Hello.
I am repairing a RCA 120 with the following tubes: 80, 2A5, 2B7, 58, 2A7 and 58. I have mounted the radio with new capacitors except two of them, one in RF coil and the other one in the antenna coil. I have also put all new resistors. The problem is the motorboating noise that I don´t know how to repair it. Could you help me?

Thank you very much

Azarquiel
vpamm@yahoo.es

Te escribire en español ya que soy argentino.Estoy arreglando una radio capilla o catedral con similares valvulas dandome mucho trabajo.El ruido en el parlante se lo saque con un condensador de 32 microfaradios en la fuente de alimentacion eliminando todo ripple posible.Si se te ocurre algo para solucionar mi problema porque no tengo señal de salida ,siendo que la etapa de la salida de la 2A5 anda perfecto te lo agradecere.Carlos
:Hello.
:I am repairing a RCA 120 with the following tubes: 80, 2A5, 2B7, 58, 2A7 and 58. I have mounted the radio with new capacitors except two of them, one in RF coil and the other one in the antenna coil. I have also put all new resistors. The problem is the motorboating noise that I don´t know how to repair it. Could you help me?
:
:Thank you very much
:
:Azarquiel
:vpamm@yahoo.es

Hi, Motor boating is low frequency instability and has a few causes. Look for leaky coupling capacitors or in effective decoupling capacitors. I am not conversant with the valve line up, do they have a metalized coating? If so, this can become open circuit and cause instability through lack of screening, try placing a hand around the metalizing, if the sound changes then try wrapping a few turns of thin tinned copper wire around the base of the metalizing and connect the wire to chassis.

:Te escribire en español ya que soy argentino.Estoy arreglando una radio capilla o catedral con similares valvulas dandome mucho trabajo.El ruido en el parlante se lo saque con un condensador de 32 microfaradios en la fuente de alimentacion eliminando todo ripple posible.Si se te ocurre algo para solucionar mi problema porque no tengo señal de salida ,siendo que la etapa de la salida de la 2A5 anda perfecto te lo agradecere.Carlos
::Hello.
::I am repairing a RCA 120 with the following tubes: 80, 2A5, 2B7, 58, 2A7 and 58. I have mounted the radio with new capacitors except two of them, one in RF coil and the other one in the antenna coil. I have also put all new resistors. The problem is the motorboating noise that I don´t know how to repair it. Could you help me?
::
::Thank you very much
::
::Azarquiel
::vpamm@yahoo.es

when you find out whats causing the motorboating let us know...I have the same problem with my model 120...are all of your tubes covered with tin covers?Did you replace the large 4uf (times 4) capacitor? the one in a rectangular box?
my cabinet is almost perfect and I don't want to give up on mine.
Earl

:Hi, Motor boating is low frequency instability and has a few causes. Look for leaky coupling capacitors or in effective decoupling capacitors. I am not conversant with the valve line up, do they have a metalized coating? If so, this can become open circuit and cause instability through lack of screening, try placing a hand around the metalizing, if the sound changes then try wrapping a few turns of thin tinned copper wire around the base of the metalizing and connect the wire to chassis.
:
::Te escribire en español ya que soy argentino.Estoy arreglando una radio capilla o catedral con similares valvulas dandome mucho trabajo.El ruido en el parlante se lo saque con un condensador de 32 microfaradios en la fuente de alimentacion eliminando todo ripple posible.Si se te ocurre algo para solucionar mi problema porque no tengo señal de salida ,siendo que la etapa de la salida de la 2A5 anda perfecto te lo agradecere.Carlos
:::Hello.
:::I am repairing a RCA 120 with the following tubes: 80, 2A5, 2B7, 58, 2A7 and 58. I have mounted the radio with new capacitors except two of them, one in RF coil and the other one in the antenna coil. I have also put all new resistors. The problem is the motorboating noise that I don´t know how to repair it. Could you help me?
:::
:::Thank you very much
:::
:::Azarquiel
:::vpamm@yahoo.es

Hi Azarquiel, Hi Earl,
If one of the capacitor you haven't replaced Azarquiel is C3, replace it. Actually replace the other one too. And to Earl, the 4-part capacitor contains a 10 MF and three 4 MF. All should be replaced. You might want to use a 10 MF and test jump across the filter caps you have replaced and see if it helps. These I believe could cause your motorboating noise. And unfortunately other things as stated.

Bill VA

:Hello.
:I am repairing a RCA 120 with the following tubes: 80, 2A5, 2B7, 58, 2A7 and 58. I have mounted the radio with new capacitors except two of them, one in RF coil and the other one in the antenna coil. I have also put all new resistors. The problem is the motorboating noise that I don´t know how to repair it. Could you help me?
:
:Thank you very much
:
:Azarquiel
:vpamm@yahoo.es