Electronic Design

Bob's Mailbox

Dear Bob: When scanning the index (electronic design, Jan. 6, p. 20), I saw "K2-W" and put on the brakes. Hey, I bet that's Philbrick's stuff. Yes, it is! I looked in my junk box because a couple of K2s were once in there. No, tossed out—damn. I still have a catalog pamphlet somewhere and the Palimpsest.

I was working at General Dynamics (then Electric Boat), and Jim Reswick at MIT and I put together a hydrodynamic simulator for the Nautilus SSN-571, the first nuclear boat. It was back in 1954, I think. Anyhow, we had five racks of K2-Ws with probably eight or 10 K2-Ws in each, a bunch of Philbrick multipliers, several function generators, and a monster ±300-V power supply. Even George came down to Groton, Conn., to see his stuff work! (Almost 50 years ago! /rap)

One thing that history has overlooked: I finished setting up the 3D hydrodynamics, and while I was "flying" the boat for the naval architects, the depth controllability at high speeds of the simulated boat was much better than usual. The hydro guys were mystified because their predictions were way off. I checked all of my coefficients and sure enough discovered a mistake! I had "placed" the bow planes on the sail (conning tower, to land lubbers) instead of the traditional bow position! High up there, we found the turbulence of the bow was avoided and the boat maintained depth smoothly at all speeds.

The hydro guys went back to their drawing boards (literally boards back then!), and on the next boat they convinced the BUSHIPS to really put the bow planes there. All the boats after that had bow planes on the sail, because they were more effective, much smaller, and quieter. The Russkies never caught on to this for many years. Then they did it, too. So, the K2-Ws have a place in submarine history due to my mistake! (Wonderful! What a fantastic story! /rap)

George Philbrick, Jim Reswick, and I were pleased. (Me too! But mounting those control planes on the sail would seem to be very conspicuous! Like a sore thumb? How could anybody miss seeing the planes there? Maybe they hid them, or folded them up, when on the surface? /rap) Thanks for the memories!
ROY MURPHY (via e-mail)

Pease: I bet the Russians took a long time to match our learning because (A) what we were doing looked so stupid that they couldn't believe we were doing it, and (B) they didn't have any K2-Ws!

See associated figure.

Dear Bob: I loved your article on the Philbrick K2-W! Several tube op amps I designed in the early 1980s are similar to the K2-W. I used zener diodes rather than VR tubes for plate-to-gate coupling. (The neons were usually adequate. And in 1952, they were much cheaper and more available! /rap)

I ran a spice simulation and a paper-and-pencil analysis of the K2-W. The gain spec for the K2-W must be 2000, not 20,000. If I remember correctly, the gain equation for a triode amp is (µRL)/(RP + RL). The plate resistance (RP) of a 12AX7 is 170k and the µ is 100. This works out to a gain of 56 for the first stage. (That's about the right ballpark. /rap) The gain of the second stage is reduced to about 20 by the local feedback between the two cathodes of V2. Therefore, the total open-loop gain is approximately 1100. I ran a Spice simulation of the amp and got a small-signal gain of 1100. The Micro-Cap 7.0 Spice I used does not have any VR tubes, so I used some zener diodes and tweaked a couple of resistor values.
DAVE CUTHBERT (via e-mail)

Pease: Au contraire! That's positive feedback (PFB)! The gain without the 221-kΩ resistor is about 2k, and the PFB increases it a lot. Spice should not lie so much!

Dear Bob: The schoolgirl that you quote in your column (Electronic Design, Nov. 11, 2002, p. 92) must have been peeking into M. Luther's letter to Melanchton: "Este peccator & peccate fortiter..." (be a sinner & sin hard, but believe even harder...)
GIDEON YUVAL (via e-mail)

Pease: Your point is nicely taken! But the philosophy is slightly different. After all, what if the little girl decided to "believe even harder" about sin? Remember the immortal words of Mae West: "Whenever I have to choose between two evils, I always choose the one I haven't tried before."

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