done some reading and now understand that adding limiting resistors was not a good idea - my sec resistance from ct to terminal is 220r
and from the data of the EZ81 i understand that Rt min is 200
so probaly the caps are too big and drowing too much current ?
i still dont understand way C1 being the first cap, didnt fail ?
and from the data of the EZ81 i understand that Rt min is 200
so probaly the caps are too big and drowing too much current ?
i still dont understand way C1 being the first cap, didnt fail ?
ok ,
check caps for resistance, they should be high resistance.
Maybe other members of the forum will tell you that the fuses should not be in CT as I don't think it protects adequately.
The CT should be wired to the Ground from incoming 3 prong connector and send any voltage to the ground, it is the primary that you should fuse.
For more protection you should fuse the secondary with 2 fuses,
: if the CT fuse that you have right now blow there is still potential in the circuit the transformer can operate normally without any CT connection !
when i first open the amp it was working no problems
i took v measurements from the psu
on c1 368v
10h chock
c2 356v
1k res
c3 308v B+
48v/1000 =48mA that is the correct current for 2 x 12B4 or i am wrong?
i cant understand what happend ?
could it be that the 12B4 are bad or sockets loose and the psu runs with no load drowing to much current?
tnx for your help
i took v measurements from the psu
on c1 368v
10h chock
c2 356v
1k res
c3 308v B+
48v/1000 =48mA that is the correct current for 2 x 12B4 or i am wrong?
i cant understand what happend ?
could it be that the 12B4 are bad or sockets loose and the psu runs with no load drowing to much current?
tnx for your help
WHO mentioned fusing filament CT?
Where do you pull that from?
Fusing filament windings is *required* by several Electrical Safety agencies around the World.
Check this Marshall Amplifier showing *mandatory* filament winding fusing ... on both hot wires of course, not on center tap which by the way, might even be virtual/artificial , just 2 x 100 ohm resistors.
Needed to get CSA and SEMKO approval.
In fact, standards have been updated since ... but the fusing requirement has not been dropped.
Note: if hard to read: "F6/F7 heater fuses - T6.3A 20mm"
And not news either, this schematic is from 1990 !!!!
Note: if hard to read: "F6/F7 heater fuses - T6.3A 20mm"
And not news either, this schematic is from 1990 !!!!
This is true for the case you make equipment to sale to thirty persons, but in our, whose devices are for personal use, I don't think it be necessary.
Hi
I checked the valves pins on the 12b4 and the ez81 and they full of corrosion and show poor continuity
Is it possible that I turned on the amp the psu had no load so the voltage was too high and c3 the last cap 100uf/450v broke and an ark formed to itself?
After replacing c3 I also changed the resistor between c2 to c3 (from 1k to 2k7) so c2 broke and an ark formed to itself, may be? because the high voltage was now on c3?
Does it sound like a plausible theory?
I must understand what happened before I continue
Thank you
I checked the valves pins on the 12b4 and the ez81 and they full of corrosion and show poor continuity
Is it possible that I turned on the amp the psu had no load so the voltage was too high and c3 the last cap 100uf/450v broke and an ark formed to itself?
After replacing c3 I also changed the resistor between c2 to c3 (from 1k to 2k7) so c2 broke and an ark formed to itself, may be? because the high voltage was now on c3?
Does it sound like a plausible theory?
I must understand what happened before I continue
Thank you
May be, but it is symptom of a very bad design.
Sparks may then be because the cap sometimes can "catch" voltage, and when doing it, draws lots of milliamperes, producing the arc. Also, surely, the soldered join inside will be carbonized by the sparking.
Hi osvaldo
Is it possible that the first time I open the amp everything was working fine for minutes and switching's on and off for testing, and the day after everything changed?
I am trying to understand if the design is wrong, and what's wrong with it
Thank you
Is it possible that the first time I open the amp everything was working fine for minutes and switching's on and off for testing, and the day after everything changed?
I am trying to understand if the design is wrong, and what's wrong with it
sorry but i dont understand ... ?
Thank you
I apologize for the inconveniences. I want to mean, that when cap is discharged, and voltage appears, the cap try to charge from it. If there is a non good contact, then the high voltage gradient in the site causes a spark to appear, then charging at some level, the cap. but if cap didn't acquired full voltage, then another time voltage gradient appears, trying to charge again, thus the cycle repeats until cap is fully charged, then, never.
If when load is removed, and voltage on the PSU becomes greater than the rated voltage of the caps, then a serious design error had been done.
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It would be nice to see a video on youtube...
I recently miss-bias some amps and was running el34 at 50 watts bias (33W is the design max...) for hundred of hours and nothing bad happened fortunately!
The capacitors might repair itself... please clean socket pins and your rectifier pins properly before using them.
After the spark the parts should be thoroughly cleaned of any deposits which could trigger another spark. Check the insulation to ground of every part and take voltage measurements with the amplifier turned on to see if the voltages are stable.
Always make sure you don't touch anything when testing. Isolate yourself from any basement, metals and use a GFCI plug.
Preinstall voltmeters with secured connections, then remotely power the amplifier with a disconnect switch, disconnect all power plugs then take more measurements the same way!
I recently miss-bias some amps and was running el34 at 50 watts bias (33W is the design max...) for hundred of hours and nothing bad happened fortunately!
The capacitors might repair itself... please clean socket pins and your rectifier pins properly before using them.
After the spark the parts should be thoroughly cleaned of any deposits which could trigger another spark. Check the insulation to ground of every part and take voltage measurements with the amplifier turned on to see if the voltages are stable.
Always make sure you don't touch anything when testing. Isolate yourself from any basement, metals and use a GFCI plug.
Preinstall voltmeters with secured connections, then remotely power the amplifier with a disconnect switch, disconnect all power plugs then take more measurements the same way!
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