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Old 19th October 2007, 12:45 AM   #1
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Default 811A amp Class A2

My new project, 6AK5, VT-25, 811A Single Ended Class A2 amp

Advanced project, chassis perforated, tomorrow painting
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Old 19th October 2007, 02:55 AM   #2
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Looking pretty good so far Are you running the 6AK5 triode strapped?
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Old 19th October 2007, 03:35 AM   #3
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Thanks, No, as pentode is similar to WE717A
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Old 19th October 2007, 04:07 AM   #4
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hi,

I also prepare to DIY one 811 SE tube amp.

several friends use this circuit was test stable & sound quite good when drive Yamaha NS-1000 ebony.

pls try study this circuit.

any comment.

thx

thomas

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Old 19th October 2007, 04:43 AM   #5
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Thanks, the circuit with my modifications, diodes rectifier and 6AK5 very close WE717A
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Old 19th October 2007, 04:52 AM   #6
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Hi, Tube lover, thanks again, Yamaha NS-1000 ebony?, 811A in this schematic, only 10 watts, ideal for my Altec Lansing 97 db, sorry my bad english
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Old 19th October 2007, 05:26 AM   #7
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hi MartinV56 ,

at first l also think cann drive or said good control of NS1000 because long time ago I was NS2000 user. NS2000 was very hard to drive!

But when my friend told me that his NS1000 stardard version & FX-1 can very easy to push.

Use 300B SE also can use. But use interstage couple will better bass.


Then I order one pair of Ebony & try to use 300B. yes, it cannot full control for classic music. But for room music & jazz, ( not heavy Jazz) it can do well. I will try 811SE & 211SE. I will continous report to share experience.

this one was very easy to drive/

Yamaha FX-1

http://page.freett.com/knisi/fx-1.html


thx

thomas



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Old 19th October 2007, 10:39 AM   #8
316a is offline 316a  England
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The output transformer secondary could go in the cathode circuit of the 811A and the loop feedback could be reduced . On the VT25 'dynamic coupled' driver there is no way of selecting the required bias on the 811A which may need attending to . See schematic , this amp uses a tertiary winding on the transformer to offset anode current against filament current which may be confusing , so ignore the coil marked '55t' . It also uses filament bias for the input valve which may be unfamiliar to some .

cheers

316A
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Old 19th October 2007, 04:51 PM   #9
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Thank 316, I will consider that change and its benefits
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Old 19th October 2007, 05:34 PM   #10
316a is offline 316a  England
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Quote:
Originally posted by MartinV56
Thank 316, I will consider that change and its benefits
It's easy to try the cathode feedback and see if it's to your liking . A2 amps can be made to sound good but do need a lot of work , so far I've barely just scratched the surface . Good luck with your project

cheers

316A
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