Crosley 9-201 Weak volume on AM

9/12/2009 1:30:22 AMDave Froehlich

Hello All,
This radio really receives well on AM distant stations are being picked up very well (its a strong signal) however the volume is very weak. It doesn't make any sense to me. All the components and voltages are correct and connected correctly as far as I can tell. FM is nice and strong too but can be made very loud.. Not so for AM. The band switch is clean. What could be causing this problem? It's very mysterious.

Thanks,

Dave

9/12/2009 7:06:36 AMEdd

Sir Dave. . . .

The picking up of several different AM signals would tend to signify that the frontal RF and first IF stages are OK
in alignment.

After that, there is just the RF signal at the plate circuitry of the IF amp that feeds into the AM detector circitry.

With some known problems of 6T8's, can you sub in another unit for it ?(considering only,its sole AM det diode section)

(Another viable test is to shunt the det diode section of the 6T8 with a solid state det diode . . . .1N914-4148.) [Its anode going to plate-its cathode to ground] If it then more efficiently, detector rectifies, go for it.

One then sees that the audio is all handled the same . . . .gain wise . . . from the band switch over to the top side of the volume control and thru the auduio circuitry.
.

Also, can you check the peaked tuning of the 2nd AM IF transformers plate coil and the following detector grid coil winding ?

Could even be a def 2nd AM IF transformer.

73's de Edd

9/12/2009 10:54:03 AMDave Froehlich(78836:78832)

Edd,
I thought it could be the 6T8. I don't have a 6T8 but I might have signal diode. When I measure the 2nd IF transformer, all seems to be well. This really picks up distant stations and strongly. I have never seen the AM detector fail in a 'T8 type tube. Usually it's the "discriminator" plates for the FM. If it's true, this will be a first for me.
Thanks,
Dave
:
:
:
:
:Sir Dave. . . .
:
:
:
:The picking up of several different AM signals would tend to signify that the frontal RF and first IF stages are OK
:in alignment.
:
:
:After that, there is just the RF signal at the plate circuitry of the IF amp that feeds into the AM detector circitry.
:
:
:With some known problems of 6T8's, can you sub in another unit for it ?(considering only,its sole AM det diode section)
:
:
:(Another viable test is to shunt the det diode section of the 6T8 with a solid state det diode . . . .1N914-4148.) [Its anode going to plate-its cathode to ground] If it then more efficiently, detector rectifies, go for it.
:
:
:
:One then sees that the audio is all handled the same . . . .gain wise . . . from the band switch over to the top side of the volume control and thru the auduio circuitry.
:.
:
:
:Also, can you check the peaked tuning of the 2nd AM IF transformers plate coil and the following detector grid coil winding ?
:
:
:Could even be a def 2nd AM IF transformer.
:
:
:
:
:
:73's de Edd
:
:

:
:
:

9/12/2009 11:13:01 AMDave Froehlich(78837:78836)

Edd,
Also, I'm having trouble visualizing the signal path from the 2nd IF transformer, through the detector and where is the point at which the audio appears after the carrier is removed by the detector (rectifier) diode. It looks like it comes through to the other side of the secondary winding, through the 33K ohm resistor into one end of the volume control. The wiper selects the level to the triode pre-amp. Being all in one tube is probably what makes it so difficult to visualize. Same trouble visualizing with 'Q7 or 'T7 or 'V7 tubes.
Am I correct in saying that there is no AVC for the AM in this radio or is it accomplished in some other way?
Thanks,
Dave
:Edd,
: I thought it could be the 6T8. I don't have a 6T8 but I might have signal diode. When I measure the 2nd IF transformer, all seems to be well. This really picks up distant stations and strongly. I have never seen the AM detector fail in a 'T8 type tube. Usually it's the "discriminator" plates for the FM. If it's true, this will be a first for me.
:
:Thanks,
:
:Dave
::
::
::
::
::Sir Dave. . . .
::
::
::
::The picking up of several different AM signals would tend to signify that the frontal RF and first IF stages are OK
::in alignment.
::
::
::After that, there is just the RF signal at the plate circuitry of the IF amp that feeds into the AM detector circitry.
::
::
::With some known problems of 6T8's, can you sub in another unit for it ?(considering only,its sole AM det diode section)
::
::
::(Another viable test is to shunt the det diode section of the 6T8 with a solid state det diode . . . .1N914-4148.) [Its anode going to plate-its cathode to ground] If it then more efficiently, detector rectifies, go for it.
::
::
::
::One then sees that the audio is all handled the same . . . .gain wise . . . from the band switch over to the top side of the volume control and thru the auduio circuitry.
::.
::
::
::Also, can you check the peaked tuning of the 2nd AM IF transformers plate coil and the following detector grid coil winding ?
::
::
::Could even be a def 2nd AM IF transformer.
::
::
::
::
::
::73's de Edd
::
::

::
::
::
:

9/12/2009 1:01:55 PMDave Froehlich(78839:78832)

Edd,
Yes, it was the diode in the 6T8. I used the small signal diode as you suggested across the defective tube diode, and "like magic" (actually with a working diode detector), I have beautiful AM sound again.
Thanks very much,
Dave
:
:
:
:
:Sir Dave. . . .
:
:
:
:The picking up of several different AM signals would tend to signify that the frontal RF and first IF stages are OK
:in alignment.
:
:
:After that, there is just the RF signal at the plate circuitry of the IF amp that feeds into the AM detector circitry.
:
:
:With some known problems of 6T8's, can you sub in another unit for it ?(considering only,its sole AM det diode section)
:
:
:(Another viable test is to shunt the det diode section of the 6T8 with a solid state det diode . . . .1N914-4148.) [Its anode going to plate-its cathode to ground] If it then more efficiently, detector rectifies, go for it.
:
:
:
:One then sees that the audio is all handled the same . . . .gain wise . . . from the band switch over to the top side of the volume control and thru the auduio circuitry.
:.
:
:
:Also, can you check the peaked tuning of the 2nd AM IF transformers plate coil and the following detector grid coil winding ?
:
:
:Could even be a def 2nd AM IF transformer.
:
:
:
:
:
:73's de Edd
:
:

:
:
: