drd c3g/300b - help needed

[garbage]

hi all

finally wired up the remaining circuit of my breadboard. everything is wired p2p, even the 300b rectified filaments.

used my ipod as source and one of my totem model 1 as output.

powered up (not the first time, i did checks on voltage and dc on outputs before this) and played a track from bic runga's album.

it works!!! there is music... very delighted. really different sound from SS. i listened only for a short while as i know my resistor and regulator needs a larger heatsink (do not want to blow them).

measured the 300B anode, it is 605V(3V higher), c3g anode is 180V(10V higher)... i have to tweak the resistors a little.

first impressions from one speaker... warm and mellow. no harshness, but there is some humming which went away when i moved the input wire a little. i think the hum and buzz is due to incorrect termination of the input rca ground.

this is where i need advice on grounding. where to ground? before or after my switch? i'm going with a conventional single point ground, not sakuma's 2 point ground (due to chassis construction issues)

i am also having some problems which i will describe below.

my circuit is as follows:


connected to ipod as source:


description of circuit:
driver is triode strapped siemens c3g pentode post tube(http://www.jacmusic.com/nos/C3g-C3m-info.html) ac filaments, biased by 2 x 1.2V 2300mA NiMh at the cathode, output is 300b, dc filaments voltage regulated, rectifier is rca 83 mercury vapor tube.

psu part is 480-0-480 to rectifier to 4uF input cap to 10H choke, to 55uF GE oil cap to 5H choke then 55uF GE oil cap.

at the 480-0-480, there is a switch to open/close the 0v (ground). the same switch is used to turn on/off the primary 0-240v. this switch is a carling double pole triple throw, i am using it to switch primary 0-240v and also to switch the B+.

grounding:
my grounding for the psu caps are after this switch.
the 100k resistor from input signal to ground goes before this switch, but i terminated the input ground from the rca to after the switch (i think this should be moved to before the switch to reduce hum/buzz, any ideas?)

the cathode batteries are grounded after the switch, initially they were before the switch, but the OPT buzz with the powercord connected to mains even though the switch is off. removing the powercord stops the buzz. strange... what's the reason for this?

c3g filaments:
i added 0.5R to both pins of the c3g and got 6.8 something VAC with only the c3g tube in. then i replaced these with 1R and got 6.15VAC or so. thought i got it right. the moment i add other tubes in and switch on the filaments, it goes to 7.15VAC... not sure why.

murphy's AC heatsink?:
i tried to touch the heatsink to see if it is hot, but felt something... like little ants crawling on my fingertip... actually the heatsink is running 50 to 60 odd VAC when the filaments are on. there is no continuity from my lm317 nor my resistor that is mounted to the heatsink... but strangely... there is voltage. must be murphy's law. :P how can i isolate this? when i'm gonna build a chasis and tie the earth pin to it, will fireworks occur?

closeup of amp:


c3g:


heatsink just added last night:


drd while on:


83 while on. the blue glow is only visible from the top... bummer...


day 2:
left it on for 5 to 10mins with the heatsink, no time to play with it yet. seems ok, no burning smell and no smoke.

i have replaced my tesla VR with 2 x 470R to get 940R(the required resistance from calculations), but this caused the c3g anode to go to 288VDC. will put in the tesla VR and try 900R tomorrow.

any ideas? especially regarding the c3g filaments? and thanks for reading this long post.

cheers
garbage

[audiousername]

Originally posted by garbage
at the 480-0-480, there is a switch to open/close the 0v (ground). the same switch is used to turn on/off the primary 0-240v. this switch is a carling double pole triple throw, i am using it to switch primary 0-240v and also to switch the B+.

grounding:
my grounding for the psu caps are after this switch.
the 100k resistor from input signal to ground goes before this switch, but i terminated the input ground from the rca to after the switch (i think this should be moved to before the switch to reduce hum/buzz, any ideas?)

the cathode batteries are grounded after the switch, initially they were before the switch, but the OPT buzz with the powercord connected to mains even though the switch is off. removing the powercord stops the buzz. strange... what's the reason for this?

I read this over, and over, and.... well I'm still not entirely sure how you've got things connected. If you drew a schematic including PSU etc and your current grounding scheme it would help greatly.

Originally posted by garbage
c3g filaments:
i added 0.5R to both pins of the c3g and got 6.8 something VAC with only the c3g tube in. then i replaced these with 1R and got 6.15VAC or so. thought i got it right. the moment i add other tubes in and switch on the filaments, it goes to 7.15VAC... not sure why.

It is common for the unloaded voltage to be higher than the loaded voltage on the transformer (regulation and all of that...). As I understand this, you have added resistance in series with the C3G heater to reduce the voltage across the heater, yes? Now, when you add any other heaters in parallel on the same transformer winding the voltage rises? Weird. This may be a stupid question, but did you measure the voltage at the transformer secondary or across the C3G pins?

Originally posted by garbage
murphy's AC heatsink?:
i tried to touch the heatsink to see if it is hot, but felt something... like little ants crawling on my fingertip... actually the heatsink is running 50 to 60 odd VAC when the filaments are on. there is no continuity from my lm317 nor my resistor that is mounted to the heatsink... but strangely... there is voltage. must be murphy's law. :P how can i isolate this? when i'm gonna build a chasis and tie the earth pin to it, will fireworks occur?

You said you measured continuity, but continuity from which pin of the LM317 to the heatsink? The centre pin of the LM317 (Vout) is electrically connected to the case. So unless you have used mica and thermal grease or the like, the heatsink is at the same potential as the Vout of the LM317. You may have already known this, but I thought I should say this anyway just in case. I'm not sure what the 50 to 60 odd VAC is that you're measuring but it may be the 300B's drive signal as it appears at the cathode, yet there should be little to no AC voltage appering across the cathode resistors because of the ultrapath configuration... Isolate the chip if you haven't already and see if it goes away.

[garbage]

thanks for the response audiousername.

Originally posted by audiousername

I read this over, and over, and.... well I'm still not entirely sure how you've got things connected. If you drew a schematic including PSU etc and your current grounding scheme it would help greatly.

quite confusing huh? i will post one tonight.

Originally posted by audiousername

It is common for the unloaded voltage to be higher than the loaded voltage on the transformer (regulation and all of that...). As I understand this, you have added resistance in series with the C3G heater to reduce the voltage across the heater, yes? Now, when you add any other heaters in parallel on the same transformer winding the voltage rises? Weird. This may be a stupid question, but did you measure the voltage at the transformer secondary or across the C3G pins?

the c3g heaters is dedicated, not shared with any other tubes. 300b has it's own 0-7vac which is then rectified and regulated, 83 has it's own 5vac. voltage is measured across the c3g filament pins (1 and 8) with tube in socket.

Originally posted by audiousername

You said you measured continuity, but continuity from which pin of the LM317 to the heatsink? The centre pin of the LM317 (Vout) is electrically connected to the case. So unless you have used mica and thermal grease or the like, the heatsink is at the same potential as the Vout of the LM317. You may have already known this, but I thought I should say this anyway just in case. I'm not sure what the 50 to 60 odd VAC is that you're measuring but it may be the 300B's drive signal as it appears at the cathode, yet there should be little to no AC voltage appering across the cathode resistors because of the ultrapath configuration... Isolate the chip if you haven't already and see if it goes away.

sorry, i meant i tested for continuity. there is none between the lm317 and heatsink and none between resistor and heatsink.
lm317 has a thermal pad between it and the heatsink, but the screw is not insulated. will check this out tonight if i have time. resistor has thermal grease applied.

[garbage]

psu layout as follows:



tied at G1: 100k resistor from signal to ground and 0 winding of 230-0.

tied to G2: battery bias for c3g, rca signal ground, psu caps ground and 300b cathode resistor.

does the above grounding look correct?

regarding the c3g voltage filaments, i made a mistake when taking measurement... i measured from the wrong end of the resistors... duh...

they are actually at 6.15vac.

cheers
garbage

[pedroskova]

Originally posted by garbage

measured the 300B anode, it is 605V(3V higher), c3g anode is 180V(10V higher)... i have to tweak the resistors a little.

Ouch...I thought the rated Va max for a 300-B is ~450vdc?

[garbage]

Originally posted by pedroskova


Ouch...I thought the rated Va max for a 300-B is ~450vdc?

yes it is, and higher for some 300b variants.

i should have made myself clear. the anode of the 300B is at 606vdc, but anode to cathode voltage of the 300B is 342vdc.
the 300b at the moment is running at 342v, -59v, 62mA. much different from my design of 350v, -74, 60mA. will have to tweak the resistors somewhat.

[audiousername]

Garbage,

I don't see anything much obviously wrong with the PSU....

I assume you use the switch from the transformer CT to ground to allow the 83 time to warmup, yes?

You haven't drawn it, but you should ground the CT of the C3G filament heater winding (or one side if it doesn't have a CT). If it's already grounded - or referenced to some higher voltage leave it

[garbage]

Originally posted by audiousername
Garbage,

I don't see anything much obviously wrong with the PSU....

I assume you use the switch from the transformer CT to ground to allow the 83 time to warmup, yes?

You haven't drawn it, but you should ground the CT of the C3G filament heater winding (or one side if it doesn't have a CT). If it's already grounded - or referenced to some higher voltage leave it

thanks for looking.

yes, the switch from transformer CT to ground is to allow for warmup manually.

ok, will try grounding the CT of c3g.

right now i am playing norah jones' come away with me cd with it.

very very slight hum(maybe bcos speaker is 87db) when i place my ear right next to the woofer.
i think this is expected, as i put the drd choke right in the middle of the 2 psu chokes. easier to breadboard.

in the actual construction, the drd choke will be mounted above the psu chokes at 90degrees.

cheers
garbage

[garbage]

updates on amp chassis building... below are pics of one mono side.

front and side panels 10mm aluminium.
bottom and back 2mm aluminium.
top 2mm copper.

side view:


other side view:


rear view:


panels on:


top view, waiting for 300b:


cheers
garbage

[Stixx]

Garbage,

nice chassis design you got there....love that vault-like look!

Keep posting ,
Oliver