[munosmario]

Let me add some more to my story and I hope at least your enjoying it. I found a 1/2A fast fuse in my Mc tuner. Then, I decided to call Cary. The person who I spoke with, not Dave like I said yesterday, Mark was a sheer pleasure to talk with. I was taking tubes out and sticking the multimeter leads in slots like I knew what I was doing! Turns out its a fixed bias amp, which surprised even him. When I verified, but black on ground and red in slot 5, that each socket was controlled by the 1 bias adjustment. The amp was definitely biased too low when I got it, hence the horrible sound. I finally biased it at 200ma, which he said should be 50ma per 6550. KT88's would be more like 240-250.
I think I may just listen to the music now, and pick up a quad of GL's. I saw a decent price of less then $200 from a decent vendor.
Thanks everyone for your help and comments, invaluable!!!

fz1jmp, I am very glad you connected with Mark as I had suggested...as you say, he is a true delight on top of being extremely knowledgeable about virtually all Cary products--and willing to spoon fed you that knowledge if you are up to it. Since, it appears, you plan to change output tubes, I suggest to call him again and ask him what is the plate voltage for the output tubes...tube bias requirement changes from type to type and often from same type brand-to-brand, but it also depends on the voltage plate setting of each particular amplifier and whether it is Class A or Class AB (Class A tolerates higher bias without compromising tube life). Once you have that info PM me if you feel like so I can PM you back  a chart with the bias ranges for that particular plate voltage and the particular tube type you plan to buy. Is it a set of GL kt-88s?

Mario

[fz1jmp]

Mario;

Mark was a gem and I thank you for the suggestion! He certainly spoon fed me and taught me as much as I could learn. I did mention to him I was thinking of putting in the GL KT88's and he said then I should raise the bias to 240 - 250.

I'm going to re-pour over the forums regarding plate voltage. He mentioned that I could bias it as Class A or AB (?) and that AB would be 50%? But he said so much and I was just trying to keep my head above water quite honestly.

I sat back and put on MOG (squeezebox duet) and listen to a variety of tunes and I have to say it put a smile on my face.

[Tyson]

IMO, class A generally sounds better than class AB.  Try to optimize for that.

[munosmario]

Mario;

Mark was a gem and I thank you for the suggestion! He certainly spoon fed me and taught me as much as I could learn. I did mention to him I was thinking of putting in the GL KT88's and he said then I should raise the bias to 240 - 250.

I'm going to re-pour over the forums regarding plate voltage. He mentioned that I could bias it as Class A or AB (?) and that AB would be 50%? But he said so much and I was just trying to keep my head above water quite honestly.

I sat back and put on MOG (squeezebox duet) and listen to a variety of tunes and I have to say it put a smile on my face.

fz1jmp, what Mark meant is that for Class AB the bias has to be set in reference to 50% of the KT88 tube rated "Maximum Plate Dissipation" (MPD), which happens to be 40 watts (it is 35 watts for the 6550SV). In practice most people use 70% as reference but I surmise Mark is being conservative for the sake of tube life--you can adjusted by ear in line with your SQ preference. For Class A one can use 100% of MPD as reference.

If you happen to know the Plate Voltage, bias setting for Class AB is calculated by taking 50% (or 70%)  of MPD and dividing it by the Plate Voltage. For Class A you take 100% of MPD and divide it by the Plate Voltage--you could use less than 100% to extend tube life, if you don't hear objectionable change in sound quality (given your SQ preferences). I imagine the bias settings Mark gave you for the 6550SV and KT88 tubes correspond to Class A (at a100% of MPD or maybe less...we need to know the Plate Voltage to be sure (call him and ask). Clearly, these calculations give you the bias value for a single tube.

Mario

[doug s.]

hi jack,

it seems you have finally gotten these amps working properly, good news!     here's a suggestion for you.  since the speakers you are using, klipsch cornwalls, are wery efficient (98.5 to 102 db/1w/1m depending on series), you may want to consider having your amp converted to triode from ul.  your speakers would likely sound better w/the triode setting, and 15wpc in triode will still be plenty of power to drive your klipsch's to extremely loud spl's, even in a big room.  and, maybe it is possible to wire it w/a switch to allow changing from triode to ul on the fly.  you might wanna contact cary again, to get their input on this...

doug s.

[munosmario]

hi jack,

it seems you have finally gotten these amps working properly, good news!     here's a suggestion for you.  since the speakers you are using, klipsch cornwalls, are wery efficient (98.5 to 102 db/1w/1m depending on series), you may want to consider having your amp converted to triode from ul.  your speakers would likely sound better w/the triode setting, and 15wpc in triode will still be plenty of power to drive your klipsch's to extremely loud spl's, even in a big room.  and, maybe it is possible to wire it w/a switch to allow changing from triode to ul on the fly.  you might wanna contact cary again, to get their input on this...

doug s.

Great suggestion, doug s. 

Jack, as you may have learned from the reviews, in Triode mode, the Super Amp was characterized as basically sounding more like a top class, high power SET--compared to its equivalent Push-Pull peers. Since unit was originally designed to be sold as a relatively easy kit to build, the conversion was accordingly designed to be rather simple...just desoldering and resoldering a wire. Since I gather you are not prepared to send unit to Cary (at least no yet), if you can handle a soldering iron, I am sure you would be able to do it. I am also sure Mark will be able to get you copy of the original instructions (I believe a separate page distinct from the overall kit assembly instructions). If you feel brave enough, you could implement doug s's suggestion of installing a switch...make sure, though, to get advice from Mark on proper electric rating for switch as well as confirmation if switching could be done on the fly--not all Triode/Ultralinear switchable amps can take on the fly switching without risk of damage to amp, some require unit to be turned off before switching mode.

Mario

[doug s.]

agreed - if you contact cary they should be able to walk you thru this mod - it should be quite easy.

doug s.

[jjc1]

  The Cary website has an excellent write up on how to bias properly. I suggest you read this. If u have a problem finding the write up, let me know.
 

[fz1jmp]

Couple of comments;

Mark from Cary did walk me through the bias procedure. I've personally never seen a 1/4 input as a bias point, so that sort of threw me. Plus I did not know what to bias to. I'm still trying to understand what plate voltage has to do with the bias amount, but I think I may be able to pass a very simple tube test now!

I completely agree with you all about wiring the amp into triode mode. I wish I had the manual, I think that will make the amp sound even better. I'm going to call Mark next week and see how hard it is.

[jjc1]

  Mark from Cary should be able to tell the proper bias for your amp.

[munosmario]

  Mark from Cary should be able to tell the proper bias for your amp.

Mark already did, see replies #39 & 41, and Jack has already implemented the recommended bias adjustment (after some tribulations dealing with Cary’s single-point bias measurement/adjustment approach).

Problem with this particular Super Amp is that it is not a regular production unit. It was one of the prototypes containing premium parts which was used in designing the amp--intended primarily as a kit. However, although the "final" version that reached the market (and subsequent ones) had auto-bias as the proclaimed major feature, which allowed the use of different types of power tubes without need for the user to adjust bias, the unit that Jack owns--the subject of this thread--does not have that feature; it has fixed bias. So, Jack is now facing the need to adjust manually the bias whenever he changes power tube types (or even same type if tube quad is not balanced). It appears that Cary does not have any user manuals but hopefully they have assembling instructions and/or schematics. Interesting enough, Jack was originally told by Dave (the service manger) to use 30mv per tube (30x4 at single measuring point) for the 6550SV (Reply#15), but Mark (senior technician) suggested 50ma per tube (50x4). Given my personal experience in dealing with him, I tend to believe Mark’s number...besides, given that particular tube maximum Plate Disipation (MPD), 30mv bias per tube  for the 6550SV would imply a plate voltage in excess of 650 Volts, for Class A operation (an unusual large number).

Mario

[TheChairGuy]

Not to say you can't get good sound from those Cary's...but any tube amp without voltage has ultimately left me wanting.  The music just rolls out there - georgeous midrange always evident - but with uncontrolled bass and less-than-crisp/exciting treble sounds.

Leave open the possibility that no matter the tube rolling you do - the lack of voltage regulation on a whole helluva' lot of amps out there (even crazy priced ones) simply don't have tight voltage regulation.

Don't mean to be a wet rag here...just injecting some additional perspective to consider.

[Ericus Rex]

50 ma per tube sounds a bit high.  I'm sure it will sound great at that bias but you're getting into the range that wears a tube down quickly.  Start at 50, listen a while and then drop it down by 5ma/tube at a time and see if you still get a satisfying sound.  If so, keep going down until the sound changes then go back to your last setting.  The idea is to keep the bias as low as possible (for tube longevity) while still keeping good sonics.

The 1/4" plug for bias is rare these days but I once owned a pair of Quickilver 8417s that were biased the same way.  I had a anologue meter with a 6" cable and 1/4 plug I used for biasing.  Much quicker than what you're doing now (unless you solder together a specific cable, like I mentioned before).

[Quiet Earth]

All of the fixed bias amps that I have encounterd had a trim pot for each output power tube. That is how you are able to set the bias current to exactly X mA per tube and match the bias for the set. How are you supposed to set and match four tubes at the same time with one bias pot on this amp? I'm having trouble visualizing it from the descriptions.

ChairGuy,
You're talking about regulated output tubes right? Please elaborate for fun.

[opnly bafld]

All of the fixed bias amps that I have encounterd had a trim pot for each output power tube. That is how you are able to set the bias current to exactly X mA per tube and match the bias for the set.

I have a parallel and a push/pull that have a pot for each pair, just need to run matched tubes.

[rollo]

  Well glad to hear the bias is now set correctly. Your speakers have a wonderfull synergy with SET amps. After hearing an SET amp the push pull design will push you away.
   IMO any time an SET amp can be used properly meaning with sensitive speakers [ 95db+] it is a win win. I callit the "Humpty Dumpty Affect" , thats right just could not put Him together properly. No voltage splitters no feedback. Simple as simple gets. KISS.
   If it were me investigate the cost of converting to SET. Weigh the cost against a new SET Amp and tube set. The most natural Klipsch we have heard were powered by SET amps.
    Have fun.


charles

[munosmario]

I have a parallel and a push/pull that have a pot for each pair, just need to run matched tubes.

As far as I know, Jack got amplifier to work properly and is now very happy with its sound quality...he is planning to audition it for a while before next steps--likely to be the mod for triode operation and move away from  SV6550 into KT88 (Jack will be consulting with Cary's Mark re those next steps).

Bottom line, instead of a regular production unit with auto bias, Jack got a unique prototype amp with fixed bias and a single-point measurement/adjustment approach, which makes mandatory a fully matched quad of power tubes to start with...nothing unusual or difficult at all. On the plus side, for those who believe in the benefits of premium parts, Jack's prototype has a chock full of them 

Cheers,

Mario

[opnly bafld]

Not sure why you quoted my response to Quiet Earth. 

I was just pointing out that there are a variety ways to skin the cat concerning manual bias.

[munosmario]

Not sure why you quoted my response to Quiet Earth. 

I was just pointing out that there are a variety ways to skin the cat concerning manual bias.

Yes, actually I almost deleted it, but, then, I left it in. Reason was that, in a way, I wanted to hinge on your statement that those amps of yours had two measurement/adjustment pots, each one handling a pair of tubes and, accordingly, the pair of tubes corresponding to any given one of those two pots had to be matched. In other words, if I understood your statement correctly,  two pairs of matched tubes were needed--not  a matched quad. The latter being precisely the case for Jack's Super Amp given that it has only one pot for all four power tubes. This was what I was trying to "hinge" to your response.  I am sorry if the connection was not that clear or up front.

Mario

[Ericus Rex]

All of the fixed bias amps that I have encounterd had a trim pot for each output power tube. That is how you are able to set the bias current to exactly X mA per tube and match the bias for the set. How are you supposed to set and match four tubes at the same time with one bias pot on this amp? I'm having trouble visualizing it from the descriptions.

You MUST use gm matched quads with this amp since the bias pot will adjust all four tubes simultaneously.