DRBILL

Bob, Thanks for the offer. Frankly, I don't hope to repeat this excercise. I just wanted to bring some joy to an old buddy. On the other hand, being retired and somewhat lethargic mentally, I find these excercises to be very beneficial. Sometimes you have to spark the corrosion off the old synapses to restore them. It is interesting to get into the minds of the early engineers to see how they solved problems. My kids find me bent over at my bench and shriek, "God, it looks like an old horror movie!" "Momma, you are going to have to do something with him!" Yes. DRBILL

DJK, Thanks for the "heads up". I don't think there will be much of a problem. We are talking about 100vdc. The choke was not where we would have expected it to be in modern amplifiers. Remember, this is 1939 and we were still feeling ourselves around. I'll see if I can scan this schematic and post it. They were just trying to find some fairly clean DC to provide a magnetic field for the speaker. Any improvement in the B+ was largely negated by the hum induced in the speakerby the field coil (choke). This is why the PM speaker was on the drawing board. DRBILL

I spent the better part of the day surfing the net on the subject before us. The consensus is to replace the electrodynamic speaker with a permanant magnet speaker. Replace the choke with a 10W wire wound resistor of the same impedance. Double the capacitance of the first stage electrolytic (In this case it would be 16µF!). It would seem that the field coil did little except introduce hum to the speaker cone. The choke effect to the power supply was minimal. I've got a lot of stuff on order. The NOS tubes were easily found and very inexpensive! We shall see. The under-chassis is a nightmare. This set is the same age as I. My wife wondered if my insides were as bad. Probably! DRBILL

Yes. It was a long time ago. Almost all parquetry comes that way. It is a good idea. It provides a uniform surface for the adhesive. DRBILL

TO: BOB & GILL -- I managed to find a schematic that had the value of the coil noted. I don't know if I will ever have another occasion to use it but I bought an inductance/capacitance meter on e-bay. It was remarkably inexpensive. It will probably be remarkably unreliable! Or calibrated in Ferds instead of Henrys! Thanks for your help and suggestions. BILL

Bob, You have probably fooled with old gear that used the "electrodynamic" field coil speakers. I wonder how critical a replacement could be? Most of the research that I have looked at says to measure the ohms of the coil and replace with a similar value resistor at 10-15W. I'm sure this would work, but I am also sure that it would compromise the power supply and probably result in excessive hum. I wonder how much damage I could do with trial and error. I have a box of old (but good) chokes from Dynaco amplifiers. I'm tempted to hang one in and see if it smokes. BILL

I am restoring a 1939 Zenith radio for an old friend who is quite ill. I want to replace the field coil speaker with a PM speaker. The field coil provides the magnetic field for the speaker and it also serves as a power supply choke. I need to replace it when I install the PM speaker. How can I measure the value of the old one so I can replace it with something similar? I looked this subject up in the Radio Amateur's Handbook, and had a flash-back to my first week of Greek grammar back in graduate school! I don't need several decimal places. I just need a BPF (ball park figure). Anybody? DRBILL

I am not inclined to dismiss this offhand. Although we might not "hear" the >20kh sounds, we may react to them emotionally. Tube TVs used to emit a supersonic whistle from the HV supply. It would make me edgy to be around them in close proximity. As in all academic endeavors, "more research is needed." DRBILL

I have a couple of DYNACO tube tuners that I rebuilt with better power supplies and network boards that corrected a bad design error. Sadly, they don't perform well here in the Fort Worth/Dallas area where the FM band is covered up with strong stations. The design probably worked very well in the '60s where you had only four or five stations available in typical city. I make a real exception to my vacuum tube rubric and run a DYNACO FM-5 (SS) in my system. I can think of no reason that would justify the use of vacuum tubes in FM tuners. The SS damage has been done, long before the signal reaches your antenna! The band is pretty much a wasteland with a few exceptions. We have a city-owned classical station, an NPR station, and two university stations. I don't know if this list justifies having a tuner. Another reason not to spend a lot of money on a rebuild or upgrade of an FM tuner is that FM radio is going to be replaced with a digital signal in the near future. DRBILL

Wow, Maurice, You should be writing the wine review for the Sunday Paper! DRBILL

Back in the '60's, when I was an organ builder working out of St. Hyacinthe PQ, there were a number of stories told on our fellows in the trade. They were just barely believable. Nevertheless they were repeated and "improved" like urban legends. One was told about an English installation foreman who had constructed a dummy #25 (middle C) principal pipe. It looked like a regular pipe except there was no toe hole, languid, or mouth. When he worked in churches that frown upon the use of spirits, he would fill his special pipe with porter or ale and bring it on the job and put it in the rack instead of the real pipe. Being English, he didn't care if it was at room temperature and fairly devoid of fizz. At every break he would quaff from his special pipe! I could believe this story except for the fact that pipes are made from varied metals including tin and lead plus several other heavy metals which were used to increase strength. Enough of this would leach into beer to make a deadly draught. But it is a fun story. I have been known to hide the Christmas Rum in the top of my Klipschorns! DRBILL

I'll probably get booed off the forum for sugesting this as an everyday proceedure before playing vinyl. Put the disk on the moving turntable and hold a Swiffer pad lightly against the surface. You can actually see the dust jumping off the surface. DRBILL

I have never been a casual listener. I find critical listening to be taxing. I limit myself to two hours a day --more than that, I lose my edge. Do I enjoy it? You bet! Like PWK, there is a time to listen to speakers and a time to listen to music. You can't do both at the same time. DRBILL

Oh, Boy. I remember when it was: Klipsch Hope, Ark. PRospect 7-3395 DRBILL

Well, as for me, I have made a grammar mistake only once in my whole life. And when I seen I done it, I taken it right back. DRBILL

I have detected some acrid asides about spelling, lately. I would urge all the brothers to be charitable. It is the content that is important. Mark Twain once said that it was a dull man who couldn't think of more than one way to spell a word. DRBILL

"Straight Wire with No Gain." (From Raising Cain) No. No poetry or imagination. It doesn't roll off the tongue. You had better see me after class.[] DRBILL

I have been building so called "passive pre-amplifiers" for a while, trying to find something that suited me and was easy to use. My latest opus has seven inputs controlled by a gang switch. There is a volume control (linear) and a trimmer pot on one channel for balance. I have never once regretted putting my three preamplifiers on the shelf. It is all Bob Crites' fault! New crossovers and tweets revealed the inadequacies of my pre's. Getting rid of them was like cleaning a dirty window. The only concession was the magnetic phono. I mounted a small line amp in the base where the wires emerge from the arm. This provided an immense improvement in eleminating hum and providing clarity. It would take an almost miraculous preamplifier to cause me to go back. Somebody think of a truthful name for "passive pre-amplifier." "Signal Processor?" What? DRBILL

"I remember something that pipe organ do is psychoacoustically make it seem like there is deep bass then present in the music. Something like mixing tones to get lower tone." It is called "Resultant" or "Resultantbass" and is often used to provide a 32' stop in situations where there isn't room for pipes that large. It takes a rank that doesn't produce many harmonics, mostly fundamental. If you sound low "C" on such a rank and play low "G" (5th above) the result is an octave lower than the original C. It is a heterodyne (for those of you who used to fiddle with AM radio receivers). It isn't "psychoacoustic". You can see it on a scope. It will rattle windows. DRBILL

The short answer is "Gestalt." But the ear and brain have to know what low C on a 32' Open Diapason sounds like before they can fill in the blanks on a recording no matter how good or bad the system. The moral of this story is to hear all of the live music you can possibly endure. Your Klipschorns will sound much sweeter! I had never heard much live saxophone music until recently. Recordings sounded rather raw with clicking sounds and gurgles. Ugh. Then I heard several first class saxophonists at University of North Texas (including Blue Lou!). Now I know what I am hearing and it is musical. Same recordings, same system. I saw it on a billboard. "The mind is a terrible thing to waste!" PWK was a concert goer every chance he had. He didn't invent in order to replace. DRBILL

Hmm. Did you ever consider getting a piano? Seriously. DRBILL

"He quotes the lyrics from Day by Day, which Is actually from Godspell, but somewhat similar." Actually, it is from the 1940 Hymnal of the Episcopal Church, copyright 1943 by the Church Pension Fund. Melody: Arthur H. Biggs (d.1941), lyrics by St. Richard of Chichester (1197-1253). DRBILL

Erik, If this is going to be a "Williamson" design, let me know and I can send you some interesting reads. You might want to consider using 6BG6s instead of 6L6s. The 6BG6 is a 6L6 with a plate cap and NOS Phillips is $6! DRBILL

When I was making these boxes for forum members I used "project boxes" from Radio Shack. They have seven of them from 3X2X1 to 8X6X3. They are black and made of one of the resins. They built up with considerable ease. Of the ten or so that I sent out, everyone commented on how "professional" they looked. I remember that they were c. $3. And there is likely a R-S within walking distance of most of us! Hope this helps. DRBILL

WOW! I can tell that this is going to be big. Somehow, I am remembering the old grad school mantra, "Narrow your subject," and "More study is needed." Many thanks for your input. It is going to be very helpful. I'll report back to you. LET RESEARCH BEGIN! DRBILL