Whoops
Well spotted John - that was a whoopsie.
I love cathode followers. I have argued with lots of folk about this, but to my limited knowledge (dangerous admission perhaps?) the logic of using them is irrefutable - high impedance in, low resistance out.
Opposing this principle could be held to be promotion of distortion by default!
7N7
Well spotted John - that was a whoopsie.
I love cathode followers. I have argued with lots of folk about this, but to my limited knowledge (dangerous admission perhaps?) the logic of using them is irrefutable - high impedance in, low resistance out.
Opposing this principle could be held to be promotion of distortion by default!
7N7
slowmotion said:Thanks 7N7
Took me a little while to figure out what the wigly bits
on the anodes of the 13D3 was , until I rememberd you have both current source and - sink, I'm not so bright sometimes
Hello there.
Thanks for the comments. Please note dhaen's comments - I made a ****-up with the 1N4148!
7N7
THE VENERABLE CF.
Hi,
I remember that vividly and the whole topic is worthy of a thread of its' own.
I second that,although not all CF are the same they come in very handy.
Moreover,for all the SET fans adoring simpicity and lots of distortion they're a godsend.
Granted,it will take'm a while as to the why of this.
Cheers and well done 7N7,
Hi,
I remember that vividly and the whole topic is worthy of a thread of its' own.
I second that,although not all CF are the same they come in very handy.
Moreover,for all the SET fans adoring simpicity and lots of distortion they're a godsend.
Granted,it will take'm a while as to the why of this.
Cheers and well done 7N7,
Another update
A couple of changes to mention:
First, the 4.7k 5W suppling the D3A G2 board is now 6k @ 5W
The potential dividers feeding the two MPSA42 transistors have been changed; the top resistor in each one is now 200k
Vg2 on the D3As is now 120V. The load resistors have been changed also: the 100k parallel resistors have been removed leaving just the 15ks
This bloody computer is having one of its go-slows this evening (5 minutes just to post this) so I'll re-send the diagram when it starts behaving again
7N7
A couple of changes to mention:
First, the 4.7k 5W suppling the D3A G2 board is now 6k @ 5W
The potential dividers feeding the two MPSA42 transistors have been changed; the top resistor in each one is now 200k
Vg2 on the D3As is now 120V. The load resistors have been changed also: the 100k parallel resistors have been removed leaving just the 15ks
This bloody computer is having one of its go-slows this evening (5 minutes just to post this) so I'll re-send the diagram when it starts behaving again
7N7
Updated Diagram
Here as promised, is the updated circuit diagram for the Instock amplifier.
I have marked most of the changed components with an asterisk.
The principal effect of this is that Vg2 on the D3As is now 120V - note also that the cathode loads are now 15k instead of 13k as previously (forgot to mark these! )
7N7
Here as promised, is the updated circuit diagram for the Instock amplifier.
I have marked most of the changed components with an asterisk.
The principal effect of this is that Vg2 on the D3As is now 120V - note also that the cathode loads are now 15k instead of 13k as previously (forgot to mark these!
)7N7
Re: In-stock and working...
That's a very good question; now that you have pointed it out I wonder myself.
On the other hand, 6528A is a beefy valve; if it should decide to run away....
I may try operating it without the grid leaks when I have caught up a bit on the other things that I have to do.
I meant to try reducing the value of the grid stoppers, since the very low output resistance of the driver stage (gm is about 25 on the D3As) should mean that I should be able to get closer to 0V on the 6528A - i.e. a sort of p-p class A2. Obviously I would need a very low value - or none at all to achieve this, and with such high gm in the 6528 things could quickly get out of hand.
However, I have now dismantled the 13E1 amplifier; replaced the front end, tried two alternatives and managed to cause (I think) the CCS to pack up after years of reliable operation.
As a result the Instock has to stay where it is for the time being.
I appears to be completely reliable, which is a good thing as without music I am sunk!
7N7
dhaen said:Paul,
Just picking......
What is the purpose of the 470K's on the 6528 grids?
And how is it sounding? Have you built 2 channels yet?
Cheers,
That's a very good question; now that you have pointed it out I wonder myself.
On the other hand, 6528A is a beefy valve; if it should decide to run away....
I may try operating it without the grid leaks when I have caught up a bit on the other things that I have to do.
I meant to try reducing the value of the grid stoppers, since the very low output resistance of the driver stage (gm is about 25 on the D3As) should mean that I should be able to get closer to 0V on the 6528A - i.e. a sort of p-p class A2. Obviously I would need a very low value - or none at all to achieve this, and with such high gm in the 6528 things could quickly get out of hand.
However, I have now dismantled the 13E1 amplifier; replaced the front end, tried two alternatives and managed to cause (I think) the CCS to pack up after years of reliable operation.
As a result the Instock has to stay where it is for the time being.
I appears to be completely reliable, which is a good thing as without music I am sunk!
7N7
470k grid-leaks
I don't know what those 470k resistors are doing there either. Snip 'em out, and rebias if necessary. Any grid current can only develop grid voltage across the grid-stoppers (the output resistance of the cathode followers is negligible in comparison).
And yes, Bombay Sapphire is the best. Partly because it can (and should) be kept in the freezer. Keep the (thick-based) short glasses in the fridge. Ultimately, however, the best gin is the one that is in your glass and not someone elses.
I don't know what those 470k resistors are doing there either. Snip 'em out, and rebias if necessary. Any grid current can only develop grid voltage across the grid-stoppers (the output resistance of the cathode followers is negligible in comparison).
And yes, Bombay Sapphire is the best. Partly because it can (and should) be kept in the freezer. Keep the (thick-based) short glasses in the fridge. Ultimately, however, the best gin is the one that is in your glass and not someone elses.
Re: SEE?
Quite so, but I didn't say that they were gridstoppers!
7N7
fdegrove said:Hi,
Hold on..those 470K Rs aren't gridstoppers, you're 1Ks are.
And you better keep the 470K Rs just in case your valve decides to go into thermal runaway.
Kampai and holding the G+T firmly in hand,
SayoKetchup,
Quite so, but I didn't say that they were gridstoppers!
7N7