I dropped my amp and now it hisses again! Help!

[poweredbypoptarts]

GAAAH!

Tonight was suppose to be the night when I finished working on my Elk amp. All the caps have been changed out. I had new 12AX7 tubes in place. My AC ripple on my B supplies was near to nothing. I was done done done done! On the bench my amp sounded KA-LEEEEN!

I was flipping my chassis over and I lost my grip. It fell down flat - HARD. I cursed at myself but didn't take much notice of it... until I turned it on. All the hiss that I had worked so hard to eliminate was back. I started removing tubes one by one starting from the pre-amp to the phase splitter. As each 12AX7 tube came out the hiss and crackle became less and less. When the last one was out and all I had left was my rectifier and EL84's there was silence. Then I added them back in, one at a time, and the noise got louder and louder.

AAAAAAAAAAAAAARRRRGGGGGHHHHHHHH!

The 12AX7 tubes were purchased new from Tube Depot. They are Electro Harmonix units.

I read on some other forum (can't remember where) that all 12AX7 tubes are microphonic. Is that really true? If my amp gets bumped again will another set of 12AX7 tubes go bad? What can I put in their place that is a bit tougher? Should I go with another brand like JJ?

This episode just cost me something like $36!!

And what is it with all these Google Malware warnings I get when I try to visit this site?!

-=- Boris

[Enzo]

Microphonics does not mean the tube is ruined, it is just a natural phenomenon. Some are moreso than others. And it matters a great deal which stage we look at. The first or input stage will naturally be a lot more sensitive than the later stages.

Hiss is not likely microphonics.

If you "fix" a problem, and whacking the amp makes it come back, I might think I hadn't really fixed it the first time. A lot of times just opening an amp or moving things around in it will temporarily stop a symptom. This happens when an iffy connection heals itself enough to disappear. People have a symptom, flip the board over, solder some part, then put it back together and problem is gone. Only later the problem reappears because the thing they soldered was not the issue, but moving it all around changed what was at fault.

All tubes in. Turn all controls to zero, still hiss? Turn all controls up to normal settings, hiss there I assume? Now turn each control up and dowwn. Which controls affect the hiss is ANY WAY? ANy change its volume or tone?

[poweredbypoptarts]

Microphonics does not mean the tube is ruined, it is just a natural phenomenon. Some are moreso than others. And it matters a great deal which stage we look at. The first or input stage will naturally be a lot more sensitive than the later stages.

Hiss is not likely microphonics.

If you "fix" a problem, and whacking the amp makes it come back, I might think I hadn't really fixed it the first time. A lot of times just opening an amp or moving things around in it will temporarily stop a symptom. This happens when an iffy connection heals itself enough to disappear. People have a symptom, flip the board over, solder some part, then put it back together and problem is gone. Only later the problem reappears because the thing they soldered was not the issue, but moving it all around changed what was at fault.

All tubes in. Turn all controls to zero, still hiss? Turn all controls up to normal settings, hiss there I assume? Now turn each control up and dowwn. Which controls affect the hiss is ANY WAY? ANy change its volume or tone?

All controls at zero = hiss and pop.
Controls to "normal" = hiss and pop.
Manipulating controls does not affect hiss and pop.
There is no change in its volume and tone.

-=- Boris

[soundguruman]

GAAAH!

Tonight was suppose to be the night when I finished working on my Elk amp. All the caps have been changed out. I had new 12AX7 tubes in place. My AC ripple on my B supplies was near to nothing. I was done done done done! On the bench my amp sounded KA-LEEEEN!

I was flipping my chassis over and I lost my grip. It fell down flat - HARD. I cursed at myself but didn't take much notice of it... until I turned it on. All the hiss that I had worked so hard to eliminate was back. I started removing tubes one by one starting from the pre-amp to the phase splitter. As each 12AX7 tube came out the hiss and crackle became less and less. When the last one was out and all I had left was my rectifier and EL84's there was silence. Then I added them back in, one at a time, and the noise got louder and louder.

AAAAAAAAAAAAAARRRRGGGGGHHHHHHHH!

The 12AX7 tubes were purchased new from Tube Depot. They are Electro Harmonix units.

I read on some other forum (can't remember where) that all 12AX7 tubes are microphonic. Is that really true? If my amp gets bumped again will another set of 12AX7 tubes go bad? What can I put in their place that is a bit tougher? Should I go with another brand like JJ?

This episode just cost me something like $36!!

And what is it with all these Google Malware warnings I get when I try to visit this site?!

-=- Boris

ALL tubes are microphonic, there is no such thing as a non microphonic tube. Never has been...
However, you can select "low microphonic" tubes...by hand, one by one...
If you dropped it, the tubes can be replaced, the solder joints can be re-soldered.
That's pretty much it.
I have little faith in "NOS" tubes. I would rather buy new ones.
JJ has been pretty consistent, at a reasonable price. I have almost zero problems with JJ tubes, very pleased. But they are not drop proof.
So, now you know, pretty much what to do.

[poweredbypoptarts]

Update: With the whole family awake now (it's the afternoon, next day) I decided to play through the amp a little. This time I was able to crank it a bit and strum harder. Something very interesting happened. The hiss almost disappeared after some hard playing! It isn't as quiet as before the drop but it's a lot quieter than immediately after the drop. If I let the amp sit then the hiss slowly comes back but less. I can once again lower it by some hard strumming and before it comes back yet again. The amp also crackles and pops a bit sometimes too but then stops.

Can someone explain this?

I'm going the let the amp sit idling for a while and see if something in the tubes just needs to "burn off" after being "shaken around".

Either way, I think I need new tubes so I haven't escaped that consequence.

-=- Boris

[soundguruman]

Bad tubes, or bad solder connections, that's it. Resolder the circuit board and test again.

[g1]

Does wiggling the tubes in their sockets make any difference to the noise? If so, it may be as simple as dirty/oxidized tube sockets, try cleaning them if you haven't already done so.

[poweredbypoptarts]

i haven't tried wiggling the tubes. Wouldn't that make a microphonic tube go crazy? Cleaning the sockets sounds like a good idea. How do I go about doing it?

I poked the circuit board with a wooden chop stick and nothing crackled or changed with the pokes. There were some microphonic moments but the hiss didn't change. I have a VHT Special 6 Ultra amp that has two 12AX7 tubes. When I put those tubes in the Elk the hiss was seemingly cut in half. Then, when I strummed hard the noise disappeared. It came back after a little bit but a good hard strum seems to clear it each time.

I strongly suspect the tubes got a good rattle when I dropped the amp and something inside them is damaged. Playing hard through the amp may be increasing the current, temperature, electron flow, etc and burning something off.

-=- Boris

[olddawg]

12ax7s are not that expensive. You need at least one fresh new one to swap in and out with the current tubes to see if it indeed makes a difference. It could also be old carbon composition resistors as well. Resistors can be microphonic and intermittent too. A little freeze mist might help in isolating the problem if you don't have a scope. Btw, I AM a BIG fan of NOS tubes. Of course you can get a bad one just like you can get a bad new tube right out of the box. But I at least try to put a NOS tube in V1 of all of my amps. I have a 50 year old RCA 12ax7 in my go to am I pulled from a crushed clock radio. Huge noticeable difference.