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Old 5th May 2013, 12:57 PM   #171
nhuwar is offline nhuwar  United States
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Lexan is very handy in those application. I had a scanning electron microscope that the whole high voltage side was encased in the stuff. Can't beat it.


Nick
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Old 5th May 2013, 09:37 PM   #172
Magz is offline Magz  United States
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That Corona Dope looks like good stuff; similar to the MG Chemicals conformal coating I'm using but with a higher dielectric strength. Maybe I'll pick up a bottle, but I won't put it on the stuff I've already coated...never know if it's compatible or not.

Thanks for the tip.
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Old 5th May 2013, 09:54 PM   #173
Magz is offline Magz  United States
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I completed the two mirror-imaged C2 cap banks (see pics). They test at 127uF and 126uF at 120Hz using my LCR meter, a little lower than nominal but well within the 20% spec. The balancing resistors will be bent away from the caps when the banks are mounted; for now they take up less space flat against the caps.

The banks are constructed on a Lexan panel with the caps in series order around the panel. The panel serves to separate the caps with the highest potential difference from each other, and also gives rigidity and a place to mount the brackets. The banks will be screwed to the side panels of the enclosure underneath the OPT; I left some clearance at the back of the panel so the cap vents can expel their contents if something goes wrong. Caps are secured with hot-melt glue and zip-ties through holes in the panel.
Attached Images
File Type: jpg 833 Amp C2 Caps 1.jpg (370.5 KB, 885 views)
File Type: jpg 833 Amp C2 Caps 2.jpg (357.3 KB, 864 views)
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Old 11th May 2013, 12:07 AM   #174
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Default My own Midlife Crisis 833C Amp

Hi,

This is an very intresting thread, because I was starting my own "Midlife Crisis 833C Amp" nearly at the same time (On March 18 I was ordering two of this "Monster-Tubes" to playing around with this ).

So I try to discribe this project in my bad english...

The starting Point was the german "silvercore-project". But in my opinion is 15W out of this Monsters like sex with no touching . For this I don't need to build a new amp, I could use some of my older projects...

The frist step were a lot of simulations with LTSpice...and some tests with the B+
The Picture shows the current and at the voltage near 1kV...
833c Test | 833ctest | hifi-forum.de Bildergalerie

And yes, the Spice-model of the 833A is far away from real 833C!

I was calculating the amp for about 50W sine...makes a B+ of about 1kV and a bias current of 200mA.

The reason were, I want to use normal available parts for all... And 1kV is much more handy like 2.3kV ...Over all it was expensive enough to be an "Midlife Crisis Amp" also.
The first two stages are build from one 12AT7 followed by an SRPP (2 x 6CV7/EL34) in triode mode driving the 833 with up to 100V peak to peak
trough an electolytic capacitor of 47uF (briged by 100nF MKP).
I use a lot of Hammond transformers, including the OTP 1642SE.
Kupfer und Eisen...1642SE | eisen1642se, kupfer | hifi-forum.de Bildergalerie

Ok, the 8ohm outputs of this transformers are useless, but because I have 8ohm speakers only I can use the 16ohm output so I have a Raa of 10kohm and this seems to fit perfectly for the 833C...

Here some photos of one the ready monoblocks...while testing...
833C Endtest | 833c, endtest | hifi-forum.de Bildergalerie
SAM 0226 | sam0226 | hifi-forum.de Bildergalerie
833c | 833c | hifi-forum.de Bildergalerie

And some scope photos...
833C 20Hz | 20hz, 833c | hifi-forum.de Bildergalerie
833C 100Hz | 100hz, 833c | hifi-forum.de Bildergalerie
833c 1KHz | 1khz, 833c | hifi-forum.de Bildergalerie
833C 10 kHz | 10, 833c, khz | hifi-forum.de Bildergalerie
SAM 0234 | sam0234 | hifi-forum.de Bildergalerie
power...About 60V peak to peak are 50W sine...
833C 50W Audio | 50w, 833c, audio | hifi-forum.de Bildergalerie
And some photos at live action...
833C Amp | 833c | hifi-forum.de Bildergalerie
833C | 833c | hifi-forum.de Bildergalerie
833C Amp | 833c | hifi-forum.de Bildergalerie

Matthias.
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Old 11th May 2013, 12:41 AM   #175
grufti is offline grufti  United States
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Goil! ..... [translation for the moderators: delightful] Gefaellt mir! ..... [translation: I like!]
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Old 11th May 2013, 03:04 AM   #176
Magz is offline Magz  United States
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Nice job. What are your impressions of the sound? How much power at clipping? 50W?
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Old 11th May 2013, 11:42 AM   #177
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Hi Magz,

The Sound is gigantic , like the tubes...
It sounds better than the best 300B I have, but with much more power!
This is a tube amp that sounds like a tube amp but with the power of a transistor amp. When I use the Klipsch Cornwalls it is like an earthquake at higher volume and with very small compact speakers it works also...so you don't miss a subwoofer.


Click the image to open in full size.

As you can see at this pic there are about 60V peak to peak at a 8ohm load...50W sine without anny clipping (The blue curve, the yellow is the Input Signal). The amp clips at about 60W. ( By the way, the Driver stage is clipping first )

Matthias
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Old 12th May 2013, 10:52 PM   #178
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Hi Magz,

Did You testing your B+ at Kathode voltage and Grid voltage in real?
I think you get MUCH more anode current as you have simulated...because the spice model You are using is far from the reality!
Be carefull please!

Matthias
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Old 13th May 2013, 01:23 AM   #179
Magz is offline Magz  United States
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I'm on the road this week and replied yesterday but apparently it didn't post.

I'm still waiting for my OPTs and HV chokes so I'm taking my time and building subunit by subunit and testing each. Next are the DC supplies for 6E5P heater and 833 cooling fan, then the driver circuit. Then I'll determine the best location for each to give the least noise and shortest signal path, then drill the holes, then get the panels anodized/powder coated/mirror polished, then finally assembled.

I'll be sure to bring it all up on a variac, and the bias supplies are regulated so I can adjust them as needed to get the target Ia.
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Old 14th May 2013, 01:43 PM   #180
Magz is offline Magz  United States
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I received an update from Monolith on the progress of my OPTs. The amorphous cores have been received and the bobbins have been wound. Performance is a little better than specification:

L=68H (spec>60 H)
-3dB FR = 7Hz - 66kHz (spec 8Hz - >60kHz)
32 Hz saturation frequency at 1400 Vrms input (spec <35 Hz)

Attached is a picture of the core from one OPT with the bobbin in place. Note the teflon dielectric. An metric ruler and an ECC83 are in the picture for size reference.

They are still waiting on the laser-cut enclosures; once those arrive the OPTs will be assembled and on the way to me!
Attached Images
File Type: jpg 833 OPT coil and core.jpg (166.4 KB, 621 views)
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