Date: Fri, 7 Mar 1997 19:02:49 GMT From: rdkeys To: Multiple recipients of list Subject: More Regenerator Shielding Musings..... Whilst on the thought of regenerator shielding and tube availablilty..... Art Winterbauer thoughtfully mused and pondered..... >I use a couple of #30 tubes in my homemade regen receiver. I picked >up several of these at a hamfest last year (Sylvania-made) for $1 >each. They look new. Does anyone know: >1) How long these tubes were manufactured My recollections would suggest from about 1928 through WWII. That is as close as I can come. >2) Any direct substitutions There are about 15 or so direct pin-for-pin base subs, taking voltages into mind. The 00 and 01 series were the predecessors. There may have been a '15 type that fit. The '20 should fit. The '40 and '50 both fit. The '71 fits. There were several 800 series tubes that fit but they were mostly transmitting tubes, and there were some 1600-2000 series tubes that fit and one or two in the 6000 and 8000 series. Most were transmitting tubes, though. I have a complete list from a little TungSol book about 3 inches square with every basing and every type of any particular basing up through the 1950's, when it was printed. A very worthwhile book if you ever find one at a hamfest. >3) Their availability on the market: scarce? plentiful? They are not plentiful, but not on the scarce list, yet. The military used many of them in WWII in various pieces of test gear and small rigs. Thus, many are in surplus. I would rate them about half as scarce as the '01 series. The '30 and '01 series tubes are what I think of generically as the 50's 6SN7 or 6J5 style tube. In the 60's that was the 6C4 and 12AT7. By the way, any old triode will sub with the proper wiring into a 4 pin generic classic triode base like the one on the '30. Most such subs will work fairly well, but some tend to be overly sensitive. But, that little '30 is a very nice performer in regens. The 1H4 and related 1.5 volters are the 40's equivalent battery tubes, and there is no mini battery triode of the 50's/60's that I can find, other than the submini peanut tubes. Just remember to keep yer filaments at the right voltages, and you may need to compensate low/high resistance in the filament rheostats if you get to power triode subs for '30s. One time I subbed an 801A for a '01A and it worked pretty well, aside from draining the filament battery.....(:+}}..... >Additional note: the receiver has one stage of audio amplification. >It seems that, in addition to using an extra wall of foil-covered >insultation behind the front panel, hand capacitance and stability are >further enhanced by shielding the audio tube (with no additional >benefit from shielding the detector). Shielding consists of about 7 >layers of kitchen foil wrapped loosely around the tube and clipped to >receiver ground with alligator clips. Well said! Behind the panel shielding is very important in a good regen, although I use it or don't use it on mine, depending upon how parts are laid out. Even as early as the 1915 Siemens Spark tuner that a friend has, they used copper sheeting behind the panel reduce body capacity, and lined the wooden box with copper sheeting for more shielding. Almost all of the wooden boxed military/commercial regen receivers from marine use were lined with some sort of copper shielding or foil shielding. All of the airways regen receivers (both air and ground) were metal boxed. But, interestingly, most of the Army air and ground units were wooden boxed. Shielding will help, and is usually a good idea, but not always mandatory in the average run-of-the-mill ham radio regenerative set one finds. Unshielded sets are more AC hum pickup prone in the open breadboard unshielded panel set compared to a boxed up one or your tube shielded one. The shielding does further reduce hand body capacity to pleasant levels. One part of the reason that I used large throttle condenser values (250pf or more) is to help reduce the net effect of a few pf of body capacity. That will often get around the need for a panel shield if I don't have a piece of aluminum of the right size handy. That is a neat use of builders insulation(?) as a panel liner. Plain tin foil works pretty well, but you need strips to hold it down in place. The tube tinfoil shield is simple and would be great as long as nothing shorted out. My guess is that there may be enough metal tube shields, even from the early era to be found at hamfests and the like, for folks to use if they do some digging in the boxes under the tables. In lieu of the originals, creative regen shielding with Mom's kitchen tinfoil is a great idea. Also, things like tin cans of various sorts work well, too. Alas, the classic pound coffee can is no more.....(:+{{..... That used to make a great tube shield for vfo's and regens and growlers. >Art WA5OES 73/ZUT DE NA4G/Bob UP