CV2799

If they glow, this is the place to be
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pre65
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#121

Post by pre65 »

I've got ferrite beads on the two grids. Sort of triode connected sounds good, in keeping with the ethos of this project.

Sounds sweet enough at the moment, still got the 220uf caps in, but have been through the spares box and found some 100uf and 150uf. Might try the 150uf first, but that will be a Tuesday job.

Just listening to Nat "king" Cole and his voice is really "fluid", can't think of another word to indicate the superbitivity of the sound. :lol:

So its now a parallel single ended beam pentode sort of triode connected with positive grid bias. Must be unique. :lol: :lol:
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

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Mike H
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#122

Post by Mike H »

"superbitivity" :thumbleft:
 
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pre65
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#123

Post by pre65 »

Ah yes, nice to have a new word now and then.

Been taking a few voltage measurements this morning, and all seems well. There was a squeeky noise so proper grid stoppers will be fitted in addition to the ferrite beads.

I think the top hardness I heard the other night was clipping. :shock: Backing off the volume a gnats gentleman's sausage made it stop. :wink:
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

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#124

Post by Mike H »

Really? Any idea which bit was clipping?
 
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pre65
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#125

Post by pre65 »

Mike H wrote:Really? Any idea which bit was clipping?
No. Probably driver valve (6N7)

Before I added the cathode bypass cap to the 6N7 the volume pot went to full on without any clipping.

Might take it off today and see what happens, probably will be below the clipping threshold.

I have a feeling that a bit more positive bias (more than 12.4v) might help, but my bench supply(12v) is on MAXIMUM.
The only thing necessary for the triumph of evil is for good men to do nothing.

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G-Popz THE easy listening connoisseur. (Philip)
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pre65
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#126

Post by pre65 »

Perhaps I should go back to basics.

The 6N7 data sheet suggests the valve is run at 250v anode, 6ma on the cathode and -5v on the grid. Both grids and both anodes connected together, cathode is already common.

So, I calculated the cathode resistor @ 833 ohms and ended up with 778 ohms.

Max anode dissipation (per plate) is 1W, and I'm achieving 690mw , 230v on anode and 3ma per plate.

So,
A) does that allow sufficient headroom for line level CD ?

B) does the Danbury interstage primary provide a good load for the 6N7 ? Data sheet says 11.3K for class A .
The only thing necessary for the triumph of evil is for good men to do nothing.

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pre65
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#127

Post by pre65 »

I've taken this amp out of service for a while, and put the 811a A2 amp back in use.

Judging by the dust on 811a it has not been used for a while.

And WOW, this is what an amp should sound like. I might forget about the CV2799 for a while and concentrate on a 2A3 (or 6B4-g in fact) preamp like Nick exhibited at Owston. :)
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

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#128

Post by Mike H »

pre65 wrote:B) does the Danbury interstage primary provide a good load for the 6N7 ? Data sheet says 11.3K for class A .
15k for 2 windings in series.

That assumes 15k load on the other 2 windings in series.

Looks like you'll have to get 'scope out to see what it's really doing, and where, at the moment we're just guessing.
 
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#129

Post by pre65 »

I was going to pinch the interstage out of this to try in my KT66 PP project, but before I do that, I might try another driving valve.

I thought a trioded 12GN7 that was last used on the GM70 project might be worth a try, so I will investigate that first.
The only thing necessary for the triumph of evil is for good men to do nothing.

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pre65
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#130

Post by pre65 »

I've removed the driver valve (6N7) as it was not giving enough gain, so now looking for a suitable octal driver.

I was interested by Pauls idea of a trioded 6V6 and am investigating how best to set it up.
The only thing necessary for the triumph of evil is for good men to do nothing.

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pre65
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#131

Post by pre65 »

In the end I went for a trioded D3a, but after much head scratching because the anode voltage was different from L-R it seems one of my pair of valves is defective.

BUM. :(

So, into the spares box we co, and out pop a couple of 12HG7, last used to drive GM-70.

The 9 pin sockets are being rewired. :wink:
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
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pre65
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#132

Post by pre65 »

I got everything changed over, but on test the anode volts were much too high.

After a lot of faffing about it seems that although the heater wiring on the base PCB was correct, I had not wired pin 6 to pin 6 on the valve base, so no heaters and no cathode conducting. :oops: :oops: :oops: Pin 6 is not used on D3a, that's why I'd not wired it up originally.

Anyway, it's back working now, just need to alter the dropper resistor before the interstage to get the anode volts up a bit.

It's nice to have it back in working order. :D
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
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