Sunn 2000S Guitar & Bass Heads

[Daniel]

My name is Daniel,
I was wondering how I might be able to obtain a Owner's Manuel for the Sunn 2000s Amphead?
Also, I was wondering what is the difference between the 2000S basshead, verses the 2000S guitarhead?  The reason I ask is, because when I look into the back of my 2000S there is a socket that does not have a tube in it, and I've always wondered if it should have one?
I bought my 2000S head from my friend Mike about 20 years ago, and he did not have a Owner's Manuel,...... I guess it used to belong to his Uncle, who later gave it to him in 77', and I bought it from Mike, for $75.00 in 83'  (I love this Amp!!)
Then there is also the curiosity of what the one 1/4 phone jack and 1/8 red input jack is in the middle of the chassis, located between the 6550 rectifier tubes?  (Footswitching jacks?  Direct out?)
There is also a 2 prong female AC looking outlet, which is marked 400 Wattts,..could someone tell me what it is, and what is it used for?
Another question, is being how there is 4 Inputs, and I'm just guessing, but I take it that this is a two channel amp, and it does have 2 large size transfomers?  And if so, could I run both at the same time by running a patch cord form the top right input, (Upper Normal Input) then running it down to the bottom left Input, (Lower Bright Input) with the guitar in the top left Input, (Upper Bright input) so that both the bright and normal would both be in use at the same time?  (That is if it works that way?)
Also this amphead that I have, has a red boost switch on the front, and the 2 speaker output jacks are rated at 8 Ohms & 4 Ohms.
Any help, PDF, Images or resources would be most appreciated,
Thanks,
Daniel

[Anonymous]

Daniel,
Don't know where you will find an owner's manual for your 2000S. Your empty tube socket is most likely for a second 5AR4 rectifier (the two sockets of the far left-hand side of the amp as you view it from the rear). My 1969 2000s has two rectifier tubes. I'm not sure if Sunn changed to diode rectifiers later or not. You need two rectifier tubes due to the current draw on the power supply by four 6550's......so put the tube in. There is no such thing as a 2000S guitar head. The 2000S is a bass head. The equivalent guitar head is a 1200S that has reverb and tremolo. The 1/4" jack between the 6550's is the bias adjustment pot.....it just looks like a jack. The smaller red "jack" is actually a socket for a VTVM or VOM test lead when setting the bias for the output tubes. The 2000S is not a two channel amp. The transformers have nothing to do with the number of channels in any amp. All tube amps have a power transformer (to convert line voltage to the high voltage required for the tube plates, etc.) and an output transformer to couple the relatively high impedance output of the tubes to the low impedance speakers.
Good luck!
Ryan

[loudthud]

The 2000S came with an 8 ohm speaker cabinet equipped with two 16 ohm JBL speakers. It was intended to be plugged into the jack marked Speaker. When you plug into the second jack marked Extention, a mechanism on the jack switches from the 8 ohm tap to the 4 ohm tap on the output transformer which is what you'd want to do if you had two 8 ohm cabinets. If you are using a 4 ohm cabinet, you should just plug into the extention jack and you'll be connected to the proper tap on the output transformer. If you connect two 4 ohm speaker cabinets, you could easily fry the amp. Take it to someone who can make you a Series connected Y cord. The sound you get with series connected speakers is usually terrible though. It's best to stick with one or two 8 ohm or one 4 ohm cabinet.

A 2000S should have 1) 12AX7, 1) 6AN8, 4) 6550, 2) 5AR4. It will work with one 5AR4 but not for very long if you play at high volume. I've seen a 2000S on Ebay that had silicon diodes in place of the 5AR4's and it looked like it was a factory change. This is a mod that could be installed by your local Amp Tech. Don't try this at home. The 5AR4's will give you a smoother sound but slightly less power. Get a fresh pair and keep the one you have as a spare. Expect to pay about $15.00 each.

The 1000S was a guitar amp that came with a 2-15 JBL cabinet, the 1200S came with a 6-12 cabinet. The amps are identical except for the name on the front. Early ones did not have tremolo and reverb. They can be modified to be like a 2000S with a couple of resistor and capacitor changes. Later the name changed to 350B for bass and 350L for guitar. I think these had silicon rectifiers ( no 5AR4's).

The four inputs are really just separated with some resistors and capacitors so there isn't any advantage to jumpering them together like on a four input Marshall or the Model T's Both input. Just plug into the one that sounds best to you.

The outlet on the back that is marked 400W was just ment to be used to connect another amp or accessory. It's marked 400W so you won't overload it.

Your 2000S most likely has a two prong plug and a ground switch. It was made in the day when three wire grounded outlets weren't all that common. Back in those days durring sound check you would step up to the microphone and touch one of your guitar string to it. If you saw any sparks, you would reverse the ground switch on your amp. Otherwise if your lips touched the microphone, you would get a mild electrical shock. Ouch ! If you had any effects boxes that plugged into a 120V outlet sometimes reversing the ground switch wouldn't totally fix the problem unless one of them had a grounded plug. The best and safest thing to do is to have a 3 wire grounded cord installed on your amp by a qualified technician. Don't try this at home.

Hope this helps.