Octal CCDA kit - help needed! - diyAudio
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Old 12th April 2013, 11:24 PM   #1
diyAudio Member
 
Join Date: Aug 2012
Location: Tel Aviv, Israel
Default Octal CCDA kit - help needed!

Hey guys.

The John broskie Octal CCDA kit arrived a couple of days ago and while l build most of it i do have a few questions..

disclaimer: I am a complete novice and a language barrier does exist here - please please please be patient with me.

the manual can be downloaded here:
http://tubecad.com/Product_PDFs/CCDA%20Octal.pdf

R18 has two slots alowing two resistor to sit in sequence - but i only recived one.. should i just place and bridge were the other should be? not sure what to do here.. after double checking this it seems the unknown resistor is actually R17 - which dosnt make too much sense (to me..). it says in the manual the R17 and R16 set the voltage to the heaters - but they are on the B+ suuply...

also, just above C7 (if you look at the picture of the board in the last page) there is a slot for a resistr and it is unmarked.. is it a test point or do i need to place a resistor there?

on page 9 there is an explantion about R9 (two resistors in parallel - R9a and R9b) and how to choose their correct value. im not sure how to go about it.. from what it says, i can either choose a shorter tube life and better sound or the other way around.. what values should i place there in order to go with the first option (better sound..). im using 6sn7.

on page 7 you can read about the how to connect the cathode resistor. i am totally confused by this. im not even sure at this point which resistor RK is or which value i use. also, im not sure if i need to go with the conventional of Positive feedback option.. the manual got me completely confused on this part (should i use a bypass cap or not, what is the bypass cap, which values.. etc..)

and finaly..
ok, is it just me or s there a substantial difference between the schematics and the PCB as far as the tube connections go?!

here is the pcb:
Click the image to open in full size.

for example, R4 connects to leg 2 on the board but according the schematics it is supposed to connect to leg 1 and 6. same with R5 - connect with leg 4 on the board but leg 7 on the schematics.

what am i missing here

(i just hope im not asing too many questions at once )

here are some pictures from the build for you guys to inspect:
https://picasaweb.google.com/1111097...eat=directlink

thank you so much for your time and help.
tank out.

Last edited by Tankpopper; 12th April 2013 at 11:35 PM.
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Old 13th April 2013, 12:45 AM   #2
lexx21 is offline lexx21  United States
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Join Date: Mar 2011
Location: North Carolina
Is this a double sided board? Flip it over and see if there is a trace going from R4 to leg 4 of the tube on the other side of the board.
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Old 13th April 2013, 07:52 AM   #3
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Join Date: Aug 2012
Location: Tel Aviv, Israel
it is a double sided board but no, R4 does not connect with leg 4 on either side.

also, R2 connects with leg 6 and R3 with leg 4 - both unlike the schematics:

Click the image to open in full size.

Last edited by Tankpopper; 13th April 2013 at 07:55 AM.
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Old 13th April 2013, 02:42 PM   #4
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the plot thickens..

according to the schematics, R2 connects to leg 3 but on the board it connects to the input ground on one side and C4 on the other. im pulling my hairs out here..
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Old 13th April 2013, 09:07 PM   #5
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Everything is fine except that in the manual the pinout of the tube is numbered wrong - it is numbered for the noval tubes where 1 is anode, 2 is grid etc. Octals have different pinout.

R2 connects to leg 3, which is cathode, but with octal cathodes are 3 and 6.
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Old 13th April 2013, 10:39 PM   #6
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Join Date: Aug 2012
Location: Tel Aviv, Israel
thanks! ill correct the schematics.

one more question though.. on page 7 the manual talks about the option to build to line stage in a positive feedback application. you need to use j4 and leave caps c15 and c3 off the board. Resistor 2 should be half the normal value (215 insted of 430 for 6sn7). i do want to give positive feedback a try but removing c15 makes no sense as it is a cap in the heater power supply. obviously this is a typo.. so what do i do? which cap do i remove insted?
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Old 14th April 2013, 05:18 AM   #7
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Remove cathode bypass cap on the first triode.
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Old 14th April 2013, 09:21 AM   #8
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Not sure which cap that is.. I will try to follow the tracers.

As I said, I'm a complete novice and still struggling to make what's what.
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Old 14th April 2013, 12:42 PM   #9
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Learn what on schematics is anode, grid and cathode.
Cathode bypass cap connects from cathode to ground and it is located on the leftmost triode in the manual.
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Old 14th April 2013, 08:22 PM   #10
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Location: Tel Aviv, Israel
ok.. final problem!

first, r9(a&b) - this control the current and voltage. i can go for better sound and shorter tube life with high voltage and current or the other way around. it has two slots two place two resistor on3e next to the other in parallel.

question is - which resistors should i use for the first option (better sound shorter tube life)? i understand that you need to place two resistor in paralel to drop the final resister while maintaining the high W rating. right now i have 1.6k,2k,3k,3.9k,6.8k,10k.. i was thinking to go with the 1.6k and 2k in parrallel - is this the right call?
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