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01a > 71a DHT Line Preamplifier.

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sph
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01a > 71a DHT Line Preamplifier. - Page 2 Empty Re: 01a > 71a DHT Line Preamplifier.

Post by noodle88 Thu Dec 19, 2013 4:23 pm

dixchen wrote:

interesting, which model lundahl trans were you using before this? 


I used LL1660/18mA which optimized for 10Y.
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Post by dixchen Thu Dec 19, 2013 5:06 pm

I see, with the 10ma version you have much more inductance thus lower bass extension. Thanks for the info.

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Post by noodle88 Thu Dec 19, 2013 6:12 pm

Hi!

Yes, more than half. So as the plate and filament choke. I'm getting more and more favorable towards passive filtering.

Cheah
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Post by noodle88 Sun Jan 19, 2014 4:25 pm

Hi!

Just completed a all new power supply for my 71a/ 12a preamp. 

01a > 71a DHT Line Preamplifier. - Page 2 Image64


This PSU will power the 71a and 12a preamp just by connecting the umbilical without any switching.

71a preamp

01a > 71a DHT Line Preamplifier. - Page 2 Image65

12a preamp
01a > 71a DHT Line Preamplifier. - Page 2 Image66

The hard part is that my 71a is using ultra path bias where else 12a using filament bias . So heater voltage for 71a have to be 5Vdc but 12a is at 16Vdc.

This new PSU also quieter. As I first power it up with my 12a preamp, I notice the noise floor is lower. Later this is being confirmed by lower Vac at B+.

Will upload more photos and info later.


Cheah
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Post by noodle88 Thu Jan 23, 2014 11:40 am

Hi!

One B+ and two filament power transformers are placed on top of the PSU.

01a > 71a DHT Line Preamplifier. - Page 2 Image67


Filament choke, diodes, 30,000 uf filtering capacitors are placed under the top plate.

01a > 71a DHT Line Preamplifier. - Page 2 Image68


For B+, Black Gate NH capacitors are used. One pair is wired in Super E-Cap configuration.

01a > 71a DHT Line Preamplifier. - Page 2 Image69

The best part of this PSU are two of the vintage Weston panel meters. I like to see their needle moving when B+ is being turn on.

01a > 71a DHT Line Preamplifier. - Page 2 Image70


Best regards,
Cheah
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Post by noodle88 Mon Aug 25, 2014 10:22 am

Hi!

I have done some update for my 71a preamp. I can foresee I  will need more gain from my preamp as I move on to 211 power amp.
I need a driver stage for this Preamp. Thomas did suggest UX-201a. So , I can have 15db of gain with output impedance of 150ohm. on top of that, I can have balance line output for my PP-2cs ( differential push pull amp) as well.
Other than that Tamura A-4714 has a 6 ohm output tapping that rated for 3W. This can be used as speaker output, but 71a amp only push out 700mW of power.
So, it's a preamp with balance or unbalance line out and also a power amp.

01a > 71a DHT Line Preamplifier. - Page 2 Image24

Cheah
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Post by vt4c Mon Aug 25, 2014 8:26 pm

Hi Cheah,
   Thanks for the project updates.

   BTW, which design are you going for the 211 SE amplifier?
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Post by noodle88 Wed Aug 27, 2014 7:32 am

Hi STC, 

I'm working on a 2 stage 211 amp with 801a as driver tube which design by Thomas Mayer.

Cheah
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Post by vt4c Wed Aug 27, 2014 9:34 pm

Hi Cheah,
  Sounds like you're going to be very busy and smelling lots of solder fume..cheers

   Any concern on the gain as 801A has an amplification factor of about 8 driving the 211 to full power?
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Post by noodle88 Thu Aug 28, 2014 7:13 pm

Hi STC, 

This 211 SET design do include an input transformer that require 1.8VRMS to full power. That's why I decide ti make this 2 stage 71a preamp.

Cheah
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Post by vt4c Thu Aug 28, 2014 8:51 pm

Hi Cheah,
   Ah....That's how it's done. Thank you for the explanation. Smile 

    Great choice of tubes...All DHT.
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Post by STC Fri Aug 29, 2014 8:22 am

noodle88 wrote:Hi STC, 

This 211 SET design do include an input transformer that require 1.8VRMS to full power. That's why I decide ti make this 2 stage 71a preamp.

Cheah

noodle88 wrote:Hi STC, 

I'm working on a 2 stage 211 amp with 801a as driver tube which design by Thomas Mayer.

Cheah


Morning Mr.Cheah,

STC or Vt4c? Laughing  or am I always in your mind? lol!
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https://stchelvam.wixsite.com/ambiophonics3dstereo

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Post by noodle88 Fri Aug 29, 2014 8:49 am

Hi STC,

Oh! A typing error. Sorry for that.
Indirectly I also promoting your name. ;-)

Cheah
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