premp tube hum rejection

[pula58]

I had quite a bit of 60Hz in the output of a build I am working-on. I finally isolated it: It seemed to be caused by the preamp tube.


Replacing a RI tung sol 12AX7 with an electro-harmonics "Gold" got rid of most of the hum. I tried another tung sol, and it had the same problem,
a lot of 60Hz hum.

My heater wiring is super neat and carefully done.

Which leads me to wonder how various 12AX7 tubes vary with respect to rejection of the heater signal?

[dorrisant]

That is odd... I have been using them (TS reissues) a lot lately. Haven't heard any real issues with hum.
I will keep my ears open though.

Tony

[Reeltarded]

Are you absolutely positive it isn't the socket? Just a thought. I have a couple problem sockets that only accept certain tubes, and not ones that make sense.

Every tube has a personality, for sure. Usually that is a problem I find in the output though. Hummin' and stuff.

[ToneMerc]

I had quite a bit of 60Hz in the output of a build I am working-on. I finally isolated it: It seemed to be caused by the preamp tube.


Replacing a RI tung sol 12AX7 with an electro-harmonics "Gold" got rid of most of the hum. I tried another tung sol, and it had the same problem,
a lot of 60Hz hum.

My heater wiring is super neat and carefully done.

Which leads me to wonder how various 12AX7 tubes vary with respect to rejection of the heater signal?

The EH has a spiral wound filament, which in theory would reject hum better.

TM

[briane]

keep in mind every manufacturer makes tubes differently - their NOT all the same - so you should not expect the same performance.

I know - I know - its pretty simple.

Not just in manufacturing, where the metal is, also in what chemicals where and who did it - does it have barium?

mmmmmmmmmmm - barium (sooo tasty)

[rdjones]

I had quite a bit of 60Hz in the output of a build I am working-on. I finally isolated it: It seemed to be caused by the preamp tube.


Replacing a RI tung sol 12AX7 with an electro-harmonics "Gold" got rid of most of the hum. I tried another tung sol, and it had the same problem,
a lot of 60Hz hum.

My heater wiring is super neat and carefully done.

Which leads me to wonder how various 12AX7 tubes vary with respect to rejection of the heater signal?

Yes, different types of tube construction can greatly effect hum.

I have a bunch of Japanese made Radio Shack 12AX7s (probably 1980s) that all have the same very high level of hum when used in preamp stages.
They all test at or near 100% but are unusable in a guitar amp.
In the same circuit other good 12AX7s are dead quiet.

rd

[Reeltarded]

mmmmmmmmmmm - barium (sooo tasty)

The secret to me mum's Christmas cookies! Shhhhh!

[Bob S]

V1 - need I say more...

[Reeltarded]

Scourge of London!

And V2!

[Bob S]

I installed a lot of equipment in a Lever Bros plant in Vlaardingen, Holland.
Still had the rail tracks used to launch V1 & V2 rockets.
Did more damage to the local area apparently.
Mustn't have been Amperex.

[pula58]

Are you absolutely positive it isn't the socket? Just a thought. I have a couple problem sockets that only accept certain tubes, and not ones that make sense.

Every tube has a personality, for sure. Usually that is a problem I find in the output though. Hummin' and stuff.

Do you mean that certain preamp tubes are loose in the socket, making a bad connection?

[Bob S]

Sorry about the de-rail.
Some of the guys have had probs with ceramic pre-amp sockets.
Don't know about hum, but hiss for sure.
Some manufacturers tubes are more susceptible apparently.
V1 is always a candidate for tube rolling.
Slight de-rail...
Mr Google has not responded with his tube of choice.
Good Luck,
Bob

[Structo]

Also different tubes can have different sized pin diameters.

So, say you have been running a tube with fat pins, you sub in a different one but it has smaller pins.
If the socket is old and not real tight anymore, the tube with the smaller pins can have difficulty making good contact.

This is especially true with power tubes that have more voltage and current.

[Reeltarded]

Exactly. I had a couple sockets in a reworked amp that refused to take any tube that wasn't a very particular brand and type made in the 80s. Everything else completely failed or make a tremendous hum. Socket swap and all happy.

Couple times I have also had single tubes that wouldn't like a socket too. A thought at least before you start working on everything else

[jamme61]

I had quite a bit of 60Hz in the output of a build I am working-on. I finally isolated it: It seemed to be caused by the preamp tube.


Replacing a RI tung sol 12AX7 with an electro-harmonics "Gold" got rid of most of the hum. I tried another tung sol, and it had the same problem,
a lot of 60Hz hum.

My heater wiring is super neat and carefully done.

Which leads me to wonder how various 12AX7 tubes vary with respect to rejection of the heater signal?

I had the same thing happen to me. It is the tung sol tube IMHO. I had several of them create hum. The tube created hum in my plexi, in V2, which is the cathode follower position.I liked the sound of them but they hum, I've had no luck with them.