i bought this cuz it said SUNN

[mckinnon audio]

  Hi there,the 3rd socket over on the extreme left,looking from the rear of the amp,is for your rectifier tube.Should be a GZ34 or a 5AR4,good luck Mel.

[Ryan Phelps]

I've owned several Sunn Sonaro heads over the years and I recalled that in one of the later incarnations Sunn did change the output tubes to 6550. I dug through my stack of vintage Sunn catalogs (that I've been dragging around since high school!). In the 1970, 8-1/2" x 11", red and blue, single page, 4-fold flyer, the Sunn Sonaro is listed as producing 80 watts RMS (180 watts peak). The Sorado, 200S, Solarus and Sceptre are listed with the same output in this flyer. And as we all know, these amps used a pair of 6550's. I'm not sure you could really squeeze 80 watts out of a pair of 6550's, but that is the output listed.

The Sonaro is pictured with a slightly tall 1x15 cabinet (29" x 24" x 9-1/2" tuned-port design) with a Sunn bass transducer or Vega speaker as an option. The Sonaro was gone by the time the 1972 catalog was issued.

While the Sonaro was a 40 watt amp (2 x EL24) for several years, in both the combo (styled to look like a head and cabinet) and head versions, Sunn did upgrade it to 6550's late in it's run. The transformers in the 40 watt version are about the size of a baseball, while in the 80 watt version they are about the size of a softball. Bigger iron for more output. If you have the older version, I would not recommend installing 6550's. I don't think the 40 year-old transformers would last too long!

Ryan

[EdBass]

I've owned several Sunn Sonaro heads over the years and I recalled that in one of the later incarnations Sunn did change the output tubes to 6550. I dug through my stack of vintage Sunn catalogs (that I've been dragging around since high school!). In the 1970, 8-1/2" x 11", red and blue, single page, 4-fold flyer, the Sunn Sonaro is listed as producing 80 watts RMS (180 watts peak). The Sorado, 200S, Solarus and Sceptre are listed with the same output in this flyer. And as we all know, these amps used a pair of 6550's. I'm not sure you could really squeeze 80 watts out of a pair of 6550's, but that is the output listed.

The Sonaro is pictured with a slightly tall 1x15 cabinet (29" x 24" x 9-1/2" tuned-port design) with a Sunn bass transducer or Vega speaker as an option. The Sonaro was gone by the time the 1972 catalog was issued.

While the Sonaro was a 40 watt amp (2 x EL24) for several years, in both the combo (styled to look like a head and cabinet) and head versions, Sunn did upgrade it to 6550's late in it's run. The transformers in the 40 watt version are about the size of a baseball, while in the 80 watt version they are about the size of a softball. Bigger iron for more output. If you have the older version, I would not recommend installing 6550's. I don't think the 40 year-old transformers would last too long!

Ryan

This is getting curiouser and curiouser.
I know in '69  the Sonaro was an EL34 amp, if it after that upgraded to the 6550 spec and was rated for 80 watts, (not at all unrealistic for a pair of 6550's in a push pull AB1, particularly with a SS power supply) it would have been SS rectified, right?
So...
Doesn't the extra "plug in for a larger tube" in the chassis almost have to be for a rectifier tube?

as for the tubes...
like i said i have 2 6550s but i just noticed another plug in for a larger tube. should this this have 3 6550s and maybe i am missing one?
also i popped open the cab to see the goodies and it looks like it has 4x12 original sunn transducer? speakers...at least that what the stickers say on the speakers. no other markings anywhere though. the head does say 60 watt.

Of course Sledgeguitar also mentions a "60 watt" rating.

Hey Sledgeguitar, can you post a pic of the chassis for us Sunn geeks?

[Ryan Phelps]

I agree with EdBass; a picture of the back of the amp, showing the transformers, would answer the question if this particular amp was designed for either EL34's (small transformers) or 6550's (larger transformers). The 1970 vintage Sunn flyer says nothing about the tube compliment in any of the amps. However, solid state rectification would tend to deliver higher B+ voltages than a tube rectifier (5AR4 / GZ34), all things being equal, allowing for increased power output.

Checking my 1973 RCA Receiving Tube Manual, a pair of 6550's in Class A1 are indeed capable of an output of 80 watts with plate voltages of 500V, grid #1 voltage of 54V, fixed bias and 2.75% total harmonic distortion.
There are no specs for operation in Class AB1, but I imagine these can be found.

Are our beloved Sunn tube amps actually operating in Class A1 or are they Class AB1? I would guess Class AB1.

Checking several Sunn schematics with 6550 output tubes and tube rectifier, I find the voltage to the 6550 plates to be 500V - 510V. So it seems that, if the grid voltage and bias are sufficient and the amp is operating in Class A1, a tube-rectified circuit is capable of producing 80 watts power output. If the amp is operating in Class AB1, does it require a higher plate voltage than 500V - 510V? If so, this might require solid state rectification.

Can any of you tech-heads provide more illumination on this arcane, yet fascinating subject?

[djc]

also, can you describe the difference between class A and class AB.  I'd appreciate that.

[EdBass]

also, can you describe the difference between class A and class AB.  I'd appreciate that.

Yes, I could. But instead of spending my day typing, how about reading this;
http://www.duncanamps.com/technical/ampclasses.html

Be careful, it might cause you to do more research! Next thing you know, you're a flood panted, pocket protecter wearing, full fledged dork!

[mckinnon audio]

  Hi there,the main difference between class A and class AB is that in class A,the plates draw maximum plate current 100% of the time(cycle).In class AB,it's drawn in proportion to the signal,more signal,more current draw on the plates,more output.
  The downside to class A is the heat generated by the output stage being maxed out all the time,hard on your tubes,but the amps have a great dynamic range,Mel.

[Sledgeguitar]

i will get a picture up soon. thanks for all the help.

[Ryan Phelps]

I reviewed some of my amp books today and, if I understand this correctly, Class A amps are always cathode biased, not fixed bias as are Sunn tube amps. Not all cathode biased amps are Class A, but fixed bias amps cannot be Class A ( tech-guys chime in here if I have this wrong).
In guitar amps, the preamp tubes are always cathode biased (Class A operation). You can tell this because there is a resistor, or resistor & capacitor, between the tube cathode and ground. But amps are typically classifed according to the bias scheme of the output tubes. All single-ended (a single output tube vs. a pair or quartet) amps are always Class A.
Also, Class A operation requires lower B+ plate voltages and lower bias than Class AB. Class AB will put out more output power than Class A.
So what does this mean with regards to this thread? Higher B+ voltage available from a solid state rectifier (accompanied by a comensurate increase in the fixed bias voltage) would result in increased power output from the amp, up to the maximum dissipation rating for the tube.
Yikes! I'm getting into full amp-dork territory here!

Ryan

[Sledgeguitar]

i have no idea what half of the stuff is that you are talking about!haha! its like listening to charlie browns teacher!

i really need to learn this stuff though if i have going to buy antique equipment.

[djc]

[

Be careful, it might cause you to do more research! Next thing you know, you're a flood panted, pocket protecter wearing, full fledged dork!

thanks Edbass!

[Sledgeguitar]

if any one wants to buy this or trade let me know. i would like to get a marshall jcm800 head & 1960 cab(straight pref)for a trade. let me know
fudgelivingston@yahoo.com

[mckinnon audio]

  Hi there,the third socket would be for your rectifier tube,GZ34 or 5AR4,but if the amp is operating without a tube in the socket it means someone has wired up some diodes to the circuit and the tube is not needed,good luckMel.

[Isaac]

if any one wants to buy this or trade let me know. i would like to get a marshall jcm800 head & 1960 cab(straight pref)for a trade. let me know
fudgelivingston@yahoo.com

You think you're going to get a Marshall jcm800 head and a 1960 cabinet for a Sunn Sorado head? Not likely, IMO.