hi. on this Magnavox tube tuner. yea I know. CR330AA1. the dreaded if trans. removed the capacitor and now have the radio playing on FM only. big hum on am but no am at all. need to know the value of the caps. the cap type wafer is so bad cant get a reading of off it. any help please. thank you paul. and yes every cap under the sun has been replaced except this thing.

Probably in the neighborhood of 100pF. Exact value isn't critical provided you have enough slug adjustment to peak the circuit. I'd start with 100pF and see if it's possible to tune the transformer to resonance. If not, try 120 pF. If still no peak, try going down to 80 pF for the caps.

:Probably in the neighborhood of 100pF. Exact value isn't critical provided you have enough slug adjustment to peak the circuit. I'd start with 100pF and see if it's possible to tune the transformer to resonance. If not, try 120 pF. If still no peak, try going down to 80 pF for the caps.
:
well tried subbing in a few caps. still no am. just loud hum. am worked fine before the if cap shorted to ground. hum is adjustable with volume. I don't have a signal tracer nor a signal generator. FM works great though. thank you

Make sure each IF transformer is wired back together properly.
Double check your wiring within each can and externally to the tubes etc.

:Make sure each IF transformer is wired back together properly.
:Double check your wiring within each can and externally to the tubes etc.
:
:
hello peter. thank you. only one transformer was shorted. installed it back in the radio according to the schematic. 11 ohms on each side. plenty of room to install small pf caps. 120 pf seems to be right. still hum no am at all. paul

How do you know 120pf is right if you have no am reception?

:How do you know 120pf is right if you have no am reception?
:
well guess I don't know. but the caps greatly affect fm reception.

::How do you know 120pf is right if you have no am reception?
::
:well guess I don't know. but the caps greatly affect fm reception.
:
Aren't the FM IFs in different cans?
The FM IF transformers use much smaller values.

As far a getting your AM IFs working ... if it's wired properly ... you might try putting the tuning slug in the middle of its rage as a starting point.

However a scope or at least a signal generator would really help.

Also ..are you sure that the local osc is still running?

To determine if everything else is working ok.. There is a way to temporarily BY-pass the AM IF by removing the IF can and using a capacitor to couple the two stages. You'll also need a resistor to feed B+ to the plate on the primary side.

Norm Leal wrote/published a description of how to do this. It's online :
Here's the link:
http://www.antiqueradios.com/chrs/journal/transformers.html

:::How do you know 120pf is right if you have no am reception?
:::
::well guess I don't know. but the caps greatly affect fm reception.
::
:Aren't the FM IFs in different cans?
:The FM IF transformers use much smaller values.
:
:As far a getting your AM IFs working ... if it's wired properly ... you might try putting the tuning slug in the middle of its rage as a starting point.
:
:However a scope or at least a signal generator would really help.
:
:Also ..are you sure that the local osc is still running?
:
:To determine if everything else is working ok.. There is a way to temporarily BY-pass the AM IF by removing the IF can and using a capacitor to couple the two stages. You'll also need a resistor to feed B+ to the plate on the primary side.
:
:Norm Leal wrote/published a description of how to do this. It's online :
:Here's the link:
:http://www.antiqueradios.com/chrs/journal/transformers.html
:
:
thank you peter. replaced the 120pf caps with 250pf 500v caps and am came back loud and clear. thank you to every one for your help.

That's great...
...but how did you come to determine that the 250pf value was right?

:That's great...
:...but how did you come to determine that the 250pf value was right?
:
all I did was remove the 120pf 500v caps im using clip leads so to make it easy to experiment. radio was on broadcast band subbed in the 250pf caps and a radio station started playing. also I checked antenna coil and am oscillator coil first. they were fine. thank you radio is playing fine on am and fm.