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01a > 71a DHT Line Preamplifier.

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Re: 01a > 71a DHT Line Preamplifier.

Post by noodle88 on 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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Re: 01a > 71a DHT Line Preamplifier.

Post by dixchen on 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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Re: 01a > 71a DHT Line Preamplifier.

Post by noodle88 on 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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Re: 01a > 71a DHT Line Preamplifier.

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

Hi!

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




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

71a preamp



12a preamp


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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Re: 01a > 71a DHT Line Preamplifier.

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

Hi!

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




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




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



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.




Best regards,
Cheah
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Re: 01a > 71a DHT Line Preamplifier.

Post by noodle88 on 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.



Cheah
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Re: 01a > 71a DHT Line Preamplifier.

Post by vt4c on 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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Re: 01a > 71a DHT Line Preamplifier.

Post by noodle88 on 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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Re: 01a > 71a DHT Line Preamplifier.

Post by vt4c on 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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Re: 01a > 71a DHT Line Preamplifier.

Post by noodle88 on 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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Re: 01a > 71a DHT Line Preamplifier.

Post by vt4c on 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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Re: 01a > 71a DHT Line Preamplifier.

Post by STC on 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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Re: 01a > 71a DHT Line Preamplifier.

Post by noodle88 on 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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