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Old 12th March 2014, 01:54 AM   #1431
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Ian,

Thanks for your help, I really appreciate it!

Kind regards
Andrew
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Old 28th April 2014, 05:56 PM   #1432
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Hi,
quick question: Can any one spot glitches on this one,
or
is this schematic architecture conform to the original hand drawing?
Thanks
J.
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File Type: jpg bh_fixed_bias_a.jpg (79.9 KB, 519 views)
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Old 28th April 2014, 10:52 PM   #1433
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J.
It looks fine.
The Ultralinear connections are not shown, that would require splitting L1 and L2 into 2 inductors each. Also remember that D3 and D4 are LEDS (D3 Green, D4 Blue).
Cheers,
Ian
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Old 29th April 2014, 01:07 PM   #1434
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Thanks! I'm going to build one of these for me, but EL34, and full pentode. Nevertheless I'll post a UL schematic with the same components numeration and figures, as per the "Dud Amp" BH2, for best use of other builders.
Besides, how difficult could be implement the H.Dean suggestion of driving the finals by the cathodes? No more a BH though...
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Old 29th April 2014, 06:06 PM   #1435
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Ok
Cheers
J.
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Old 4th May 2014, 01:29 PM   #1436
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Hi Ian
Im trying to change the pre/driver stage in a Sunsui AU70 to an ecc83 diff.
The thing is I am getting a lot of distortion at lowish level.
The power stage is fixed bias at 12.7V, 1K stopers, 300K load, catode feeback from opt, anode voltage is 420V,
grid 2 is 300V, driver is 285V anode with 150K load, no ccs at this- time 560 ohm catode for 1ma, 2nd grid has 220 ohm to ground.
Any sugestions to what is wrong?
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Old 5th May 2014, 04:50 AM   #1437
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asddd,
For some reason I'm not getting notifications on posts to this thread anymore, I only just noticed your post.

I take it that you are replacing the 6AN8 pentoder + triode concertina splitter with a 12AX7 LTP to make this amp Baby Huey'ish.

To get you going join the 2 off 12AX7 cathodes together and wire them via a 15K resistor to the -18V point or if easier via a 27K resistor to the -37V point. If using the -18V point then you may want to reduce the 6K series resistor to say 4K7 to get back to the -18V after the extra load current has been added. Once that works you can then add a real CCS in place of that resistor.

Hope this helps,
Cheers,
Ian

Last edited by gingertube; 5th May 2014 at 04:52 AM.
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Old 22nd July 2014, 04:38 PM   #1438
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I'm trying to make a list of parts and get a handle on costs for my own BH build. Is it still considered Ok to use the Hammond 1650E output xfmrs, and 270FX for Pwr? Those 1650s run almost $100 ea, so I want to be sure I'm right.

Also, out of curiosity, what is it about a Blackgate cap that takes 100 hrs to burn in?

Thanks all...
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Old 22nd July 2014, 11:57 PM   #1439
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Since you are in the US I would be looking for a pair of Dynaco Z-565 Output Trannies
OR
cheaper option - Edcor CXPP25-MS-8K
https://www.edcorusa.com/cxpp25-ms-8k

I don't know why Blackgates take 100 hours to break in - in fact I did'nt believe the stated "break in" times until I experienced it for myself.

Anyway Blackgates are now difficult to find and expensive.
Elna Silmic II are a good alternative.

Cheers,
Ian
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Old 23rd July 2014, 12:37 AM   #1440
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Thank you!
If I may, since I have NO experience in either theory or spec comparison: If cost were no option - what would you choose? First: between those two - then a "good" one. I've read the majority of the thread, and I can see that there's little wisdom in going cheap at the goal. I can do this once, but not over and over for comparison. I want "good-approaching-great" transformers. I won't be buying others to play with for quite some time...
Thanks!
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