Got my pentode driver working but ...

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First off, thanks to those who helped me diagnose a few bad connections in a pentode driver. I had a bad connection from the top of my VR tube to the screen. All voltages check out fine now.
well things work now but I still have a couple of issues (schematic in previous thread):
1. the VR tubes abruptly switch off when the volume pot (cheap RS 100K pot) is at the minimum or close to maximum position !!! The circuit works fine at all positions in between. I do have grid leak resistors on the input control grid.
2. Hum. This is definately from my SV83 pentode driver stage, the DHT power tubes are dead silent. Hum is almost 0 at low volume and increases as the volume pot is opened up. Any suggestions?. My power supply is CLC (from memory) roughly about 0.6uF->5H->100uF->4H->200uF . I'm wondering whether cutting down to a single choke and tuning it a la http://www.diyparadise.com/tunedchoke.html might help.
3. After installing the VR tube regulators and 3V worth of battery bias on the cathodes, I also hear what can only be described as high frequency broadband noise (similar to the noise of many crickets at night). Is this the VR tubes? I have them bypassed with a 0.04uF cap. The VR tubes regulate between the cathode (not ground) and screen ? Or am I oscillating?

Thanks

My previous thread (incl. schematic) (Open in New Window)

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Topic - Got my pentode driver working but ... - zobsky 09:05:19 10/18/06 (5)

Re: Got my pentode driver working but ... - PÃ¤r 23:53:28 10/18/06 (0)

am I oscillating - Russ57 10:24:47 10/18/06 (3)

Re: am I oscillating - zobsky 14:16:18 10/18/06 (2)

The cathode of the VR tube should connect to ground ... - mikeyb 16:17:38 10/18/06 (1)

update: - zobsky 18:12:17 10/18/06 (0)

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