it still has a hum

8/8/2011 11:52:51 AMjesse hancock

Before the if can repair radio had a slight humm not the normal with bad electrolytics but a slight humm and no reception of anything but the noise. Now its more pronounced I have recapped the radio which is a ge202 so where should I look???? Getting a little frustrated at this point

8/8/2011 3:57:27 PMMitch

:Before the if can repair radio had a slight humm not the normal with bad electrolytics but a slight humm and no reception of anything but the noise. Now its more pronounced I have recapped the radio which is a ge202 so where should I look???? Getting a little frustrated at this point
:
jesse,

Lets clear any doubts first.
Test all of your tubes looking leakage or shorts, let them cook foe ahile.
Then use the voltage chart on the schematic and check all of the voltages at the tubes using a VTVM, pay attention to the grid voltages, you may have an oscillator problem.

8/8/2011 3:59:09 PMMitch

:Before the if can repair radio had a slight humm not the normal with bad electrolytics but a slight humm and no reception of anything but the noise. Now its more pronounced I have recapped the radio which is a ge202 so where should I look???? Getting a little frustrated at this point
:
jesse,

Lets clear any doubts first.
Test all of your tubes looking for leakage or shorts, let them cook for awhile.
Then use the voltage chart on the schematic and check all of the voltages at the tubes using a VTVM, pay attention to the grid voltages, you may have an oscillator problem.

8/8/2011 4:51:26 PMNorm Leal

Jesse

Mitch has good idea. Here are a couple simple things. Is hum there with volume turned down? Is the loop antenna connected?

Norm

::Before the if can repair radio had a slight humm not the normal with bad electrolytics but a slight humm and no reception of anything but the noise. Now its more pronounced I have recapped the radio which is a ge202 so where should I look???? Getting a little frustrated at this point
::
:jesse,
:
:Lets clear any doubts first.
:Test all of your tubes looking for leakage or shorts, let them cook for awhile.
:Then use the voltage chart on the schematic and check all of the voltages at the tubes using a VTVM, pay attention to the grid voltages, you may have an oscillator problem.
:

8/8/2011 7:27:28 PMJesse Hancock

:Jesse
:
: Mitch has good idea. Here are a couple simple things. Is hum there with volume turned down? Is the loop antenna connected?
:
:Norm
:
:
: ::Before the if can repair radio had a slight humm not the normal with bad electrolytics but a slight humm and no reception of anything but the noise. Now its more pronounced I have recapped the radio which is a ge202 so where should I look???? Getting a little frustrated at this point
:::
::jesse,
::
::Lets clear any doubts first.
::Test all of your tubes looking for leakage or shorts, let them cook for awhile.
::Then use the voltage chart on the schematic and check all of the voltages at the tubes using a VTVM, pay attention to the grid voltages, you may have an oscillator problem.
::

The Hum is goes up or down with the volume. Its not constant as would be a bad filter section. But today, I did read on the tips and tricks section that on these old radios that have a floating b- at times the filter ground needs to be moved to make connecions that are correct.. I have checked voltages and they are all extremely low.
:
:

8/8/2011 7:34:55 PMJesse Hancock

:Jesse
:
: Mitch has good idea. Here are a couple simple things. Is hum there with volume turned down? Is the loop antenna connected?
:
:Norm
:
:
: ::Before the if can repair radio had a slight humm not the normal with bad electrolytics but a slight humm and no reception of anything but the noise. Now its more pronounced I have recapped the radio which is a ge202 so where should I look???? Getting a little frustrated at this point
:::
::jesse,
::
::Lets clear any doubts first.
::Test all of your tubes looking for leakage or shorts, let them cook for awhile.
::Then use the voltage chart on the schematic and check all of the voltages at the tubes using a VTVM, pay attention to the grid voltages, you may have an oscillator problem.

The Loop Antenna is connected. I have it all connected via test leads for now, until I put it all back together in the cabinet !

::
:
:

8/9/2011 10:48:18 PMEdd

Sir Jessee. . . . .

Hmmmmmmmm . . . . you certainly must not have palsy . . . . with the successful repairing of that IF transformers inner and minute intracacies . . .Taaa Daaaaa !

Exactly HOW much down is your main ~125VDC B+ and its sub ~88VDC B+ voltages from those given values . . . . and DO confirm that you were having your metering mediums NEGATIVE lead being on the floating ground buss.. . . . and NOT using the sets chassis ground for that referencing.

Also is the negative of the filter capacitor to a good connection into the floating B- buss and not being made near any connections that the 12SQ7 1st AF amp is near, in case a previous repair person made filter changeouts and moved their grounding position(s) where an undesirable ground loop might have been created in a 1st audio region.
Also, that the old can / capacitor set is not still in circuit and having new electrolytics just shunting across the old sections ?

FORBID . . .that they didn't make the very common assumption that the low/bottom side of a volume control is always ground and have connected in there.

An optimal physical position for it / them to be connected to. . . . (in case 2 separate units are involved now) . . . would be at the very BOTTOM lead (B-) of the 150 ohm cathode resistor of the 35L6 AF output tube.

Soooo the Hummmmmmmm is there irregardless of the volume control position . . . of particular interest is hummmmmm being present, while being at its at its minimum-um-um position.

Quickee-quickee . . . analytical troubleshooting procedure :

Take maybe like a 20-47-50 mfd at 150VDC eeee-lectrolytic capacitator in hand and then turn on the set.

Be sure the cap is shorted out to initially be totally discharged, place the negative of the sub cap to B- buss and the caps + lead goes to the plate of the 12SQ7 . . .brace for the initial . . . .POP . . . . what say now . . . chum . . .got any hummmmmm ?

If still having that hummmm level, discharge the capacitor and use the same ground again, but THIS TIME place the caps+ to B- ground and the caps negative to the 1st grid of the 35L6 for about 5 seconds of evaluative time to then see if the hummmmmmm disappears.

IF not, then the hum must be coming in from insufficient filtering of the power supply.

Now, just exactly WHAT were you doing just above ? ? ? . . . well . . . when you ran the volume control to absolute minimum, you should have shut down any incoming HUMMMMM from the sets RF front end stages and the final detected audio sourcing . . . .ergo . . . the problem is further on to the right , down the AF processing circuits trail.

That placing the source of the hummmmm untroduction, being AFTER being amplified by the 12SQ7.

When you placed the filter across the plate of the 12SQ7, that huge amount of capacitance "dead shorted" any present AC audio or hummmmmm directly to ground. That further confirmed the hummmmmm not being amplified by the 'Q7 nor creeping in from its power supply source. . . . seems that the offending trouble source is yet further on to the right.

Now one slight last circuit eccentricity before we move on to the examining and testing the B+ supply sourcing, a last hidden possibility is associated with the negative feedback loop circuitry tied in from the cathode of the 35L6 tube back into the 1st audio amp circuitry .

To wit . . . see the cathode of the 35L6 and its cathode, where above its 150 ohm cathode resistor there is inserted a series 47K and .01 capacitor network that has their other ends feeding to a series 1K resistor with its other end then finally ending up at the low end of the volume control WHICH is being held ABOVE B- level with yet another 1K resistor(R9).

Place a jumper lead a short across that R9 resistor to see if it has any effect upon your hummmmm problem.

If that proves fruitless, we have covered the AF aspects so take that ? 47 ? ufd electrolytic subbing capacitor again and jumper across the C21 B 88V supply filter capacitor . . . . . any hummmmm abatement ?
Then since we are stepping up to a HIGHER voltage threshold, merely move its positive lead up to then be shunting the main C21A capacitor.

How about the HUMMMMMM situation of the last two tests ?. . . . . what say you ?. . . .standing by for results. . . . .

73's de Edd

::Jesse
::
:: Mitch has good idea. Here are a couple simple things. Is hum there with volume turned down? Is the loop antenna connected?
::
::Norm
::

:: ::Before the if can repair radio had a slight humm not the normal with bad electrolytics but a slight humm and no reception of anything but the noise. Now its more pronounced I have recapped the radio which is a ge202 so where should I look???? Getting a little frustrated at this point
::::
:::jesse,
:::

:::Lets clear any doubts first.
:::Test all of your tubes looking for leakage or shorts, let them cook for awhile.
:::Then use the voltage chart on the schematic and check all of the voltages at the tubes using a VTVM, pay attention to the grid voltages, you may have an oscillator problem.
:
:

:The Loop Antenna is connected. I have it all connected via test leads for now, until I put it all back together in the cabinet !
:
:::
::
::
:
: