deliver the first ±0.15 volts into a 32 ohm load and the first ±1.5 volts into a 300 ohm load. Thereafter, the bottom tube will share in the active driving of the load, as once the input signal exceeds the difference between zener and cathode voltage, the bottom tube becomes active. The potentiometer does not set the idle current, as the current source will adjust the cathode voltage to track the potentiometer's movements. Instead, the potentiometer is used to adjust the transition point between the two tubes. The potentiometer's adjustment should be made with a dummy load and the feedback loop opened. A triangular waveform is perfect for showing discontinuities.
    Where do we go from here? The next installment will bring us closer to a final design. Until then, your comments are encouraged and if anyone knows of any readily available high quality output transformer's, please let us know about them.


                              //JRB

Subject: printing articles, dropping filament voltages, balanced phono amps

    Hi, I got your address out of the current Audio Electronics.  I have tried printing out 2 articles, so far. I have a Compaq Presario running IE5 You have stops between each page, so they are printed out individually, each with your header! So, the second page comes out with just one line, listing the title and page 2 or a short remainder, pushed down by the space your header takes up. This wastes twice as much paper!  Why don't you fix this? Otherwise, your magazine is quite informative.
    A comment on John Atwood's Ultrapath circuit.  I tried it with the Fender stand alone reverb CKT - a single ended 6K6 - as I was building a new guitar amp which included it, recently.  The output hummed loudly and I traced this to the fact that the capacitor was coupling power supply noise to the cathode of the 6K6 and the tube was amplifying it! I had to add a second choke and cap section to get rid of the residual hum on the B+.
Hot Wall Voltages
    I work on guitar amps. Out here on Cape Cod they "improved" the power system a while back.  In summer, when it is so hot in Boston that they send the government workers home... and predict brown outs, the line voltage down here is still 123-4 volts!  This means that you have 7V on you filaments - perpetually (5.7V on rectifiers) - in your 115-117V amplifier.  What to do?  You mention in-rush current limiters and there are not many choices.  The only applicable ones are CL-10 (CL-11), CL-20 (CL-22)  and - I believe - CL-100 (Keystone parts - they have re-numbered them!)   These are the three lowest resistance values @ 6, 8 & 16 amp ratings.   In practice, they all work about the same. A single one in a typical BF/SF Fender Pro, Twin, etc. with non CT filament winding will bring the voltage down to about 6.3 (or 5) volts.   Check it out!