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Old 19th August 2003, 10:15 PM   #11
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Hi,

Quote:
If I can't make it sound good using a couple of healthy chokes in the PSU then I will look elsewhere.
You surely could.

Just make it a big well filtered supply and with the help of the chokes it will be great.

Just to tease you:


Cheers,
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Old 19th August 2003, 10:32 PM   #12
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Thanks Frank. I assume that you would not post this unless you think it has a good chance of sounding good. I thank you sir.
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Old 19th August 2003, 10:47 PM   #13
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Hi,

Quote:
I assume that you would not post this unless you think it has a good chance of sounding good.
I'd like to think so...

When I talk PS, I mean business...real business.

Either use well filtered, well regulated supplies ( my approach), or have a look at this brute force approach; yep, 6.000+ F/400+ VDC.

Cheers,

SRPP preamp.
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Old 19th August 2003, 11:44 PM   #14
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Default Checked out

Gavin, you are right on. Downloaded the data for the 5687 tube and checked out. Cathode resistors should be approx 750 ohms for 10ma.
I wonder if/how the sound would change if the two "cathode" resistor values were changed, but kept the 10 ma flow? Or if the B+ were reduced?
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Old 19th August 2003, 11:58 PM   #15
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Hi,

Quote:
Might try varying the two cathode resistors to distribute voltages differently, or reduce the B+ and see how it sounds? Just an idea Gavin.
Steve,

With all due respect...Either we opt for a SRPP circuit or a mu follower.

We can fiddle around with that no end but assuming Gavin is an amateur with little laboratory equipment to back up his findings he's going to experiment with resistor values no end.

I think I know what you're hinting at, from experience though I feel it's just another one of those half baked solutions that just isn't worth breaking your head over.

If I misread you, I apologise.

Cheers,
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Old 20th August 2003, 12:25 PM   #16
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Dunno Steve. I could try putting a 1K pot in serires with a 500 ohm resistor and play with the values and see what happens.
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Old 21st August 2003, 09:42 PM   #17
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Default listening purposes

Fdegrove, no offense taken. I was merely thinking if the supply wasn't built and the preamp wasn't for headphones, that one could try lower voltage B+ or by changing the voltage on the upper tube that:

1) raising the voltage on the upper tube would make it more of a constant current source because any changes from plate to cathode would be a lower percentage and visa versa

2) see if G could hear any sonic changes

3) If B+ could be lowered, the tube would probably last longer. But granted the 5687 is cheap in price.
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Old 21st August 2003, 11:48 PM   #18
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Hi,

Sure...could do that too.

If you have years of experience you can probably pick a value for the intermediate R and optimise it by ear.

Still, I feel it's best to go through theory first and then decide which way to go.

If we want to stick to our twin triode SRPP then this is worth reading:

IMPROVED SRPP

Cheers,
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Old 23rd August 2003, 01:04 AM   #19
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Default Your right

I think you are right Fd (hope you don't mind). I tend to get carried away checking all the minute details (of course that is my business) when first, we just need to get it working and get theory down.

Thanks and take care Fdegrove and G.
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