Sunn Amp & Power

[HRobert]

Here's a question that I do not believe has ever been answered.  The older 60 watt amps; Sentura II, 100S, 200S, Spectrum II, Sonic II, etc, were advertised as being 140 watts peak and 60 watts continuous ( music power ). Was that rating into 8 ohms?  If so, what is the amps power output into a 4 ohm load.

Rob

[loudthud]

Tube amp power ratings assume the load is connected to the corresponding tap on the output transformer. The transformers on the early amps had 4, 8 and 16 ohm taps. Only two of the taps are available via the jacks on the back of the amp. Some amps had 16 and 8 available but most had 8 and 4. This depended on the impedance of the speaker cabinet that came with the amp. If you added a second speaker cabinet and plugged into the extention jack, the correct impedance was automatically selected. A small sticker above the jacks usually tells you which are available.

[HRobert]

Thank you, Thud,

Speaker jcks on my 67 Sentura II just say Speaker, and Extention Speaker...So I assume that they are 8 & 4 ohm.  IF my amp is rated at 60W RMS into 8 Ohms, how many watts does it put out into a 4 ohm load.

Rob

[Soundmasterg]

Thank you, Thud,

Speaker jcks on my 67 Sentura II just say Speaker, and Extention Speaker...So I assume that they are 8 & 4 ohm.  IF my amp is rated at 60W RMS into 8 Ohms, how many watts does it put out into a 4 ohm load.

Rob

What he was trying to say Rob is that with tube amps, they are designed for a specific amount of power, and no matter the ohms, they deliver that amount of power as long as the load is matched to the tap on the output transformer. So 60 watts at 8 ohms is going to be 60 watts at 16 ohms or 60 watts at 4 ohms, as long as the speaker load is the same. If you put a 16 ohm speaker on an 8 ohm load, then your power can go down, distortion can go up, and at extreme volumes you run the risk of cauing damage in the output transformer. (arcing) The risk of damage is worse if you mismatch the other way, (4 ohm load into an 8 ohm tap) though most amps can handle a one step mismatch either way. Transistors are more efficient as they get closer to no load, unless they use an output transformer, so most transistor amps are going to give more power at 4 ohms than 8 ohms. Tube amps are different though. The limit on the power output are the tubes themselves and the voltages they run at, and the output transformer and how much current it can handle.

Greg

[Isaac]

Thank you, Thud,

Speaker jcks on my 67 Sentura II just say Speaker, and Extention Speaker...So I assume that they are 8 & 4 ohm.  IF my amp is rated at 60W RMS into 8 Ohms, how many watts does it put out into a 4 ohm load.

Rob

I wouldn't make that assumption. The output jacks on my Sentura II are 16 and 8.

Tube amps put out the same amount of power into each load, as long as the impedances are properly matched. 60 watts into 8 ohms, 60 watts into 4 ohms, 60 watts into 16 ohms.

[HRobert]

Isaac,

Thanks for the input on the output..HA HA.  I had a 1967 Sentura II that I got new in 1968.  The outputs on that amp were rated 8 & 4, so since that one that I presently own is a 1967 also, the load ratings must be the same.  However, I do know that some of the later Sunn Senturas and Spectrums were rated 16 & 8.

Toudthud,

I didn't know that a tube amp put out the same RMS power regardless of the load.  I own some Biamp equipment
( another fine produce by Conrad ) mixers and two power amps.  They are solid state and have a different ratind depending on the load.  The Biamp TC-120 power amp is rated at 120W into 8ohms, and 200W into 4ohms.  I thought that tube amps changed power output the same way. 

So regardless if I run one 8ohm cabinet or two 8 ohm cabinets, the power output will still be 60W RMS?

Thanks for the info, and I hope to have pictures posted soon on my Sentura II / 230-B cabinet project.

[pickinatit]

I think you need warning one more time regarding your output taps because I'm not sure you quite got this yet.
Back in 67/68 if you were buying a Sunn tube amp and you purchased the amp with a single 4 ohm speaker cab the amp would be wired to the 4 ohm and 8 ohm speaker taps.
If you bought a pair of 8 ohm cabs you would get the same amp still wired to the 4 ohm and 8 ohm speaker taps.
BUT, if you bought the SAME AMP,  but with an 8 ohm cab or with two 16 ohm cabs the 8 ohm and 16 ohm taps would probably be wired.
SAME AMP, different taps, depending on the speakers purchased with the cab.
Bottom line,  you can't make the ASSUMPTION that your amp is wired to 4 and 8 ohm taps just because of the year it was made.

[eclectiq]

Sorry to butt in....but is there any way to test for what load the amplifer wants? I have the Sonic II, the outs also read "speaker" & "extension spkr". I have always run into a 4X12 rated @ 8ohms. I never really push it, though. I'm not the original owner and I've never seen the cab that was originally sold with this amp. I don't want to cause damage. Again, any way to test and determine the load for which it was designed?

[mckinnon audio]

   Hi there,to be 100% sure,the only thing to do is open up the amp and look at the wires connected to the jacks.Each colour corresponds to a certain output impeadence value,(I forget so I won't quote here),but you can do a search,the subject has been covered several times on the forum.Good luck,Mel.

[loudthud]

Here's a good thread on the subject:

http://sunn.ampage.org/sdp/index.php/topic,3833.0.html

[EdBass]

I think you need warning one more time regarding your output taps because I'm not sure you quite got this yet.
Back in 67/68 if you were buying a Sunn tube amp and you purchased the amp with a single 4 ohm speaker cab the amp would be wired to the 4 ohm and 8 ohm speaker taps.
If you bought a pair of 8 ohm cabs you would get the same amp still wired to the 4 ohm and 8 ohm speaker taps.
BUT, if you bought the SAME AMP,  but with an 8 ohm cab or with two 16 ohm cabs the 8 ohm and 16 ohm taps would probably be wired.
SAME AMP, different taps, depending on the speakers purchased with the cab.
Bottom line,  you can't make the ASSUMPTION that your amp is wired to 4 and 8 ohm taps just because of the year it was made.

It's been my experience that this is absolutely correct, the year has nothing to do with the way the outputs are wired; it's the cabinet configuration that the amp had with it that made the determination.
But, I don't think anyone mentioned that the output trannies have 16, 8 and 4 ohm taps regardless of how they were wired from the factory, and it's a simple job to rewire the amp to your personal load requirements.
As Mel suggests, search is your friend...