Re: Brandneue Gleichrichterröhre kaputt?
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Beitrag von evamatze vom November 26. 2005 um 07:54:08:
Als Antwort zu: Re: Brandneue Gleichrichterröhre kaputt? geschrieben von evamatze am November 24. 2005 um 22:44:02:
Hallo Stefan und natürlich alle anderen Aussensaiter auch
im Fenderforum hat mir noch jemand eine Möglichkeit gezeigt, wie man relativ einfach checken kann, ob die Siebelkos in Ordnung sind oder nicht. Allerdings habe ich es noch nicht gemacht, da mir noch ein Widerstand fehlt...
Hier die Beschreibung für den Fall, dass die Gleichrichter-Röhre in Ordnung ist:
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If you put a dc current meter in series with the B+ (unsolder the wire from pin 8 of the rectifier socket and insert meter there), you can measure the current the rectifier must supply. With the other tubes pulled, this should be very low after the filter caps charge up. There will be a small trickle current of about 1 mA due to the two 220K bleeder resistors but if the caps are good, not much more than that. If more, then the filter caps are leaking dc and drawing current.
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Da bei mir die Gleichrichterröhre nicht funktioniert, hatte er den Vorschlag, eine temporäre Diodengleichrichterschaltung einzubauen:
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You can temporarily solder (or jumper to avoid soldering) in two 1N4007 diodes across the rectifier socket. These are very inexpensive, like 10 cents each and should be readily available at any electronics store. If you use the 1N4007 diodes, observe polarity so you do not end up with negative B+, which would blow your filter caps immediately. One end of the diode will be plain and the other end will have a stripe.
I would use three jumpers with alligator clips to avoid soldering. Connect one jumper to pin 4 of the rectifier socket, connect the other end to the plain end of the 1N4007 diode. Connect the second jumper to pin 6, the other end of that jumper to the plain end of the other diode. Twist the two striped ends of the diodes together and connect them to the red lead of the meter, set to dc volt. Connect the black lead to chassis. Turn on and verify the dc voltage is positive and high (a few hundred volts). This first test is to make sure you connected the diodes correctly.
Power off and remove the meter. Use the third jumper to connect the striped ends of the diode junction to a 10K, 2 watt resistor. Connect the free end of the resistor to one lead from your meter. Connect the other lead of your meter to pin 8. Set meter to dc current. The resistor is to keep the current surge when the caps are charging from blowing the fuse in the meter.
Make sure this is correct before turning on the power. Both diodes have the striped end toward pin 8 (with the resistor and meter between the diodes and pin 8).
If you use jumpers with alligator clips to temporarily connect diodes, please be very carefull and make sure all connections are secure before turning on the power. Remember, this is high voltage.
Pull both power and preamp tubes so the only load on the rectifier will be the filter caps and bleeder resistors. When the standby switch is open, the rectifier will charge the first two filter caps only (the two that are in series with each other and connected to the bleeder resistors). Initially there will be significant current as the caps charge up but that current should diminish in a few seconds to about 1 mA flowing through the bleeders. When you close the standby switch, there will be another current surge as the rest of the filter caps charge but it should diminish again to not much more than 1 mA.
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Werde das demnächst mal ausprobieren, muss aber erst noch den Widerstand besorgen, hier an der Schule haben wir nur 1W-Versionen.
Viele Grüsse aus dem schweizerischen Exil
Matthias
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