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#1
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Adapting an older design? (was Tube AM Tuner...)
Jon Noring wrote:
Since my interest is in building a tube-based AM tuner using modern components, adapting the circuit design of a highly reputed older radio is certainly intriguing. Just remove the final audio amplifier section (and tweak the line-out as necessary to conform it with today's standards), and maybe replace a few other "autonomous" sections with modern solid-state equivalents if there is any advantage to do so (e.g., the DC power supplies.) Of course, it continues to be suggested to just find an older radio and cannibalize it to my heart's content. In my case, by the time I've cannibalized it and rebuilt the chassis, the mechanicals, replaced all wiring, resistors, caps, etc., etc., it probably would have been better to just build the damn thing from scratch per a schematic and general layout. Thus the idea is to come up with a general schematic and layout design, and build from that. There is the issue that building an AM radio from scratch is more difficult then you might first think. The problem is taming undesired feedback loops in say the IF amp for example. You will likely end up with howls and whistles as the stage self oscillates. Stray capacitences from input to output, also couplings thru the B+ supply, etc. Modifying an existing radio is easier in that you are starting where some tube radio engineer left off in creating a stable design. Gaining enough experience to create from scratch a good tuner takes many iterations of homebrew designs. The thing to remember is that, while AM radios were cheaply made, a lot of design skill was used to create a design that could yield decent performance using low cost parts with loose tolerances and layouts that don't cause problems. This knowledge usually doesn't show in textbooks, but was essentially "passed down" from seasoned engineers to younger ones in the same company in the tube era. If you do want to design and build something from scratch, realize that you may need to modify and iterate several times before you "get it right". |
#2
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The magic brain tuner from an RCA 9-T and add the variable selectivity
IF of the Philco 37-116 would be a good radio. Check out the military BC-314 receiver; 2 RF stages, 2 IF stages at 85KHz with BFO. 4 bands from 150 to 1500KC. I can hear the stations in between the US stations with it. A local station on 1030KC does not stop me from listening to Des Moines on 1020KC. The broadcast range ARC-5 receiver has variable selectivity IF and along with the BC-314 one of the best dial drive mechanisms available. Me thinks you are going to want two seperate IF channels, one for the DX receiver and the other for the high-fidelity section. The RF and coverter part are probably good for either purpose, but the same IF design is not going to be good for both DX and quality sound without some trick IF transformers like those in the Philco 37-116. If complexity is not a significant issue, you might consider using a second crystal-controlled converter to change the 455KC IF for the fidelity channel into 100, 85, or 50KC for the DX section. If you want everything you are seeking from one receiver design, I suggest the Hammarlund SP-600. Jeff Goldsmith |
#3
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Jon Noring wrote:
I appreciate the feedback, and yes, designing it from scratch is not a good idea except for those who want and cherish the challenge. As rereading my full message indicates, I am focusing on adapting an established, older design. Thus my call for candidates from the "vintage" era. Hence my comments about using something like the Kenwood KT-313 or KT-5100 (Or is that 5500) chassis as a good starting point. All the physical cabinet stuff, dial etc. is already there. And there's enough room inside to put a chassis, tubes, and other electronica inside. Jeff -- "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." Benjamin Franklin "A life lived in fear is a life half lived." Tara Morice as Fran, from the movie "Strictly Ballroom" |
#4
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Jon Noring wrote: Mark Oppat wrote: snipeth some interesting considerations, Of course, it continues to be suggested to just find an older radio and cannibalize it to my heart's content. In my case, by the time I've cannibalized it and rebuilt the chassis, the mechanicals, replaced all wiring, resistors, caps, etc., etc., it probably would have been better to just build the damn thing from scratch per a schematic and general layout. Thus the idea is to come up with a general schematic and layout design, and build from that. Well, then off to the workshop with thee, Pray, do not tarry by thy square framed flickering lantern, permitting all confabulation of betwixing figures, but to your forge process, and produce fine chassis, and musical equipments to adorn thy courts of pleasure. Ye will need to spende much evening hours at vexing toils, and refrain from such course wordage, which will do no effect to hasten your productions. When you have achieved such sweet tones of music, conveyed across the ether, as if sent by teams of angels, hasten here to tell us your igenuities, and dazel us with glowing wonders. And once a group of enthusiasts have come up with a working design...... Deteteth many more conditions and fascinations..... in the concern of sweet brevities.... And within this worldly Web, there resides enomous talent, and much resolve is mused by minds considering, seated in plush easy chairs. The real vexations of possiblities anew, were solved by my grandfathers, and humbly you may try, to take their brighter view. Their carries on, and propels our new inventions, and so it is with patience, we await your new constructions. Shakespeare, 1504, After considering the possibilities of "casting broad the song and mirthe of playes throughout the lande" .... |
#5
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"Jon Noring" wrote in message Of course, it continues to be suggested to just find an older radio and cannibalize it to my heart's content. In my case, by the time I've cannibalized it and rebuilt the chassis, the mechanicals, replaced all wiring, resistors, caps, etc., etc., it probably would have been better to just build the damn thing from scratch per a schematic and general layout. But, a good design would give you the mechanical layout, the RF section would include the tuning cap and matched coils for tracking, the IF transformers would be there and mounted.. Even if you gutted 90% percent of the existing electronics, just having the RF and IF sections available for modification represents a majority of the time consuming work. Never mind the cost of trying to dupicate a dial drive and tuning system. Pete |
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