Tubes are going bad in my amp

I just pulled the manual online and it says you need:
Preamp: Five 12AX7 tubes
Power amp: Two EL84s and two 6V6s

If you can change light bulbs, you can change tubes. Preamp tubes have a specific pin alignment and socket hole layout and because of that it's rare that you can install them incorrectly. Same goes for 84s and 6V6s. In the case of the latter, there is a guide pin on the middle black tab that can only be installed in the socket one way.

In most amps, you have to set the bias (like a car engine's timing/idle) to match a new set of power tubes to the amp, but the Egnater manual indicates it's fixed bias and that any re-bias you can do is not necessarily needed. And from my experience, re-bias isn't critical anyway in low-wattage, lower volume EL84 and 6V6 platforms.

You can buy pre-packaged tube sets from reputable companies like TheTubeStore.com, dougstubes.com, eurotubes ... I've done business with all three and was pleased with their knowledge and products and my experiences. Popular tube brands, like Tung-Sol, Ruby, Groove Tubes, Mullard, Electro-Harmonix, Sovtek ... you can spend a year researching and reading opinions online and not walk away any more enlightened. If all else fails, find out what tubes Bruce Egnater used designing the amp, or what brands the amps currently ship with from the factory. He/they surely used modern, readily available tubes.

If you want to support a local musical instrument small business, reach out to Kenny at Red Stick Guitar and Amp. He can likely build you a custom tube set from his shop stock that will do the trick just fine. And if the amp happens to need or could benefit from a re-bias, he's the guy to do that for you. Tell him Jeff from The Fret Shack sent you.

This reminds me-

I think the preamp tube in my Marshall is failing - clean and crunch channels sound like the amp is covered with a sandpaper pillow while underwater. I thought my instrument cable was shot, (because when I wiggle it in the input jack, it tries to correct) but amp sounds the same with a new cable.

Don't know if its the jack itself or the pre amp tube.

Know anyone in Houston you recommend?
It's a JCM900 dual reverb 4100.

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I think the preamp tube in my Marshall is failing - clean and crunch channels sound like the amp is covered with a sandpaper pillow while underwater. I thought my instrument cable was shot, (because when I wiggle it in the input jack, it tries to correct) but amp sounds the same with a new cable.

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Sounds more like the jack is the problem but it should be easy enough to try another 12AX7 to see if the problem goes away. Also maybe try wiggling the jack with no guitar plugged into it. If it makes a bunch of noise, it's probably a bad solder joint. If the jack itself is dirty some contact cleaner and a nylon bristle brush should do the trick. Make sure the nut that holds the jack on is good and tight.

Be careful what you touch. You could die.

That’s not a joke.