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Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum |
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#1 |
diyAudio Member
Join Date: Dec 2005
Location: Welsh Hills
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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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#2 |
diyAudio Moderator Emeritus
Join Date: Jan 2003
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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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#3 |
diyAudio Member
Join Date: Dec 2005
Location: Welsh Hills
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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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#4 |
diyAudio Member
Join Date: Dec 2005
Location: Welsh Hills
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Hugo,
On second thoughts better to post it to tubes thanks Dave |
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#5 |
diyAudio Moderator Emeritus
Join Date: Jan 2003
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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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#6 |
diyAudio Member
Join Date: Dec 2005
Location: Welsh Hills
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Hugo,
This is first translation:- V72 Dave |
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#7 |
diyAudio Member
Join Date: Dec 2005
Location: Welsh Hills
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V77
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#8 |
diyAudio Member
Join Date: Dec 2005
Location: Welsh Hills
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V78
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#9 |
diyAudio Moderator Emeritus
Join Date: Jan 2003
Location: Near London. UK
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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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The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference... |
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#10 |
diyAudio Member
Join Date: Dec 2005
Location: Welsh Hills
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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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