Hello:
I have just completed recapping an unknown model RCA Victor AM/SW bakelite set and as I had no schematic to follow, I used the layout in the 66X series as a guide. The main difference between the set I picked out of the junk and the 66X schematics is the filter electolytics -- the schematic show only a double cap. and I discovered during the recap. that the electrolytic (paper tubular type with absolutely no value markings) had three sections.

I used 47mfd. caps. at 450V for the connections shown on the schematic and a spare 47mfd.@350 for the surprise connection. The set now works but it exhibits a loud hum during initial warm-up and it will greatly diminish when the volume control is turned to maximum. While this reduces the hum level, the station audio is a bit hard on the ears! If I knock back the volume level, the hum gets louder until I reach the switch-off position.

Would larger values for one or more of the electolytics help or could this originate elsewhere such as the AVG?

Thanks for any info.

Dave

Hi Dave

Hum that varies with the volume control usually isn't lack of electrolytic filters. Did you connect the negative in same place as original? Does your ground connection of the volume control have good connection to B-?

If this is an AC/DC radio, one that uses 35Z5, 50L6 or similar tubes, chassis is Not negative connection for electrolytics.

Norm

:Hello:
:I have just completed recapping an unknown model RCA Victor AM/SW bakelite set and as I had no schematic to follow, I used the layout in the 66X series as a guide. The main difference between the set I picked out of the junk and the 66X schematics is the filter electolytics -- the schematic show only a double cap. and I discovered during the recap. that the electrolytic (paper tubular type with absolutely no value markings) had three sections.
:
:I used 47mfd. caps. at 450V for the connections shown on the schematic and a spare 47mfd.@350 for the surprise connection. The set now works but it exhibits a loud hum during initial warm-up and it will greatly diminish when the volume control is turned to maximum. While this reduces the hum level, the station audio is a bit hard on the ears! If I knock back the volume level, the hum gets louder until I reach the switch-off position.
:
:Would larger values for one or more of the electolytics help or could this originate elsewhere such as the AVG?
:
:Thanks for any info.
:
:Dave

:Hi Dave
:
: Hum that varies with the volume control usually isn't lack of electrolytic filters. Did you connect the negative in same place as original? Does your ground connection of the volume control have good connection to B-?
:
: If this is an AC/DC radio, one that uses 35Z5, 50L6 or similar tubes, chassis is Not negative connection for electrolytics.
:
:Norm
:
::Hello:
::I have just completed recapping an unknown model RCA Victor AM/SW bakelite set and as I had no schematic to follow, I used the layout in the 66X series as a guide. The main difference between the set I picked out of the junk and the 66X schematics is the filter electolytics -- the schematic show only a double cap. and I discovered during the recap. that the electrolytic (paper tubular type with absolutely no value markings) had three sections.
::
::I used 47mfd. caps. at 450V for the connections shown on the schematic and a spare 47mfd.@350 for the surprise connection. The set now works but it exhibits a loud hum during initial warm-up and it will greatly diminish when the volume control is turned to maximum. While this reduces the hum level, the station audio is a bit hard on the ears! If I knock back the volume level, the hum gets louder until I reach the switch-off position.
::
::Would larger values for one or more of the electolytics help or could this originate elsewhere such as the AVG?
::
::Thanks for any info.
::
::Dave

::Hi Dave
::
:: Hum that varies with the volume control usually isn't lack of electrolytic filters. Did you connect the negative in same place as original? Does your ground connection of the volume control have good connection to B-?
::
:: If this is an AC/DC radio, one that uses 35Z5, 50L6 or similar tubes, chassis is Not negative connection for electrolytics.
::
::Norm
::
:::Hello:
:::I have just completed recapping an unknown model RCA Victor AM/SW bakelite set and as I had no schematic to follow, I used the layout in the 66X series as a guide. The main difference between the set I picked out of the junk and the 66X schematics is the filter electolytics -- the schematic show only a double cap. and I discovered during the recap. that the electrolytic (paper tubular type with absolutely no value markings) had three sections.
:::
:::I used 47mfd. caps. at 450V for the connections shown on the schematic and a spare 47mfd.@350 for the surprise connection. The set now works but it exhibits a loud hum during initial warm-up and it will greatly diminish when the volume control is turned to maximum. While this reduces the hum level, the station audio is a bit hard on the ears! If I knock back the volume level, the hum gets louder until I reach the switch-off position.
:::
:::Would larger values for one or more of the electolytics help or could this originate elsewhere such as the AVG?
:::
:::Thanks for any info.
:::
:::Dave
Hello Norm:
Thanks for your reply.
I was not able to connect the negative leads to the original point as the insulator crumbled to pieces when I took off the paper electro.. I used a couple of terminal strips to provide the "floating" ground (or I thought this would work as I realized the chassis was not negative.

I have a possible schematic coming via email from another enthusiast so I'll peruse that to see if I can get a lead on things.

Regards
Dave

If this is an AC/DC type radio, the general area where you want to ground your volume control is to the return side of the AC cord. The side that connects to 35Z5/35W4 is NOT the return side. The other side of the line cord, usually connecting to the power switch, is the return line. Connecting your volume control ground directly to this point may still introduce a small amount of hum. Using a resistor from 100 to 200 ohms in series, with a .05 MFD condenser in parallel with the resistor can sometimes eliminate this problem. There are many different methods to eliminate this problem. I must make an important note, that you DO NOT want to connect the volume control directly to the return side of the AC cord. Connect it AFTER the switch. Sometimes, too, the hum I describe, which is not at all the same as your hum, can be eliminated without the resistor/condenser combination. Simply select a point in the radio where the wiring from the switch (return line/also known as B-) has traveled some distance. Sometimes by selecting a point in the B- wiring far away from the switch can help eliminate a lot of hum.

T.D.

:::Hi Dave
:::
::: Hum that varies with the volume control usually isn't lack of electrolytic filters. Did you connect the negative in same place as original? Does your ground connection of the volume control have good connection to B-?
:::
::: If this is an AC/DC radio, one that uses 35Z5, 50L6 or similar tubes, chassis is Not negative connection for electrolytics.
:::
:::Norm
:::
::::Hello:
::::I have just completed recapping an unknown model RCA Victor AM/SW bakelite set and as I had no schematic to follow, I used the layout in the 66X series as a guide. The main difference between the set I picked out of the junk and the 66X schematics is the filter electolytics -- the schematic show only a double cap. and I discovered during the recap. that the electrolytic (paper tubular type with absolutely no value markings) had three sections.
::::
::::I used 47mfd. caps. at 450V for the connections shown on the schematic and a spare 47mfd.@350 for the surprise connection. The set now works but it exhibits a loud hum during initial warm-up and it will greatly diminish when the volume control is turned to maximum. While this reduces the hum level, the station audio is a bit hard on the ears! If I knock back the volume level, the hum gets louder until I reach the switch-off position.
::::
::::Would larger values for one or more of the electolytics help or could this originate elsewhere such as the AVG?
::::
::::Thanks for any info.
::::
::::Dave
:Hello Norm:
:Thanks for your reply.
:I was not able to connect the negative leads to the original point as the insulator crumbled to pieces when I took off the paper electro.. I used a couple of terminal strips to provide the "floating" ground (or I thought this would work as I realized the chassis was not negative.
:
:I have a possible schematic coming via email from another enthusiast so I'll peruse that to see if I can get a lead on things.
:
:Regards
:Dave

The better AC/DC radios had the chassis connected to the return side of the cord through a condenser or condenser/resistor combination. This eliminated a lot of the danger for lethal shocks and fire hazards. You still can get quite the shock from this type of radio, but it isn't as dangerous.

In such a radio, since the chassis is no longer connected directly to the line cord, it cannot be used as a path for direct current anymore (for the volume control and various other parts). It now serves simply as a shield for all of the components.

Thomas Dermody

:The better AC/DC radios had the chassis connected to the return side of the cord through a condenser or condenser/resistor combination. This eliminated a lot of the danger for lethal shocks and fire hazards. You still can get quite the shock from this type of radio, but it isn't as dangerous.
:
:In such a radio, since the chassis is no longer connected directly to the line cord, it cannot be used as a path for direct current anymore (for the volume control and various other parts). It now serves simply as a shield for all of the components.
:
:Thomas Dermody

Hello Thomas:
Thanks for your replies.
I have determined the set is an RCA Victor 531D and I am perusing the schematic this P.M.. I noted from a quick check that one section of the electrolytic is 80mfd. and the other two are 40 and 50mfd. respectively.

I am going to borrow a tube tester as I suspect the audio o/p tube may have a possible cathode - heater short.

Dave McL.

The audio output tube would cause hum all the time. It would not be affected by the volume control. Furthermore, in my opinion, since the output tube filament is at the high end of the string, things would likely get kinda ugly. Either some filaments would start glowing really brightly or the cathode bias resistor would overheat. Though this is a good idea to check the tube, you want to make sure that your control is grounded appropriately. It is somewhat possible that a mild short has developed that is not visibly obvious.

T.D.

T.D.

:The audio output tube would cause hum all the time. It would not be affected by the volume control. Furthermore, in my opinion, since the output tube filament is at the high end of the string, things would likely get kinda ugly. Either some filaments would start glowing really brightly or the cathode bias resistor would overheat. Though this is a good idea to check the tube, you want to make sure that your control is grounded appropriately. It is somewhat possible that a mild short has developed that is not visibly obvious.
:
:T.D.
:
:T.D.
Thanks Thomas - will do.
Dave