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Still plodding through the mysteries of this radio...!!! I found something curious when trying to input an IF frequency of 460. I used the control grid of the 78 tube to send the signal through. Still confused about where to attach the SG lead??? No signal was heard...but I did hear a quiet signal at around a setting of 380 on band A of my Eico 324. What would cause a shift of the IF frequency??? I did substitute an AES oscillator for the original and it is working.
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You should be injecting 460kz into the 6a7 grid cap. Connect the Gnd lead to chassis.
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Just to be clear, if you remove the grid lead from the 6A7, Connect the signal generator to the cap on top of tube, not the clip on the end of the wire.
Steve
M R Radios C M Tubes
(This post was last modified: 08-12-2014, 06:07 PM by Steve Davis.)
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Well, I do hear the 460 signal injected at the 6A6 grid less the cap clip. But it is very weak and I can't seem to peak it at any measurable deflection on the output meter with the probe on the plate of the 42 tube???? Also, I hear quite a few signals across the dial...beyond the effect of harmonics???? Again I had the radio working before...so still confused.
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Are your IF transformers (both) still good and exhibit conductivity on both coils each?
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Morzh: the IF's ohm out right on the money. As for conductivity, I would guess that would most likely be ok based on the resistance testing, right?
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Conductance/resistance are used interchangeably depending on context, one being simply 1/the other (this is why the units are Ohm/Mho respectively) so when I say "conductance" I simply refer to the measure of dependance of current from voltage.
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I'm am very interested in this thread. My model 60 is similar. My audio works but the RF signal doesn't get thru for some reason (too). I did the alignment via the 6a7 and the audio was loud but not roaring. Now, I can connect my Eico 324 to the antenna end and tune to any station but only in the "int mod af mode", nothing on the RF mode. At one point I could hear dimly the prominent AM station along with the AF signal but not now. we seem to be encountering a similar issue. Thanks, Rich
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Winston...welcome aboard...misery loves company. I am wondering if the IF coils ....although they ohm out great...break down under the heavy load of the high B+ with the new caps and higher line voltage. I tried to input an IF 460 signal through the diode of the 2nd detector and no signal through the speaker. Even my AF audio signal seems weaker...so who knows????
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If you can peak out every IF transformer using BOTH sides of each one, the coils are OK, as the only way for them (if the winding looks not mangled) to be bad if they have good continuity is to have turn short, and this would result in the trasformer not working and certainly not peaking.
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This sounds really familiar. IF stage is working more or less, output is working. No, or little, oscillation.
Charlie in San Antonio
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I found that the prior owner put "grounding" on 78 that was damping my tuning. Also I did what I stumbled on from other restorations and I replaced some of the wires related to the tuning capacitor and the speaker. Then I was able to get enough signal to use the recommended tuning procedure documented by this site. Now I have several stations but the volume is very low, but decipherable. The the volume control works but I am missing amplification. So that's my situation. This is progress for me but I don't know if it applies to you. If someone has ideas on amplification - I would appreciate it. I'm so close I don't want to go backwards. Rich
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tubes was a logical suggestion but I replaced all my tubes and I still suffer from the same low volume but good clear frequency for all stations. I wonder why I am not getting power to amplify the clear signal.
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Not sure it hlps but pay special attention to 6A7.
Thing with those, the amp section that is used as RF-amp/mixer is often weak while the osc is good. While 1000 is new tube reading most will be below 700 and many belw 300. I enountered way too many of those.
This might impede amplification, especially when the 6A7 is the first tibe nd is the only RF amp.
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