Bjorn Zetterlund
Well-known member
Hello all!
My previous post was very rudely interrupted, so I thought I'd post an update.
My G9 problem (an 8ch point to point version) was that the cathode voltage for the first stage was far too high. Alas, due to recent copyright disputes, the copyright of the value of this voltage no longer belongs to me, and so I'm not at liberty to disclose this information. Let's just say it was somewhere between 90V and 100V, and actually closer to 100V. My HT supply was a little high as well, something like 295 instead of 245, so this would have contributed some. However, I did try one channel with a 230V HT supply, but the cathode voltage was still about 90, so I obviously have something wrong here. My next step will be to wire up one valve out of circuit with just the HT and bias resistors, and see if I can get that to settle at the correct operating point.
What turns out to be the second problem, is the fact that my HT supply does not appear to be regulating; as in the tl783 does not actually drop any voltage. I have tried replacing the regulator, and the surrounding circuitry measures fine. I have not tested the three zener protection diodes, nor the diode that is wired in parallel to these. I just thought I would run this by you folks to see if anyone spots anything wrong in my redesign for this supply to power 8 channels instead of 2...
The 783 can supply up to 700mA, and I thought this must be plenty for 8 channels. It is mounted on a big-ass heatsink, before you ask! Therefore, I decided to use the original G9 supply, but with suitable scaling of components. The input series resistor (R33) I changed to 120 Ohms, so as to drop the same voltage but at four times the current of the original supply. C14, the resevoir cap, is three 330UF in parallel. The output filter (R37, C15) is actually located on each channel rather than in the (external) PSU unit. Given that each is supplying only one channel rather than the two channels of the original G9, I decreased R37 to 220 Ohms to drop the same voltage for half the current, and I made C15 47UF instead of 100UF. That all seemed like common sense to me, but I thought I'd double check with you all, just in case I've done something stupid (and I obviously have done somewhere down the line!)
I have tried this supply both with the 8ch G9, and also with a dummy load of about 3K, but the results are the same. Any thoughts on this?
:sam: :sam: :sam:
Bjorn
...are there any UK techies that know if you can get Sam Adams here??
My previous post was very rudely interrupted, so I thought I'd post an update.
My G9 problem (an 8ch point to point version) was that the cathode voltage for the first stage was far too high. Alas, due to recent copyright disputes, the copyright of the value of this voltage no longer belongs to me, and so I'm not at liberty to disclose this information. Let's just say it was somewhere between 90V and 100V, and actually closer to 100V. My HT supply was a little high as well, something like 295 instead of 245, so this would have contributed some. However, I did try one channel with a 230V HT supply, but the cathode voltage was still about 90, so I obviously have something wrong here. My next step will be to wire up one valve out of circuit with just the HT and bias resistors, and see if I can get that to settle at the correct operating point.
What turns out to be the second problem, is the fact that my HT supply does not appear to be regulating; as in the tl783 does not actually drop any voltage. I have tried replacing the regulator, and the surrounding circuitry measures fine. I have not tested the three zener protection diodes, nor the diode that is wired in parallel to these. I just thought I would run this by you folks to see if anyone spots anything wrong in my redesign for this supply to power 8 channels instead of 2...
The 783 can supply up to 700mA, and I thought this must be plenty for 8 channels. It is mounted on a big-ass heatsink, before you ask! Therefore, I decided to use the original G9 supply, but with suitable scaling of components. The input series resistor (R33) I changed to 120 Ohms, so as to drop the same voltage but at four times the current of the original supply. C14, the resevoir cap, is three 330UF in parallel. The output filter (R37, C15) is actually located on each channel rather than in the (external) PSU unit. Given that each is supplying only one channel rather than the two channels of the original G9, I decreased R37 to 220 Ohms to drop the same voltage for half the current, and I made C15 47UF instead of 100UF. That all seemed like common sense to me, but I thought I'd double check with you all, just in case I've done something stupid (and I obviously have done somewhere down the line!)
I have tried this supply both with the 8ch G9, and also with a dummy load of about 3K, but the results are the same. Any thoughts on this?
:sam: :sam: :sam:
Bjorn
...are there any UK techies that know if you can get Sam Adams here??