Hi,
I'm entertaining a pre-amp using RE084 valves and supplying the heaters from a battery, using cathode bias. How would the heather supply affect the operating point? Or am I overthinking this?
I want to use the RE084 at a operating point of ~4V, 4mA, which would need a cathode resistor of ~1k.
Can I simply use two 2k resistors going to ground (one from each side of the heather), this would drain the batteries least as they are from the battery perspective are in parallel with the heather. The alternative would be two smaller ones, from the heater that go to a larger one to ground (for example 2*80 + 1* 960)
Furthermore one side of the heather would in this case be 2V and the other at 6V (the heather are 4V and assuming I have a perfect 4V battery) relative to ground/grid, would this affect the bias point? I could understand that with a higher cathode voltage (relative to grid) such as for a 45 or 300b this becomes more of an issu, but given the grid voltage
Thanks!
Matthew
I'm entertaining a pre-amp using RE084 valves and supplying the heaters from a battery, using cathode bias. How would the heather supply affect the operating point? Or am I overthinking this?
I want to use the RE084 at a operating point of ~4V, 4mA, which would need a cathode resistor of ~1k.
Can I simply use two 2k resistors going to ground (one from each side of the heather), this would drain the batteries least as they are from the battery perspective are in parallel with the heather. The alternative would be two smaller ones, from the heater that go to a larger one to ground (for example 2*80 + 1* 960)
Furthermore one side of the heather would in this case be 2V and the other at 6V (the heather are 4V and assuming I have a perfect 4V battery) relative to ground/grid, would this affect the bias point? I could understand that with a higher cathode voltage (relative to grid) such as for a 45 or 300b this becomes more of an issu, but given the grid voltage
Thanks!
Matthew
Thanks Euro, that's indeed one of the options I had in mind. To make it more specific I was considering one of these options:
The left would have the benefit of only needing one capacitor, however effectively there is a 100 ohm resistance in parallel with the heathers causing an addition 4/100 = 40mA from the battery.
The option on the right requires an additional capacitor, however now the battery sees an extra 2k resistance parallel to the heather, which should only cause an additional 4/2000 = 2mA from the battery. However because R4 and R5 being at ground, would this imply that current flows from the ground to the end of the heather that's at -2v? and that the cathode (in this case equal to heater) effectively is at ground as well? Did I just answer my own question? 🙄
The left would have the benefit of only needing one capacitor, however effectively there is a 100 ohm resistance in parallel with the heathers causing an addition 4/100 = 40mA from the battery.
The option on the right requires an additional capacitor, however now the battery sees an extra 2k resistance parallel to the heather, which should only cause an additional 4/2000 = 2mA from the battery. However because R4 and R5 being at ground, would this imply that current flows from the ground to the end of the heather that's at -2v? and that the cathode (in this case equal to heater) effectively is at ground as well? Did I just answer my own question? 🙄
May I ask , Do you mean grid-cathode bias voltage of -4VDC and anode voltage of 150V ?
Are you thinking push pull or single ended?
Are you planning a separate battery for each filament ?
The right version has 500R (1k//1k) effective bias resistance, so 2k resistors would be better. 😏
Both versions gives the same bias voltage (in the middle of the RE084 filament), so lower battery current version (right) is recommended.
Both versions gives the same bias voltage (in the middle of the RE084 filament), so lower battery current version (right) is recommended.
Little "upper" operating point (higher current, higher Uak) gives better distortion.
sample:
sample:
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I’m thinking to use it as a “driver stage” so single ended, potentially followed by a cathode follower (another RE084 or perhaps a 6Sn7GTB).
As for the batteries I’m for now planning to use 3 or 4 1.4 NiMH penalties per RE084
Ouch basic math error 🙂
And thanks for the suggestion on operating point, I finally succeeded to get a RE084 model working in spice, will play around with that (one day I’ll figure out to do distortion In spice as well)
