No OCR software? Here is a plug for Caere software: after trying many of its competitors, I am convinced that OmniPage Pro 10 is the one to beat. It easily recognizes old ratty pages that the other OCR programs treat as hopelessly meaningless images.
    Yes, the heater-to-cathode voltage limit is often ignored and should not be. Here is a quote from the Sylvania Engineering Information Service Vol. 1. No 5, 1952.

   "Maximum allowable heater-cathode voltage has been a serious problem in many applications where it is desirable to operate at high heater-cathode voltages. The question has often been raised as to why the voltage must be so low. Physically, the reason is quite simple. The heater is usually operating at a temperature of 1400°K. The thickness of the insulator coating is about .006 inches. If the heater is in contact with the cathode (which it always must be at some point) with a voltage of 300 volts, the gradient will be about 50,000 volts per inch. As yet, no material capable of consistently withstanding this potential gradient at that temperature has been found. This particular item also deserves considerable attention from the fact that heater-cathode insulation failures brought about from over voltages are generally inoperative failures. Thus, when operating above the maximum rating for heater-cathode voltages, the equipment designer runs a dual risk of equipment failure due to an inoperative tube and the possibility that other circuit elements will be subject to overloads caused by this type of failure. Furthermore, experience has shown that failures of this nature are accelerated when the heater is positive DC potential with respect to the cathode and/or the filament voltage is operated above Design Center."

Subject: What no digital!?
   Audio, Audio and more stinking Audio. Where are all the digital projects? How about a special segment on forgotten display devices-

Tubes. Nixie and vacuum florescent still I think are the best looking displays for computers, calculators and clocks.
   Having found a nice source of nixie tubes
http://www.sphere.bc.ca/test/nixies.html#catalog  I was thinking of making a nice Octal front panel to go with a FPGA kit I am getting. Searching for Nixie-tube clock plans the designs just seem to be too primitive or have unsafe power supplies. I was wondering if you could add a few thoughts on the modern designs for using the quaint display devices. Now back to the Audio segment of this program.

Ben.

    I love nixie tubes and I have a box of them and their sockets. I once drew up a schematic for adding a nixie tube readout of the frequency a Dynaco FM-3 was tuned to. Unfortunately, I never followed through and built it. I believe TI used to make high voltage driver ICs for numerical displays that could be used readily. Maybe these chips are still available on the surplus market. Please, if anyone has much experience with using these tubes, let us know.
   
Subject: CCDGC
   I am a big fan of your webzine, which gives me interesting ideas about tube design every month.
    I have been using the CCDGC as a line amplifier for my 300b amps. It is probably one of the best line amps today in terms of specs and sound quality. I use it with high gain tubes, but the gain is still not enough to excite fully a power triode. May I use a capacitor in the cathode of the first tube to increase the gain of the unit? Will this modification worsen the marvelous specs of the CCDGC ?

AMG

     NO, is the quick answer. However, the bypass capacitor is a sore spot in many designs.