Restoring my 1969 Sunn Sentura II

[gui_tarzan]

I bought this years ago and frankly don't even remember where but it didn't work when I got it. I got back into repairing amps recently and decided it was time to restore this beast. I have the matching 2x15 cabinet and it's in really good shape except for one hole in the grille and no speakers but it should make a darned nice unit for someone.

As you can see in the gutshot it was a terrible mess. I don't know who got their hands on this originally but I wouldn't let them take my trash out, they'd probably drop it and scatter junk everywhere. The chassis is not warped or bent, it's straight as an arrow but my camera must do something funky with the angles.

Someone changed the power transformer at some point, but it seems to check out with good voltages. And why they would remove the treble control is beyond me.

I stripped all the wiring and need to make another trem/reverb PCB but that won't be an issue if I can get a photo of the bottom of the board.

The last shot is of the new heater wiring and a couple of the pieces wired up. I'm also going back to a GZ34, someone put diodes in its place along the way.

Parts are on the way, wish me luck... woohoo!

[Phil_S]

Welcome to TAG! Nice project you have there. I'm not sure what you are showing use with the two pictures of the chassis wired with the cap board and choke(?) moving around. Maybe you are just showing us the bad stuff? Yeah, that looks pretty awful. Even an amateur like me can do better. No worries, you've already done away with that and have a fresh start.

For the tremolo, why do this on a PCB? It seems to be more work than it's worth. There aren't that many parts. Buy a piece of turret board -- something like this http://www.tubesandmore.com/products/P-HTUR-60 You can cut it down to size. Buy some extra turrets so you can modify the layout a bit to fit your needs. If there is room for a PCB, there is room for one of these. Just my 2 cents!

Wishing you the best success on your project.

[gui_tarzan]

Thanks Phil. I have the trem/reverb circuit drawn out on a replacement board from the schematic but I want to verify the traces to make sure I haven't missed anything.

Yeah, those "before" pics are just to show how nasty it was when I started tearing it apart. The breadboard was my first clue...

[Phil_S]

Oh, how silly of me. I thought the breadboard moved from one pic to another -- a real head scratcher. I see now, it is right side and left side. Fugly it was.

If you have the schematic (easily found on the web), then just build it and forget about looking for a picture on an old PCB. I doubt you'll find it. If it works, you know it was built right. If not, you try again.

[gui_tarzan]

I do have schems, I just wanted the layout to look stock. It's no big deal I suppose. In fact someone on here actually posted a correction to the Sentura II schematics and the fix looks right to me after comparing it to many others. That means there are a bunch of incorrect schems out there.

[eddie25]

It's might be difficult to find a tremolo unit for that. There are also a bunch of transistors involved for the trem and verb that might make turret-boarding it a little difficult, though I can't imagine a PCB would be easy either.

If the voltages on the PT are correct and your wall voltage is at all high you may actually be over the voltage ratings for the first two cap sections which are rated for 525!). Especially with a SS recto. Part of me suspects that maybe that's why the big breadboard with the series caps. I would also use JJKT88's if that is the case.

[Richie]

I'll look around tomorrow. I may have the board in an old amp. I kept a few for parts over the years. I think I have 4 or 5 of them. But i'm pretty sure I have one. Probably anything else you might need, let me know.

[Jered]

It looks to me like someone gutted it but still used some of the original parts. The original Sunn amps I've looked inside the wiring was nothing short of perfection.

[Stevem]

My 71 Sonaro head which is the same power section makes its best power with 6550 tubes no matter how well a set of KT88s test out in my Hicok tester!
Also in regards to power sections those IC brand filter caps are the Ghost note kings and atleast for the first filter section of the amp I would swap them out for atom brand filters as soon as I could!

[Structo]

My first tube amp was a Sunn Sonaro.

I didn't know what was inside it but it was fun.

[Jered]

Is this what you are looking for?

[Stevem]

Sorry, mine is a sorado, not a sonaro, boy these amp names are like a tung twister!

[eddie25]

It looks to me like someone gutted it but still used some of the original parts. The original Sunn amps I've looked inside the wiring was nothing short of perfection.

Without a layout, or a lot of really good photos I feel like this would be an extremely trying project. These amps are one of the more difficult to 'trace' in my opinion just because of the wiring style they use. Certainly doable though. Do you need pictures still? I may have some of a Solarus, thats the same as your Sentura II, I think.

[gui_tarzan]

That's it. Thanks for the pics! I already made a test board and just got some copper-faced PCB today so I'm ready to make the new board. Odd parts including the correct transistors are on the way, just need to find one of the tremolo cubes. I found out they use a neon bulb instead of a traditional bulb so the Fender roaches won't work.

[gui_tarzan]

Yeah, someone substituted diodes for the GZ34 which I found out is the same as a 5AR4 so I have one of those on the way to put it back to factory. I'm going to sell this once I have it put back together and working, it's too big and heavy (2x15 cabinet) to haul to gigs.