehab this amp. Get an estimate.

Whoops, I didn't notice the unplugged cables in the pic. I had just unplugged them in order to remove the chassis, so that definitely isn't the problem. They had been plugged in before and while the reverb technically works, it gives off a loud buzz. So what you are saying is that the rectifier socket had been modified at one time. Thanks for the response & the info.

[EdBass]

I've got a Solarus schematic, but it's from 1968 and it's an EL34 amp. I'll bet the Sceptre schematic with mid boost is almost dead on your Solarus, but the onle Sceptre schematic I have is the same one posted on this site.

[Isaac]

The empty socket on the left is where the rectifier tube went. The fact that it powers up and works at all means that it's been replaced with solid state rectifiers.

The "metal shaft" is a multi-cap, several electrolytic capacitors combined in one housing. Those caps will almost surely have to be replaced, but many people leave the multi-cap in place for esthetic reasons.

The Sceptre schematic is identical, as are the Sentura II and Solarus, but I've yet to see a Sceptre schematic including the mid boost switch.