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Old 13th January 2013, 08:11 PM   #81
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These are the measurements on the second amp:

1V rms
2,73V rms
5,66V rms
Attached Images
File Type: jpg 1V rms.jpg (595.4 KB, 416 views)
File Type: jpg 2.73V rms.jpg (555.1 KB, 402 views)
File Type: jpg 5.66V rms.jpg (651.4 KB, 388 views)
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Old 13th January 2013, 08:26 PM   #82
euro21 is offline euro21  Hungary
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For example my 300B SE (d3a, CCS, source follower, 300B, 5K OPT) measuring at 1kHz.

PWR L_THD R_THD L_Ug THD R_Ug THD

1W 0.35% 0.31% 22V 0.11% 21V 0.12%
4W 0.86% 0.80% 47V 0.31% 45V 0.31%
6W 1.23% 1.08% 57V 0.39% 54V 0.38%
8W 1.52% 1.37% 65V 0.43% 63V 0.45%

Fonnesbek, most of soundcard distort at full level. Don't go over the -10dB.

Sample (1kHz, 4W/8R):
Attached Images
File Type: jpg 300B SE 4W.jpg (61.5 KB, 379 views)

Last edited by euro21; 13th January 2013 at 08:33 PM.
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Old 13th January 2013, 08:35 PM   #83
Alexsk is offline Alexsk  Canada
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Quote:
Originally Posted by euro21 View Post
For example my 300B SE (d3a, CCS, source follower, 300B, 5K OPT) measuring at 1kHz.

PWR L_THD R_THD L_Ug THD R_Ug THD

1W 0.35% 0.31% 22V 0.11% 21V 0.12%
4W 0.86% 0.80% 47V 0.31% 45V 0.31%
6W 1.23% 1.08% 57V 0.39% 54V 0.38%
8W 1.52% 1.37% 65V 0.43% 63V 0.45%

Fonnesbek, most of soundcard distort at full level. Don't go over the -10dB.

Sample:
i guess, if. there is CCS, you are running d3a in triode mode, and i probable not at 2ma, correct ?
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Old 13th January 2013, 08:49 PM   #84
euro21 is offline euro21  Hungary
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Quote:
Originally Posted by Alexsk View Post
i guess, if. there is CCS, you are running d3a in triode mode, and i probable not at 2ma, correct ?
Yes, of course triode mode, 10mA.
LED bias (old type green LED), cascode DN2540 CCS, capacitor coupling to FET source follower (5mA), direct driving 300B (375V, 70mA, 5K:8 OPT).
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Old 13th January 2013, 09:42 PM   #85
Alexsk is offline Alexsk  Canada
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Quote:
Originally Posted by euro21 View Post
Yes, of course triode mode, 10mA.
LED bias (old type green LED), cascode DN2540 CCS, capacitor coupling to FET source follower (5mA), direct driving 300B (375V, 70mA, 5K:8 OPT).
The topology here is c3m in pentode, with current ~ 2ma, anode load of 110k Capacitor coupled to 300b, another words almost weco-91 clone.
Distortion figures of your driver and this one, should be different, that is given. However DHT driven by pentode is very interesting subjectively due to distortion cancelation and resulting distortion distribution.
Admittedly, the question remains, is we91 the best what can be done, or driving 300b with much more capable pentode, such as c3m, EL84, el34 etc. at 15+ma is the way to go. Personally i have made my choice, after trying 6sn7, 5687, 6em7, we810, c3m in triode and a few different operating points of c3m pentode, i have ended with similar to Thorsten "legacy" c3m-300b. However the only recommendation i can make is to try as much as possible. Everyone of the above amplifiers has it pluses and minuses. The same c3m pentode - 300b combo, configured a-la a09s plays small jazz combo wonderfully, but don't try to play Mahler 6th with it... running c3m at 15-16 ma brings Mahler to life, but unfortunately Ben Webster is not that intoxicating, like he was with a09 clone.
Again, my eyers, my speakers, my taste..
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Old 13th January 2013, 10:09 PM   #86
euro21 is offline euro21  Hungary
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Independently of the driver topology, in my opinion Fonnesbek THD measuring too high.

Measuring many dozens of C3m (and C3g), all of them capable swinging 150Vpp at about 0.3-0.4% THD (most of them 200Vpp below 0.5% THD). Driving 300B with this low distortion signal, correct 300B SE circuit don't produce 1% THD at 1W.
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Old 13th January 2013, 11:22 PM   #87
Alexsk is offline Alexsk  Canada
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Quote:
Originally Posted by euro21 View Post
Independently of the driver topology, in my opinion Fonnesbek THD measuring too high.

Measuring many dozens of C3m (and C3g), all of them capable swinging 150Vpp at about 0.3-0.4% THD (most of them 200Vpp below 0.5% THD). Driving 300B with this low distortion signal, correct 300B SE circuit don't produce 1% THD at 1W.

Whatever you have mesured in triode-connected c3m has nothing to do with the discussed amplifier.
In operating mode of a09 (140 Ua, 66v G2, 350v B+, 110k anode R) at 20vrms
c3g has about 2 %THD . I did not measure many dozens, just about 6 or 8,
with 16 ma current and G2 =150v (Siemens recommended oper. points), c3m
has about 0.8 % THD at 20vrms and about 2.3% at 50vrms.
If you know about pentode caable of swinging 150vpp with 0.3-0.4 % THD please let me know.
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Old 5th January 2017, 07:54 PM   #88
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I finally did the rebuild of the input stage, as I expected the distortion is much lower, I havn't had a time to listne to it yet.

I'm running the c3m at 18mA utilizing the "best pentode" described by Frank Blöhbaum in LinearAudio vol.1

2,73V RMS 1 W 0,3113%
5.65V RMS 4 W 0,7857%
8.00V 8 Watt 1,629%

I would like to lower the 50Hz noise, but that requires a rebuild of the power supply, I'm using a eletronic chocke which requiers bigge caps then I can use with GZ37, I think I'm pushing it how with the first cap being 60uF
Attached Images
File Type: jpg 2.74 1 Watt 0,3113%.jpg (635.8 KB, 89 views)
File Type: jpg 5.65V 4 Watt 0,7857%.jpg (643.3 KB, 22 views)
File Type: jpg 8.00V 8 Watt 1,629%.jpg (679.0 KB, 20 views)
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Old 6th January 2017, 11:17 PM   #89
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Are you using DC on the 300B filament?
If so, what is the ripple on the DC filament supply?

AC poured filaments can use a balance pot to get the 2 ends of the filament to balance to the "mid-point" of the filament. But unfortunately, that is only part of the problem. The magnetic field of 1.25A AC filament current can cause vibration of the filament wires if there is any difference of spacing from the filament to the 2 sides of the plate (magnetic field of filament, is attracted to a steel plate).
You will find some 300Bs have less hum than others when the filament pot is adjusted optimally for each tube.

Hmm. Stainless plates anybody?
Who is producing such DHTs?
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Old 7th January 2017, 07:04 AM   #90
euro21 is offline euro21  Hungary
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The 1kHz carrier has +12dB level, the 50Hz is at about -57dB (the measurement software vertical subdivision is almos useless, the decade division is commonly used).

About 69dB distance for 50Hz hum is enough good.

If the 300B heater is not so good (poor AC cancelisation, DC filament with hum etc.) you have +/- 50Hz, 100Hz, etc. sidebands around the carrier.
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