Building a Sunn 200s

[Fuzzonaut]

Hello dear Sunn lovers

I’ve been lurking around on this forum for a while, soaking up information and inspiration. Great place!

As I’m a bass player living in Switzerland, my attempts to get an old Sunn 200s (or any other of the similar models) were not successful, I instead asked a friend, if he would built me one. That guy knows how to do that and he even does it for free, I just pay all the parts.  As he is the techie, but doesn’t know English too well – and I’m completely lost if it comes to amp guts - I’ll be posting here, but without any real techie talk. You can still ask that kind of stuff, I’ll just have to pass it on to my friend.

So, we got the “big iron” (Dynaco transformers etc.) and tubes from “Triode Electronics” in the US and all the rest (small parts, headshell) from TubeTown (Germany).  It will be a pretty straight replica, just the “ground” switch thing is left out and there will be a “gain” knob for the preamp. Otherwise “bass” and “treble” with a boost switch each and “volume”.

The parts are in, some of them you’ll see in the picture (if I manage to upload). Faceplates are also custom made to my liking.
I’ll try to post regularly, as the building advances. As my friend has a full time job, it will be kinda slowly though. Feel free to ask questions or just drop your 2 cents – or any spare change you got. It will be appreciated.

Thanks.
Fuzzo

[loudthud]

The schematics from Sunn that you can find show the Mains wiring that was used at the time the amps were made almost 50 years ago. Things have changed here in the US and you won't find any amps made today with ground switches or two wire mains cords. Amps are much safer now that they all have a third wire safety ground in the mains cord. Your friend should be familiar with the safety and mains wiring practices in your country and follow those. DO NOT install the ground switch or the capacitor that goes from the ground switch to the chassis. We call that capacitor the "Death Cap" because if it shorts out, it can kill you.

For a fuse, you should use one about half the rating of that specified on the US schematic

[Fuzzonaut]

Thanks for the input about "grounding". "Death Cap" really sounds like something to avoid, yeah! I'll double check on that, but I'm pretty sure it's been taken into account acording to today's standards and the "Swiss electric situation", as my friend has built several amps so far. He actually explained that to me but I forgot the details ... as I remember, there will simply be no ground switch as that's in the power cable now (3rd prong).

[Fuzzonaut]

The schematics are fine, I was assured, if anybody wants to have a look, I can upload them.

And then we have a ... well ... a board with some of the parts.

[Watson]

Please do, thanks!

[Fuzzonaut]

Please do, thanks!

Here you go!

[Fuzzonaut]

So, got this together, and will be moving on to knobs and wires.

[loudthud]

There is a mistake on the original 200S schematic that was copied to your schematic. None of the amps I have found are wired like the Volume control in the original schematic. Check this thread: http://sunnforum.ampage.org/index.php/topic,4961.28.html about half way down on page 3.

C13 should be 12pF and C16 should be 330pF. V1 should be a 12AX7, a 12AU7 won't bias properly with the bias resistsors shown.

[Fuzzonaut]

C13 should be 12pF and C16 should be 330pF. V1 should be a 12AX7, a 12AU7 won't bias properly with the bias resistsors shown.

Thanks a lot for going through the schematic and those exact values - I transferred the information to the builder.

[Fuzzonaut]

C13 should be 12pF and C16 should be 330pF. V1 should be a 12AX7, a 12AU7 won't bias properly with the bias resistsors shown.

Thanks a lot for going through the schematic and those exact values - I transferred the information to the builder.

I got a reply from the builder and he thanks for pointing out the values for C13 and C16 - he agrees and will change them.

As for V1 and what tube should go there: as we want to stick to what Sunn was doing - they did put a 12Ax7 in there, didn't tehy? Or did the actaul amps never ever have one of those?
I mean, both would possible, it's just a question of taste, isn't it?
Couldn't we try both and just take whatever sounds better (to me)?

Thanks for the inputs.


 

[Fuzzonaut]

Making some progress ...

[loudthud]

Making some progress ...

Is that the Mains connected to the Fender style pilot light. That is EXTREMELY DANGEROUS. That style lamp holder was never intended to be connected to the Mains. Serious injury or death could result. DO NOT connect the amp to the Mains until that is changed. It is possible to touch one of the lamp terminals or short it to ground from outside the amp when changing the lamp. Even if only connected to 6.3VAC, the power transformer could be damaged if one side of the lamp shorts to the chassis.

[Fuzzonaut]

Hello again,

it's been a while, I know. But now, the amp is finished and was turned up for the first time last weekend. Actually it was up and running a few weeks ago, but it was a bit noisy and so some of the signal chain was rearranged and now it sounds just great.

As the testing was done at the builders place, I haven't heard it through my cab (an Ampeg 2x15" & 2x10"), but as I said, the tone I heard was great: BIG, fat, round, deep, full, whatever words might do to describe it. I surely was wearing a big smile on face.
As we are currently moving to a new practice room, I'll have to wait a few days to test it with my own stuff. I'm really curious to hear how it handles pedals.
Until then, the thing is sitting at home, radiating it's beauty ...

By the way, as the faceplate was customized, I decided to use my native dialect (kinda Swiss mountain german) instead of the obvious "bass, treble, volume" thing. RW, the builders initials, and the slightly "enhanced" Sunn logo are engraved. In the back, "OM" for the impedance selector is not a typo, but a reference to one of my favorite bass players. 

So, I'd like to thank again for the input I found on this forum. And if you want to know something, just ask.

I'll probably be back with some impressions after running the amp with my stuff for a while (I have different cabs, will try it also with an old Acoustic 301 or a MusicMan 1x15").