[strat95]

Hi there,

I own AVA gear that use vacuum tubes.  I have a Transcendence Seven EC Preamp and a Fet Valve 400R Amplifier.

I am wondering what signs may be exhibited to show that vacuum tubes need to be replaced?

Currently when I power up my system, I turn on the preamp followed by the amp and after a few seconds I hear a short blast of white noise that lasts for a split second.  Another way to describe the noise is it sounds similar to TV channels broadcasting 'snow', or no signal at all for that matter.

Sometimes late in the evening after the units have been on for a while, sounds of static and pops come through the music almost like the sound of frying bacon... and it makes me feel I need a snack!   This does not happen often, which is good, or I would have serious weight gain!  I wonder if this is related to the tubes or perhaps the quality of power?

The white noise sound while powering on the components has been going on for a while now.  I upgraded to the 400R about a year ago so my guess is it may be the tubes in the T7 EC, which have been in there since it was last upgraded in 2002.

I'm also having a hard time noticing the music sounding any different, such as being softer at the same volume setting or having less punch.

Any insight is appreciated.

Thanks,

Ted

[JerryM]

Call Frank. 

When I had a tube go south in my T8, it sounded like a microphone being rubbed against a person's jacket. It was discernible from my listening area with no music playing, and also during quiet passages. It was a muffled, fluttering sound that disturbed every note of silence.

Most importantly, it was a change from the norm, and had never happened before. A quick swap of tubes remedied the situation.

I'd call Frank. 

Have fun,

Jerry

[avahifi]

First of all, give me a call at 651-330-9871 and I will walk you through the methodology of tracing down your noise issue.

However as this might be of interest to all using tube equipment, or not, here goes as to how to go about it.

Note that all changes that need to be made are to be done only with the equipment turned off and unplugged from AC power except as noted.

First, lets find out if an issue is with your preamp or your power amp.  This one is easy.  Turn off the system, let the amp die down, and then unplug the interconnect cable at the power amplifier so the amp is connected to the speakers, but not to the preamp.  The interconnect cables must be disconnected at the power amp end.

Now turn on the power amp. Obviously its not going to play music now, but does any of the noise issues now reappear?

If not, the power amplifier is off the hook.  If the noise reappears, its the power amp that is guilty. At this point lets assume you have isolated the issue to the power amplifier.

Now, is a one channel or both channel issue? 

In an audio component using vacuum tubes, the most likely part to cause noise is a tube. However it would be very unlikely that the same exact noise would be coming from both channels at the same time unless two channels share the same tube.  If you have the identical noise issue in both channels, the problem is probably not a tube.  Lets assume the noise is a single channel issue. The next step requires that you unplug the unit from AC and remove the cover to access the tubes.  Let the amp sit turned off for an hour or so to allow it too cool off (tubes run very hot) and to allow power supply voltages to discharge.  In a Fet Valve 400R or 600R avoid touching the black heat fins on the vertical regulated power supply board, or on the audio boards, these are at 275 volts DC when the unit is energized.

Assuming it is a single channel issue, the next logical step is to switch the tubes from one channel to the other and see if the noise follows a tube  Do this with only one pair of tubes at a time and make sure you have identified which tubes you are dealing with in a unit using several tubes or kinds of tube.  In the Fet Valve amps there are only two tubes, one 12AT7/ECC81 tube per channel.  Pull them straight out (no twisting!) and swap them to the other channel.  Connect the amp to the speakers only again and turn it on.  Does the noise change channels?  If so you found the issue.  If it does not change channels you have done all you could, but since electronic parts unfortunately do not have little pop up red flags built into them to pop up and say "replace me" the unit now will need professional service attention, almost always the manufacturer can do this best, most economically, and promptly, including us.

If the problem was the same on both channels, check with the manufacturer for more help.

What if the earlier test absolved the amp as the source of the issue?  Well, now lets back up the signal chain.  Put the amp back together and connected to the system.

Now, before turning the AC back on, disconnect all source interconnect cables from the preamp, so it is connected only to the power amp with the volume control turned all the way down.  Now turn on the preamp, wait for it to warm up for 30 seconds, and then turn on the power amp.  Does the issue reappear? If it does, it is a preamp issue because we have eliminated all the sources as they are not now connected to the system.  If it is a tube preamp and it is a one channel issue, its time to do the tube swap thing again.  Follow the routine, turn system off, remove the preamp from the system, unplug from AC, and remove the cover.  If the unit is a recent model of ours, there will be two tubes closest to the front of the unit,  depending upon the model, these could be 12AT7/ECC81, 6N1P, or 6CG7 types.  Assuming the issue still is a one channel issue, swap the two line tubes to the opposite channels and plug the preamp in again.  Does the noise change channels?  If so, you just identified a noisy tube.  If it does not change channels it is a more annoying issue and you should call us for more help if it is an AVA preamp, or not, we will try and help anyone with an equipment issue even if its not our equipment.

If your issue is intermittent, and a single channel issue, note which channel was the problem and then swap the tubes channel to channel in first the power amp and go ahead and play the system again until the problem reappears.  If it changed channels it was a power amp tube.  If not, do the swap the tubes in the preamp routine again and listen again for the issue to come up again.  You can still find the bad tube, if it was a noisy tube, with a bit of patience.

Do remember that a noisy FM tuner, DAC, CD player or whatever connected the system could be the issue if you have eliminated the amp and preamp.  It just takes a bit of logic to figure this out, again we will try and help you with this, a call to us is much less expensive then shipping costs.

Regards,

Frank Van Alstine

[simon wagstaff]

In my case it was a extremely hot glowing tube followed by sparks and flames, hard to miss.

[strat95]

Frank,

Thank you very much for the lengthy reply and procedure to find the source of the problem.  I followed your advice and it sounded like it was one of the 12AT7 tubes in my Fet Valve T7 Preamp, the one on the right channel.  After calling in and speaking to Dean, he recommended I swap tubes for further certainty.  I did as Dean advised and surely enough the swapping of the tubes made the harsh white noise sound when powering up the Preamp and Amp move to the left speaker.

It is so great to own gear that is supported so well by the manufacturer, taking the time and effort to explain and troubleshoot my problem.

Cheers to Frank, Dean, and the rest of the AVA team.

Ted