Author Topic: Single Ended 6L6 amplifier  (Read 4230 times)

Offline fredeb

Re: Single Ended 6L6 amplifier
« Reply #15 on: December 15, 2017, 09:07:32 PM »
I am reading just under 10V over the 100ohm resistor. Basically 25 watts dissipation. So 6L6GC it is.

I built a SET 807 recently, and the B+ was about 320V. It sounded very good, maybe even better than the 250V B+. My feeling is to go with the 320V B+. The sound was very good. Load impedance was 2500 ohms.

What are the losses through the transformer ? Do you think maybe 20% ? With 20% transformer losses you still end up with 20 watts power , which is a serious amount of power for class A single ended .
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Offline Mars

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Re: Single Ended 6L6 amplifier
« Reply #16 on: January 09, 2018, 04:08:56 PM »
I am working at 6 watts for triode mode, and 12 watts for single ended tetrode mode. The transformer losses are as close to 5 watt total as I can get.

Here is a 6L6GC single ended triode amplifier I built for a forum member:

IMG_20171229_151554 by Karel Mars, on Flickr

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Online King_Julian_S

Re: Single Ended 6L6 amplifier
« Reply #17 on: January 09, 2018, 04:40:52 PM »
🥂


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Offline itscraig

Re: Single Ended 6L6 amplifier
« Reply #18 on: January 09, 2018, 04:42:01 PM »
very nice is it a headphone amp? :sd:

Offline capetownwatches

Re: Single Ended 6L6 amplifier
« Reply #19 on: January 09, 2018, 08:52:18 PM »
very nice is it a headphone amp? :sd:

I don't see a hole in front... :nfi:


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Offline itscraig

Re: Single Ended 6L6 amplifier
« Reply #20 on: January 09, 2018, 11:20:39 PM »
I have a drilling machine

Offline kubusi

Re: Single Ended 6L6 amplifier
« Reply #21 on: January 10, 2018, 06:07:00 AM »
Hi Mars,
Been following this thread with interest, just a quick question. Have you ever tried a GEC type DA41  triode in a single ended output stage?  One of them should give an output without any trouble in the region of 25 to 30 watts. After all it was designed specifically as an audio valve.
If you have tried one I would like to read your views on this particular valve as to how good or bad they sound compared to your 2A3 and triode connected 6L6/807 designs.

Kubusi
FIRST LAW OF VALVE AMPLIFIERS
Hot glass looks exactly the same as cold glass.

Offline fredeb

Re: Single Ended 6L6 amplifier
« Reply #22 on: January 10, 2018, 03:08:10 PM »
I had the pleasure of listening yo the prototype of this amplifier ( which is a further refinement of the protype ) , and let me tell you - it sounds fine indeed . Drives average efficiency  speakers with ease . Well done Karel !
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline Mars

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Re: Single Ended 6L6 amplifier
« Reply #23 on: February 13, 2018, 04:46:09 PM »
Hi All

The amp was completed, burned in, and delivered. Here is a photo with the cage on top:

IMG_20180205_105602 by Karel Mars, on Flickr

IMG_20180205_105654 by Karel Mars, on Flickr

At the last moment, I decided to use a pair of KT66 Gold Lions for output duties. They sounded better than the stock 6L6GC I had. They look cool too:

IMG_20180205_105803 by Karel Mars, on Flickr
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Offline fredeb

Re: Single Ended 6L6 amplifier
« Reply #24 on: February 13, 2018, 06:00:56 PM »
Wow ! Looking goooood Karel .
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
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Online King_Julian_S

Re: Single Ended 6L6 amplifier
« Reply #25 on: February 13, 2018, 06:51:50 PM »
as always ...
Karel , the more people order your stuff the more they will understand
Non audiophile music lover...

Offline Ampdog

Re: Single Ended 6L6 amplifier
« Reply #26 on: February 14, 2018, 02:06:52 AM »
Also following Karel's activities with interest.

.... After all it was designed specifically as an audio valve.

One must be careful here. The data sheet description reads " ... for class B audio work."  The acccent is on 'class B', which was mostly used at the time for powerful p.a. and cinema amplifiers. Such a valve features almost cut-off conditions at zero bias so as to avoid a separate bias supply. This usually meant a fairly non-linear Vg/Ia characteristic at low Ia, with high 2nd harmonic distortion, not conducive to class-A operation as S.E.T.  (Remember, in class-B 2nd harmonic products cancel out.)

Not saying it could not happen, but one would probably be better off with a 'normal' more linear triode. The new generation high dissipation KTxyz valves would be easier to use should one be interested in high output S.E.T. amplifiers. I doubt whether the price would be higher; after all, a DA41 might be pretty scarce these days.

(There is the school-of-thought that triode connected tetrodes are not 'pure' triodes, but that is a subject for another day.)   

Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Online King_Julian_S

Re: Single Ended 6L6 amplifier
« Reply #27 on: February 14, 2018, 09:06:27 AM »
I do not like the Ktxxx stuff .. all amps I heard/owned with them is very SS like .. perhaps too little distortion or   None of the roll off most older valves give ( I am not sure what it is ,but I like it ...)
Non audiophile music lover...

Offline Mars

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Re: Single Ended 6L6 amplifier
« Reply #28 on: February 14, 2018, 09:36:15 AM »
What are the losses through the transformer ? Do you think maybe 20% ? With 20% transformer losses you still end up with 20 watts power , which is a serious amount of power for class A single ended .

fredeb, only 25% of the DC power is turned into music; so 6 watts triode music. The losses in the transformer is 0.7 watt copper (0.2dB) and 1.7 watt iron. 15 Henry primary inductance; so bandwidth is better than 30Hz to 60kHz. The tube's limit will be reached before the transformer saturates.
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Offline charles

Re: Single Ended 6L6 amplifier
« Reply #29 on: February 14, 2018, 11:19:03 AM »
Did you check the Total Harmonic distortion (THD) at rated output of the amplifier with an audio analyzer

It is good practice to do it specially when using different types of valves.   

I normally check the THD of my completed valve amplifier restoration/projects
in order to be sure of its specifications.