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Will the Mystery Amp Sign in Please?
Will the Mystery Amp Sign in Please?
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Old 29th January 2018, 08:55 PM   #1
wrenchone is online now wrenchone  United States
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Default Will the Mystery Amp Sign in Please?

Here's a board of mine that just came in from PCBWay that will be the basis of a new P-P hybrid amp using 6N3P-E and 7591A with some solid state help. I remarked to a friend at work how the PCB file looked like a mandala - maybe that name will stick...
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Old 5th February 2018, 12:21 AM   #2
wrenchone is online now wrenchone  United States
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I made some progress stuffing the board, will finish the job when a Mouser order comes in.
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File Type: jpg P1000235.jpg (40.4 KB, 381 views)
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Old 5th February 2018, 01:01 AM   #3
Bigun is offline Bigun  Canada
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Will the Mystery Amp Sign in Please?
I don't get the thread title at all ?
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 5th February 2018, 01:23 AM   #4
wrenchone is online now wrenchone  United States
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I's a reference to the very old TV program, "What's My Line", where panelists tried to guess a mystery guest's occupation. Its iconic line (beginning of every show) was, "will the mystery guest sign in please", and the guest would write his name/occupation on a white board shown to the audience, but not to the panelists.
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Old 5th February 2018, 02:33 AM   #5
Bigun is offline Bigun  Canada
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Will the Mystery Amp Sign in Please?
Lost on me :-)
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 5th February 2018, 02:42 AM   #6
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Will the Mystery Amp Sign in Please?
for Kitty Carlisle fans - hear her sing in "Murder At The Vanities" Murder At The Vanities 1934 - Victor McLaglen, Jack Oakie, Kitty Carlisle, Carl Brisson, Duke Ellington, Gertrude Michael
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Old 5th February 2018, 01:04 PM   #7
12E1 is offline 12E1  United Kingdom
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So while trying to figure this out, I spotted some likely errors on the PCB. R21A has both ends connected to the bias supply rail, R21B appears to be correct (red elipses). There is also a strange difference between the two lower octal bases (I assume they should be very similar). The left base has a connection from R16A to pin 1, but nothing to pin 5. The right base has a connection from R16B to pin 5 but nothing to pin 1 (orange elipses). The assumption is that the filaments are always on pins 2 and 7 based on the silk screen and wired connections, and valves on the reverse side of the PCB as per the other photos.

I was trying to figure out the role of the transitors, but I struggled to accurately identify the tubes, and thought flagging the possible errors might be more helpful.

I tweaked the photo in Photoshop to make the underside tracks more readily visible.
Mandala possible errors.jpg

Last edited by 12E1; 5th February 2018 at 01:09 PM.
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Old 6th February 2018, 03:11 AM   #8
wrenchone is online now wrenchone  United States
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Nope on all...
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Old 6th February 2018, 08:27 AM   #9
12E1 is offline 12E1  United Kingdom
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Quote:
Originally Posted by wrenchone View Post
Nope on all...
OK - so I missed the tube numbers in the first post for some reason... I think I was probably half asleep yesterday. I also counted the pins wrong (oh dear, never done that before). Of course, pins 4 and 8 on the 7591 are internally connected. Therefore my second point was completely wrong (my apologies).

But R21A is definitely not doing anything since both ends are connected to the same track...
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Old 6th February 2018, 04:09 PM   #10
wrenchone is online now wrenchone  United States
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I will look, but I think your eyes have been deceived. If not, a Dremel will save the day. This board was pretty much laid out freehand, if that's the biggest mistake, I'll be quite relieved.

Last edited by wrenchone; 6th February 2018 at 04:12 PM.
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