Switching On/off

[glassglow]

Should headphones always need to be disconnected whenever the Mainline is powered up or down?

[Rocketman248]

I always leave mine plugged it.  Haven't had any issues.

[Adrian]

Probably won't cause any major problems.
However, be aware that small signal tubes (e.g., the 6922 in the EROS, etc) can experience flash-over during startup.  This is not a concern for small signal tubes but is a major problem in larger power tubes.  If your input (like the EROS or the like) has a signal tube that does flash-over during startup, then you would send the resulting signal to the headphones IF the Mainline was turned on first.

One way to eliminate this from happening is to start up your equipment in the proper order.
First start up any input device like a phono stage, CD, DAC first, THEN start up other devices in the order of their connection (pre-amp then amp; headphone amp).
This prevents the signal from startup/warmup from pre-devices feeding all the way through the down stream ones.
Shutdown is just the opposite, amps then pre-amps then inputs.

This still does not prevent any flash-over signal to the plugged in headphones from the Mainline signal/driver tube should that occur.

[Doc B.]

I think one needs to not over-generalize. Flashover is primarily a problem in high voltage tubes like those used in transmitters, and occurs mostly when a tube is gassy. So if one uses tubes prone to be gassy and that might run at several hundred volts - a 50 is a classic example of a tube that is notorious for being gassy - one needs to use some caution. Another potential issue is running without a speaker load. One of the things that is considered important in guitar amps is to have a speaker connected when starting, because the self inductance of the primary can create a high voltage when signal hits it, that can go back into the tube and create an arc. A third situation in which flashover can occur is between directly coupled stages where the first tube warms up and conducts more slowly than the second tube, creating a positive bias issue with the second tube that makes it draw excess current and flash from the filament. This might be the mechanism you are referring to in the Eros. However those tubes have slow warmup heaters which eliminate that problem. It is a more common issue in directly coupled stages where the second stage uses a directly heated tube that heats up very quickly and can conduct before the first stage warms up and pulls the second stage grid voltage down to the proper operating point.

Neither inductive kick nor positive bias at startup are a problem in the Mainline or any of our other current production amps. The single gain stage Mainline has a relatively gentle and slow startup and runs at relatively low voltages, and the 6C45pi is a very rugged tube that does not have a reputation for being gassy. In amps that are two stages that are direct coupled, like the Eros and the now retired Paramount 2A3, we employ ways to slow the startup of the tubes.

[Adrian]

Thanks, Doc for the clarification.  Very informative.
I know the recently installed E88cc in my EROS has slight flashover at start so I will be watching it to see if there is anything else going on.

[Doc B.]

Also do not mistake the very bright glow at turn on of many (primarily European) indirectly heated tubes for flashover. It is simply the way the heaters warm up.

[Adrian]

When I first installed the Telefunken E88cc a couple of weeks ago there was definately a small amount of flashover for the first couple of times I turned on the EROS.  I saw and heard it through the headphones (I didn't follow my advice from above).
After about 10 or more starts, I removed the shields and noticed last night that there was no flashover as I had seen before.  I powered it up three times (after about a 10 minute wait between starts) and did not see nor hear it anymore.  The heaters do start up bright but without the observed small amount of flashing as before.

[Doc B.]

That would be a gassy tube. After the getter warmed up and absorbed the gas it stopped shorting.