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Antique Radio Technical Forum
Brunswick model 15 1930-31

Posted by nom on 04/21/2009 03:52

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::: Wow, EDD...thanks a bunch for giving me guidance. Now I hope that I have the brain power to interpret what you've written. I appreciate all the time you took to give me a proceedure and enlighten me on just exactly what I've got here. I will start the proceedure soon and if I get stuck I'll post questions...Neal
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:::It didn't take me long to get stuck. The center frequency is 800kc.
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::: Nope, that’s not getting stuck, its merely finding that the center mechanical and and the center of the BC band on that unit of yours is not the usual 950-1050, as found on a smaller “two lunger” superhets tuning condenser, but being 800, on that mammoth
:::capacitors set's bank of your set.
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:::Ed: Were my questions to basic that you've given up on me?...Neal
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:::Heeee’s Baaaack. . . . .Nope, over the weekends are just not the best time for my WWW communicating. . . . PLUS I didn’t have all of my research info until just now.
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:::Is the detector tube considered a stage?
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:::Yes, the detector stage is the fourth tuned circuit down on the sets circuitry.
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:::What do you mean by "with your Sig Gens RF input lightly coupled in from from the earlier stages plate circitry". Do you mean 1rf pin 2?
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:::I was merely referring to keeping the injected RF test signal at an absolute minimum, such that the RF amplifier circuitry is not swamped with a signal level and thus makes the tuning adjustment broader; with you then not being able to set the tuning more precisely, to then be optimized for the most sensitive adjustment possible.
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:::I was basically referring to the use of the typical alligator clip at the “hot” end of the RF output of your RF Signal Generator and it being merely clipped onto the INSULATED wire of that PREVIOUS stages plate wire connection. That resultant "gimmick" capacitance, along with the attenuator of the sig gen, should then let you set the RF injection level way on down into the just barely perceived presence of its 400/1000 cycle tone modulation thru the speaker.
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:::IF there is any possibly of spurious oscillation, by virtue of a previous RF stage also picking up the input test signal, merely unplug that tube until you get the tuning of that stage done and then are progressing on towards the front of the set.
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:::Is the L-C cluster one of my 4 adjustment bolts?...Neal
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:::NO, with that terminology, I am referring, in general, to the four sets of coils and their associative companion tuning capacitor sections that are associated with the 4 tuned sections in the frontal RF portion of your set.
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:::Refer to accompanying GRAPHICS. . . as the bottom attachment.
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:::(sic)
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:::I have an intemittent open/short in the audio signal that I have to find before I can go on. By tapping ever so lightly on the chassis, it will loose/gain audio. Could it be a component? Or is it what I just mentioned, An open or a short. My come and go is more prevelant around the tuner.
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:::Looks like that final little aspect is EXCLUSIVELY for you to be zeroing in on. . . since you physically have the set. . . and I am DEAF. . . .BLIND. . . .AND DUMB. . . (and that's HEEEEAVVVVVY ON THE DUMB aspect.)
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:::I would be doing a light. . . . and then progressively stronger. . . tapping, flexing, bending and pulling in the “sensitive area”
:::which you seem to have already located.
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:::A common associative problem:
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:::Check the tuning condenser phosphor bronze tensioning and pressure contacting strips associated with the grounding
:::of the rotor sections mechanisms, to the frame of the tuning condensers sections.
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:::In some cases, they can be silver plated and have a poor / intermittent contacting action thru some degree of rotation due to a heavy black AgO2 build up. . . with time and environs.
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:::(Afore times, nesting rodents urine depositions, can also take the balls off of a pool table.)
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:::Also with time, and much use, they just loosen up and loose their tensioning, along with a resultant intermittent connectivity.
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:::HOWEVER, on looking at the only photos which I seem to have for that unit it looks as if you will be dependent on the gang to gang tuning being dependent upon how it currently is mechanically positioned.
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:::On the first generation TRF’s they had separate tuning condensers for each RF stage, on yours we can see that the units are ganged inline and all acting as one combined cluster instead of individually tuned units.
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:::ALSO there is no provision for mechanically changing their rotational coupling position on that common shaft.
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:::I see no associative, adjustable trimmer capacitors used in conjunction with each stage.
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:::On some sets they had different set screws around an end vane so that different segments of that end vane could be moved in or out for increasing or decreasing the contributed capacitance on that final end vane.
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:::NOW in looking at the figures below, it does look as if all of your rotors are using a common strap across the rotor segments[YELLOW ]. . . .EXCEPT. . . . that end vane which could be moved in or out a bit in its proximity to its companion end stator vane.
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:::Now, I can’t see that end rotor vane in order to see if it is slotted up into segments, but I would suspect so.
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:::If so, this balancing adjustment between different sections would almost be a factory adjustment during final tune-up.
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:::ASIDE:
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:::If attempting to do that tuning myself, I would be connecting a Boonton RF voltmeter onto the end circuitry in order to get a visual indication of the mechanics adjustment versus the RF effect via the voltmeter readout. . . . .it being , much, much to small to determine aurally.
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:::PLUS that fine adjustment of a rotor plate segment by a “micro” bend is one HECK (x10 !) of repetitive task to locate and optimize a final position.
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:::I also possibly might experiment with a 2-10pf trimmer placed across each tuning stator and then seeing if any improvement could be acquired, an alternate would be the adding of an adjustable slug to each RF transformer core, but somehow, inside those cans, I would be expecting to see each of them wound on a big old 3-4 to 1 inch coil form.
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:::Overall, seems like to me, that you will be settling for what matching of tuned circuits you have on that tuning gang, being as it is currently.
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:::73's de Edd

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:::BRUNSWICK GRAPHICS:
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:::The only way I can get a stable signal is by prying the vane assemblly away from the chassis on the end near the detector. I can get a strong signal but it still is prone to intermittent behavior. I'm about ready to take the whole assembly out and see if I can locate the source of my problem.
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::My set is much stronger on the frequencies above 800kc than the lower ones. 1931 was a good year for radio. And I hope to see this set through to be playing in 2009.
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::All my tubes are good and I happened to have some spare 45's here at the house...the 80 is going for $100 bucks on antique electronic supply. If that goes out it would make it hard to continue, but it seems to be holding strong...Neal
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:Can the tuner vanes physically touch one another?...Neal


I realize I'm pretty much talking to myself, but maybe someone has been following my posts.

I took the tuner out and found the vanes touching each other and grounding out. Expecially when I was on the low end of the BC. I tweaked and worked with them until they were not touching in any of the four sections. I put it back together and voila! I have full range frequencies coming in with the same audio level up and down the dial.

Now I can incorporate what tuning guidance that I got from EDD and this old 1931 model will be playing loud and clear...Neal



Brunswick model 15 1930-31 
nom 03/31/2009 02:04 
Edd 03/31/2009 12:04 
nom 03/31/2009 16:31 
Lewis L 04/01/2009 11:11 
nom 04/02/2009 00:40 
nom 04/02/2009 05:18 
Edd 04/02/2009 16:44 
nom 04/03/2009 02:41 
nom 04/03/2009 09:55 
nom 04/04/2009 21:45 
Edd 04/10/2009 17:23 
nom 04/11/2009 22:24 
nom 04/16/2009 08:15 
nom 04/18/2009 22:40 
nom 04/19/2009 11:29 
nom 04/21/2009 03:52 
Lewis L 04/21/2009 13:42 
nom 04/22/2009 01:32 

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