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Old 17th March 2015, 01:22 PM   #1
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Default LA2A PCB

Hi guys

I just finished designing a LA2A pcb and would like to have some advice, if the design is well made, some tips I should care, etc. I made the HT 50mils, on the bottom layer, from the psu to the anode of each tubes, and I ground filled the layer. The top layer is the audio traces, 30mils. I tried to not running the ht in parallele with the audio traces. For now, I don't draw the heaters at all. I don't know if I could put it on the bottom layer with the ht or i'm better of to connect it with twisted wires.

Also, I made 4 ground fill path. One for the inout, one for the output, one for the audio and one for the psu. I was warned to do it that way with tubes design.
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Old 17th March 2015, 02:59 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by deepdark View Post
I just finished designing a LA2A pcb and would like to have some advice,
All of the grounds must be connected together for proper operation. The way this is done is critical.
The large capacitors are rather far from the circuit. I would rethink the layout.
Make sure that there is enough creepage between the HV pads and the ground plane.
http://www.smps.us/pcbtracespacing.html

Last edited by rayma; 17th March 2015 at 03:24 PM.
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Old 17th March 2015, 03:03 PM   #3
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They will be connected to the star gnd, like dripp electronic did for their LA2A pcb, and other people did with their tube pcb. I agree the caps are a little far from the circuit, I'll put them closer to the rest of the circuit. other than that, does it looks right?
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Old 17th March 2015, 03:09 PM   #4
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Quote:
Originally Posted by rayma View Post
All of the grounds must be connected together Make sure that there is enough creepage between the HV pads and the ground plane.
PCB Trace Spacing Calculation for Voltage Levels
What do you mean by that? enought clearance between ht traces and pads vs gnd?
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Old 17th March 2015, 03:53 PM   #5
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ok just saw the link. concerning the creepage, is it a value we can set in the pcb designing software, or a specification we set when ordering pcb? For what I see, within my voltages, I'm more than ok with the traces width I set. Should I place my ground fill on the top layer with all the audio traces or on the bottom with the ht (and maybe the heaters) traces?
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Old 17th March 2015, 07:55 PM   #6
marce is offline marce  United Kingdom
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you got a schematic for this...
What voltage is the HT.
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Old 17th March 2015, 07:58 PM   #7
rayma is offline rayma  United States
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Quote:
Originally Posted by deepdark View Post
ok just saw the link. concerning the creepage, is it a value we can set in the pcb designing software, or a specification we set when ordering pcb? For what I see, within my voltages, I'm more than ok with the traces width I set. Should I place my ground fill on the top layer with all the audio traces or on the bottom with the ht (and maybe the heaters) traces?
Yes, there should be a setting for the ground pour creepage. Even if all the traces are on one side and the ground plane is on the other side,
you will still have the same creepage problem with the tube pin pads, since they're also on the bottom layer.

Last edited by rayma; 17th March 2015 at 08:01 PM.
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Old 17th March 2015, 08:01 PM   #8
marce is offline marce  United Kingdom
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Why are R16 and R17 so far apart, also R19 and C3?
C4 seems to be shorted out with a trace through R22.
Move R14 so its connection is shorter to the valve.
C2 can be swung round making its connections shorter.
R12 seems to be shorted to ground via C1.
C1 could be nearer the pin, some sort of decoupling?
R34 and R35 could swap places.
R31, C8-1 and C8-2 could be rotated and the routes made neater.
Move C9 and connect direct to pin1 of valve (direct route to C12)... This will allow routes to above to be tidied up.
R26 is only connected at one end.
R27 connects to GND and then has a long route to pin 5 of a valve.
C7D no connection to GND.
There is not enough clearance round the HT leads.

Just a quick revue, without a schematic I can only guess at some things connection wise.

Last edited by marce; 17th March 2015 at 08:18 PM.
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Old 17th March 2015, 08:25 PM   #9
marce is offline marce  United Kingdom
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Is the board going to be have plated through holes?
If so what are the pin sizes and how much bigger is the finished hole size.
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Old 17th March 2015, 11:14 PM   #10
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Thanks for the advice guys. @ marce, i revised several trouble while looking back at the schematic. You were right about them all haha. I Will revised a couple of run, too. Yes the holes Will be plate through. For the size, it depend upon the part i connect. Dont remember the general diameter, thought.
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