[munosmario]

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

Thanks, Ericus Rex, exactly my point.

Mario

[sebrof]

Not to say you can't get good sound from those Cary's

Good, because I'd be very surprised if you can't get very good sound from them

If it were me investigate the cost of converting to SET.

I'd say it would not make sense as this amp is neither Single Ended nor Triode.
Unless you meant converting to Triode (i.e.: wiring the Pentodes as triodes) but keeping it Push Pull?

[TheChairGuy]

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

Hi...voltage regulated power supply.

Even better, voltage regulated power supplies as the best imaging comes from dual mono amps - best to have two separate trannies with amps....tho you can probably get away with single tranny feeding independent transmission lines in preamps without notable loss in imaging (they draw less, so they need less)

It's not to say you can't have an amp without voltage regulation and lacking dual mono configuration to sound really nice....but, the two together really improves the breed.

Personally, I don't consider any amp or preamp that isn't dual mono now.  If an amp doesn't have voltage regulation, preferred are tube voltage regulators, I take a pass.  It's not that I'm a snob, it's just what I have near conclusively found in the past that works for me.

van Alstine designs are all very tightly regulated...but, for whatever reason (probably cost), not dual mono.  So, despite being very curious, I've passed on taking a shot on his designs for this reason. Others are out there, however, at fair prices (Decware comes to mind)

[fz1jmp]

I thought I would put my "final" thoughts. It turned out that the prior owner pulled his KT88's out, put in the 6550's and never re-biased, nor did he tell me to do it. I thought it was auto bias, but if you change out types of tubes, well you have to reset the bias. I actually went with some nos 6550's and they sounded great, after all that! However, I found a Hogan SET amp of my dreams and while I ended up enjoying the sound of the AES, especially with the Cornwalls, the AES is looking for a new home.

Thanks for all the great comments!!!!

[Freo-1]

Happy to hear all went well.  That's the story we all like to hear. 

Good luck with the sale, and enjoy the SET.  Feel free to post your observations about the SET on the Low Wattage circle.   

[raindance]

deleted.

Glad you got it figured out. Sorry you had to buy another amp to do so.

[Quiet Earth]

What's so amazing? Reply #6 clearly asked if all of the tubes were functioning optimally. If the bias was not set correctly the answer should have been no.

Lot's of people ask all kinds of questions about all kinds of issues. Are we supposed to assume that everyone is a newbie every time we jump in to make a reply? Am I supposed to have the same crystal ball that you have?

[doug s.]

Amazing. All these posts from tube enthusiasts and no mention of biasing. The symptom was classic under-bias causing tons of crossover distortion (thin and almost distorted sounding).

And yes, you can get warm full sound from a push pull amp. Especially a Cary - IMHO probably a little too warm for my tastes.

Glad you got it figured out. Sorry you had to buy another amp to do so.

huh?  perhaps you were reading some other thread?  30 posts in this thread mention bias...

doug s.

[Steve]

  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.

charles

Sometimes simple is deceiving. There are several major problems with SETs because of its simplicity, not necessarily all presented here:

1) Bass response is weak since the OPT inductance is compromised by DC primary current, with bass frequency response fluctuations. If Parafeed is utilitzed, then a choke and coupling capacitor become more limiting factors in bass and sound quality reproduction. As such, the midrange/highs are emphasized, hence "midrange magic".

2) The amp output impedance (Z), hence damping factor, varies wildly and non-linearly, dependent upon the signal level. For simplicity, as the plate current rises in relation to the idle current, due to the musical signal's varying level, the plate resistance remains relatively constant. As the plate current continues to fall below the idle current, per signal applied, the output Z rises/varies dramatically, the damping factor actually swings to zero just as cutoff is reached. So control of the driver/speaker varies wildly. Thus it is important to run an SET amp conservatively.

3) High harmonic distortion (HD), even though low order, influences the sound, while intermodulation distortion (IM), being several times that of HD, causes problems with complex music.

4) If AC is used with directly heated triodes, then one has to deal with hum elimination, just as one has to deal with power transformer hum. Some object to even slight amounts of hum. If indirectly heated tubes are used, problem is usually lessened.


I have also seen some others, in the past, who have mentioned the "humpty dumpty affect". However, the signal is not taken apart in any way, shape, or form; therefore there is no need to put the signal back together again as those guys  have claimed. It just does not work that way. The circuit is like any other, except two power supplies are sometimes used.

FZ1, a JJ E88cc will fill out the sound a little, if it is too thin, lacking a little bass. Just a thought. I would suggest to specify "balanced" sections and "low noise" if interested.

Cheers and have a great week guys.