No Signal withOut scope probe
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City: Boulder, Colorado
Hi All;
On my Philco 34, I can get a Signal thru the Radio and can tune it, ONLY If I have my Scope probe connected to the Grid Cap (G4) on my 1C6 converter tube.. I am feeding a signal directly from my Precision E-200-C Signal generator to the Antenna Clip..
I have put in a New Old Stock 1C6 and NOS Tubes in the Signal generator and adjusted it for the new tubes with it connected directly to my scope.. The scope has a frequency display directly on it..
Any Ideas ?????
THANK YOU Marty
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City: Las Vegas NV
Grid leak resistor open? The scope probe would act as one.
keithw
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Marty
Check the integrity of the connection between the G4 (1C6 grid cap) and 3 and 7 caps.
You introduce about 10pF of capacitance with your scope. This may be enough if the other caps are disconnected.
Keith: where do you see gridleak res. in the 1st 1C6?
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Hi All;
I am sorry, I forgot to include a schematic for this radio..
http://www.nostalgiaair.org/Resources/185/M0013185.htm
Morzh, Thank You for your reply, and Keithw, Thank You for your input.. I know that at least partially, I do have a connection and for some reason, that I can't figure out.. It also connects 7 and 8 together.. And it does ohm out that way, But I will re-check all connections to that line (connection)..
Since the schematic shows the switch pin out for Band 4 (SW), instead of the Broadcast Band, (Band 1).. I am not entirely sure of what all the Grid Cap should connect to.. I will see If I can figure it out with my ohm meter.. So, I hope I can find what is causing the problem, it is so close to working, (I think)..
THANK YOU Marty
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Marty
Do you actually have oscillation? You have a scope, see if you do.
How about the switch connection do you have it?
Does this "no signal without scope" happen in all bands? Or just in one? If in all, this shows to more common cause.
PS. THinking about it, it seems to point to the packet switch - somehow not being well connected to that 4th grid.
A Stupid question - did you make sure the trap filter coil (is it?) #2 in series with antenna is intact?
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It sounds to me like an open coil in the antenna circuit somewhere. Regardless of whether the generator is connected to the antenna clip, it sounds like what is happening is that when you connect your scope to the grid cap of the 1C6, you are supplying a sort of "antenna" which is then picking up the generator. Check your coils, especially the RF coil and the IF trap coil as Morzh mentioned.
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Hi All;
Morzh, Thank You for you answers and further questions..
I have a scope that does do frequency and so, I did adjust the Oscillator coil, and Capacitor when I had the Dial set for 600 KHZ and my IF is 460 KHZ, so I set the Oscillator frequency at 1010 KHZ.. I couldn't have done it without my scope..
When the switch is in Band 1 or Broadcast band, the switch does connect the two Capacitors together, now whether it needs to or does connect anything else together, I don't know at the present..
In the Morning I will check and let you know If the problem persists when it is in Band 4 (SW) and the other two as well.. I will also see if it will receive any signals while in the other three bands, both with and without the scope attached to that point..
I am Not sure if the Antenna Trap is completely working, it passes a signal thru, but I am not sure that it is trapping any signals.. When I have put 460KHZ to it and try to make it less or none extinct, it doesn't seem to dimish any at all.. As per the Philco instructions.. The Cap maybe bad or off value, or for that matter so could the coil be as well.. But, 600KHZ passes thru nicely..
Brenda Ann, Thanks for Your Input.. "I need more Input".
I have ohmed out the RF Coil both with the resistor attached and with one end removed and the coil ohms out, according to the specs from a Philco 44, which has the same front end.. But, I will ohm out all of the RF coil connections and see if something is wrong or missing..
I will also connect my generator directly to the cap and see If I still works without the scope connected and then work my way back to the antenna connection.. THANK YOU for the Suggestion..
THANK YOU Marty
(This post was last modified: 09-06-2013, 11:45 PM by marty.)
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Hi All;
Well, I just found out that the Coil on my Wave Trap is open.. So only the Capacitor was passing the signal thru..
I have jumpered the "Wave Trap" and the Signal from the signal generator is heard from the Speaker now and No Scope probe is attached to the 1C6.. It still won't receive any Radio Broadcast Stations, but just the fact that the signal from the Signal Generator is now getting thru is a major breakthru..
THANK YOU, Brenda Ann for suggesting that the signal might not be getting thru and
THANK YOU Morzh for suggesting that the Wave Trap needs to be checked..
THANK YOU Marty
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It did look like the wave trap, as (which Brenda also pointed out) when you touch the cap you supply the antenna and then it works.
So the logical thing to think is - the trap is open 
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Hi All;
I packed my old Computer, a Varian 620i for shipping, so now that is done, and I can get back to my Radio..
I extended the Antenna to the Outdoors, it is about 40 to 50 feet in length.. But, still no Broadcast stations,, The scope shows a signal from the Antenna, and so I am going back (for now) to the signal generator..
THANK YOU marty
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