That is a bit hard on the power transformer, and is a bit hard on the rectifier tube.
But they probably survived.
If the 300B grid did not arc to the filament, or the result of that is not permanent, it probably survived too.
I hope you have a 2.5A or more filament winding to run the bridge and 20000uF cap and 1.25A filament of the 300B. DC needs at least 1.8 times the AC current rating of the winding.
You need 2 separate filament windings so that each 300B has its own self bias resistors, its own bypass cap, and its own 15 ohm resistors (2.5A winding and another 2.5A winding).
Yes, I am up very late in the US. I think that is hard on my body, I hope to survive too.
I can hardly wait for you to tell us how the amplifier sounds when it is up and running.
But they probably survived.
If the 300B grid did not arc to the filament, or the result of that is not permanent, it probably survived too.
I hope you have a 2.5A or more filament winding to run the bridge and 20000uF cap and 1.25A filament of the 300B. DC needs at least 1.8 times the AC current rating of the winding.
You need 2 separate filament windings so that each 300B has its own self bias resistors, its own bypass cap, and its own 15 ohm resistors (2.5A winding and another 2.5A winding).
Yes, I am up very late in the US. I think that is hard on my body, I hope to survive too.
I can hardly wait for you to tell us how the amplifier sounds when it is up and running.
Not on this transformer.
I have another one with separate windings for filamants, but the hv is 380v-0-380v
It is quite higher than required. Should I change anything in the circuit?
I have another one with separate windings for filamants, but the hv is 380v-0-380v
It is quite higher than required. Should I change anything in the circuit?
380-0-380VAC, wow!
So, completely remove the 47uF cap that is connected from one end of the rectifier filament, and the other end of that cap is connected to ground.
Replace it with a 1uF to 4uF cap. If it is a non electrolytic, it needs to have a 440VAC or higher rating. If it is an electrolytic, it needs a 600VDC or 630VDC rating.
If you do not have a cap that has that high of a voltage rating, then stack 2 caps in series, from the rectifier filament to ground. Use 2uF to 8uF in series (but always use two with the same uF value), with a 300k across each cap to equalize any cap leakage current. An electrolytic that is 400V rated or higher, with 2 caps in series will work.
two 2uF caps in series = 1uF, two 4uF caps in series = 2uF, two 6uF in series = 3uF, etc.
After you get the amp up and running, check the B+ voltage again.
I am guessing about 2uF of capacitance (or two 4uF caps in series) will give about the right B+ voltage.
Signing off for now.
So, completely remove the 47uF cap that is connected from one end of the rectifier filament, and the other end of that cap is connected to ground.
Replace it with a 1uF to 4uF cap. If it is a non electrolytic, it needs to have a 440VAC or higher rating. If it is an electrolytic, it needs a 600VDC or 630VDC rating.
If you do not have a cap that has that high of a voltage rating, then stack 2 caps in series, from the rectifier filament to ground. Use 2uF to 8uF in series (but always use two with the same uF value), with a 300k across each cap to equalize any cap leakage current. An electrolytic that is 400V rated or higher, with 2 caps in series will work.
two 2uF caps in series = 1uF, two 4uF caps in series = 2uF, two 6uF in series = 3uF, etc.
After you get the amp up and running, check the B+ voltage again.
I am guessing about 2uF of capacitance (or two 4uF caps in series) will give about the right B+ voltage.
Signing off for now.
You can do a preliminary check of the B+, and the 300B tubes.
Just remove that first 47uF cap that connects between the rectifier filament and ground.
If the parts are still working, you will get some B+, and some current in the 300B tubes.
Just remove that first 47uF cap that connects between the rectifier filament and ground.
If the parts are still working, you will get some B+, and some current in the 300B tubes.
Will do for sure! Thank you so much for your help!!
I'm now looking for the caps to replace, does not seem so easy to find here in Italy..
It does need to be electrolitic, right?
I may have to come up with a series 😀
It works!!!!!
Thank you!
No hum at all, just a bit of difference between lh and rh channel sound.
I finally used 3x 10uf in series.
Voltages make sense now.
Thanks again!
Thank you!
No hum at all, just a bit of difference between lh and rh channel sound.
I finally used 3x 10uf in series.
Voltages make sense now.
Thanks again!
Working. That is great!
Use 3 resistors to balance the DC voltage across the 10uF capacitors that are in series.
Example, 3 each 100k, one across each 10uF should work.
Or, with a DMM (floating leads), you can check if the DC voltage across each of the 10uF caps is nearly the same.
But the leakage of each individual capacitor can change versus temperature and with aging.
Use 3 resistors to balance the DC voltage across the 10uF capacitors that are in series.
Example, 3 each 100k, one across each 10uF should work.
Or, with a DMM (floating leads), you can check if the DC voltage across each of the 10uF caps is nearly the same.
But the leakage of each individual capacitor can change versus temperature and with aging.
Yup! Each cap has its resistor .
One last question, should I ground one lead of the output transformers, or leave it free?
Thanks!
One last question, should I ground one lead of the output transformers, or leave it free?
Thanks!
If your amplifier chassis is grounded and if that is a safety ground, then you should ground one end of the output transformer secondary.
In the US, most home outlets have Hot, Neutral, and [safety] Ground.
I use a 3 wire IEC power cord, and IEC socket on the amp.
The chassis is grounded to the power mains ground. The output transformer is also grounded to the chassis.
Sometimes, output transformers have shorted from primary to secondary. You can imagine what happens if the secondary is shorted. Now you have B+ on your speaker wires!
It is one more cause of the "Surviving Spouse Syndrome".
Safety First!
In the US, most home outlets have Hot, Neutral, and [safety] Ground.
I use a 3 wire IEC power cord, and IEC socket on the amp.
The chassis is grounded to the power mains ground. The output transformer is also grounded to the chassis.
Sometimes, output transformers have shorted from primary to secondary. You can imagine what happens if the secondary is shorted. Now you have B+ on your speaker wires!
It is one more cause of the "Surviving Spouse Syndrome".
Safety First!