832 TWEEKS

What people are working on at the moment
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Mike H
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#166

Post by Mike H »

Nick wrote:Remember to isolate them from the heat sink, the tab will be at b+ voltages.

They have the magic thing called writing on them so you can tell them apart :-)
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Mike H
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#167

Post by Mike H »

pre65 wrote:Well it works, had no doubts really !

Had to drill the reg mounting hole out to 4mm as the only plastic "top hat" washers I had were in a TO-3 kit. Forgot I'd used all the proper ones and I could not see any in the electronic choke kit
If it's a TO247 package don't need top hat washers. The hloe is insualted

Or the hole is insulated, even!

Obviously can't touch type that well :lol:

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pre65
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#168

Post by pre65 »

Mike H wrote:
pre65 wrote:Well it works, had no doubts really !

Had to drill the reg mounting hole out to 4mm as the only plastic "top hat" washers I had were in a TO-3 kit. Forgot I'd used all the proper ones and I could not see any in the electronic choke kit
If it's a TO247 package don't need top hat washers. The hloe is insualted

Or the hole is insulated, even!

Obviously can't touch type that well :lol:

.
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Mike H
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#169

Post by Mike H »

Strangely, no!

Oh wait looks like they're TO220 package, as you were then.


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pre65
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#170

Post by pre65 »

832a is now going to be re instated in the original white MDF base with the 3 "modules" (1 psu + 2 separate amps) as it was when first built. A bit of nostalgia as it was my first amp.

I will be keeping the cathode CCS on 832a and the simple phase splitter so only 1/2 the 12AT7 is being used.

All the screw wire connectors will be eliminated and the layout tidied up a bit and an on/off switch fitted to make it easier to use.

One "mod" I was considering is to use the Ixys chip as an anode CCS on the 12AT7. do the "experts" think that would be worthwhile ?
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andrew Ivimey
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#171

Post by andrew Ivimey »

This is the best thing you've ever built. (challenge! go on... prove me wrong ;-) ) It came into its own when you added the new outpout transformers. Adding any sort of CCS to the driver valve will do nothing whatsoever to improve things (go on... prove me wrong ;-) )
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#172

Post by Dave the bass »

Go on Phil, prove him wrong :lol:

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pre65
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#173

Post by pre65 »

Dave the bass wrote:Go on Phil, prove him wrong :lol:

DTB
I might ! :wink: :lol:
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pre65
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#174

Post by pre65 »

Going through the original circuit and trying to work out what happens it seems the 12AT7 is only drawing a gnats over 0.5ma (0.53) with an anode voltage of 128V

Looking at the grid lines that seems wrong ?

I would have thought 5ma was more like it.

But then it did work before, and as Andrew said it was OK. :wink:
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Nick
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#175

Post by Nick »

What is the circuit? I got a bit lost.
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pre65
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#176

Post by pre65 »

The original circuit is here.

http://www.audiohobbyist.com/images/832/832sch.jpg

I'm not using the 2nd half of 12AT7 and the voltage before the 3K3 resistor is (or was) 275V

One grid of 832a is cap coupled from anode of 12AT7. The other grid is earthed, and I have a CCS on 832a cathode.
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pre65
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#177

Post by pre65 »

duplicated post.
Last edited by pre65 on Wed Jan 20, 2010 5:26 pm, edited 1 time in total.
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Nick
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#178

Post by Nick »

Yep, it does seem a bit of a odd place to be if the valve you have matches the curves. Not sure it would be my choice of a op point.

Using a CCS could work out well in this case. I would suggest setting the CCS for 4ma and changing the cathode resistor to 620R. Should give you about 200v on the anode, I would connect to the top the CCS to the B+ on the output transfomer and ignore any decoupling so you have the most voltage to play with.
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andrew Ivimey
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#179

Post by andrew Ivimey »

gggggggrrrrrrrr, the voice of reason.

Bet it doesn't sound any better though! :wink:
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pre65
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#180

Post by pre65 »

Thanks for the help Nick.

I have to amaze the "Bedford Bopper" at our next mini fest. :wink:
The only thing necessary for the triumph of evil is for good men to do nothing.

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