| Author | Message | ||
     Jimmie Åkerström (rudeez) Username: rudeez Registered: 12-2012 |
So i just retubed my HD130 head tonight. JJ E34L matched quad set. It's the early model with 12AX7 Phase inverter. I tried to get the biasing done but once i were there i was quite unsure what to do. Took ground from chassis and measured pin 8 at the resistor crossing there. When measuring DC volt with my multimeter i adjusted it to be at 0.460 mV, but when checking the same place using the mA setting on the multimeter i had readings at about 70 mA, is that normal? Couse 70/2 (two tubes) is 35 and the mA should be around 23-25 mA? Im confused really. Im not an expert with measuring these types of things eaither really, i usually only do ohms and caps measuring. I really need some support here on how and what i need to check and if someone could tell me the diffrences between measuring mV and mA i would be really glad. Did everything else as told. Amp sounds fantastic but im worried that it runs to hot. The chassis gets really hot and you cant really touch the back of it because of the heat. I don't really know what normal heat is supposed to be and i have no clue realyl when the amp is running to hot other then using EHX EL34 in hogh power made the tubes go up in smoke haha. Also ive been told that the tubes should show any blue light, they do now but it's only a small shade of it in the middle of the tube. Does not show in half power mode. if someone could clear things up for me i would be really really happy! /Jimmie, Sweden | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
If you measured at the same spot but had the meter set to mA, you were NOT reading the actual current. It was an error reading. The actual CURRENT would have to be measured in SERIES with that resistor, which really isn't a good idea unless your meter is great and you have a solid connection. Measure the voltage ACROSS that resistor and leave it. That shows the VOLTAGE drop across a valid resistance. A quad of EL34's develop a lot of heat. I usually have a fan on miine. | ||
| Lars Verholt (lmv) Username: lmv Registered: 11-2009 |
460mV is fine. The baseline is 500mV so you are ok. Blue light is not unusual in high power mode and is not a great cause for concern if the amp otherwise sounds ok. Yes, they do get quite hot. Just play it and enjoy it. Don't put a can of Pripps on it to cool it down - spilling liquids into a Music Man amp will result in smoke. Hejhopp! /Lars | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Ok-I'll bite. What is(are?) Pripps? | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
OK-so it's beer! Must be up North way. I'm a Miller Lite guy myself! Mike. |