What is the Ohm rating for the Sonic 2

[django7866]

I got my sonic 2 back from the amp repair guy, I was trying to find info on this amp particularly the Ohms. What I have come across in doing searches on this forum is that the sonic 2 is the same as the 200s which could be run at either 16 & 8 or 8 & 4 ohms depending on the speaker enclosure That came with the amp when purchased new. My question/concern is: was the sonic 2 the same in regards to the ohms depending on speaker enclosure? what I have seen in the catalog that is posted on this site, is that they really only had 1 type of speaker enclosure but could not find what it was rated for or if there were other types of speakers. Were the sonic 2's generally 16 & 8? or 8 & 4? I am a bit confused, needless to say. Any help would be great!!! I am excited to really hear this thing and I don't want to blow it up trying to run something it can't handle. Also I have two 6550 in it, I read some where on here that you can change them out with KT88 with out having to bias them. I want to say that I read this when doing my research on this amp. So is this really possible?
Thanks in advance
Django7866   

[HRobert]

Django,

Do you know the year of the amp?  I believe that the 67 and 68 Sunn amps like the Sonics, Senturas, 100S and 200S etc. had 8 and 4 ohm outputs, and that in 1969 a lot of the amps were then changed for to 16 and 8 ohm outputs.  Loudthud would probably have more information on this subject. 

It seems to me that my electronics guru said that the output transformers had 3 output taps; 16, 8 and 4 ohms that were used in pairs; 16 & 8, or 8 & 4, and that they could be switched by a technition depending on the need.  Other than that I have no other info.

Rob

[EdBass]

I'm not exactly sure what determined whether an amp left the factory wired 16 & 8 or 8 & 4, but I suspect it was determined by the cabinet(s) configuration rather than the year. Possibly the availability of drivers had some influence; the D140/130 JBL's were available in 8 or 16 ohm, and using the more common 8 ohm JBL's you can't get an 8 ohm cab. To run a pair of 2 driver cabs loaded with 8 ohm drivers correctly, in the absence of a 2 ohm tap you would need to wire the cabs themselves in series and use the 16 & 8 ohm taps for the parallel output jacks.
Regardless, it's an easy switch if a particular amp isn't wired for your particular application.

Django7866, I personally wouldn't even put different 6550's in an amp without re-biasing, but you are correct about the interchangeability between 6550's and KT88's. The 6550 is the American version of the British KT88, and either will work dandy in the Sunn circuit. Up until 1969, Sunn used imported KT88's and then switched all of the amps to domestic 6550's. The amps themselves stayed the same; 6550's or KT88's is really just a matter of personal preference.

[django7866]

Django,

Do you know the year of the amp?  I believe that the 67 and 68 Sunn amps like the Sonics, Senturas, 100S and 200S etc. had 8 and 4 ohm outputs, and that in 1969 a lot of the amps were then changed for to 16 and 8 ohm outputs.  Loudthud would probably have more information on this subject. 

It seems to me that my electronics guru said that the output transformers had 3 output taps; 16, 8 and 4 ohms that were used in pairs; 16 & 8, or 8 & 4, and that they could be switched by a technition depending on the need.  Other than that I have no other info.

Rob

The guy I bought it from said it was a 67 or 68. He was not exactually sure the exact date but know it was around that time frame. When I asked him if he know what the ohms where for this amp he did not remember if it was 16 & 8 or 8 & 4 but he knew it was one of those configurations. ThanKs for the help.

[HRobert]

If the amp is a 67 or 68, I would bet that the outputs are 8 and 4 ohm.  Sunn didn't change the outputs to 16 & 8 untill around 1969.

Rob

[loudthud]

This question is ask quite often here. There should be a sticker on the back of your amp below the speaker jacks. It will tell you if your amp was originally setup for 16 and 8 ohms or 8 and 4 ohms. Both jacks are connected to the same tap but when you plug into the "Extention" jack, a mechanism on the jack switches the tap on the output transformer to the lower impedance. Despite what it says back there, your amp may have been modified sometime in the last 35+ years to the other impedance. Another possibility is that the switching mechanism wore out and someone just connected both jacks to a single tap. This is especially true on the 120W amps so to be safe, it's a good idea to look inside to make sure everything is as it should be.

I'll verify this info next week and post some pictures.

The 16 ohm tap always goes to a terminal strip where it connects to the negative feedback loop. If your amp is connected for 8 and 4 ohms, the colored wires for those taps will go to the "Extention" jack. If you amp is wired for 16 and 8 ohms, either both wires go to the jack or possibly the 8 ohm tap goes to the jack and a wire comes from the terminal where 16 ohm tap is connected. The unused 4 ohm tap will go to a lug on the terminal strip where nothing else is connected.

Impedance      40W/60W    120W

16 ohms          yellow        yellow

8 ohms            orange       white

4 ohms            brown        brown

Ground            black         black

[Johnny Guitar]

loudthud,
When I was 16 I bought a used Spectrum 1 with the "short" 115 D130 cab that was probably 16 ohms.  I added another D130 in the cab for probably 8 ohms.  Not knowing how the switch jack worked I think I moved the 8 ohm tap over to the regular speaker jack but I also moved the feedback loop to the 8 ohms.  The next week we played at my High School ( of course ) and my amp volume dropped and got very distorted about half way through the night.    I took it to the local Sunn dealer and the tech told me I blew the output transformer and shouldn't have moved the feedback loop but didn't tell me why.  I have a little knowledge of electronics but wondered what the effect of the loop on the different taps would have.
Thanks,
Johnny G.

[loudthud]

Without knowing exactly what you did, first let me say that in theory, simply moving the feedback to the 8 ohm tap would not cause the amp to be un-stable or oscillate. It would just cause a slight increase in voltage gain of maybe 2dB and a little more distortion. Now if you shorted the 8 ohm tap to the 16 ohm tap, that would cause a drop in volume and eventually fry the transformer if you continued playing.

The correct way to connect one 16 ohm and one 8 ohm speaker is to connect the 16 ohm speaker to the 8 ohm tap and the 8 ohm speaker to the 4 ohm tap. This lets the tubes operate with the intended load. If you can't do that, connect both speakers to the either the 4 ohm or 8 ohm tap. There is a mis-match either way but tube amps can tolerate a slight mis-match.

[Johnny Guitar]

Thanks loudthud,
What I did was add a second D130 of 16 ohms to get a total of 8 ohms.  But I did not understand the speaker jack switch back then ( 38 years ago  ) .  I moved the 8 ohm tap to the standard speaker jack and unhooked the external jack.  I also moved the feedback loop from the 16 ohm to my 8 ohm speaker jack and always wondered if that really had anything to do with frying the output tranny.  The tech probably didn't think a 16 year old kid should be messing around in that amp, wasn't my first or my last time either.
Johnny G

[django7866]

This question is ask quite often here. There should be a sticker on the back of your amp below the speaker jacks. It will tell you if your amp was originally setup for 16 and 8 ohms or 8 and 4 ohms. Both jacks are connected to the same tap but when you plug into the "Extention" jack, a mechanism on the jack switches the tap on the output transformer to the lower impedance. Despite what it says back there, your amp may have been modified sometime in the last 35+ years to the other impedance. Another possibility is that the switching mechanism wore out and someone just connected both jacks to a single tap. This is especially true on the 120W amps so to be safe, it's a good idea to look inside to make sure everything is as it should be.

I'll verify this info next week and post some pictures.

The 16 ohm tap always goes to a terminal strip where it connects to the negative feedback loop. If your amp is connected for 8 and 4 ohms, the colored wires for those taps will go to the "Extention" jack. If you amp is wired for 16 and 8 ohms, either both wires go to the jack or possibly the 8 ohm tap goes to the jack and a wire comes from the terminal where 16 ohm tap is connected. The unused 4 ohm tap will go to a lug on the terminal strip where nothing else is connected.

Impedance      40W/60W    120W

16 ohms          yellow        yellow

8 ohms            orange       white

4 ohms            brown        brown

Ground            black         black

thanks for the info, I will take it to the amp tech and have him take a look at it for me. Upon looking at the amp more closely I noticed that one of the 6550's socket was loose. I need to get that fixed as well  I was also wondering is it true that you can replace the 6550's with KT88's without having to bias them? I heard that if you do this it will give you more "head room". Help on this would be great!! 

[EdBass]

This question is ask quite often here. There should be a sticker on the back of your amp below the speaker jacks. It will tell you if your amp was originally setup for 16 and 8 ohms or 8 and 4 ohms. Both jacks are connected to the same tap but when you plug into the "Extention" jack, a mechanism on the jack switches the tap on the output transformer to the lower impedance. Despite what it says back there, your amp may have been modified sometime in the last 35+ years to the other impedance. Another possibility is that the switching mechanism wore out and someone just connected both jacks to a single tap. This is especially true on the 120W amps so to be safe, it's a good idea to look inside to make sure everything is as it should be.

I'll verify this info next week and post some pictures.

The 16 ohm tap always goes to a terminal strip where it connects to the negative feedback loop. If your amp is connected for 8 and 4 ohms, the colored wires for those taps will go to the "Extention" jack. If you amp is wired for 16 and 8 ohms, either both wires go to the jack or possibly the 8 ohm tap goes to the jack and a wire comes from the terminal where 16 ohm tap is connected. The unused 4 ohm tap will go to a lug on the terminal strip where nothing else is connected.

Impedance      40W/60W    120W

16 ohms          yellow        yellow

8 ohms            orange       white

4 ohms            brown        brown

Ground            black         black

thanks for the info, I will take it to the amp tech and have him take a look at it for me. Upon looking at the amp more closely I noticed that one of the 6550's socket was loose. I need to get that fixed as well  I was also wondering is it true that you can replace the 6550's with KT88's without having to bias them? I heard that if you do this it will give you more "head room". Help on this would be great!! 

Django7866, I personally wouldn't even put different 6550's in an amp without re-biasing, but you are correct about the interchangeability between 6550's and KT88's. The 6550 is the American version of the British KT88, and either will work dandy in the Sunn circuit. Up until 1969, Sunn used imported KT88's and then switched all of the amps to domestic 6550's. The amps themselves stayed the same; 6550's or KT88's is really just a matter of personal preference.

It’s been my experience that there is very little difference between modern 6550/KT88 types; traditionally KT88’s had a little more output/headroom, but I think current production tubes are pretty similar in performance. I have 2000S’s with Groove Tube KT88’s and Groove Tube 6550’s, and any performance differences that I can determine would easily fall into the range of hand wired circuit discrepancies; to my ears swapping the tubes exhibits the same nuances between the two amps.
However, it’s my opinion that the most consistent and best performing new production KT88/6550 type is the JJ KT88 (https://ssl.eurotubes.com/cart/index.php?page=view_products&category_id=3&sub_category_id=23), and it can be used in any application that a 6550 can be used in.

Biasing is a simple operation, and I recommend doing it any time you change output tubes.

[django7866]

This question is ask quite often here. There should be a sticker on the back of your amp below the speaker jacks. It will tell you if your amp was originally setup for 16 and 8 ohms or 8 and 4 ohms. Both jacks are connected to the same tap but when you plug into the "Extention" jack, a mechanism on the jack switches the tap on the output transformer to the lower impedance. Despite what it says back there, your amp may have been modified sometime in the last 35+ years to the other impedance. Another possibility is that the switching mechanism wore out and someone just connected both jacks to a single tap. This is especially true on the 120W amps so to be safe, it's a good idea to look inside to make sure everything is as it should be.

I'll verify this info next week and post some pictures.

The 16 ohm tap always goes to a terminal strip where it connects to the negative feedback loop. If your amp is connected for 8 and 4 ohms, the colored wires for those taps will go to the "Extention" jack. If you amp is wired for 16 and 8 ohms, either both wires go to the jack or possibly the 8 ohm tap goes to the jack and a wire comes from the terminal where 16 ohm tap is connected. The unused 4 ohm tap will go to a lug on the terminal strip where nothing else is connected.

Impedance      40W/60W    120W

16 ohms          yellow        yellow

8 ohms            orange       white

4 ohms            brown        brown

Ground            black         black

thanks for the info, I will take it to the amp tech and have him take a look at it for me. Upon looking at the amp more closely I noticed that one of the 6550's socket was loose. I need to get that fixed as well  I was also wondering is it true that you can replace the 6550's with KT88's without having to bias them? I heard that if you do this it will give you more "head room". Help on this would be great!! 

Django7866, I personally wouldn't even put different 6550's in an amp without re-biasing, but you are correct about the interchangeability between 6550's and KT88's. The 6550 is the American version of the British KT88, and either will work dandy in the Sunn circuit. Up until 1969, Sunn used imported KT88's and then switched all of the amps to domestic 6550's. The amps themselves stayed the same; 6550's or KT88's is really just a matter of personal preference.

It’s been my experience that there is very little difference between modern 6550/KT88 types; traditionally KT88’s had a little more output/headroom, but I think current production tubes are pretty similar in performance. I have 2000S’s with Groove Tube KT88’s and Groove Tube 6550’s, and any performance differences that I can determine would easily fall into the range of hand wired circuit discrepancies; to my ears swapping the tubes exhibits the same nuances between the two amps.
However, it’s my opinion that the most consistent and best performing new production KT88/6550 type is the JJ KT88 (https://ssl.eurotubes.com/cart/index.php?page=view_products&category_id=3&sub_category_id=23), and it can be used in any application that a 6550 can be used in.

Biasing is a simple operation, and I recommend doing it any time you change output tubes.

Thanks for the help!!! I will make sure that I get them biased.

[Paul of the Bastards]

The 16 ohm tap always goes to a terminal strip where it connects to the negative feedback loop. If your amp is connected for 8 and 4 ohms, the colored wires for those taps will go to the "Extention" jack. If you amp is wired for 16 and 8 ohms, either both wires go to the jack or possibly the 8 ohm tap goes to the jack and a wire comes from the terminal where 16 ohm tap is connected. The unused 4 ohm tap will go to a lug on the terminal strip where nothing else is connected.

Impedance      40W/60W    120W

16 ohms          yellow        yellow

8 ohms            orange       white

4 ohms            brown        brown

Ground            black         black

Nice!

[loudthud]

Here's the pictures I promised. The 2000S pictured looks like it has been modified from the original 16/8 to an 8/4 configuration. The output transformer has cloth covered wires and it's a little hard to tell white from yellow. Also note on the Sceptre how the brown 4 ohm wire goes to an unused terminal on the terminal strip.

Keywords: Impedance tap black

Edit: Replaced corrupt pics