[Flim]

Just finished my Cornet build... no smoke and plate voltages are OK, but when I plug in BOTH channels (and only when both) from my phono there is a loud squeal (about 200Hz) from the right only. Only the right channel has audio coming out. I noticed my heater voltages are only 5.88v, not 6.3v... problem? I have an oscilloscope, but might be a few days before I can dig that deep. Anybody have a starting place to check? The only thing not to spec is the eight 910 ohm resistors (used in the C4S and cathode pull-down) are only 890 ohm (waiting for the right ones to come in). Per a phone call to Jim, this was deemed OK. Thanks

Jason Stahl[/b]

[billwjr]

But here are some thoughts. The heater is a little low, and your tubes might not be happy. As far as resistor tolerance +/- 5% is the norm. I bought a bunch of popular #'s when Welborne had a sale (they still have some) and pick through the bunch and find a matched pair. I've been over mine, can't anything miswired/cold joint, out of spec, but the hum won't go away. Maybe it's the Audioquest arm?? I've also tried 3 different phono cables. No hum in the system with Little Rat, old reciever pre through the tape out, or a borrowed QuickSilver phono pre.

[hagtech]

A squeal at 200Hz?  That should sound more like a thumping.  Is it a hum, buzz or high pitched squeal?  Are other supply voltages ok?  Have you tried another phono in this system?

Can you send photo?  Easiest way to see how things got wired.

jh

[Flim]

Well, solved some problems. My rca jacks were not insulated-types. Unmounted from the chassis, the pre-amp works! (that and I had a hook-up issue I corrected) I have on order new Cardas connectors. I went back and measured voltages again... Heaters are now 6.01v... When I first checked them, my line voltage was 116v. It was 119.2v now and has been as high as 121v so I have issues there it seems. I think I might drop the heater resistor to 2.2 or 2.0 ohm to bring it in a better range. What would be the result if the heater voltage went above 6.3v occasionally? Thanks for a great kit and all the info. I look forward to tuning my system. I'm looking to get a signal generator to test amps with my oscilloscope... what functions are useful? (sine... squarewave) What is the best way to check distortion and bandwidth?

Jason

[hagtech]

I don't think you'll need to drop heater voltage any more.  It's ok to go above 6.3V a little.  Drop too far and the transconductance goes down and rp goes way up, changing gain and EQ.  Makes a new tube act like an old tube.

I like all 3 signals, sine for distortion and frequency response, square for transient and phase response, triangle for delay.  For distortion, you'll need some good equipment.  Hard part is finding a low distortion oscillator as a signal source.  On eBay, the trusty HP333 or 334 are cheap and work great.  The Tek SG505 is a beautiful oscillator, but big bucks.  I made my own, one of my early posts here.  

http://www.audiocircle.com/index.php?topic=2773

jh

[Laudanum]

Hi Flim.  Post is a bit old, I know.  Wanted to share a similiar situation with input voltages.  Line drops under 110 here, usually peak times in the summer.    Heater voltage on my classic cornet I've measured as low as 5.6 volts (270BX tranny).   I know it ultimately can affect gain and eq but I can't say that I hear any differences when the voltage is up or down.  Thing is, line voltage will be up near 120 early day and later at night.  Power company won't do anything about it.  Point is, it's been well over a year and tubes and everything else are holding up ok and like I said, the sonics don't seem to vary.  BTW, I left resistor values as spec'd because of the wide voltage fluctuation.  You're not alone.