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Valve problems
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BobTheDog



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PostPosted: Sun Nov 27, 2011 4:45 am    Post subject: Valve problems Reply with quote  Mark this post and the followings unread

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
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DrJustice



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PostPosted: Sun Nov 27, 2011 7:42 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sun Nov 27, 2011 9:19 am    Post subject: Reply with quote  Mark this post and the followings unread

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?
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DrJustice



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PostPosted: Sun Nov 27, 2011 12:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sun Nov 27, 2011 4:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

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!
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DrJustice



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PostPosted: Sun Nov 27, 2011 5:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Mon Nov 28, 2011 1:32 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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MadScientist



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PostPosted: Mon Nov 28, 2011 5:07 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
Very Happy

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.
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BobTheDog



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PostPosted: Mon Nov 28, 2011 5:27 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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BobTheDog



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PostPosted: Mon Nov 28, 2011 6:55 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Mon Nov 28, 2011 7:07 am    Post subject: Reply with quote  Mark this post and the followings unread

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

That's what we all are here for thumleft

You're right of course, in that it may well be passive components or connections. Still, I think tube-rolling is a good first try since it only takes a few minutes to see if it has an effect, especially if your amp is out of warranty and you don't fancy diving into the circuit - and everybody has a few 12AX7 lying around, don't they Laughing

However, if one wants to attempt a simple diagnosis that doesn't require special equipment or knowledge, using a insulated device, poking components and connections, applying a slight pressure, can reveal bad connections (the big daddy of all faults).

But anyway, it seems Andy have the solution in progress... didn't know it was in warranty.

DJ
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MadScientist



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PostPosted: Mon Nov 28, 2011 1:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

DrJustice wrote:
MadScientist wrote:
Sorry for jumping into the middle of a conversation in progress. Embarassed

That's what we all are here for thumleft

Heh. I am trying to decide whether I should post another introductory post in the relevant forum section, assuming I have actually posted one before now. thinking

DrJustice wrote:
You're right of course, in that it may well be passive components or connections. Still, I think tube-rolling is a good first try since it only takes a few minutes to see if it has an effect, especially if your amp is out of warranty and you don't fancy diving into the circuit - and everybody has a few 12AX7 lying around, don't they Laughing

Why yes, of course we do. Cool

I realize my experiences may not be typical, as I mostly work on vintage tube gear and contemporary semiconductor stuff, and rarely on contemporary tube gear. However, as far as I can recall, I don't believe I have been asked to look at any problems beyond normal tube wear, which could have been fixed by a simple tube swap. If a particular tube is too noisy for the intended application, then it is usually obvious the moment it is plugged in.

Worse, then tubes are quite resilient to excessive power dissipation, high heater voltage and similar abuse. As a result you may - after a fashion - 'fix' a problem, at least temporarily, by replacing a dead tube, which was caused by a passive component failure. The previous tube died due to excessive power dissipation or something similar, and the new one may actually last a few hundred hours even when run *way* outside normal ratings. I have seen cases, where people thought it normal that an amp ate tubes for lunch, dinner and supper, and expensive NOS ones at that, because their 'tube rolling' seems to fix things for a while. The real problem was a leaking DC blocking cap, of course...

To me tube rolling to try and fix a problem feels a bit too much like taking the car for a long drive in an attempt to fix a problem with the engine, after having replaced the spark plugs. They are easy to replace and they absolutely can go bad. But chances are if the problem is more severe, you are only going to make things worse by insisting on keeping the car running.

DrJustice wrote:
However, if one wants to attempt a simple diagnosis that doesn't require special equipment or knowledge, using a insulated device, poking components and connections, applying a slight pressure, can reveal bad connections (the big daddy of all faults).

The audience on E-M is almost certainly heads and shoulders above your typical consumer when it comes to handling electronics. Yet in the general case people will make things *much* worse if they attempt your suggestion. I have seen the results in the trenches, and they tend not to be pretty. In desperation and ignorance people will use *way* excessive force in a wain hope of avoiding having to pay someone to find and fix the real problem. This causes the obvious results.

As a direct consequence I no longer issue self help advice for something like this to individuals without at least some experience with building and working with electronics. I have never encountered an instance, where the individual in question actually managed to fix anything.

Say, are you aware that some vintage electronics gear uses resin impregnated paper as a base for printed circuit boards? They burn pretty well... Very Happy

Frank.
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DrJustice



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PostPosted: Mon Nov 28, 2011 2:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

MadScientist wrote:
The audience on E-M is almost certainly heads and shoulders above your typical consumer when it comes to handling electronics.

Indeed. Which is why I feel it's fairly safe to suggest light poking to find bad connections and solderings.
Quote:
Yet in the general case people will make things *much* worse if they attempt your suggestion. I have seen the results in the trenches, and they tend not to be pretty. In desperation and ignorance people will use *way* excessive force in a wain hope of avoiding having to pay someone to find and fix the real problem. This causes the obvious results.

Maybe. I have little experience with 'gorillas' attempting electronics repair Laughing

Over the years I've had great success with the poking and wiggling method, cross testing of easily changed components and sub assemblies with known good ones and also "PCB-massaging" for old computer equipment. I'm likely to use methods like that as an initial attempt at diagnosing, before I spend hours with schematics and instruments. I've never needed to repair tube-equipment since my active ham days though.

Quote:
Say, are you aware that some vintage electronics gear uses resin impregnated paper as a base for printed circuit boards? They burn pretty well... Very Happy

I know, I've seen a few instances of well cooked and burn-marked pertinax Shocked

But we're getting a bit OT here...

DJ
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BobTheDog



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PostPosted: Mon Nov 28, 2011 2:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Mon Nov 28, 2011 2:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.

DJ
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MadScientist



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PostPosted: Mon Nov 28, 2011 2:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

Well, the large, orange mallets made from high density nylon are kind of an universal tool for instant tube gear fixes... Twisted Evil
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BobTheDog



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PostPosted: Fri Dec 02, 2011 8:43 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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DES



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PostPosted: Sun Dec 04, 2011 8:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

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...
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BobTheDog



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PostPosted: Mon Dec 05, 2011 12:47 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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MadScientist



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PostPosted: Mon Dec 05, 2011 1:12 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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DES



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PostPosted: Mon Dec 05, 2011 9:10 am    Post subject: Reply with quote  Mark this post and the followings unread

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

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BobTheDog



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PostPosted: Mon Dec 05, 2011 9:44 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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BobTheDog



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PostPosted: Mon Dec 05, 2011 10:46 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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MadScientist



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PostPosted: Mon Dec 05, 2011 11:31 am    Post subject: Reply with quote  Mark this post and the followings unread

DES wrote:
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....

In theory yes to all of the above, in practice you are overlooking a few things.

Firstly, then the radio beam from a radar isn't continuous when seen from a distance. All you'd hear *if* you receive interference, would be a brief 'click' every time the beam swept by. Radar antennas are amazingly directive, and they simply don't direct the energy anywhere but in a thin, vertical sheet in a single direction at a time.

Secondly, I seriously doubt there are *any* (civilian) radar systems still in service, which operates at a wavelength long enough that a vacuum tube, any vacuum tube, could ever hope to rectify and much less amplify it. The highest series resonant frequency of any of the common receiver vacuum tubes is 800MHz, which happens to be found in a small duo diode intended for RF demodulation. This means it will be very hard to use the tube for rectification above 800MHz, even under ideal, laboratory conditions. The preamp tubes mentioned above, 12AX7, are orders of magnitude worse than this when it comes to processing radio frequencies.

As for parasitic rectifications in rain gutters and more, this is/was a problem mostly associated with powerful medium and shortwave transmitters. Same problem. The natural diodes formed by bad connections are pretty much useless above 50MHz or so. Try making an envelope detector for FM transmissions using an old skool crystal detector some day (100MHz).

Despite the smaller size you are actually much more likely to get interference in your modern cell phone, compared to a piece of vacuum tube equipment. The electronics in there actually are able to rectify and even amplify at least some of the frequencies used in modern radar systems.

DES wrote:
Hopefully the Orange amp will work out. Razz

Yep. Sounds like he has found a solution, so I am just wasting bandwidth here. Should get back to the soldering iron instead. Very Happy

Frank.
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DES



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PostPosted: Tue Dec 06, 2011 9:56 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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