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Old 6th March 2013, 10:07 AM   #8551
fas42 is offline fas42  Australia
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You trying to beat me in the pessimism stakes ...??

Frank
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Old 6th March 2013, 10:15 AM   #8552
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No , I gave a meaningful measurement !
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Old 6th March 2013, 11:36 AM   #8553
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This is the RH 88 I rejected . An interesting design which should beat the Jardis on measurements . The ECC81 allows it to function as intended due to high Rp . I did try all sorts of modifications and would say his design is ideal for what it set out to do . My own has better distortion and sensitivity for no more money . I think an EF184 in semi pentode would be better . EF184 is almost an ECC81 if triode . The idea is that the output valve functions as a pentode as far as drive is concerned . The Rp of the KT 88 is greatly lowered by anode to g1 feedback via Rfb 100 K . The ECC81 sort of blends in as it's impedance is high . One could say it becomes a super triode . A lot of effort has gone into throwing things away . There s no cathode capacitor on the ECC 81 , that is important and also means no quality of capacitor to debate . The KT88 can be triode connected . Results are about the same with lower sensitivity ( 30 % if I remember ) . What I like is the blocking cap is doing more than usual . If using an EF184 the same cap can offer shunt input feedback . One cap with 3 vital jobs .
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Old 6th March 2013, 08:30 PM   #8554
a.wayne is offline a.wayne  United States
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Just want to let you guys know, this is actually one of the few places one can discuss Audio and i dont just mean DIY, I mean as in "here" , anywhere outside of these fences are nothing but little men lurking in knickers ...


Rant off .....
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Old 6th March 2013, 08:39 PM   #8555
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Old 7th March 2013, 06:26 AM   #8556
dvv is offline dvv  Serbia
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Nige,

I wonder how that little dinky amp you posted above would sound if you dished out the extra money and effort to eliminate even that last capacitor by adding a DC servo?

If you went all grand about it, you could use an LF412 dual FET input op amp to control both tubes, working on the assumption that the best capacitor is the one not there.

Just musing ...
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Old 7th March 2013, 06:33 AM   #8557
dvv is offline dvv  Serbia
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@wayne, john dozier

Yep, it's a good set of people here, all easy going, no strife, nobody is trying to prove his point at all costs - rare indeed.

Frankly, this is one of only two forums I go to, the other being a more local one, from Zagreb, Croatia; it has the added benefit of being 360 km (app. 220 miles) away from me, so I get to meet the people there in person, something I sorely miss here.

The other thing I do miss here is good, old Thorsten; I find his ideas intriguing and miss the discussions coming from them.
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Old 7th March 2013, 08:45 AM   #8558
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Quote:
Originally Posted by dvv View Post
Nige,

I wonder how that little dinky amp you posted above would sound if you dished out the extra money and effort to eliminate even that last capacitor by adding a DC servo?

If you went all grand about it, you could use an LF412 dual FET input op amp to control both tubes, working on the assumption that the best capacitor is the one not there.

Just musing ...
The famous pre 1939 Loftin White tackles that . TubeCad makes it safer .
The Tube Cad Journal: Design Idea-A safe Loftin-White amplifier

I honestly had no interest in valve amps a year ago . I don't love them espeailly now . They are great fun to play with . One thing it has helped me to understand is , what is amp and what is source . Mostly what I heard with a domestic grade of CD player would not justify a preference of valve over transistor . I would even dare to say identical would be the observation using an average CD player . What a condemnation of CD players . None of my amps are especially euphonic .

The 2A3 is a lovely valve . I have some Gu 50 which are clones of Telefunken LS50 . An interesting valve as it is a development of the Harries Valve company Beam Tetrode . Harries designed it in 1935 , RCA bought it and produced 6L6 ( or similar ) . 807 was not so special so plate to plate feedback was introduced to help tame it a bit ( as used by Alex Kitic in RH88 ) . In 1942 the Telefunken " Ray Pentode " LS 50 was introduced . Much like a KT 88 or 6550 ( EL 156 ) . Captured by the Soviets and cloned . The KT 88 was introduced Nov 56 ( me September ) . LS 50 is truly a milestone . said to be the better fake triode and able to run silly voltages .


These are the sources of information I found most informative
How to design valve guitar amplifiers
Patent Specification No. 496,083
http://www.clarisonus.com/Archives/T...er%20Tubes.pdf
Single-Ended Applications

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Old 7th March 2013, 12:36 PM   #8559
a.wayne is offline a.wayne  United States
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+10 On Thorsten ...


Paul McGowan of Ps Audio fame got off on McIntosh when he got into not using Output transformers in SS Designs , basically he thought they were using it to skirt the FTC test , well along with all the negatives of having them there ...

Article : McIntosh transformers | PS Audio

Ironically a Mac501 amp failed to pass the 1 hr preconditioning test when JA attempted to test it ...

McIntosh MC501 monoblock power amplifier Measurements | Stereophile.com

The funny part is Mac owners believe theres an advantage to autoformers on the outputs of SS amps and while i will admit to being a mac fan and have owned their stuff over the years , there is no doubt to their limitations , weak drive and dark sounding , working at their best where power is required at 8 ohm , the autoformer allows them to cheat a bit by being able to provide high wattage at 8 ohms and not worry about load tolerance ...

Thoughts ...

Last edited by a.wayne; 7th March 2013 at 12:38 PM.
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Old 7th March 2013, 01:03 PM   #8560
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Auto transformer output has plenty to recommend it especially if one can access the direct output for 8 /4R . If the 1R tap is used any crossover distortion is reduced . My bet is nicer all round . In the the late 1970's I was invited by Sony to a show . There I saw a class D amp . The engineer said it had a nice sound not unlike valves . He reasoned the output choke was doing that . His words " now we understand it was the transformer we liked " . The amplifier was not produced , a range of conventional amps called Esprit instead .

BTW . 5.7 R was said to be an optimum power transfer resistance . Most 8 R speakers approximate to that . 16 R generally helps distortion in an AB amp . The 1 R tap used with an 8 R speaker should offer excellent performance . Class AB should be almost as class A if so . It is like having a gearbox . I love their amps , even more so now I know .

Last edited by nigel pearson; 7th March 2013 at 01:22 PM.
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