375 Ohm.
So about 15Vdc across DCR assuming 40mA.
Implying somethings not pulling current.....are your el84s at heater voltage and current spec?
So about 15Vdc across DCR assuming 40mA.
Implying somethings not pulling current.....are your el84s at heater voltage and current spec?
Indeed. Something (EL84's) are not pulling current.
Will check the voltage. The transformer supplies 4A or should supply.
Hello,
It is clear they are not pulling the current they should do because Bas already told us.
I think it could be the heater supply because after all we have another power transformer.
Maybe use the old power transformer for the heater supply and check if things remain the same.
Greetings Eduard
P.s if it cant supply it will run hot. maybe you used the wrong soldertag and connect it to 5 volts instead of 6,3. I have done that once!!!
It is clear they are not pulling the current they should do because Bas already told us.
I think it could be the heater supply because after all we have another power transformer.
Maybe use the old power transformer for the heater supply and check if things remain the same.
Greetings Eduard
P.s if it cant supply it will run hot. maybe you used the wrong soldertag and connect it to 5 volts instead of 6,3. I have done that once!!!
The heater supply loaded with all the tubes in is 6,7VAC (a little too high). Unloaded above 7VAC.
Hi Bas!
So with the black probe at ground you measure 20V at the cathode, 0V at the grid, about 300V at the plate, how much at G2?
The cathode resistor is still 130R?
So with the black probe at ground you measure 20V at the cathode, 0V at the grid, about 300V at the plate, how much at G2?
The cathode resistor is still 130R?
Hello Bas,
I think we are getting closer to the solution. I am in Vietnam now so don't have all the information available like in my home. And my screen is very minimal both resolution and seize
But if you check all possible voltages it must be easy where the culprit is.
Could it not just be a cold solder joint?
Greetings Eduard
I think we are getting closer to the solution. I am in Vietnam now so don't have all the information available like in my home. And my screen is very minimal both resolution and seize
But if you check all possible voltages it must be easy where the culprit is.
Could it not just be a cold solder joint?
Greetings Eduard
Could be. But weird that it is for both.
I must admit I have not been looking for a solution...busy with work and other commitments. But hopefully this evening.
Wait, wait, wait, measured from where? Is there both a "fixed" bias to the grids and a cathode resistor bias? I've missed something since the posted schematic.
All good fortne,
Chris
There is no fixed bias. But I measured with black probe on ground. Red probe on grid. (Never measured it before) And my multimeter said -19v.
Whoa! Something is not as we suspected. Not being on-site, I can't immediately guess, but do expect the grids to be very, very close to zero VDC, and since they're not, must wonder about the cause. Both channels the same, so not likely a parts failure, etc. so maybe a wiring issue?
What wiring mistake could cause an issue like this? Maybe look first at the path from the "bottom" of the grid leak resistors to signal "ground", then from that "ground" to the rest of the signal "grounds". Sorry, not smart enough to imagine it, but the issue is definitely in the wiring, so conceptually "easy".
Maybe another of your beautiful photos, showing that wiring, might help an outside observer, if you haven't already discovered it.
Chris
What wiring mistake could cause an issue like this? Maybe look first at the path from the "bottom" of the grid leak resistors to signal "ground", then from that "ground" to the rest of the signal "grounds". Sorry, not smart enough to imagine it, but the issue is definitely in the wiring, so conceptually "easy".
Maybe another of your beautiful photos, showing that wiring, might help an outside observer, if you haven't already discovered it.
Chris
Aha..Ok...did not know this...since I always thought a grid should be negative something.
Will have a peek during my lunch break.
Hello,
On a big screen you could open up a split screen to compare the photo/ circuit drawing that has correct current to the one that doesn't have and you should be able to locate a difference. There should be one that will create the difference. Probably you just need to check the wires related to the EL84.
At the end of this day the problem will be found and you will enjoy choke input supply.
Greetings Eduard
On a big screen you could open up a split screen to compare the photo/ circuit drawing that has correct current to the one that doesn't have and you should be able to locate a difference. There should be one that will create the difference. Probably you just need to check the wires related to the EL84.
At the end of this day the problem will be found and you will enjoy choke input supply.
Greetings Eduard
The voltage between cathode and grid is what the tube 'sees', the (voltage across the) cathode resistor is generally setting up the (usually) 0V grid to be below cathode voltage.
This is a lovely simple circuit, and as none of the voltages/currents seem correct, I would disconnect the power, drain the caps, remove the tubes, and get a print out of schematic + tube bases, and carefully use the ohm-meter to check the wires and resistors in the schematic are correctly connected to all the places you think they should be.
Check each pin of each tube for this.
Check each pin of each tube for this.
Hello Bas,
I know but some time ago you had a build with different currents in the left and the right but both were kind of correct. You should compare those pics with the present build and probably you will spot a difference.
Greetings Eduard
I know but some time ago you had a build with different currents in the left and the right but both were kind of correct. You should compare those pics with the present build and probably you will spot a difference.
Greetings Eduard
Hi Bas, where are the 680k grid leak resistors for the EL84? I am seeing the connection from the cap to the 750R grid stopper, the 680k grid leak should go from that point to ground?
They were not in at that time.
Yes indeed. That's something I forgot. No sound from the amp. And then I soldered in 680k. Currently 470k since I thought that could be an issue.