Orange Amps Forum

So I swapped out a microphonic preamp tube on my TT. when I replaced it with the new one I noticed when I preformed the "tap test" again it was an even sound with the other preamp tube but it was still much more audible through the speakers. It happens to be the preamp closest to the output transformer and furthest from the main. since its a tiny terror it is the preamp on the right side (looking at the face of the head) and above the gain knob. So I guess what im wondering is if in the TT or in tube amps in general if it is normal to have the preamp for this stage be more audibly noticeable then the others or is this the sign of a bad socket or whatever is in/order the socket? The amp does sound great again now that I have done the swap. it was overly fizzy and now its back to its gearthy, sweet self. Any thoughts are appreciated.

Okay well I have done some more research and according to another brands web site it is normal for the valve closer to the input to be louder since it is being pushed be the other tubes? Hopefully this is a halfway correct answer as the TT has been a workhorse and has a voice which I love compared to the other low watt amps on the market. I would hate to have to pay to take it to my towns legendary (expensive lol) amp tech. by the way the JJ's sound MUCH better than the ehx or groove tubes I also tried in it, I also found the mix of an ecc83 and 12ax7 to be a little nicer to my ears at least. Don't know if there is a valid difference but I have heard the 12ax7's have a little more output/gain. not sure if this is valid. Anyways it seems I have at least a little better idea but I would prefer to hear some thoughts from other "Orange" owners.

Alan H. wrote:Okay well I have done some more research and according to another brands web site it is normal for the valve closer to the input to be louder since it is being pushed be the other tubes? Hopefully this is a halfway correct answer as the TT has been a workhorse and has a voice which I love compared to the other low watt amps on the market. I would hate to have to pay to take it to my towns legendary (expensive lol) amp tech. by the way the JJ's sound MUCH better than the ehx or groove tubes I also tried in it, I also found the mix of an ecc83 and 12ax7 to be a little nicer to my ears at least. Don't know if there is a valid difference but I have heard the 12ax7's have a little more output/gain. not sure if this is valid. Anyways it seems I have at least a little better idea but I would prefer to hear some thoughts from other "Orange" owners.

Yeah the first stage preamp valve (nearest the input in 99% of amps) will be amplified by all following stages, so that's normal.

ECC = 12AX7. Those are just the European / US terms for the same valve type.


Andy.

Just so ya know if the amp isn't howling or making weird overtones or anything at higher volume,don't tap the tubes I ruined a NOS JAN Sylvania 12ax7 doing the #2 pencil thing. Longplates tend to be more prone to microphonics than shortys but still...best to not fix it if it ain't broke as far as microphonics go...ya know.
Also grab a couple New Sensor Mullard 12ax7s the TT sounds sweet with them(in the PI atleast)

Any tube that dies after being tapped by a pencil probably wouldn't have survived long in an amp anyway, especially not a gigging one.

Interesting old technical paper from Mullard on cause of microphony here:
http://www.pearl-hifi.com/06_Lit_Archiv ... ophony.pdf" onclick="window.open(this.href);return false;

If the amp sounds normal and good, I wouldn't worry about how tapping sounds.

jontheid wrote:Any tube that dies after being tapped by a pencil probably wouldn't have survived long in an amp anyway, especially not a gigging one.

+1000. Good valves are in fact surprisingly robust. You obviously don't want to mishandle them but they have to be able to take at least some shock / vibration in their stride. Remember that they used to build them into jet fighters, spacecraft etc. In fact they are still used for radar and even in some spacecraft where things will (literally) get too hot for some solid state components, such as landers for the 'rather warm' planet Venus!

Duff valves are only going to get duffer, and it is good to be able to weed them out. Don't worry about making a good valve into a duffer just by giving it a couple of gentle taps though - that is totally OTT!

jontheid wrote:Interesting old technical paper from Mullard on cause of microphony here:
http://www.pearl-hifi.com/06_Lit_Archiv ... ophony.pdf" onclick="window.open(this.href);return false;

Great link jontheid - will read that through later. But yeah I see there is even mention there of a machine built specifically to test (and measure) microphony by 'shock excitation' = tapping the valve with something!

Jondog wrote:If the amp sounds normal and good, I wouldn't worry about how tapping sounds.

Sure. All valves are at least slightly microphonic but that is only a problem if it becomes a problem. If the amp sounds fine, fine. If not tap testing is helpful for tracking down problem valves. What you are actually testing for though is excessive microphonics.


Andy.

jontheid wrote:Any tube that dies after being tapped by a pencil probably wouldn't have survived long in an amp anyway, especially not a gigging one.

Yes true but my "wacking" tubes when I first started swapping tubes some years back,just to "test" them caused what was a decent sounding Sylvania to become a Howling unusable tube after a good wack.

Guitar-Sam wrote:

jontheid wrote:Any tube that dies after being tapped by a pencil probably wouldn't have survived long in an amp anyway, especially not a gigging one.

Yes true but my "wacking" tubes when I first started swapping tubes some years back,just to "test" them caused what was a decent sounding Sylvania to become a Howling unusable tube after a good wack.

Well you maybe hit it too hard then? There is a difference between tapping something gently and giving it a good whack!


Andy.

VT1000. All solved. No whacking/tapping necessary

Jondog wrote:VT1000. All solved. No whacking/tapping necessary

Thought it didn't test for microphonics. Not to worry though, tapping works for me...


Andy.

a.hun wrote:

Jondog wrote:VT1000. All solved. No whacking/tapping necessary

Thought it didn't test for microphonics. Not to worry though, tapping works for me...


Andy.

Really don't know. It'll tell you if a tube is almost worn out I think.

Yep, it'll rate a valve as 'meaty', 'stringy' or 'gone off'. (Or something to that effect.)
But not for noisy or screechy. That is what amplifiers and your ears are for.

http://www.orangeamps.com/products/acce ... nt/vt1000/" onclick="window.open(this.href);return false;


Andy.

a.hun wrote:...There is a difference between tapping something gently and giving it a good whack!

Sometimes the situation requires both techniques...