1967 Sunn 200S help!

[j_archuleta]

I just purchased a 1967 Sunn 200s bass head and I am running it through an 8ohm cabinet.

On the back of the head there are two speaker inputs, one labeling "Speaker" and one "External Speaker".

I am unsure of which input is 4ohms and 8ohms. I have attached a schematic for the head from 1967, I do not know how to tell which speaker input corresponds to which ohm load.

I would appreciate any help.
Thanks!

[OneWayPunk]

If you are just hooking up one 8 Ohm cab use the speaker output.
If you are hooking up one 4 Ohm cab use the Ext speaker output.

If you are hooking up 2 8 Ohm cabs use the Ext speaker output.
2 16 Ohms cabs use the speaker output

etc....

Speaker = 8 Ohms
Ext Speaker = 4 Ohms

[anderbass]

Originally Posted by j_archuleta

I am unsure of which input is 4ohms and 8ohms.

On mine, the 4-ohm jack is on the outside, closest to the end of the amp.

[edbass]

Originally Posted by OneWayPunk

If you are just hooking up one 8 Ohm cab use the speaker output.
If you are hooking up one 4 Ohm cab use the Ext speaker output.

If you are hooking up 2 8 Ohm cabs use the Ext speaker output.
2 16 Ohms cabs use the speaker output

etc....

Speaker = 8 Ohms
Ext Speaker = 4 Ohms

Well, sort of...

In the output wiring illustrated in the schematic you attached, the jacks are wired to be used with a single 8 ohm speaker in the "speaker" jack or a single 4 ohm speaker in the "ext. speaker" jack.
However, when both jacks are used they default via switching in parallel to the 4 ohm tap.
That means if you have two 8 ohm cabs you plug them into the two jacks in the back of the amp.

There is no provision for plugging in two 16 ohm speakers into the back of the amp simultaneously; UNLESS the amp is specifically wired for 16 ohm and 8 ohm operation.

As the schematic indicates vintage Sunn tube amps came with OT’s that have 4, 8, and 16 ohm taps, and the amps came with the jacks either factory wired for 8 ohm and 4 ohm OR 16 ohm and 8 ohm, and it’s easy (as well as not uncommon) to switch them back and forth.

So while the schematic you posted shows the 8 & 4 configuration, you should make sure that it is indeed factory wired for 8 and 4 ohm operation or that no one has performed any output tap surgery to suit their personal needs over the past 45 years.

[j_archuleta]

Originally Posted by edbass

Well, sort of...

In the output wiring illustrated in the schematic you attached, the jacks are wired to be used with a single 8 ohm speaker in the "speaker" jack or a single 4 ohm speaker in the "ext. speaker" jack.
However, when both jacks are used they default via switching in parallel to the 4 ohm tap.
That means if you have two 8 ohm cabs you plug them into the two jacks in the back of the amp.

There is no provision for plugging in two 16 ohm speakers into the back of the amp simultaneously; UNLESS the amp is specifically wired for 16 ohm and 8 ohm operation.

As the schematic indicates vintage Sunn tube amps came with OT’s that have 4, 8, and 16 ohm taps, and the amps came with the jacks either factory wired for 8 ohm and 4 ohm OR 16 ohm and 8 ohm, and it’s easy (as well as not uncommon) to switch them back and forth.

So while the schematic you posted shows the 8 & 4 configuration, you should make sure that it is indeed factory wired for 8 and 4 ohm operation or that no one has performed any output tap surgery to suit their personal needs over the past 45 years.

From what I can tell there has been no modifications to the output tap.

Would it be safe to run two cabs into both outputs, one 8 ohm and one 4 ohm cab.
Or would it default to something that could be harmful.

I have run two 8 ohm cabs wired in series into the 4 ohm output and it has worked just fine. But I have not tried two different ohm loads.

Thank you for the help and clarification.

[j_archuleta]

Originally Posted by anderbass

On mine, the 4-ohm jack is on the outside, closest to the end of the amp.

What year is your head? Does it specify whether it is 'external speaker' or 'speaker'?

The stickers on my head were not labeled with ohm loads.

[edbass]

Originally Posted by j_archuleta

What year is your head? Does it specify whether it is 'external speaker' or 'speaker'?

The stickers on my head were not labeled with ohm loads.

How are you determining that you have a '67?

I'm just curious; I don't think it matters what year the amp is for the purposes of your question. And as I mentioned earlier, depending on how your amp is wired it either jack could be 16, 8 or 4 ohms so it's a moot point.

The only way to tell for sure is to open it up and look. The OT tap color coding on your schematic is correct, see which color goes to which jack.
It only takes a couple of minutes, but if you aren't sure what you are looking for, just take a good pic of the inside of the chassis around where the jacks are located and post it on the Sunn Forum.
Someone will set you straight on "what is what" in there!