811a SET amp.

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Paul Barker
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#241 Re: 811a SET amp.

Post by Paul Barker »

Hope so, it is going really well.
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pre65
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#242 Re: 811a SET amp.

Post by pre65 »

I'm having an 811a session. 8)

All the parts of the amp were retrieved from their various hiding places, and vast quantities of accumulated dust have been removed.

Everything was connected up (once I had found the wires) and on power up everything seemed OK, although the hum is still there.

Playing now is Solid Air, and it seems more "dynamic" with 811a than it was with GK-71. :o

So, shall I bring it to Owston ?
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#243 Re: 811a SET amp.

Post by IslandPink »

Wow ! - yes if you have space !
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#244 Re: 811a SET amp.

Post by pre65 »

It (the 811a amp) has been to Owston before.

But, as I'm bringing the van there should be room for it. :)

Should also be room for a good selection of music to annoy DTB. :lol: :lol:
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#245 Re: 811a SET amp.

Post by Cressy Snr »

pre65 wrote:
Should also be room for a good selection of music to annoy DTB. :lol: :lol:
My 3 will be Val Doonican, James Last, and Richard Clayderman.
Hope your 3 are as good.
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#246 Re: 811a SET amp.

Post by pre65 »

Mantovani, Des O'Connor and Mozart. :lol:

I thought I'd try and do something about the hum.

First thing was to make a pseudo centre tap for the 6.3v windings on both the mains transformers.

I really wanted 100R, or 220R, but none were found, so matched (as near as poss) 470R 3W were used. Each pair of 6.3v windings (per transformer) is paralleled, and supplies one pair of 6D22s damper diodes and one 6CG7 driver/cathode follower.

Back in action now, and there is deffo a bit less hum, more a touch of hiss now. :D
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#247 Re: 811a SET amp.

Post by pre65 »

I was looking for Arabian Nicks capacitor list on the old computer, when I came across a circuit for 811a in A2.

Now, I never really got my version working as I would like so I studied this circuit with interest. It uses a 56 and a "powerdrive" mosfet to drive the 811a.

56 seem quite rare, but it seems 76 is the same but 6.3v filaments, and I do have a pair of 76 in the valve drawer. So, another project waiting in the wings. :wink:

I'll add a picture of the circuit soon. Can't seem to log into Photobucket at the moment. :(
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Mike H
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#248 Re: 811a SET amp.

Post by Mike H »

pre65 wrote:Mantovani, Des O'Connor and Mozart. :lol:

Now there's a combo you don't see every day.
 
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#249 Re: 811a SET amp.

Post by pre65 »

Try this for size.

Image
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#250 Re: 811a SET amp.

Post by Mike H »

Pondering...
 
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pre65
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#251 Re: 811a SET amp.

Post by pre65 »

In the article the author states that feedback from the OPT to 811a cathode might be beneficial. :)
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#252 Re: 811a SET amp.

Post by jack »

pre65 wrote:...Arabian Nicks capacitor list...
Pah. Today is Martyrs' Day, so is a national holiday; tomorrow is Friday so it's really Saturday, but on Saturday (the real one) we're all off to the Dubai 7s. Even though Friday is a weekend day, this Friday is special - it's UAE National Day, so there are flags everywhere (they are very proud of their country).

I even saw some hummus in the supermarket decorated with coloured herbs to make the national flag. There was also a sheep's head in there attached to a fake tinfoil body.... I thought that the parsley/grass was a nice, if somewhat surreal, touch...

Anyway, back on topic, I'll be in Blighty over "the holiday season", if anyone wants some caps...
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pre65
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#253 Re: 811a SET amp.

Post by pre65 »

In the 811a A2 amp circuit there is a cascaded CCS in the driver valve anode.

Is there likely any performance preference in using either

A) 10M45s
or
B)DN2540

:?:
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#254 Re: 811a SET amp.

Post by IslandPink »

What's a cascaded CCS ? Is there a circuit diagram somewhere ?
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pre65
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#255 Re: 811a SET amp.

Post by pre65 »

IslandPink wrote: Mon Nov 13, 2017 10:56 am What's a cascaded CCS ? Is there a circuit diagram somewhere ?

http://usr.audioasylum.com/images/2/22845/CCS1.jpg
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