crosley 106P poor sensitivity

[charlesa]

Recapped radio very weak ( only 1 or 2 broadcast stations ) with lots of interference and noise. Set works the same with RF Amp. tube in or out (6SK7). Is that the right RF Amp? It's the same as the IF. Voltage seems about normal except screen is 75V. and Plate is 160v. but I can't find a good readable schematic. If I put wire ant to grid of conv. tube (6SA7) signal is better, several stations but lots more noise. Ant coil seems ok, no opens but switching is hard to follow on my schematic. Short wave bands work great Pushbuttons same as variable tuned broadcast band. Only station received is at 1120 Khz. and 30 miles away No strong Phila. stations only noise. I usually only work on pre 50 TV's but this is now a challange for a friend and I'm stumped. Can anybody help?
Chuck Azar

[Chad Hauris]

Sounds like there may be an open coil in the rf amp/antenna circuit..had a Ford tube type car radio that would work only if the antenna were connected to the converter grid. There was an bad solder connection to a coil in the RF stage.
Double check anything in that circuit.
If it is working right, pulling out the RF amp should stop the signal, so the only way the signal is getting in is in a roundabout way.

If there is noise...have you eliminated all causes of man-made noise such as touch lamps, lamp dimmers, fluorescent lamps, switching power supplies, etc.

Also how is the alignment of any trimmer capacitors in the broadcast band RF or antenna circuit?

If you have an RF generator, set it to the modulated tone and use it to introduce a signal and vary it to different frequencies and see if the test signal is picked up. It may be good to double check your IF alignment on broadcast bands too and make sure the adjustments are peaked for highest amplitude.

[Tom Bavis]

Schematic is here, DjVu format (get the plug-in from Lizardtech.com): http://techpreservation.dyndns.org/s...cs/Crosley.htm

It's in Sams #7, I should have a copy. email tbavis(at)rochester(dot)rr(dot)com

[charlesa]

Thanks for all the help and the schematic sources and the voltage chart. TROUBLE!! The trimmer on the rf section of the variable was partially shorted. On this set the rf amp is only used on the broadcast variable band. I was making resistance checks from ant to grid of rf amp trying to find out if a switch contact or coil was bad and found a short to ground and isolated that as the variable rf section trimmer.
The75mm cap in the grid of the rf amp isolated it from the short and that was why I could touch the rf amp grid or plate or the converter plate and get more signal. Very unusual to find that the rf amp was only used on broadcast. Set still has lots of noise but I will try another location as computer cables and electronic phone systems may be causing that.
Thanks again,
Chuck Azar