| Author | Message | ||
     Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
Hello, I from Honduras, i have a problem with my 210HD/130-12AX7, i put 0.5 Vdc bias, i play when the sound going down, only sound hum, i look the output tubes, they are RED RED(2 of them)to hot, i use the JJ/tesla E34L blue bottle, old RCA 12AX7, i don't know what is the problem (sorry for the orthography) Help please!!!! | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
If I read you correctly, you have TWO tubes glowing red and the amp is humming. You have either lost control grid voltage(bias voltage) to those two tubes or you just have two tubes that went up in smoke,maybe one taking the other out. Remove all four power tubes and turn amp on. Measure the voltage at pin 5 on the power tubes. BE CAREFULL as there is a lot of voltage(700V) floating around in there. You should have at least -35-40 volts from pin 5 to ground. If you have the identical same negative voltage to each pin five, you lost tubes. If you have drastically less voltage on the two tubes that red up, you have to find out where you are losing bias voltage. The bias feed comes from a little pot on the main board and feeds through two 330k resistors at point "B" on the driver board so if you lost only half the bias voltage, I'd start there. Let me know. Mike. | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
Thanks Mike, but, now wen i play the amp only sound very smooth and what it is listened to he is very "crich crich" sound, i will try your advice, tomorrow i post the situation, the translation i did it with a online translator sorry | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
one thing, i try change the 2 reheated tubes with the older tubes, noting, no change, only for information | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
Hello, i did it, i check the grid voltage an when the tubes are out, in the out 5 i read, -24vdc, when the tubes are in i read -22vdc, i follow the schematic (the tubes reheated are the two in the right side looking from the front) and i find a diode in short, the number is 1N4745, this is my foul, because I removed the original diode in my ignorance, I think “to old” , I change for the original(keep the original pieces), and the amp now Work fine, but the voltage in the pin 5 are -22vdc in the 4 tubes this is ok? | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
the tubes are ok, but or less   | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
If you're not red plating anymore, you should be ok. I would suggest measureing the voltage across the 10 ohm resistor in between the pairs and setting the bias to around 22ma which translates on that resistor to right at 460mV across the 10 ohm resistor/ Then play away. Mike. | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
tank you Mike for you Help, i very appreciate, and the amp sound great, Hey I by chance found tubes of the old ones, telefuken 12AX7, it sounds very very excellent, my grandfathers tapeworm an old equipment of projection and used American tubes in the equipment of I found them there, is a great acquisition for my amplifier, i am so Happy Greetings    | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Congratulations. Hope it works a long time for you. Mike. | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
thank You very much!!!!!!!!!! Roberto | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
Hello again, i have bad news, the tubes goin red or reheated, again, wen i play about 30 min. or less in the high power the amp sound "crancky" (this is not a word, but...), only two of them looking from the back going red, the two on the left, i don't know what's the problem, i guess is i need replace the old parts, Help me please!!!  ok, Jorololo | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
ha!!! other things i read 720-25 VDC in the plate, i guess the filter capacitors are ok, but i don't know the 150MF/50V, i thin this are part of the problem, but I'm not sure | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
Help please!!!! | ||
| Peter Maziar (mosfet) Username: mosfet Registered: 11-2006 |
725 volts seems kind of high. Have you checked the resistors in the high voltage power supply? Perhaps they are out of tolerance by too much. In my Music Man amp, they are under the amp by the main filter capacitors. Make sure to discharge the caps before doing anything. Also, what is your supply voltage? Perhaps you need to regulate your supply going to the amp? Good luck. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Sorry, been gone. If you only have two tubes redding out, it sounds like you are losing bias control voltage on just those two tubes. I would check first to see what the negative voltage on pin 5 is with all the power tubes out. Make sure that they are the same. Wiggle the wires a little going to pin 5 and see if it drops. Then start tracking back to the bias supply. If nothing else, it COULD be bad tubes but with two tubes on a side doing it, I;m more inclined to think bias problem. | ||
| Josue Roberto Lopez Lobo (jorololo) Username: jorololo Registered: 01-2008 |
Thank you Guys, i really appreciate the help, i will check the amp and i give you answers soon, i hope find the problem. Ok, thank you again, Peter/Mike You're Fantastics people and this site is great!!!!! Soon!!!! Roberto |