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Old 23rd April 2018, 11:29 PM   #101
hirscwi is offline hirscwi  United States
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Join Date: Mar 2014
Location: Indianapolis, IN, USA
F-5 boards
Default Slight humm from my new F-5

Greetings, I have just finished building my F-5. The Build Guide from 6L6 was very helpful. I have it biased correctly and it sounds very nice.

I have a couple questions. I am getting a slight hum even with the volume all the way down or with the preamp disconnected. I tried to follow best practices for internal wiring: cross psu wires and input/output at 90 degrees; keep input and output wires separated, etc. I think I followed the revised grounding scheme from the thread. But obviously I've missed something. It would be great to have a couple suggestions of what to look for.

Also I wondered if there are any particular guidelines for a preamp? I am building a B1 but in the interim I am using a McIntosh C36. I wonder if this is contributing to the problem?

Attached are a couple photos. I appreciate any assistance you can provide.
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File Type: jpg P4230012 (1).JPG (457.5 KB, 231 views)
File Type: jpg P4230008.JPG (459.3 KB, 229 views)
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Old 21st May 2018, 02:43 AM   #102
WKCox is online now WKCox  United States
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Location: Verona, WI
F-5 boards
Default Availability of LSJ74/LSK170 JFETs

Originally Posted by 6L6 View Post
Didn't realize they were sold out. I'll get the ball rolling on another batch.
Have been thinking about building an F5 for about a year, but have held off due to the lack of availability of matched LSJ74/LSK170 JFETs. Any possibility of these coming back to the diyAudio Store? Any reputable alternate suppliers?

Thanks in advance for any assistance.
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Old 12th July 2018, 03:52 AM   #103
MadInventor is offline MadInventor  United States
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Join Date: Jun 2015
Location: Iowa
Default V5T v2 or v3


So if I understand this, the F5T boards using two outputs per rail, these can be mounted on one heat sink side, two channels per chassis. The v3 four outputs can't have two channels in one chassis (I was going to lower the bias a lot ), because it uses four output boards per channel, is this correct? The big diodes are mounted to heat sink? What idss is used on the j-fets?

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Old 15th July 2018, 11:29 PM   #104
MadInventor is offline MadInventor  United States
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Join Date: Jun 2015
Location: Iowa
Fine, JTTAFW, have my own design now.
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Old 20th September 2018, 08:53 PM   #105
invaderzim is offline invaderzim  United States
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I just fell off the wagon and ordered the boards, parts kit and JFETs for the F5.
I was going to wait for the new SIT amp but then realized I would much more likely go "why didn't I get those JFET pairs while they were available?" rather than "why do I have so many amps to choose from?".
Plus I have nephews that are done with college and it may be time to get one or both of them into audio with a nice gift.
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Old 1st December 2018, 07:32 PM   #106
theRog is offline theRog
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Join Date: Nov 2015
Hello hirscwi,

Just finished my F5 and experience a minor hum on the speakers when listening closely.
I guess it’s power supply ripple residue on the outputs. My power supply looks pretty identical to yours. 400VA transformer, CRC with 4 times 15000uF and 0.47R per rail.

Anyone else have this?
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