Hi,
I rebuilt my Chinese 300B amp as per Skunkie design. I try to reuse as many components as possible to see how much better this amp can sound. I am pretty impressed with the result.
This is my first tube project and I would like to get some clarification on the 300B tube biasing.
Measured values (red numbers on the attached picture):
The plate voltage is 396V
The voltage drop on the OPT is 11.1V and the DCR is 149 Ohm that gives 74.5mA of plate current.
Grid voltage around -65V
Plate curves:
When l look at the anode curves (picture attached), for the -65V grid and 74.5mA the plate voltage should be around 325V which is 71V lower that actually measured.
Questions:
Is it ok to run 300B on the higher voltage comparing to voltage got from the plate curves?
Any benefits or drawback?
Recommendations?
Thanks.
Jacek
I rebuilt my Chinese 300B amp as per Skunkie design. I try to reuse as many components as possible to see how much better this amp can sound. I am pretty impressed with the result.
This is my first tube project and I would like to get some clarification on the 300B tube biasing.
Measured values (red numbers on the attached picture):
The plate voltage is 396V
The voltage drop on the OPT is 11.1V and the DCR is 149 Ohm that gives 74.5mA of plate current.
Grid voltage around -65V
Plate curves:
When l look at the anode curves (picture attached), for the -65V grid and 74.5mA the plate voltage should be around 325V which is 71V lower that actually measured.
Questions:
Is it ok to run 300B on the higher voltage comparing to voltage got from the plate curves?
Any benefits or drawback?
Recommendations?
Thanks.
Jacek
Attachments
396V - 65.56V (74.5mA*880R) = 330.44V
Datasheet always relative to anode-cathode voltage potential!
Datasheet always relative to anode-cathode voltage potential!
This is for all the 300B tinkerers, designers, experimenters and just plain curious out there . . .
Look at all the operating conditions of the 300B on Page # 4 at the following link:
Link:
http://www.tubebooks.org/tubedata/we300a_b.pdf
Have Fun!
Look at all the operating conditions of the 300B on Page # 4 at the following link:
Link:
http://www.tubebooks.org/tubedata/we300a_b.pdf
Have Fun!
@6A3sUMMER - thank you! That helps a lot.
@jeff, yes it Willsenton R300. It sounds very good now. I plan to squeeze in some Schottky diodes and regulate the 300B filament voltage with TL1085. Let's see if that will help with the hum or I need a bigger choke for B+. It is a playground and learning project for me 🙂
@jeff, yes it Willsenton R300. It sounds very good now. I plan to squeeze in some Schottky diodes and regulate the 300B filament voltage with TL1085. Let's see if that will help with the hum or I need a bigger choke for B+. It is a playground and learning project for me 🙂
