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 AC line voltage and plate

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PostSubject: AC line voltage and plate   2011-11-21, 4:26 pm

Howdy all, I am starting to check tube voltages on my first restore set and would like to know what line voltage I should use for these AA5 radios. I have an isolation and varable transfomer combo and I can adjust the AC.

Also what is a good rule for a plate voltage on a tube. I am measuring on a 12SG7 (RF Amp) and pin 8 (Plate) calls for 62vDC and I am reading about 103v ?
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Cliff Jones
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Join date : 2010-11-22

PostSubject: Re: AC line voltage and plate   2011-11-21, 11:25 pm

Here's a couple of Schematics of AA5s

http://antiqueradios.com/gallery/d/148198-1/AA5+voltage+chart.png


http://illiweb.com/fa/pbucket.gif

Trouble.-High plate voltage.
Symptom.-Distortion, or increased output, or both. Ip and Esg may be higher than normal.
Cause.-Decreased plate load, caused either by a lowered resistor value, or by a partially shorted transformer, High Ep may also be caused by abnormal grid or power supply circuit conditions.

Do you have the brand name and model #?

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PostSubject: My GE Repair   2011-11-23, 3:39 pm

Thanks for the info and diagrams Cliff I have a General Electric Model 200-201. I changed all the caps and I only get the one local very strong station and its really touchy to tune in. If I dial past it all I get is motor boating.

I just picked up a nice Knight KIt signal generator and may try to hook it up. Never used one. But what I read I will need a capacitor on the main positve probe and clip to chassis for ground? Any good procedure on the internet to show what pins I should set the signal point on and follow the signal through the radio?. Guess I would start at antenna input but where from there?

Here is what I picked up. Will have to make a cable for input.

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PostSubject: Re: AC line voltage and plate   2011-11-25, 1:47 pm

I will do some editing of this post so wait till I mention I am done, as I am going to do some research on documentation from Riders and Beitmans seem to be in conflict on using a external cap on the generator.


Make sure to have and use isolation transformer, for the radio. The use of an isolating capacitor is not recommended, as A-C through the capacitor will introduce hum modulation and/or create the possibility of a burned-out signal generator antennuator.
First point don't hook up ground to ground.
I will digress a little bit first. I will look-up the schematic if I can, so we are both on the same page.

I found Schematic in Bietmans 1947 (Vol 7 page 50)

Following instructions :
l. Turn dial scale pointer as far counterclockwise as pos- .
sible The pointer should coincide with the first marking at
the left of the scale. If it doesn’t, remove chassis and slip
pointer on shaft until the pointer is under reference mark
when chassis is bolted in place.

2. For l-f and r-f allgnments, the (AC) Output meter ls Con-
nected across the loudspeaker voice coil terminals.

3. Keep radio volume control at maximum and attenuate
test oscillator signal output so that the output meter reading
never exceeds 1-1/4 volts.

4. The chassis must be removed from the cabinet during
I-F alignment, For R-F alignment bolt the chassis in the
cabinet securely.


5. Connect the capacitor as listed ( .05mf ), between
the output "high Side" of test oscillator and the point of
input specified.

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