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Old 22nd April 2013, 11:42 AM   #51
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Default cathode resistor

Thomas (or someone else),
What value did you put in your 801A amp?
Did you try some values of bypass cap?
Thanks
Pierre
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Old 22nd April 2013, 01:50 PM   #52
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Quote:
Originally Posted by crazyfrog View Post
What value did you put in your 801A amp?
Value of what ?

Thomas
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Old 22nd April 2013, 02:51 PM   #53
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I put "cathode resistor" in title but actually my question was about R3 and C4.
Thanks
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Old 22nd April 2013, 03:11 PM   #54
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Hi!

I didn't read the title, sorry.
try 1.5k. Leave C4 out and try. You shouldn't need it

Best regards

Thomas
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Old 24th April 2013, 05:16 PM   #55
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Default testing 801A

I wanted to test the output tubes (801A) so I attached a 375k resistor from ground to the grid (no input tube connected). Is the value ok?
Thanks
Pierre
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Old 24th April 2013, 06:58 PM   #56
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Hi!

Check the tube datasheet for the max allowed grid to ground resistance. 500k for cathode bias. 100k for fixed bias. For testing you can also connect directly to ground, assuming you have a cathode resistor installed

Thomas
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Old 24th April 2013, 08:14 PM   #57
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Quote:
Originally Posted by Vinylsavor View Post
Hi!

Check the tube datasheet for the max allowed grid to ground resistance. 500k for cathode bias. 100k for fixed bias.
I did. But an experienced person's advice is always welcome.

Quote:
For testing you can also connect directly to ground, assuming you have a cathode resistor installed. Thomas
Ah! I didn't know that. Yes I have a 1.5K installed. Thanks again.
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Old 24th May 2013, 01:12 PM   #58
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Default Choke for 6N7?

Hi. I was thinking to add a choke for the 6N7 line filter but they only draw few mA. Do you think it worths the "effort"?
Thanks
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Old 24th May 2013, 02:20 PM   #59
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Hi Pierre,

I do it in my more elaborate amps. But that is more for the piece of mind. I would first built it with the RC decoupling stage. Once that works you can still experiment with a choke

Thomas
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Old 8th June 2013, 03:04 AM   #60
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Default Change

I'd like to look for a different HV line filter for the 801A. The MOSFET in my regulator blown...Voltage too high. Would have to change some part values. Actually, it would need a power resistor just before the regulator but a lot of energy would be lost. Since I have already a Hammond 193C (20H, 100 mA, 600V) I could try a LCL (with a small cap after the bridge) using it as a second choke. However, looking at other Hammond chokes, I would have to put two in series to get a "first choke combo" that holds the voltage.
Does someone have another suggestion?
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