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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

845 class A2??

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Tubes ordered

Fuling, since you already have the 813 tubes on order, why not go ahead and try them? Would be using one tube, like Fd and others mention, and is a good idea. Of course I am not the one spending the money, but would be a neat experiment if nothing else.
Kt88s would be nice too, but you will have to totally redue the circuit, parts changes etc. as the KT88 is an entirely different critter to work with.
 
Oh yeah, I expect to recieve my first pair of 813´s tomorrow or the day after tomorrow. NOS STC with graphite plates.

I will probably use Hammond 1629SE output trannies (6,5k/8 ohm and 159H primary inductance!!), C3m or C3g input stage coupled to the power tubes by Lundahl IT´s.
Or maybe I´ll stick to my beloved 12B4A´s as driver stage, but they won´t allow a two-stage design.

Finding an adequate power transformer won´t be easy but maybe I can wind my own if I buy a 420VA transformer kit from a local company.
The same company also offers custom winded transformers but a friend of mine had some serious problems with a unit he bought from them. It seems that they don´t use proper insulation between the windings and I´m not willing to risk anything at these voltages (B+ 800-900V)

Haven´t decided what rectifiers to use, but maybe a 1N4007/6D22S hybrid bridge would work.
 
Fuling said:
Oh yeah, I expect to recieve my first pair of 813´s tomorrow or the day after tomorrow. NOS STC with graphite plates.

When you get them, let me know if they look like these, and if they do, could you let me know your source so I can get a fourth?
 

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ok guys not to start a war. all i wanted to know was a a tube ckt that can put out 25W+ (speaker are 87db and room is 325 sq. ft x 9.5 ft ceiling).

the reason i am asking for 25W+ is that i want to give tubes enough power to drive my speakers to reasonable levels where the music would be appreciated. if i used a 4 W SE i mgiht get disappointed as the speakers are hardly moving and then blame tubes and not the lack of power.

There is emperical knowledge that PP is preferable to parallel SE.

so what i would then look at is a good PP ckt. A friend told me that given Bombay's high humidity and ambient temps it is preferable to use PP.

Also I need a ckt that wil be safe since I have a 18 month old running around. Not that he will poke his fingers into the amp but you never know. it is better to be safe than sorry. kids will be kids.
 
...KT88 Good???

Hi Steve,

I've tried the KT88 is SE and PP amps, trioded, UL and Pentode including Partial feedback. It was quite nice but not as good as the big bottles (845 or 813 haven't used a 211 yet). I heard a couple of other people's KT88s too. About the same as mine in performance.

I preferred it to EL34s but thought it worse than 807s.

What is the secret to getting excellent sound out of the KT88?

ciao

James
 
Hi James

I can give one key. If you read around alot, every designer I have seen picks a tube and then the design/parts. Unfortunately, they have never checked the parts for sonic qualities, and therefore design the component backwards. There are several tubes that may fit a particular category such as power output, but which tube to use should be based on the best design and parts.

In my research, I tested alot of parts for neutrality (it has taken years), if they add or subtract from a natural sound, a straight wire sound so to speak. The key is to find the most neutral design and parts, and then find the tube which mates best, not the other way around.

As an example, when checking electrolytic capacitors, I think everyone knows they bloat/fatten up the bass. No way is an electrolytic cap a "straight wire" in terms of sonics. In many older designs (practically all), to compensate they use small coupling capacitors. This tends to bring down the bass level and seems to tighten up the bass. Unfortunately, how can an electrolytic cap mimic a natural string bass sound? It can't. So the bass is distorted, not really natural sounding. You also lose soundstaging because of DA and DF problems (A nice article to read is "picking capacitors" by Walter Jung and Richard Marsh.) mask inner detail.

Same thing for resistors (As an example, I have copied two articles to my website http://www.sasaudiolabs.com/theory10.htm that compared resistors and found they distort differently and seemingly in amount. Some resistors are notorious for limiting the soundstage, brightening, harshness etc. This all distorts the natural sound, changes the soundstage, changes the natural inner detail (some use distortion to create inner detail).

Now no part is perfect, sonically speaking, but for the best sound, we want to use parts that affect the sound the least. There will be some tweeking but less is better than more when designing a component.

The design/parts must be as near to perfect in all aspects as possible. This includes wire, jacks, solder as well. Then we pick the tube.

Now if we use distorted/colored sounding parts to compensate for a particular tube (by that I mean any form of distortion, not just harmonic or IM), we aren't really going to get the most natural sound. Two wrongs don't make a right (in this case many wrongs/parts).

That is why, when I hear this tube is better than that tube, I don't believe it. First, it depends on the design and second it depends on the parts associated with it. Now don't get me wrong, as there are sonic differences between brands of any particular tube. This we check as we test. As you will find, it is a continual refining process.

I agree with you, nearly no one knows how to design using a KT88, and other tubes as well. You won't find any cheapy amps (companies) that really sound good either. They almost always use gimmicks, if they even know what they are doing. (It is their decision if they like it that way.) But it isn't the best sounding. Of course, the older designs didn't have the great parts either, but they did the best they could with what they had.

When testing, I use all kinds of music, a hundred selections and more. I check all aspects, timbre, dynamics, inner detail, up front and depth test CD selections for soundstaging, solos, duets, orchestras, Jazz, selections that go up the scale. You name it and I check for it. To be natural, all aspects must be right. I can hear the differences in a spit second.

Some designs are poor, in fact most. One must check out all the weaknesses and strengths and decide. I have gone thru alot of testing and thinking about each design, which would be best.

Then, there is the matter of matching to the best speaker(s) and tweeking the speaker if need be, since the design will be out of your control. My system uses a full range setup so I can get the bass without a subwoofer. One of the worse setups I hear is tube mids and SS sub. Ick.

In conclusion, I have tried, and I think I have done so successfully, to Rid my system of nearly all forms of distortions of all kinds. This includes poor soundstaging (including depth, width, lack of inner detail, natural dynamics, imaging etc.). It will take alot of work and money testing parts for neutrality. Best to share information with others.

Hope this helps.

PS. I could probably design something with DHTs that would sound fabulous, but the cost would be very high as the neutral sounding parts are generally more expensive. And who is going to purchase it? Already too many expensive competitors.
 
diyAudio Senior Member
Joined 2002
Hi,

Steve,

Regarding what you said in your excellent post #35; I work the same way although I don't manufacture anything.

I recall some people being upset here once because someone posted a circuit diagram where the author had all the brands and types of the passive components specified and claimed that once you deviated from that list you'd made your own design.

All in all I couldn't have agreed more with the original author.

Nice having you here,;)
 
Thanks Fd.

I have also seen your deep insights in your posts. You are a pillar and do alot to help all on board here, even the new guys, without being arrogant.

Sometimes I come across pretty harsh. My apologies. It is one of my worse faults. I could be easier on the words and not so abrupt.

My main concern is that, some make blanket statements without ever hearing my product. That certainly impacts the image of what people think of me and my company, and the chances of one auditioning my components.

Anyway, keep up the good work Fd and thanks again.:cool:
 
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