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Ruined Preamp Tube?


Cole

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Posted

In my marshall modded head i have been using a tung-sol 12ax7 in the preamp. I've been searchin around here and

sewatt to find a solution to the slightly frizzy top end. I then decided while my fendery combo is on the worktable why

not try the Jan phillips 5751 in my marshally head. BINGO problem solved! It sounds amazing. My fendery combo had a wierd hum. Its kind of a howling noise that gets louder if you barely hit the pots or switches. Now my head is making this noise so im thinkin it is the tube. I took out the tube to look at it. The 12ax7's pins are shiny and silver but the 5751's pins are blackish gray. Should i pitch this tube? or would just cleaning it work, and what would i clean it with?

Posted

you can try cleaning it.

just don't be harsh.

I use a thin diamond fingernail file.. since it's light and cuts light or medium..

and just try to get all the way around each pin.

subtle pressure, more strokes.

 

tWANG

Posted

I have no idea, ijust know its a Jan Phillips. I bought it about 4-5 months ago, and the writing on it is green. Im thinkin it was about 10-15 bucks so if that tells you anything about it. Thanks twang i'll try that method of cleaning it. What do you think could have caused this?

Posted

Sounds like you just stumble on the cause of your humming problem. To make sure that was actually the cause you could take the tube you pulled from the Marshall and put it in the Fender to see if the problem truely is gone.

Posted

okay time to re-read what you wrote..

So you have a VJ-Head with the 'marshall' mod's that had tung-sol with a frizzy sound

you also had a VJ-combo with 'fendery' mod's that had a hum and a jan-philips

putting the jan in the head got rid of the frizz and sound great but it now has the hum of the combo...

 

so the hum followed the jan-philips

does the combo frizz with the tung-sol in it?

 

Watch out for the marshallized head's they have a tendancy to jumper R6 and pull r7 for the most gain which can cause too much gain going into your el84; possible cause for the frizz sound (the tung 12ax7 has the most gain the jan being a 5771 would have less gain).

 

so it sounds like you had 2 bad pre-amp tubes...

time to visit the tube store.

might as well buy 2 sets of tubes for each amp as spares.

Posted

If the hum goes away with a different preamp tube, you've got a bad tube, obviously. Why did this happen? Because, the tube is a manmade item, and therefore will eventually fail.

 

JAN Phillips are all NOS (or used). There is no such thing as a new production JAN Phillips. Phillips made these for the military, thus the "Joint Army Navy" moniker.

Posted

Yes, the hum followed the Jan phillips so im gonna get a replacement for that. The frizzyness didn't follow the tung-sol so i think it was just too much gain on the head but the 5751 smoothed it out nicely but now is humming. On the head i have R6 at 100k and R7 on a switch with 100k/1meg and i very seldom use the 1 meg so it doesn't have a ton of gain but sounds MUCH better with the 5751. I'll have to order one for each of my amps and get a replacement. And if im hearin you right m-theory my Jan phillips was used when i bought it? Whats a different good brand of 5751?

Thanks!

Posted

Buy yourself some fresh JAN Phillips 5751's from TheTubeStore and savor the good tones. I'm pretty sure TheTubeStore still has the best price going for a 5-pack.

 

I've got couple of old and very rare, gold pin Sylvania GB-5751's in my identical twins (modded VJr amps). Good luck finding those tubes. The went extinct years ago. But I recently bought a few JAN Phillips 5751's. I tried 'em out, but they sounded exactly like the Sylvania's, so the JAN Phillips went back in the box for future reference. Point was, those same two Sylvania's have been in constant use for something like 10 years old now, and they're still sounding good as new! But I know they aren't immortal and they won't last forever. Fortunately, now I'm ready. I have a stash! 8-[

 

Oddly, the modern production Sovtek 5751 sells for the same price as the NOS JAN Phillips tubes, but I'll bet they have the same short lifespan that all modern tubes (especially Sovtek) seem to suffer. Thanks to the EPA and RohS, and God knows what new regulatory agency will step in next, it's now become impossible to make tubes with the quality of metal they had access to in the 60's. NOS tubes simply live a lot longer than modern production tubes. Especially when it comes to preamp tubes.

 

Gil...

Posted
Thanks to the EPA and RohS' date=' and God knows what new regulatory agency will step in next,[/quote']

 

Yet they can put mercury into those energy efficient curly light bulbs that they are trying to push us into buying before 2012.

You can’t put them in the garbage and if you drop and break one in your home you have to have your home decontaminated. #-o8-[

Posted
And if im hearin you right m-theory my Jan phillips was used when i bought it?

not necessarily. It could've been NOS. It just couldn't be new production, since they don't make them anymore.

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