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Old 1st October 2013, 12:07 PM   #3251
H.Michi is offline H.Michi  Japan
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Quote:
Originally Posted by H.Michi View Post
Hello Rod,

Thank you very much for informative advice.
I now completed the first step of the 26 pre-amp partly modified from my 71A pre-amp. Frankly, I like the sound of 26 pre-amp.
I shall try "Filament bias method" as a next step adopting a new PSU.

Updated schematic of my 26 Pre-amp

Just one year elapsed since I posted here on my 26 Pre-amp, I have made various modifications to my 26 pre-amp adopting ideas / hints obtained from this forum namely in valuable : Rod Colman, Kevinkr, anyjevans and mogliaa.
As a result, I feel it has got a vital in vocal regardless to Jazz or Classic, though it does not fit to a soft containing wide dynamic range or ultra low end.
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Old 2nd October 2013, 12:18 AM   #3252
byang is offline byang  United States
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Default parafeed and ultrapath

Quote:
Originally Posted by juanitox View Post
any schematic to share?
do not know how to draw schematics on computer.just seach for parafeed amp.advantage of that is you can boosttrap return path of the output tranny to cathode of the tube, kind of expanding dynamic range w small amount of positive feedback.this was employed by famous western electric preamps. Also by blocking direct current to tranny, no gap is required in tranny core, capacity could be reduced for same power rating,results better high frequency response and fast sound.
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Old 2nd October 2013, 05:43 AM   #3253
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Quote:
Originally Posted by H.Michi View Post
Updated schematic of my 26 Pre-amp

Just one year elapsed since I posted here on my 26 Pre-amp, I have made various modifications to my 26 pre-amp adopting ideas / hints obtained from this forum namely in valuable : Rod Colman, Kevinkr, anyjevans and mogliaa.
As a result, I feel it has got a vital in vocal regardless to Jazz or Classic, though it does not fit to a soft containing wide dynamic range or ultra low end.
Very nice.
about those Finemet cores, where did you get them? I believe they were costly, how much for a pair?
Thanks
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Old 2nd October 2013, 02:31 PM   #3254
H.Michi is offline H.Michi  Japan
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Unfortunately, the OPT used in the schematic is not available, however possible substitute are assumed to be available, the following is catalogs for your references.
You can see the price list for Noguchi FM-20K600CT, FM24K-600CT and Andix Audio RT20K600

ttp://noguchi-trans.co.jp/index.php?main_page=index&cPath=40

ttp://www.andix.co.jp/
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Old 2nd October 2013, 08:27 PM   #3255
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Quote:
Originally Posted by H.Michi View Post
Unfortunately, the OPT used in the schematic is not available, however possible substitute are assumed to be available, the following is catalogs for your references.
You can see the price list for Noguchi FM-20K600CT, FM24K-600CT and Andix Audio RT20K600

ttp://noguchi-trans.co.jp/index.php?main_page=index&cPath=40

ttp://www.andix.co.jp/
Many thanks!
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Old 9th October 2013, 05:58 PM   #3256
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Quote:
Originally Posted by Rod Coleman View Post
Felipe -what voltage across the cathode resistor?
Left channel 8,83V
Right channel 8,76V

Isn't too low?

I measured output voltage directly at your reg:

Left 10,15V
Right 10,08V

It' seem that I have only 1,3V, have I to adjust till 1,5V, right?
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Old 9th October 2013, 06:14 PM   #3257
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Quote:
Originally Posted by merlin el mago View Post
Left channel 8,83V
Right channel 8,76V

Isn't too low?

I measured output voltage directly at your reg:

Left 10,15V
Right 10,08V

It' seem that I have only 1,3V, have I to adjust till 1,5V, right?
In my case as exemple, I have around 9V, meaning also around 1,4V on the filaments. Starved filaments seems to have better rejection to microphonics.
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Old 9th October 2013, 08:57 PM   #3258
TheGimp is offline TheGimp  United States
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I wonder if the filaments having more strength at the lower temp is responsible?
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Old 9th October 2013, 10:16 PM   #3259
kevinkr is offline kevinkr  United States
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Seems reasonable, I assume since the filament is not as hot and has not elongated (grown lol) as much that perhaps tension on the filament is also a bit higher?
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Old 10th October 2013, 09:50 AM   #3260
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It's necessary to connect the output RCA gnd to gnd?
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