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 Post subject: 8W Low voltage 845 Single Ended Power AMP
PostPosted: Tue Apr 08, 2003 5:05 pm 
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Location: Hong Kong
845 is a very attractive tube! It have the clear, air and transperence as 300B, but more linear and natural like 2A3. Just lost a bit detail and smooth but you it is easier to match with your speaker. Have you feel the power of 845? When you love to listen any classic overtune or drum present, you will love 845 (or 211 as mine).

845 is one of the most difficult tube. It not only their high plate voltage. Also it need high voltage swing with low output impedence driver. Many branded product use 300B to drive it. But it rise another problem. Since 300B also hard to drive. It don't need very high swing, but also need low output impedence driver.

To simplify and lower the difficulty, we need to add a step up interstage transformer. That IT must be very high quality. I suggest Tango NC16. 1:2 IT can increase the voltage gain but still very low in the DC resistance. Even it is not cheap, but no-way! (Tell me if you got another idea)

845 cheap? Yes on the new production. RCA, Amperex NOS cost more than HK$3000 (US$380) and very rare! So forgot them. New production of China 845 still sound excellent. Many branded product using them with great result.

To help non-expert DIYer, I draft a simple circuit for the 845 Single Ended and hope you can comments on it.

Image

I think 750V is much easier than 1000V. Also, 5k Output is much cheaper and smaller than 10k. 15W power higher than 300B, the headroom of it is much much higher. So you a 300B cannot get the same power feeling.

I think the circuit is simple enough. But the Power Supply unit? Later on, I will follow up!!

Welcome for any comments

Happy DIYer
Chung


Last edited by chung on Thu May 20, 2004 3:26 pm, edited 4 times in total.

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 Post subject: Complete circuit
PostPosted: Wed Apr 09, 2003 12:25 pm 
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My original circuit got some mistake and non-complete. This one corrected the OPT is 5k and complete with PSU. Please comments.

Also, I change the driver tube to EC88, which is a high mu mid current UHF triode. Hope it sound good. The circuit changed to self-bias and the power lower to 11W. I will report the construction and performance soon.

Image

Happy DIY
Chung
http://www.vt4c.com


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 Post subject: 6C45 IT 845
PostPosted: Wed Jun 18, 2003 5:02 pm 
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I just work out the Layout of the 845 on MS PowerPoint:-

Image

I will use 6C45 1:1 push 845. That is a bit hard for 6C45, but should workable if run 6C45 on 240V plate for 25mA. I will use James JS-6135HS for output and JS-2008N as Interstage. Good enough?

Please comments


Chung


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 Post subject:
PostPosted: Mon Jun 23, 2003 4:31 pm 
845 requires much more swing and power on the Grid than the 211.

Will it be too hard for the 6C45 and the IT?

diytfy!


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 Post subject: Yes!
PostPosted: Mon Jun 23, 2003 5:10 pm 
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Yes! Eric,

But that is low power version 845. The Bais will be around -80V, plate voltage 700-750V. It just a bit harder than a 300B.

6C45 will be set on a very high plate voltage 210V 30mA. Bais on -2.5V. It can easy swing to 250V p-p. It should be good enough for 845.

But my output transformer a bit delay, so this project will be postpone.

Chung


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 Post subject:
PostPosted: Mon Mar 29, 2004 1:38 pm 
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That is my final circuit. Much more dynamic and the parts is easier found and more choose! I have further lower the B+ to 610V. Which allow me to use Solen 630V Capacitors!

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 Post subject:
PostPosted: Wed Oct 20, 2004 5:11 am 
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Chung,

What is the final circuit? How does it sound?
Thanks

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 Post subject:
PostPosted: Wed Oct 20, 2004 12:06 pm 
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The last Circuit shown is existing circuit.


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 Post subject:
PostPosted: Wed Oct 20, 2004 11:20 pm 
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Two questions that I'd like your expertise:

1. How to calculate the resistance used with the equalizing resistors in the voltage-doubler network?

2. What drawing utility did you use for the very neat schematics?

Thanks,

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How can I tell what I'm listening is what was recorded?


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 Post subject:
PostPosted: Wed Oct 20, 2004 11:25 pm 
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Oh, another two questions:

1. What's the purpose for putting the two 1N4007 diodes in front of the 5AR4 rectifiers?

2. Is there any reasons for placing the interstage transformers in front of the tubes? My guess is the placement is not that critical. Yet, the tube in the front may allow easier replacement installation. And they show look better up in the front. :P

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 Post subject:
PostPosted: Fri Aug 19, 2005 5:42 pm 
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HKL,

Sorry for missing your message and recover so late!!

The IN4007 is used for Hybit (Tube + SS) bridge rectifier.

The schematics draw by circuit maker, Free students version and complete version found here: -
http://www.microcode.com

Chung


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 Post subject: Re: 8W Low voltage 845 Single Ended Power AMP
PostPosted: Mon Jan 14, 2013 2:00 am 
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Hi Chung, Happy New Year 2013, towards long since entered the forum, but here I am, nice project the 845 low voltage. Martin


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 Post subject: Re: 8W Low voltage 845 Single Ended Power AMP
PostPosted: Mon Jan 14, 2013 2:01 am 
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http://www.vt4c.com/teach_room/simple_power.html


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 Post subject: Re: 8W Low voltage 845 Single Ended Power AMP
PostPosted: Mon Jan 14, 2013 11:54 am 
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MartinRamon wrote:
http://www.vt4c.com/teach_room/simple_power.html

I have build this 845 lower voltage version as the link. It would fine and sound a bit more powerful than typical 300B SE, even both are around 8W output. Anyway, 845 sound not as sweet!!


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