D-AOC PCBs - the building and help Thread

[jrfred453]

I'm about to fire up my D-AOC for the first time. I noticed that my 350T regulator had continuity with the heatsink. After messing with it for a while a realized it still had continuity without the regulator even touching the heatsink. This isn't normal is it? What should I be checking for?

 

[[silent:arts]]

measured with the tubes in ?
put the tubes out ...

 

[jrfred453]

That was it.
Thanks Volker.

 

[Holger]

I have trouble with my PSU. I get 10V, 27V and some 277V AC from my transformer, seems to be ok.
The heater PSU is set to 6.3V with the tubes not fitted.
With tubes plugged in I get some 1.3V, Is that correct?
The 27V are reduced to 12V. Fine, I use a 12V reg.
The biggest problem is the high voltage part. Even with the tubes fitted I get way more than 320V (V increases over time, I measured more than 340V on one occasion), I usually disconnect mains then, so no further measurements. The 300+V are measured at R128.
I replaced the TL 783, no improvement. Any hints for me?

 

[bernbrue]

Holger,
what are the specs of your transformer? 27V to 12V regulated seems quite a lot, the regulator must get very hot. The 277V AC from transformer is too high as well, should be 250V AC. Heater voltage with tubes plugged in is way too low. Measure/compare your voltages with Volkers:

http://www.groupdiy.com/index.php?topic=26585&start=290

I suppose your transformer specs are wrong.
regards
Bernd

 

[mikeyB]

Those voltages don't look too far off spec if he's measured off load - admit - the 27V is a bit high. Is it the ring250 tx from Musikding? These were delayed batch - originals had wrong windings - I hope this not problems with new batch. I'm close to firing up DAOC with the tx I received 2 days ago.
Fingers crossed - will keep you posted :thumb:

 

[mikeyB]

[quote author="Holger"]I have trouble with my PSU. I get 10V, 27V and some 277V AC from my transformer, seems to be ok.
The heater PSU is set to 6.3V with the tubes not fitted.
With tubes plugged in I get some 1.3V, Is that correct?
The 27V are reduced to 12V. Fine, I use a 12V reg.
The biggest problem is the high voltage part. Even with the tubes fitted I get way more than 320V (V increases over time, I measured more than 340V on one occasion), I usually disconnect mains then, so no further measurements. The 300+V are measured at R128.
I replaced the TL 783, no improvement. Any hints for me?[/quote]

I had similar problem with another valve box - i had broken 0v return for heaters - so it measured ok at psu but no return from heaters. The tubes didn't heat up so the HT went well high - TL783 can't regulate if no current drawn. You may have a dry joint in heater circuit - try resoldering valve skt and psu joints. If you suspect valves - then hang a power resistor on heater pins - say 4R7 - will draw over an amp and let you know if heater circuit is ok.
Oh just remembered - some say the onboard heatsink is not enough - LM350 get too hot and shuts down resulting in high HT. Try one channel with valves in - is the heatsink too hot to touch - if so you need bigger heatsink/bolt reg to chassis(insulated of course)

 

[Holger]

mikeyB, thanks for your very good hints, I will look at my board tomorrow.
And yes, the transformer is from Musikding. I'll update this...

 

[MartyMart]

Quick transformer question, the German built one from Musikding.

Primary side, using Yellow/Lilac from fused power switch and connect the
White & Orange together and heat shrinked/ isolated.

This is correct for 250v operation right ?

Thanks,
Martin.

 

[Holger]

MartyMart, that's the way I'd connected it. Do you guys have 250V now? Here we have some 235V ;-).

 

[MartyMart]

[quote author="Holger"]MartyMart, that's the way I'd connected it. Do you guys have 250V now? Here we have some 235V ;-).[/quote]

Thanks Holger , no 240v but commonly about 244 to 248 here !!
I hope that i don't have one of the "bad" windings ones from Musikding !!!!
The written info seems correct on the traffo.

Marty.

 

[[silent:arts]]

just to clarify:
- the LM350 is for the Heaters and can regulate without a load
- the TL783 is for the B+ and needs a load to work

if the Heater Voltage drops down there must be a fault!
try out one tube after the other in one tube socket after the other.

for the B+
[quote author="silent:arts"]!!! be aware that this PSU needs a load to work properly, with no tubes inserted you will have more than 350V !!!
!!! with no tubes inserted the High Voltage caps need a very long time to discharge, read the safety rules again !!!
if you are unsure and afraid of the tubes, test with only one channel fitted first.[/quote]
fix the heaters first. I assume the B+ PSU won't make a difference between none or unheated tubes.

 

[Holger]

Thanks Volker, I'll try to fix the heater problem first.

 

[mikeyB]

Just noticed - I got 2Meg trimmers for the meter - they had no 1Meg in stock at the time - am I ok paralleling a 2M2 across the 2Meg trimmer - will this work or do I defo need 1M trimmer? Need to know b4 I bolt the pcb down!

 

[[silent:arts]]

Hi Mikey,

no problem with the paralleled resistors.
but I wouldn't be surprised if it isn't necessary.
but since I haven't tested this I can't say for sure :green:

 

[mikeyB]

[quote author="[silent:arts]"]Hi Mikey,

no problem with the paralleled resistors.
but I wouldn't be surprised if it isn't necessary.
but since I haven't tested this I can't say for sure :green:[/quote]

Thanks Volker - will try out today :thumb:

MUSIKDING transformer voltages:

Transformer ratings as follows:
9V at 2.5A = 22.5VA
24V at 0.5A = 12VA
250V at 100mA = 25VA
primaries 2x115V for 230V use in series

Total = 59.5VA

Toroidals will measure higher voltage than their ratings when off load
Data sheet for typical 60VA says regulation (off load) is 11% (ie 11% higher output voltage off load). Smaller toroids have higher regulation - bigger toroids have lower regulation.

My mains measures 239V - nearly 4% higher - compounded with regulation - about 15%

250V winding - 289V - 15.6% higher
24V winding - 27.5V - 14.6% higher
9V winding - 10.1V - 12.2% higher

Am I right assuming lower current secondaries will have higher regulation value (because of higher resistance of wire)?

Anyhow - all look about right to me.

AND YES - make sure you connect primaries as Marty stated! - for 230V operation that is.

ok - enough typing - NEED SOLDER :razz:

 

[Holger]

Bernd, Volker, mikeyB
I owe you a couple of pints for your help...
The heater:
I stuffed a 12k instead of a 220R in the heater PSU...no comment.
The hint regarding the low R test resistor test encouraged me to look for a fundamental error. This was one of my first "wrong component" problems, I'm usually quite thoroughly regarding component stuffing.
The high voltage PSU had two leaking diodes, I replaced them, everything works as expected.

Whenever you guys are in Hamburg, ping me for the beer...

Thanks
Holger

 

[[silent:arts]]

great you sorted this out :thumb:
now, give us the photos :wink:

 

[MartyMart]

Quick question .... I'm still waiting on those bloody Edcors !!

The Musikding transformer has a "shield" connection, with "earth" colours,
does this need to be earthed at the case where "Mains" earth strap is ?
Is it just a "noise" reducing screen earth ?

( sorry that's 2 questions )

Thanks,

Marty.

 

[Jonkan]

The strap goes to where your starground is, which probably is the same place you put the mains earth connection. Close to the IEC connector prefferably for safetys sake.

The answer for the second question is yes.

/J