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Old 10th October 2005, 02:19 PM   #1
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Default More Questions about A.Wrights PP1C

Hi,

as stated in an earlier post, I decided to build a slightly modified version of the PP1C amplifier as my first tube DIY project.

Now, a few more questions ocurred:

1. In http://www.diyaudio.com/forums/showt...674#post712674
A. Wright writes the following: "But if you are making one I'd suggest going up in voltage to a 420V B+ and having +380 on the front end."

Let me guess, its not enough to just raise the B+ rail to 420V... What else has to be tweaked? Resistor values? Sorry if this questions might be a bit stupid, but I am still a tube newbie ...

2. How can I estimate the total current the amplifier will draw from the PS?

3. Due to my design idea to do the project completely without SS devices, I will have to replace the Mosfet CCS by a tube based CCS. Any suggestions for that? Is it possible to run the CCS circuit from the same B+ rail as the amplifier or will I have to add another PS with separate secondary winding / rectifier / filter?

4. What about the heater supply for the CCS? Is it possible to connect the CCS tube filaments to the amplifier tube filaments (as seen in the circuit, the filament winding is lifted to a somewhat higher potential)?

5. I'd like to use a EM800 display tube for each channel to monitor the output signal visually. May I run these circuits from the amplifier B+ or do I need another PS? Any idea for a simple, tube based circuit to drive the EM800s?

So many questions, I hope you can answer some or all of them

Greetings from Germany...

Andreas
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Old 12th October 2005, 07:32 PM   #2
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...hey, what happened?

Questions too difficult to answer? Or just too stupid? Please give me at least some hints, I'll promise to use my brain as much as possible

Greetings,

Andreas
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Old 13th October 2005, 04:36 AM   #3
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Part of the answer addressed at the recent thread here.

Note that Allen's PP-1C design uses a cascode in each half of the LTP and there will be no extra voltage available to accommodate a pentode CCS, which needs at least 100v and preferably more. So, you will need a negative supply. The heater of the pentode CCS will need to be driven from a separate heater supply, connected either to the negative rail or to a potential divider to provide a negative heater potential that is safe for the tube. A 6AU6, for instance, has a limit of 100v heater-to-cathode.
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Old 13th October 2005, 08:39 AM   #4
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Quote:
2. How can I estimate the total current the amplifier will draw from the PS?
The current drawn by the output tubes plus the current through the driver stage.

Output stage ...roughly 120mA per channel?
Driver stage 10-20mA?

so roughly 150mA.

Regards,
Bas
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Old 24th February 2012, 03:48 PM   #5
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I am thinking about building this amp with some Heathkit AA-100 outputs I have. I plan to use a 10M45 for the CCS.
Can anyone tell me why the cathode bypass caps for the output stage are connected through a 68 ohm resistor to ground? They seem really large as well.

Anyone built this circuit? Thanks!
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Old 24th February 2012, 04:10 PM   #6
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Quote:
Originally Posted by mctavish View Post
I am thinking about building this amp with some Heathkit AA-100 outputs I have. I plan to use a 10M45 for the CCS.
Can anyone tell me why the cathode bypass caps for the output stage are connected through a 68 ohm resistor to ground? They seem really large as well.

Anyone built this circuit? Thanks!
The object is to encourage communication between the cathodes of the outputs so the 68R prevents the current from going straight to ground. This is the very essence of differential. I personally use a 1meg resistor in this location.

Most cathode bypass caps are marginal at best. You want the knee to be way down below 1hz so that there is no phase shift in the bass frequencies. The bigger the better in my opinion. I think these are effectively in series which halves there value.

The various design decisions are vary carefully made with this design so be careful about altering any single detail.

Shoog
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