6K7 Tube specialist needed for RCA BA86A1

[xela_92]

I have changer the 6K7 tube on a RCA BA86A1.
Checked and paired with a tube meter.

I tried with different tubes from different company.

Some produce a big hum!
When you test them, you have generally the best result with the tube tester!!!

Any one knows how to cancel this.
I just can say that when you use a RCA, it is allways good...

Best,

Olivier :shock:

 

[PRR]

Be sure nothing is connected to Pin 1 on the socket.

In the metal 6K7, pin 1 is an extra Screen (G2) connection; in the glass 6K7G(T) version Pin 1 is no-connection. If they expected 6K7G and used pin 1 as a tie-point, then plugging in 6K7 will inject Screen power into whatever is tied to Pin 1.

> I just can say that when you use a RCA, it is allways good...

Then use the RCA. Don't worry that it is 60 years old: RCA made good tubes, and anyway every 6K7 in the world is over 40 years old.

 

[ciaudio]

I have had good results with RCA and Amperex 6k7's in my Ba86's but you have to pick through a number of tubes to get low hum low noise and low microphonics.

Also if you have screen balance adjustment pot on your unit you have to adust that for lowest hum.

Chris

 

[CJ]

As mica spacers age, they can emit gas. Some of those old tube testers had a "gas" button on them, but did they really work? Tube testers usually test at far lower voltages than the actual circuit in order not to have to switch in and out a thousand different voltages.

 

[NewYorkDave]

I don't remember for sure, but I believe many tube testers measured gas by indicating no-signal grid current, either directly, or indirectly by its effect on plate current when a big grid leak resistor is switched in and out of circuit.

Radiotron 4 has more info about tube testing than ya can shake a stick at, but my copy's at home and I'm at work.