Valve problems

BobTheDog · Posted: Sun Nov 27, 2011 4:45 am Post subject: Valve problems

Hi Guys,

First of all let me say I know nothing about tube amps.

Have a look at the picture here: http://www.egnateramps.com/download/Rebel30ComboTubeChart.pdf

Now I am getting hiss on channel 1 even when the volume is at 0. This hiss doesn't increase as you raise the volume.

Now does the volume symbol between V1A and V2A/B affect V1A or V2A/B?

Any help would be really appreciated on this.

Cheers

Andy

DrJustice · Posted: Sun Nov 27, 2011 7:42 am Post subject:

Since the hiss is independent of channel 1 volume, the source must be after that, so I'd suspect V2, V4 or P.I.. Since they're all 12AX7 (aka ECC83) valves, I'd just go out and buy one and then replace V1, V2 and P.I. in turn with the new one until the hiss is gone.

I take it that channel 2 is working as normal(?) If it has the same constant hiss too, then V4 and P.I. are prime suspects.

DJ
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BobTheDog · Posted: Sun Nov 27, 2011 9:19 am Post subject:

Hi Are,

Thanks for the info.

I have actually replaced all the 12AX7s with JJ tubes and that just made it worse! The originals where EH ones.

There is hiss on ch2 if the gain is up also, but not if the gain is low.

Maybe I should put a lower gain valve. In V1?

DrJustice · Posted: Sun Nov 27, 2011 12:04 pm Post subject:

Hmmm... but the output of V1 is cut off completely when the volume is at 0. Unfortunately, I can't find a full schematic of the Rebel 30. AFAIK, noise typically comes from the preamp section. One experiment you can do is to listen to the fx send output, and if the noise is not there it has to be further downstream.

DJ
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BobTheDog · Posted: Sun Nov 27, 2011 4:04 pm Post subject:

Ok so the volume in the chain effects the preceding valve.

I have already plugged into the fx return and the hiss goes.

Do you have any recomendations for low noise valves?

I should have stayed with solid state!

DrJustice · Posted: Sun Nov 27, 2011 5:37 pm Post subject:

Sorry Andy, I don't really have a recommendation. But maybe Tube Amp Doctor can help you. The few valves I've bought come from there, German shop. Or is you want to shop in the US, BOI AudioWorks and TubeDepot offer low-noise screening at additional cost.

At least we know that the hiss comes from V2 or V4.

But hey - you being you and all, aren't you getting an Axe-FX II or a Kemper? Very Happy

DJ
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BobTheDog · Posted: Mon Nov 28, 2011 1:32 am Post subject:

Yesterday I emailed hotroxuk in the UK who sell valves and they got back to me recommending Tungsol 12ax7 (premium select) http://www.hotroxuk.com/matched-valves-links-page-12ax7-6l6-909-0/tungsol-valves-12ax7-ef86-2938-0/tung-sol-re-issue-12ax7-set-of-5-mesa-boogie-triaxis.html

I might give em a go, if that doesn't work its going back!

For amp modelling I must admit I really like the Eleven Rack I have, enough to keep me away from the Axe-FX anyway

That Kemper does look interesting though Smile

MadScientist · Joined: Nov 28, 2011 Posts: 63 Location: Denmark

Sorry for jumping into the middle of a conversation in progress. Embarassed

However I had to add my voice to the debate. Generally speaking you will accomplish absolutely nothing, save wasting your money, by 'tube rolling' when trying to fix problems with tube gear. It is unfortunately a common misconception that the tubes themselves are likely to be the cause of most problems. Maybe this is because people's only contemporary experiences with 'tubes' are incandescent light bulbs, which have very limited lifespans.

In general electronic vacuum tubes/valves are much more reliable than people make them out to be. Just think of how infrequently we had to swap picture- and oscilloscope tubes in our TVs and oscilloscopes.

In fact it is a common hoax/gluestick employed by less honest tube sellers to offer complete 'tube replacement kits' for old radios, guitar amps and other consumer appliances. They sell these at high cost to hopeful people, who in reality are likely to own equipment in need of repair, recalibration or outright renovation/restoration. This in particular is highly likely to be the case with equipment from the fifties and sixties, due to the poor quality of the passive components employed in consumer gear at the time.

My 'daily driver' FM broadcast receiver is a Grundig radio from '56 employing vacuum tubes. All the tubes in it are the factory originals, save for one I swapped due to being a perfectionist (the original still worked). However I had to replace roughly 30 passive components, mostly capacitors, as part of a complete restoration to make the radio work reliably.

Rule of thumb: Unless you absolutely *know* that a particular tube is faulty, then you may assume it isn't, and replacing it probably won't accomplish anything positive. This is true even if a tube glows red hot, the internal structure melts and finally the glass cracks. In this case the fault is likely to be elsewhere as well.

Exception: Tubes do wear out, though slowly. Audio output tubes are generally good for thousands of hours, input preamp tubes (anything low power) for tens of thousands of operational hours.

If your amp is new, then it needs to go back. There can be numerous causes for the noise, all of which would be impossible to detect without some serious prodding. This is likely to void the warranty in any case. Also, commercial amps tend to have weird schematics, so guessing at the causes for the problems without access to one will probably not be worthwhile.

I read a few reviews of the amp, and no-one mentions any excess noise. Given the noise is independent of the volume control, and the amp apparently has a preamp tube before it, I'll hazard a guess and say your amp has a more serious issue than simple tube noise. Note that noise in an amplifier device is likely to be most pronounced if if occurs in the first gain stage.

Here are a few potential causes for noise in a tube amp employing high voltage, take your pick:

Faulty passive component (capacitor, resistor), causing internal arching.
Slightly gassy tube, usually seen in the power stages, causing a weak glow discharge. Likely to be invisible.
Incorrect wire dressing/routing, or faulty/missing ground connection, causing parasitic oscillations at a very high (radio) frequency or frequencies. In itself inaudible, but can indirectly cause noise or distortion through rectification down into the audio range (bias fluctuations). May also be due to poor design, which can be a real head scratcher, as the problem may only occur in some implementations of a given schematic and not in others.
Poor electrical connection, like a missing or bad/cold solder connection, or in a tube socket.
Noisy audio preamp tube, it does happen. Some are better than others, though it depends on the signal level how sensitive an amp is to this problem. Line in: Unlikely to be an issue. Microphone or magnetic pickup: Much more problematic.

Frank.

PS: I am almost certain I made a few posts to E-M some years ago, but had to register again as I have been unable to recover my old login information. Please let me know if this is a problem.

BobTheDog · Posted: Mon Nov 28, 2011 5:27 am Post subject:

Hi Frank and welcome back.

Thanks for the advise, I think you have it covered there!

I have just emailed them about getting a replacement.

Cheers

Andy

BobTheDog · Posted: Mon Nov 28, 2011 6:55 am Post subject:

The replacement is arriving tomorrow, lets see how that one goes.

DrJustice · Posted: Mon Nov 28, 2011 7:07 am Post subject:

MadScientist · Joined: Nov 28, 2011 Posts: 63 Location: Denmark

DrJustice · Posted: Mon Nov 28, 2011 2:25 pm Post subject:

BobTheDog · Posted: Mon Nov 28, 2011 2:42 pm Post subject:

So are we saying I should put the hammer away then?

DrJustice · Posted: Mon Nov 28, 2011 2:46 pm Post subject:

No no! Not according to Jeremy Clarkson. It's the only remedy when nothing else works!

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

DJ
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MadScientist · Joined: Nov 28, 2011 Posts: 63 Location: Denmark

BobTheDog · Posted: Fri Dec 02, 2011 8:43 am Post subject:

The new one arrived, exactly the bloody same hiss and hum.

And also a knocking noise like a fan clipping on something, this changes frequency if you angle the amp.

Talked to the dealer, its going back on Monday to be replaced with an Orange TH30.

I have had enough of egnater amps!

Cheers

Andy

DES · Posted: Sun Dec 04, 2011 8:23 pm Post subject:

by any chance is there anything electrical at your house like a furnace, etc. that might be bleeding noise onto the power line? Also, if you're near an airport, etc. you could be picking up RF noise from radio and radar transmitters...

BobTheDog · Posted: Mon Dec 05, 2011 12:47 am Post subject:

Hi Dave,

I think the power is pretty good, everything has conditioners on it as well.

Also I don't have these issues with any other equipment.

About 50 miles from nearest airport.

The Orange TH30 arrives today, lets see if I get similar issues with that.

The support guy at the shop said they get loads of Egnater amps returned but he has never seen an Orange amp returned, so fingers crossed Smile

MadScientist · Joined: Nov 28, 2011 Posts: 63 Location: Denmark

New electronics sold within the EU must comply with the EMC directive on electromagnetic interference. If the amp(s) were able to pick up an airport radar, then they wouldn't be in compliance, and must still be considered defective.

DES · Posted: Mon Dec 05, 2011 9:10 am Post subject:

If you're close enough to an airport or weather type radar system I don't think you could keep it out, lol. Of course you might start to glow from the RF. (actually start to cook from the inside out)...

What I was thinking was that the RF might be getting rectified either in the amp, or more likely, somwhere nearby like guy wires, etc. What can happen is when you have metal mechanically touching metal, corrosion can develope between the two. This makes a semiconductor type junction like a diode...which is a known noise generator. The noise spectrum can extend into the RF bands and bleed into audio and video gear. While it can be blocked it can be costly to do so - its usually more cost and time effective to find the the offending connection....

Hopefully the Orange amp will work out. Razz

BobTheDog · Posted: Mon Dec 05, 2011 9:44 am Post subject:

Ok Guys I know have an Orange TH30, super silence Smile

The only issue I have is with hum whenever something is in the FX loop Sad

BobTheDog · Posted: Mon Dec 05, 2011 10:46 am Post subject:

And the FX-Loop hum is caused by having the cables at the back of the amp, drape them over the front or side and no hum!

That will do me.

MadScientist · Joined: Nov 28, 2011 Posts: 63 Location: Denmark

DES · Posted: Tue Dec 06, 2011 9:56 am Post subject:

Marine nav radars (on civilian boats) have been known to cause issues...I've been involved in tracking down these interference issues many times in the past. Especially if they are starting to fail. diode rectification issues generate broadband noise (both higher and lower in freq.) that can get into everything from TVs, radios, audio systems. Exciting the diode junction usually does take more power in general like from a local commercial radio station or amateur radio station. However it is possible with less power and higher frequencies. Depends on many variables and conditions. RF interference can be very difficult to diagnose/eliminate.