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Old 8th May 2006, 07:59 PM   #1
Dave P is offline Dave P  United Kingdom
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I have made a V76 type mic pre with a White follower output stage. (2x EF86, 1x12BH7). I have basically copied the first stage of a V76. There are 2 problems I need help with as Iv'e been working on this for months and I need fresh ideas! First problem is a very low frequency (about 2Hz) on the output which unless I have a 2k resistor across output ,spoils the 90dB S/N ratio. second problem is that the Bass rolls off from 100Hz to about 3/4 of 1KHz value by about 40Hz. Otherwise frequency response is flat to 35KHz.

By the way, I have translated from the telefunken braunbuch the technical descriptions for the V72,V77 & V78 circuits. I would be happy to place them somewhere accessible for members but I don't know how, this is my first ever post!

all the best
Dave P
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Old 8th May 2006, 08:17 PM   #2
Netlist is offline Netlist  Belgium
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Dave,
welcome.

Shall I move your thread to tubes or analogue?

If the Telefunken descriptions are not copyrighted material, you can host them here if the files size is <100k and max 800X600 pixels.

/Hugo
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Old 8th May 2006, 10:50 PM   #3
Dave P is offline Dave P  United Kingdom
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Hi Hugo,
I 'm not sure where to post, I'll be guided by you.
There are 3 pdfs of about 50k each, I did the translation so the work is mine and I got the German version freely off the web, what do you think?
best
Dave
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Old 8th May 2006, 10:50 PM   #4
Dave P is offline Dave P  United Kingdom
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Hugo,
On second thoughts better to post it to tubes
thanks
Dave
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Old 9th May 2006, 06:33 AM   #5
Netlist is offline Netlist  Belgium
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Dave,
50k will be no problem, you can only attach one file per post.
I'm looking forward to read them.

/Hugo
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Old 9th May 2006, 08:25 AM   #6
Dave P is offline Dave P  United Kingdom
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Hugo,
This is first translation:- V72
Dave
Attached Files
File Type: pdf v72.pdf (50.0 KB, 83 views)
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Old 9th May 2006, 08:25 AM   #7
Dave P is offline Dave P  United Kingdom
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V77
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Old 9th May 2006, 08:25 AM   #8
Dave P is offline Dave P  United Kingdom
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V78
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Old 9th May 2006, 08:33 AM   #9
EC8010 is offline EC8010  United Kingdom
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Now I know what my EF804s were for! The screening on the mains transformer is to protect other circuitry from the extraneous field it generates, not to protect the mains transformer.

I await diagrams with interest.
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Old 9th May 2006, 11:58 AM   #10
Dave P is offline Dave P  United Kingdom
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Thats right, this is one of the reasons why they managed to obtain such amazing S/N ratios (~120dB). Although the tubes are not canned, the steel chassis wraps around the tubes quite closely as well. The Mains TX screening stops the mic TX picking up hum in such a confined space, the components are really packed in.
Dave P
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