ART TubeMP Tube Change

[Matthew_84]

Hey guys,

I just acquired an old 12AX7A tube from an old piece of equipment. Is there anything I should know before I swap this in for a test? I've heard tubes can store power, and you must de-energize them first, is there any truth to this? And if the tube is bad, can that cause a problem to the ART preamp?

Thanks

[Electricblue]

Originally Posted by Matthew_84

Hey guys,

I just acquired an old 12AX7A tube from an old piece of equipment. Is there anything I should know before I swap this in for a test? I've heard tubes can store power, and you must de-energize them first, is there any truth to this? And if the tube is bad, can that cause a problem to the ART preamp?

Thanks

Tubes dont hold charge, you're thinking of capacitors.

If the tube is bad, it will have the same effect as the tube going iffy in your preamp. It wont damage it.

I would recommend you get the OK from a tube expert before you take my advice.

[Matthew_84]

Yeah, I didn't think they held a charge, but someone had said that they were like capacitors in that way, but I also don't think that's accurate. Everyone just says to swap them out and be careful not to damage the prongs, and yeah, you're also right about there being no damage done by a bad tube. I don't even think it is bad, nothing's burnt at all and it's an old tube made in England... May sound pretty cool actually, looking forward to trying it out. Thanks.

[will33]

Preamp tubes like that (the small ones) are simply take out the old one, plug in the new one, that's it. You may be thinking of biasing, that should be done with power tubes (the big ones). That's only if you have a tube power section like in an SVT or something.

[jimbilly]

12AX7s don't hold a charge. If it's made in England, it's most likely a Mullard, - one of the very-very best vintage tubes. Since it's just a single preamp tube, I'd plug it in and see what happens. The odds of a bad single preamp tube damaging your preamp are super low. If you want to play it 99.99% safe, somebody in your area has a tube tester, amp shops, old organ repair shops, ask on Craigslist in the musical instruments or electronics sections and somebody would probably be happy to test a single tube for a 6 pack, or for free.

[ChrisPbass]

12ax7s do not need biasing.

[90k]

not to derail this tread but I have a quick question, I hope OP doesn't mind.. I am in need of the power supply for one of these and they are no where to be found by me.. Anyone have any suggestions? You can pm me if you do not want to clutter this tread. Thanks

[JimmyM]

preamp tubes are plug and play. no hand wringing necessary.

[BassmanPaul]

The TubeMP series of pre-amps operate in what is known as starved plate (anode) mode. Their B+ voltage is 48V. The tubes are "hand selected" to operate well at this voltage. Due to manufacturing tolerances some tubes in a batch will operate better than others at that low voltage.

Try it and see what happens. If it doesn't work well you can always put the original tube back in.

[Pilgrim]

I've been around long enough to change more than my share of tubes. Just rock the old one side to side to loosen, remove it, then insert the new one. No danger, no sweat. It won't even take long enough for your beer to get warm.

[Matthew_84]

Lol, I wouldn"t do it if it took that long. Thanks guys for your help. I thought that was the case, but wanted to play it safe.

And 90k, no worries about the derailment. I'm not sure where u could pick one up, but I"m sure you can buy some transformer at circuit city or something that will do the trick. I'm not at home right now, but when I get there, I'll check on the ART's specs and let you know. You may even have one lying around from an old phone or something... That's how I've powered two pedals

[Pilgrim]

Originally Posted by 90k

not to derail this tread but I have a quick question, I hope OP doesn't mind.. I am in need of the power supply for one of these and they are no where to be found by me.. Anyone have any suggestions? You can pm me if you do not want to clutter this tread. Thanks

The ART TubeMP uses 9V AC at 700 milliamps according to its website. It can't be too hard to find a wall wart power supply that will put out 9V of AC. A quick web search ought to do it.

[will33]

Originally Posted by jimbilly

12AX7s don't hold a charge. If it's made in England, it's most likely a Mullard, - one of the very-very best vintage tubes. Since it's just a single preamp tube, I'd plug it in and see what happens. The odds of a bad single preamp tube damaging your preamp are super low. If you want to play it 99.99% safe, somebody in your area has a tube tester, amp shops, old organ repair shops, ask on Craigslist in the musical instruments or electronics sections and somebody would probably be happy to test a single tube for a 6 pack, or for free.

+1 for old Mullards.

[Matthew_84]

yup, 9 VAC is correct.

And my tube isn't a Mullard, though now I'm starting to wish it was. It's a Westinghouse, which had some decent reviews inside the TubeMP, but they're all a bit different. Can't wait to try it out. Thanks again guys

[will33]

Some of those can be great too. Find them in old organs a lot.

[Matthew_84]

Awesome! Thanks for that info Will

[90k]

Thanks for the info.. I'll check radio shack.. I purchase my unit on eBay and it didn't come with the power supply. Got way to involved when I went to find one, so it has just been sitting around.

[BassmanPaul]

Parts Express or MCM Electronics should have suitable ones. The only caveat is that you need the correctly sized plug to mate with the MP. THAT you may find at Radio Shack.

[SurferJoe46]

Anyone try these guys?

::::

Antique Electronic Supply

[BassmanPaul]

Yes I have. I like the company a lot.