Hi David,
I have the 290CX and I have about 357 Vdc at the psu output using 120 to 121 vac mains. I agree that you shouldn't worry about the difference. You will end up with slightly lower current through the 6922 but that is no problem. It might even be desirable.
Just a crazy thought. Did you happen to have your light bulb tester still attached when you measured psu voltage? I did that and had low voltage. The light bulb causes a fair bit of voltage drop, even though it's not glowing. I found that out the hard way.
Jac
I have the 290CX and I have about 357 Vdc at the psu output using 120 to 121 vac mains. I agree that you shouldn't worry about the difference. You will end up with slightly lower current through the 6922 but that is no problem. It might even be desirable.
Just a crazy thought. Did you happen to have your light bulb tester still attached when you measured psu voltage? I did that and had low voltage. The light bulb causes a fair bit of voltage drop, even though it's not glowing. I found that out the hard way.
Jac
Thanks again for all of the suggestions. I spent some quiet time, once the grandkids had gone to slept waiting for Santa, traced what R1 does on Jack's board, determined I needed a jumper there. Now I have 357vdc like Jac is showing, didn't check what was coming out of the wall though. I figure with the improved voltage I can move on to powering the preamp side of things.
And yes Jac, my first power on was with the bulb tester, much lower voltage, but no glow so I did move on to full test.
David
And yes Jac, my first power on was with the bulb tester, much lower voltage, but no glow so I did move on to full test.
David
Many thanks to all for their advice and assistance. While lunch was being prepared, went ahead and added the XLRs, connected power supply, added some EH tubes and viola sound. I am playing the preamp through some A7 powered speakers I have in the shop, no hiss just great tube sound!!
Now for the case build and connect it to the pair of bridged F4s.
The case build is the part I hate the most, rather build the circuits than plan and drill a case.
Now for the case build and connect it to the pair of bridged F4s.
The case build is the part I hate the most, rather build the circuits than plan and drill a case.
Thanks guys. Your suggestion Jac using the 290CX is spot on, a bit oversized for this application, but works well. Underload the PS is holding at about 351vdc.
I am now in the process of trying to pick a case for it, then it's off to the drill press!!
Chris I have some other tubes to try out once everything is encased and the pre is connected to the two F4s.
I am now in the process of trying to pick a case for it, then it's off to the drill press!!
Chris I have some other tubes to try out once everything is encased and the pre is connected to the two F4s.
Is it audible? I've had problems with various 6sn7s. I manage to damage both tungsol when testing by having them swing too much on the out put, they crackled every now and then, and a Jan Philips that sounded harsh. Now have a sylvania green lable(whatever...) that sounds great but hums a bit in one channel although it has improved a little.
An awful lot of change will be seen as you roll different tubes, particularly the 6SN7. I have a bunch of NOS TungSol which I grabbed a few years back and work quite well. I think that Stu was probably very judicious in his selection of input tubes, mentioning that he used a Brit military version of the 6SN7.
If you suffer from mains peaks being a bit higher than you like, please look into using smps and DC step up boosters. Recently, DC step up to 450v is available for $10 and gets switching noise well above audio band for easy filtering. A DC to DC step up paired with a CRC and a cap multiplier as a soft start for DC step up can get down to the noise floor of the measurement equipment. I too suffered with hum from mains, but not anymore. Here is FFT of one of my preamps - absolutely clean no mains leak through for the blackest blacks in the music. No hiss, no hum, nothing.
Indeed. I got another -10dB at 60Hz using a Russian 6N23P-EV. It was the best out of 8 choices. Let me see what I can get by changing the 6SN7...
As a newbie to tube HF builds, I ran across a now defunct publication from about 15 years ago called "Vacuum Tube Valley". One of the issues had a ranking of distortion levels of 6SN7 type tubes, I believe around 60 or so were tested. Rather enlightening.
I am enjoying listening to my board mounted Impasse playing through the F4s. Tubes are EH in both positions. Tube rolling to come later!!
I am enjoying listening to my board mounted Impasse playing through the F4s. Tubes are EH in both positions. Tube rolling to come later!!
SY also used a PEM.
FWIW, the Maida regulator is NOT particularly quiet -- it's the LM317 -- try bypassing R108 with a 10uF/450V electrolytic or polypropylene cap.