Working on an E672. The unit has great selectivity. But the volume can't be turned completely down. Min volume is very hearable from 20 feet. Also when volume is turned up about 1/4 turn the output is taken over by sever warble. I recapped everything hoping the warble would go away but no change. The resistors check pretty close to sams schematic. The rect. output is 101.2 across new filter. Plate volts check within 5 vdc.

Unit as AVC. Acts like something wrong in thes area. Could tube be bad?

Does anybody have any ideas?

:Working on an E672. The unit has great selectivity. But the volume can't be turned completely down. Min volume is very hearable from 20 feet. Also when volume is turned up about 1/4 turn the output is taken over by sever warble. I recapped everything hoping the warble would go away but no change. The resistors check pretty close to sams schematic. The rect. output is 101.2 across new filter. Plate volts check within 5 vdc.
:
:Unit as AVC. Acts like something wrong in thes area. Could tube be bad?
:
:Does anybody have any ideas?

::Working on an E672. The unit has great selectivity. But the volume can't be turned completely down. Min volume is very hearable from 20 feet. Also when volume is turned up about 1/4 turn the output is taken over by sever warble. I recapped everything hoping the warble would go away but no change. The resistors check pretty close to sams schematic. The rect. output is 101.2 across new filter. Plate volts check within 5 vdc.
::Looking at the schematic it would seem that your problem is in the RC module between the audio amp and output. The low side of the volume control does not go to ground.
::Unit as AVC. Acts like something wrong in thes area. Could tube be bad?
::
::Does anybody have any ideas?

:::Working on an E672. The unit has great selectivity. But the volume can't be turned completely down. Min volume is very hearable from 20 feet. Also when volume is turned up about 1/4 turn the output is taken over by sever warble. I recapped everything hoping the warble would go away but no change. The resistors check pretty close to sams schematic. The rect. output is 101.2 across new filter. Plate volts check within 5 vdc.
:::Looking at the schematic it would seem that your problem is in the RC module between the audio amp and output. The low side of the volume control does not go to ground.
:::Unit as AVC. Acts like something wrong in thes area. Could tube be bad?
:::
:::Does anybody have any ideas?

Thanks for the reply. I checked the 10 meg connected to pin 6 of the 1U5 it is 10.54 Meg. Not sure how AVC works. I understand that as the output voltage is pushed up due to increased signal a negative feedback is applied forward. If I'm on track, pin 6 of the IF amp should see a decrease in positive volts applied thus holding down emission. I don't see how this works. Does the AVC take place in the 1U5? If so then maybe a bad cap in the RC network is causing the problem as you said. If someone can help me understand AVC better, I'll have better luck. This is my second radio I'm trying to fix. The first one is still on the bench. Dad and I are both stumped, but that's another story.
Thanks for all the help.

Sir Ross:

Hmmmmm….don’t have Sammy’s 346-8 at hand for referencing , but can you confirm that the sets volume controls center wiper is getting full low resistance at its min volume setting…...thereby totally diminishing the feed thru of AF signal to the sets 1U5’s first grid to nil.
Also there potentially might be a circuit variant such that the vol controls low side ..otherwise usually grounded terminal… might be lifted up from ground a small amount with a series resistor to ground, such that some negative feedback might be injected back from the AF output stage.
Any chance that resistor has drifted up in value , such that min volume is no longer attainable?
Also, any change of PDF’ing , GIF’ing that AF output stage for reference. The howling / squeal/ golden warbler effect still sounds attune to improper bypassing OR neg feedback level problem.

73’s de Edd

:Sir Ross:
:
:Hmmmmm….don’t have Sammy’s 346-8 at hand for referencing , but can you confirm that the sets volume controls center wiper is getting full low resistance at its min volume setting…...thereby totally diminishing the feed thru of AF signal to the sets 1U5’s first grid to nil.
:Also there potentially might be a circuit variant such that the vol controls low side ..otherwise usually grounded terminal… might be lifted up from ground a small amount with a series resistor to ground, such that some negative feedback might be injected back from the AF output stage.
:Any chance that resistor has drifted up in value , such that min volume is no longer attainable?
:Also, any change of PDF’ing , GIF’ing that AF output stage for reference. The howling / squeal/ golden warbler effect still sounds attune to improper bypassing OR neg feedback level problem.
:
:73’s de Edd
:
Thanks for the info. If you can email your fax # maybe you can help me understand the cir. better. ross@itsellshere.com