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Old 7th January 2011, 04:32 PM   #11
Arnulf is offline Arnulf  Europe
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Quote:
Originally Posted by pieter t View Post
I will see what tubes might have been used (pin 4 is 6,3 volt DC I guess; pin 5 is ground).
Based on E88CC is should not be very difficult to calculate the values of the passive components.
ECC88 usually has its pin 9 grounded, especially since this looks like a two channel board which could benefit from channel separation.

If pin 5 is indeed DC heater ground, it's odd that pin 9 isn't connected to it, or better yet heater pins reversed with pin 9 grounded, which would make for easier PCB routing (this assumes point K ends up conencted to ground instead).
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Old 7th January 2011, 06:51 PM   #12
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Well I have no clue what the original tube was, but grounding pin 9 is not a problem if it's useful in this case with the e88cc.
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Old 7th January 2011, 07:20 PM   #13
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Arnulf,

We are not sure which tubes were used for this board, but E88CC could be used, and yes then it is easy to connect pin 9 to ground. Pin 9 is the shield of the E88CC between the two triodes.
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Old 7th January 2011, 09:37 PM   #14
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ok, so quick calculations and a rapid look at what should be the eq gave me the following values for the riaa eq. I used pieter's schematic and added my calculated values in blue.

Am I way off or am I slightly right?
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Old 7th January 2011, 10:14 PM   #15
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John,

I'm afraid you are way off.
330k for R6 is much too high; that will kill your gain (it is a voltage divider together with the 1meg resistor).
A good value for R6 will be 33k or so with an E88CC.
Check one of the online RIAA calculators to calculate R7 and C6, C7.
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Old 8th January 2011, 08:32 PM   #16
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I see... ok it makes sense now, I'm actually trying to learn a lot at the same time, since I usually follow a schematic without thinking. So, new calculations would be C6 0.022uf, R7 4.8k and C7 0.066uf.
Can you tell me the use of R10 and C5-C4?

thanks again
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Old 10th January 2011, 12:42 AM   #17
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I searched around the crap pile and I found a 120v to 6.3v transfo and a 240v to 120v. While I wait for the tubes to arrive I will work on a power supply.

What is C3? Can I simply leave it empty?
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Old 10th January 2011, 12:50 AM   #18
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by Antimoine View Post
I searched around the crap pile and I found a 120v to 6.3v transfo and a 240v to 120v. While I wait for the tubes to arrive I will work on a power supply.

What is C3? Can I simply leave it empty?
I don't use a cap in that position in my designs, and do use very high transconductance types like the D3A in the front end of my designs. Arguably it is in parallel with the miller capacitance of the input stage and raises the input capacitance the cartridge will see. It may be necessary for stability depending on pcb layout. I certainly would not go over 10pF or so in a passively equalized design, and my inclination would be to leave it out.

FWIW I would also leave out the input capacitor (jumper it) and install a single 47K resistor as cartridge load and dc path for the grid of the input tube. The input current should be small enough to be a non-issue with most cartridges out there. (Again I don't use an input cap in any of my phono stage designs, and have built a lot of them over the years.)
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Old 10th January 2011, 06:16 PM   #19
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Hi John,

For a good quality power supply you could look at John Broskie's site (John Broskie's Guide to Tube Circuit Analysis & Design).
He sells PCB's and parts; I guess a Janus regulator would be up to the task.
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Old 15th January 2011, 01:38 AM   #20
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Hah! Found the main board today, it does have a psu and a line stage on it. The phono stage fits perfectly on it so I'm happy, and it does answer the question as to what goes where for the heater section. It was designed for a toroidal transformer which I can't seem to find but I don't have the original tubes anyway so I'll use what I have for the psu. Weird thing, I seen to have found a second one of each of the boards, I can now make one mistake and still have a spare, ha!

I'll post the schematic and a pic tommorow and I'm afraid I'll ask for help again.
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