fallout

Re: [BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD
« Reply #500 on: February 20, 2021, 12:14:35 PM »
All diodes and Capacitors are correctly placed with their poles. What could.be the problem....🤔?

Sounds like you have a short or a bad tube/part somewhere. Did you try powering up the circuit without the tubes installed? I would first replace R3 and power up the PSU without the main PCB connected, check voltages and make sure the PSU is ok. Keep in mind, your voltage readings might be a little higher than expected without a load connected to the PSU. If all is well, I would connect the main PCB without the tubes installed and check voltages again (without tubes installed, the voltage readings might be high). I would then install 1 tube at a time (obviously install tubes when power is off) and see if you could locate the problem. Or, you mentioned the EL90 is getting hot, perhaps start there and try removing the EL90 and see if the problem persists. Could be a faulty tube? This is assuming you scrutinized your soldering for shorts/bridges, etc.

In short, I would fix the PSU and then  systematically work your way through the circuit to narrow down where the problem is.
« Last Edit: March 11, 2021, 08:19:14 PM by fallout »


hazer-drum

Re: [BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD
« Reply #501 on: March 10, 2021, 04:38:10 PM »
My 3W-rated R3 at 1k keeps frying. I know some people recommend using a 25W chassis-mounted resistor but I see build pictures with PCB-mounted resistors. Would a 5W resistor do the trick?

EDIT: I think I found the answer myself actually. If my calculations are correct, the current after rectification and smoothing cap C9 is max 0.2A * 0.62 = 0.124A which equates to a power dissipation of 7.23W at 470Ω and 15.38W at 1kΩ. Therefore, I definitely need that 25W resistor, correct?
« Last Edit: March 11, 2021, 06:26:09 AM by hazer-drum »

Dr_J

Re: [BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD
« Reply #502 on: March 14, 2021, 05:59:41 PM »
Hey Hazer-Drum,

i didn't check your calculation, but what i can say from my side my build is running fine with [email protected] called by the BOM.
It's not getting very hot...

ROCK-ON

hazer-drum

Re: [BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD
« Reply #503 on: March 15, 2021, 12:49:00 PM »
I ended up installing the 1K 25W resistor and got my B+ down from 360V to 319V (which seems a bit more reasonable now). Also swapped the meter resistor R7S to 100Ω since I couldn't zero-adjust my 1mA meter within the original trimmer range. Works flawlessly now!

Sorr

Re: [BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD
« Reply #504 on: April 03, 2021, 02:47:38 AM »
My Dual sta from drip is still thumping in the low end when compression kicks in
especially with fast release times.

I've tried the 6ba6 t-bar's with no luck, other pairs of 6v6, other brands... no diffrence.

myguess is the psu, it measures rock steady on all voltages points, the only
thing i've chosen for is not to use a choke but an extra resistor in that b+ path.
i've ordered the 5mh choke and see if it will help.

could it be something with the power feed? how to meaure that? there is an diode rectifier
into seperate voltage regulators for both channels.

i've read something about old 6AL5 tubes that could be causing this too?

I must admit it's one of the best sounding compressors on guitars, vocals and bass lines.
super rich harmonics, adds nice detail of highend character and rock steady bottomend.
try it in parallel :)

Do you have a pot between the 6V6 cathodes?  If so how are you attempting to balance them?  It must be adjusted for AC balance not DC balance.                                                       I would also remove the two feedback resistors from the 6V6's and measure them to see if they are the correct value.