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Old 11th December 2004, 11:44 AM   #1
GeirW is offline GeirW  Norway
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Default 2x8w SET choice.

Gday.

A quick question, just for saving some time.:
What tubes should i look for
in a 2x8w SET. ( not to high voltage)


(The same goes for 2x8w PPT.?)





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Old 11th December 2004, 12:29 PM   #2
Previously: Kuei Yang Wang
 
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Default Re: 2x8w SET choice.

Konnichiwa,

Quote:
Originally posted by GeirW
A quick question, just for saving some time.:
What tubes should i look for
in a 2x8w SET. ( not to high voltage)
As I always say, that's 300B territory. If you don't want 300B's you can get away using both sections of a 6AS7 in parallel, but linearity is pretty poor.

Or you could use an all EL84 Amplifier, 4pcs trioded EL84 in the output stage, loaded by 2K5 (or even 1K2) and another EL84 as driver. Then there are EL34 & KT88/6550 which can be triode connected for something in the general vicinity of 8 Watt.

Other options might be a Trpple PE 10Y Amplifier, using a 5K Primary Output Transformer. If you want to you can use a 845 at low current and get 8 Watt out of that.

Finally there are more excotic Triodes out there with High Mu and Anode Power which can be used as massive "spud" (Spud for single tube, single stage Amplifiers), there are a few around in russia as DHT transimtter types and in the US IDHT Compactron Beam Triodes like the 6HS5. I suspect even a 572 could be coaxed into a 8WPC "Spud" Amp....

So, there are no hard and fast answers, cheapest are probably triode wired generic tetrodes/pendoes, but they will likely sound worst of all options and given the cost for decent output transformers you might as well shell out for some inexpensive 300B's. The more esotheric stuff, well that is another story.

Sayonara
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Old 11th December 2004, 02:46 PM   #3
GeirW is offline GeirW  Norway
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Gday.

TnX. for the swift reply.
Well. for two 300B cheapo, it will cost me (local prices) 330$.
(i have no intension to spend that on tubes. "yet")
The 845 option looks promising, but still i reckond
this would atleast require 550-600v. (maybe less,
have just had a quick look, beside.. math is not my strongest
side.)
At the look of it, KT66 would can probably give me 8w around 400v.
I guess between theese tubes mentioned, 6550 or EL34
would be it. 6550 is rated 12w. at 250v, and EL34 is 8w. at
250/65. But distortion is high though.
6550 have 7%. and 34 have 10%, beside that, i think
6550 would perform better than 34.
As EL84 goes (i love them), well. i got the imression from various
threads, that SEP is secondary amp`s? (qualitywise)


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Old 11th December 2004, 03:36 PM   #4
GeirW is offline GeirW  Norway
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Gday.

Umm.
Edit/pentode nummbers.
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Old 11th December 2004, 04:23 PM   #5
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Hi Geir,

Do you need 8W in particular, say, over 4 or 5W, which would get you (just barely) into 2A3 territory.

I think you'll find that most members with an opinion on the subject will tell you SEP is less desireable than single-tube operation. However, once you go beyond two tubes in parallel, to three to ten tubes, the table perhaps turns, at least for some (think conrad johnson ART preamp). If you look at the distribution chart of tube characteristics and the statistical spread of deviation from ideal, you'll find that a group of tubes (say, 5-10) stands a better probability of being more linear than any given tube. If you're adventurous, you might wire together a number of, say, smaller triodes---even smaller DHTs---to see what happens on the result.

Cheers.
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Old 11th December 2004, 05:34 PM   #6
GeirW is offline GeirW  Norway
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Gday.

Interesting stuff serengetiplains.
i certainly will look into it, sooner or later.
Quote:
Do you need 8W in particular, say, over 4 or 5W, which would get you (just barely) into 2A3 territory
With this spesific amp. am would like to stay as simple as possible, triode, medium voltage and 2x10w. as a limit.
2x5 or 2x8 wouldn`t be such a big stepp. (i think)
I certainly wount be crossing 10w, for that am planning a PPT
amp.
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Old 11th December 2004, 05:36 PM   #7
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Konnichiwa,

Quote:
Originally posted by GeirW
TnX. for the swift reply.
Well. for two 300B cheapo, it will cost me (local prices) 330$.
(i have no intension to spend that on tubes. "yet")
Considering russia is just around the corner from you, why not buy direct?

That said, if you build the Amp with for example a set of James universal Outputs like the 6123 and a suitable Mains Transformer with enough +B and Output Heater taps you could start with a EL34/KT66/KT88/6550 or whatever you have and later change the Valve sockets and try 2A3's & 300B's at your lesure.

Quote:
Originally posted by GeirW
As EL84 goes (i love them), well. i got the imression from various threads, that SEP is secondary amp`s? (qualitywise)
Parallel connection looses you some, but the EL84 is readily available, sounds very good and using a truckload is actuall;y quite feasible. I mean you could use 7 in parallel and the 8th as Driver with an Output transformer around 1K or lower, something like those made for SE 6S33.

In any case, the "massive parallel" amplifiers can be quite sucessfull.

Sayonara
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Old 11th December 2004, 05:39 PM   #8
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Konnichiwa,

Before I forget, there is a qute nicely researched project by Claus Byrith which uses Standard tetrodes/pentodes in a local feedback arrangement that is very similar to what Audiopax calls "LM3" operation.

8W Singe End, EL34 amplifier designed by Claus Byrith, Royal Academy of Music in Aarhus, Denmark.

Sayonara
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Old 11th December 2004, 05:56 PM   #9
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Here's a quote from an email from John Broskie of TubeCAD re many-// EL84:

Quote:
I have long maintained that a tube amp (SE or PP) that used 20 EL84s would probably be the best sounding amp on earth. The big qualification is that the amp would not be stupidly compromised in design: insufficient idle current or driver current (remember, it takes current to charge capacitance).
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Old 11th December 2004, 06:12 PM   #10
GeirW is offline GeirW  Norway
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Gday.

TnX. Kuei.

I was reading the Mullard by Claus the other day, and seems like
i have totally missed out on this page.
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