| Author | Message | ||
| Anonymous |
Had some unclean/distsound in my amp. The four EL 34 were old so I changed them and mounted four 22K pots for separate bias for each powertube . Added 100mA glassprotection and 10 ohm resistor to each cathode. Problem 1 : to high 755V anodevoltage ..... due to 220 V has increased here in Sweden to 235V. Added a quite small 220/ 16V transformer with second. coupled in series with primary to lessen 235 to 200v. Then this 200V (AC) was connected to my amp. Now 6,9 (too high for the heaters were 6,3 and 755V became 680 V or so. The soundproblem was still there. The two 33K res. in the splitter was different , they should be equal. I had 73 V and 78V over them. After changing 75,1 over both. Have added a 47uF/35V cap over the 1,5 biasres. I have also changed both biasresistors 1,5K to 2K trimpots. That makes it possible to Balance both stages. Have Changed 12AX7 for 12AT7. Now the first triode have 145V over itself and 145V over its anoderesistor (100K). The Consertinasplitter has as I mentioned 75V over each 33K resistor. Current in the new EH EL 34 is 23mA /660 V. Sound is now powerful and clean. |
Tue, 03/25/2014 - 09:28
#1