ghiatorino
Well-known member
- Joined
- Jun 18, 2013
- Messages
- 65
Hi,
this is my first time i build a tube microphone from scratch, and first time working with vacuum tubes. Nothing exploded, so far so good.
I have some troubles making the EF86 work the right way, in attachment there's a picture with voltage readings, i summarize my measurements here:
(loaded psu)
Heater: +6,3 V . Current draw is 193 mA
Plate: +177 V on XLR, 173 on socket pin 6 (i am expecting a much higher voltage drop here...). Current is 0,18mA (should be around 1mA). The same current is entering in the 470K voltage divider.
Capsule backplate voltage: +85 V (measured between the 470K voltage divider)
Cathode: +8,2 V on socket pin 3 (i think the problem is here)
Pattern voltages are ok.
I hooked up a couple of dummy loads (280K, 30K) on PSU from B+ to ground to check PSU current capability, up to 10 mA can flow with no problems.
Double checked components values, build a second PCB with new components. Capacitors are at least 250V. 2 different brand new tubes tested.
When i plug the mic the tube heats up, but no plate current is flowing and no voltage drop on 100K plate resistor. Seems to be in cutoff region? am i totally wrong? what's happening?
Any suggestions on what's going on would be appreciated, this thing makes me wake up at night
Many thanks
t.
this is my first time i build a tube microphone from scratch, and first time working with vacuum tubes. Nothing exploded, so far so good.
I have some troubles making the EF86 work the right way, in attachment there's a picture with voltage readings, i summarize my measurements here:
(loaded psu)
Heater: +6,3 V . Current draw is 193 mA
Plate: +177 V on XLR, 173 on socket pin 6 (i am expecting a much higher voltage drop here...). Current is 0,18mA (should be around 1mA). The same current is entering in the 470K voltage divider.
Capsule backplate voltage: +85 V (measured between the 470K voltage divider)
Cathode: +8,2 V on socket pin 3 (i think the problem is here)
Pattern voltages are ok.
I hooked up a couple of dummy loads (280K, 30K) on PSU from B+ to ground to check PSU current capability, up to 10 mA can flow with no problems.
Double checked components values, build a second PCB with new components. Capacitors are at least 250V. 2 different brand new tubes tested.
When i plug the mic the tube heats up, but no plate current is flowing and no voltage drop on 100K plate resistor. Seems to be in cutoff region? am i totally wrong? what's happening?
Any suggestions on what's going on would be appreciated, this thing makes me wake up at night
Many thanks
t.