Removing inner power tubes when running at 60w

[underbedboogieman]

Hey guys, I was just wondering if any company makes any sort of plugs or covers for the power tube sockets that don't have tubes in them? I've been running my JP-2C in the 60 watt mode and have decided to pull the unused two inner power tubes out so I can save them when it's time to change out the ones left in; when they die out and need to be replaced. I've also read that is good to remove any power tube that isn't being used due to potential cathode poisoning. I don't want to leave the open sockets the way they are because of all the dust and pet hair that my room collects, no matter how much I try to keep it clean( Australian Shepherd owner that lives in FL, so he's constantly shedding while I'm shredding). Any help is greatly appreciated!

 

[bandit2013]

for the Aussie. Border collies do the same thing, but they got tails with long hair. I have gone through many vacuum cleaners over the years due to dog hair.

Not sure if there are any covers to place on unused tube sockets. Socket savers are more of an extension socket, sometimes you can find socket bases that are used to convert to a different tube like a KT88. If you measure the ceramic base, you may be able to find a rubber cap that will fit it. Not sure on the dimensions on the ceramic base. Never considered using a plug to cover unused sockets before.

 

[bandit2013]

Not sure how easy this will be to find. There is this socket base. You may be able to cut off or remove some of metal pins and leave only those that are not at a high voltage potential. It may also be possible to fill this base with expoxy or potting compound that does not have any carbon black mixed into it. You need something with a high dielectric value so it does not conduct under high DC voltage.

https://www.laboratoriomusicale.net/en/8-pin-octal-style-tube-socket-base

If the pins can be cut or removed from the tube socket base, You only need to remove pins 3, 4, 5 and leave the rest intact. the heater pins are low voltage so they will not arc over. Cathode usually connects to chassis ground as the JP2C is not a single ended Class A amp. Pins 6 and 1 are not connected inside the amp. Pin 3 is the plate pin so it will have the 460+ dv voltage as will pin 4 as that is the screen grid. You could leave in pin 5 if you so desire. Just note that the diagram below is not of the one in the link. With the tube itself, pins 1 and 6 will be missing. The socket in the amp will still have the barrel clips for those pins. They are not electrically connected.

 

[Fastforded]

Just leave it alone and leave the tubes in it.

 

[bandit2013]

Running the amp with no anode current in the inner pair with a heated cathode could result in cathode poisoning. That may result in a high resistance chemical layer that forms between the cathode tube and the oxide coating. Since you are only using the 60W power mode, that has a potential to happen. Without the tube in the socket, that could lead to other problems too when in a high humidity environment. Not sure the sockets would form any oxidation due to exposure. At least when the amp is active, the heat will dry out that immediate air due to elevated temperatures of the power tubes that are operating. I would make an inquiry to Mesa customer service through their on-line portal and see what their response is on the subject matter. The manual on that subject indicates you should rotate the tubes to extend their service life. No mention of removal except for periodical tube rotation (exchanging the inner and outer tubes). There may be reason why you may not find any types of dummy plugs or caps to cover the sockets. However, if you do opt to make use of something, without the tubes installed, I doubt the 100W setting would pose any issue as that usually is just a disconnect on the cathode circuit to chassis ground to disable the tubes. There will still be high voltage potential on the plate and screen sockets/pins of the inner pair. Something I need to consider myself but with a different amp (Mark VII) as I have been running its 45W mode more than the 90W. As for the JP2C, I much prefer the 100W but I get the point that tubes keep going up in price and may be harder to get when you need them. I sort of got into the habit of getting a stash of replacement tubes so I have them in a pinch. Easier said than done though.