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Old 11th November 2008, 01:07 PM   #1
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Default EL95 SE schematic wanted

Hey

I have 2 pcs SE outputtrafo 12k/4 ohm. Very small (maby 20 - 30 mA) or simular.

I also have 2 pcs power trafoes with ss bridge and 100 uF cap.
B+ is 360 - 380 voltage. Bias is 35 volt dc.
6V for heat.

The power trafoes is small to.

i will try to build 2 SE mono bloks based on EL95 tubes, but i can't fine any schematics. Yes I have tried to Google.

Can some help me?

Regards

Benny
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Old 11th November 2008, 04:21 PM   #2
Yvesm is offline Yvesm  France
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From Philips:

http://www.tsf-radio.org/forum/im/41...2sch-phil1.jpg

Another one: AG9016:

Another AG9016 "addict"

Yves.
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Old 11th November 2008, 05:32 PM   #3
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Benny,

I think the 1st link Yves provided points out the way. Looking at a data sheet shows power O/P will be miniscule, unless pentode mode is used.

Slew limiting is a MAJOR concern in designs that employ global NFB loops. With its very low gm, the 12AX7/ECC83 is an extremely poor candidate for the driver. Switching to the 6GK5 makes sense to me, as the type provides both high gm and high mu.

Pure pentode mode is most linear when g2 B+ is regulated. A 0A2 gas discharge type will get the job done. Another advantage of regulating g2 B+ is the modest liberty that can be taken with the anode to cathode potential difference limit. Just make sure that you scrupulously adhere to the anode dissipation limit.

Another issue in designs with global NFB is O/P trafo core saturation. Given the small O/P trafos you intend to use, attention to this detail is very important. Roll LF info. off at the amps' I/Ps at approx. 25 Hz. You bury infrasonic junk, while retaining the ability to play the lowest fundamental a double bass produces.

If extra current is available from the "6" V. filament winding, you could bring the B+ rail voltage down some by employing hybrid bridge rectifiers that use 6X4/EZ90s on the vacuum side.
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Old 11th November 2008, 07:21 PM   #4
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The ELL80 is essentially 2 EL95 in one bottle.

We built an ELL80 spud amp and i gathered quite a bit of data.

Attached is the map of the amp we ended up building. You really need some good drive to get it to full power, so an extra gain stage at the front might be needed.

It sounds fine in pentode mode (especially with single FR speakers that like the high output impedance, but sounded better in triode (but gets down to ~1w).

dave
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Old 11th November 2008, 07:23 PM   #5
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Here is the amp... (tube guards a gift from Eddie Vaughn)
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Old 11th November 2008, 07:30 PM   #6
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What it started out like ... it should be noted that these little OPTs also work with EL84/ECL92/ECL86
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Old 11th November 2008, 07:39 PM   #7
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The original schema of the output stage with voltages... (sorry about the quality of the scan)
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Old 11th November 2008, 07:48 PM   #8
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Here is a grundig EL95 SE schema (with a common PP woofer channel)
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Old 11th November 2008, 07:49 PM   #9
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and this one which is attributed to Philips, but has been rejiggered by someone...
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Old 11th November 2008, 08:11 PM   #10
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Quote:
You really need some good drive to get it to full power, so an extra gain stage at the front might be needed.

Dave,

Because of its very low RP, a stage gain of approx. 60X is easy enough with a RC coupled 6GK5. If that truly is not enough, front end everything else with a 12BH7 section whose cathode bias resistor is unbypassed. Do not put the extra voltage gain block inside the NFB loop. Between the natural linearity of the 12BH7 triode and local current NFB (degeneration), distortion is not a problem.
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