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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:
[IMGDEAD]https://lh5.googleusercontent.com/-0DDFlVLEQKU/UWiR-Cb8fhI/AAAAAAAABmk/j319szNTvSg/s512/IMG_20130413_015812.jpg[/IMGDEAD]

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 :headbash:

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

here are some pictures from the build for you guys to inspect:
https://picasaweb.google.com/111109714414066634160/OctalCCDAProject?authuser=0&feat=directlink

thank you so much for your time and help.
tank out.
 
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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?
 
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?
 
ok, after getting a hold of john broskie i decided to go with a 10k and a 3.9k resistor in parallel, which gave me 2.8k.

and im glad to say - preamp is up and running in my system and sounding lovely!

only one problem though.. every 20 seconds or so the VU meters on my SAE 2200 jumps up to about 50 percent (even without music) and then slowly comes back down. this is happening with no effect on the music. im thinking - a DC leak from the coupling caps.. what do you guys think? should i be worried or will it go away with burn in?
 
and now a new problem arose.. i shut the system down for a few hours, came back and power it and now there is a poping sound fron the speakers every few second..related?

could it be because of the complete lack of groundng right now? should i link the RCA in and outs ground to one another and the boards ground to the transformers chassie? also, should i connect the transformer chassie line to the house grid?
 

kacernator

Member
2008-01-09 10:38 pm
If it would be ground related then you would have hum.

Is the popping on both channels? If not try swapping tubes between channels.

If it is on both channels then I think something wrong with power supply. Measure all the voltages - PSU, heaters, heaters elevating point, anodes, grids, cathodes.
 
well, after some more checking it seems that the coupling caps may be too big (30uF) for this setup and something with the amp's (SAE 2200) input impedence creates some sort of an imbalance.. the symptoms up untill now:

- VU meters jumping up with no reason.
- strong thud sound at startup even though i powre the preamp about a minute before the amp (sound happens after the amps relay clicks)
- ocasional popping for the speakers while playing.

good all this be linked to the coupling caps? good this just be a case of bad tubes?
 
i checked for dc in the output and indeed it is leaking dc. so much that it put my amp into protection ealier. its out of the system for now. i changed the coupling caps to smaller ones (4.7uF) and while there is less DC, it is still there.

i will be doing some more test later, but for now i uploaded some more pics of the board for you guys to inspect (if possible or helplfull in anyway..):
https://picasaweb.google.com/111109714414066634160/OctalPart2?authuser=0&feat=directlink