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Troubleshooting (Read 2265 times)
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Troubleshooting
02/13/13 at 04:19:09
 
Hi all,

I had Rachel on for half an hour, started noticing distortion, then quickly heard most of the bridged-mono signal go out. I quickly stopped the record, turned the volume control all the way down and noticed vu meters hovering around 20 mills. When I turned the volume back up the left meter stayed around 20 mills and the right meter shot up little over 60 mills. I did this all within about 15 seconds from the signal drop before turning the amp off, as I'm paranoid about damage. I check the users manual which I remember mentioning being a way to know a tube went bad.

I have two questions. Does this mean 100% a bad tube is the cause, and if so how do I know which of the two input or output tubes to replace? I only have a spare set of 6N2P but no extra E34L right now.

I've only used the amp for less than 18 hours total since I bought it.

thanks,
78 Arch
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Doorman
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Re: Troubleshooting
Reply #1 - 02/13/13 at 19:10:24
 
Why not change out the tubes you have on hand, and swap the el34's side to side, noting any/all changes---
Don
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Re: Troubleshooting
Reply #2 - 02/14/13 at 00:57:55
 
Don,

I've never had a tube go bad on me in 13 years of using tube amps, this is my first time. Is there no risk to the amp in turning it back on with a bad tube in it?

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Steve Deckert
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Re: Troubleshooting
Reply #3 - 02/14/13 at 03:40:01
 
Don,

You can watch the meters as the tubes warm up and begin to pass current.  Once the meters start to climb it's a matter of seeing where they stop.   If a left channel tube typically draws 40 mills and now draws 20 mills the right channel tube may begin to read higher.  Certainly if the left channel tube was removed completely, the current on the right channel tube will double.

It really doesn't matter what the meters say for the first few minutes as long as one or the other isn't pegged all the way over.  Any longer can cause damage to some amps depending on the amp and what part of the tube is shorted, or how shorted it is.  This would peg the meter pretty quickly in which case you could turn the amplifier off and remove the bad tube avoiding any damage.

Since both output tubes share the same cathode resistor, you will always need both tubes to be in good working order for the meters to read accurately.

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Re: Troubleshooting
Reply #4 - 02/14/13 at 10:45:45
 
Steve,

I don't have a tube tester, are you saying I should just switch one tube out at a time with another until I find the bad tube?

As long as I turn it off after the first 15 seconds which is usually how long it takes for the meters to get up to 40 mills then this won't hurt the amp?

I noticed in the past month the left meter was averaging around 37 or 38 mills while the right meter was at a solid 40. I'm guessing I should try the left output tube first then after a replacement E34L arrives?

thanks
78
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Steve Deckert
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Re: Troubleshooting
Reply #5 - 02/14/13 at 22:02:08
 
The tubes need to match, so they should be replaced as a matched pair.  Within a couple mills is considered an acceptable match (within 10%).  

A yes, turning the amp for that 15 seconds isn't going to hurt anything so long as you're watching the meters.
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Re: Troubleshooting
Reply #6 - 02/15/13 at 17:58:57
 
I ordered a matched pair of the JJ's yesterday.

When they arrive I'll probably install them at night so I can have the room lights off to see tube glow.
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Re: Troubleshooting
Reply #7 - 02/18/13 at 07:52:18
 
Do you have (2) Rachel amps?

I'm considering adding another and bridging to mono. How does this sound? Is it perfect? Subtle degradation to the signal? Safe?

Thanks,
hifitubes
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Re: Troubleshooting
Reply #8 - 02/19/13 at 00:06:09
 
I believe that he has only one amp, bridged into mono, for the purpose of enjoying and preserving his 78 RPM collection.
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marky
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Re: Troubleshooting
Reply #9 - 02/19/13 at 12:29:23
 
Hifitubes, I have had a pair of `Rachaels` bridged as `monos`, for stereo, about a month now. Around 50 hrs playtime.
Still undergoing the `Decware improving with time` period, which, as members are allways reiterating will be a long time.
But, tube selection notwithstanding, ( mid price nos &`dun rolling for a breather` ) the amps are as good as the material being fed in. No surprise there. They go very wide, give excellent sense of depth, and back to front is all there, 3D. Even top to botttom. If the drummer sits above the band thats where he`ll be. Bass, well, I think all bands should give the recording engineer a drink (tip) to record it well, `cos there are times it goes loud`n low,...and extended. Not often they let the kick drum try and pop the cones but listening to some JJ. Cale they did and it was very nice. In fact JJ albums `do` dbl & guitar bass and these amps love it. Treble. You can definately get lost in fluid guitar tone here. S.E.T. mid range heaven. Something that really surpised me was the hitting of metallic objects. Bells, cymballs, rims. Stark, airy, snappy, and they ring with a natural decay new to my ears. I`ve heard a small amount of piano, not solo, and just as the whole deal they sound effortless.
I cant talk about emotional airy fairy stuff but it`s the kind of sound where you just enjoy, and want to play more. And yes I can hear more info into the grooves.
lol, you knew I was going to say that didn`t you, after all I do have  Decware amps. You must get the same sound from your Rachael.

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« Last Edit: 02/19/13 at 12:35:29 by marky »  
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marky
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Re: Troubleshooting
Reply #10 - 02/19/13 at 20:17:32
 
Bit off topic there 78`s.
I think I remember reading long time back that 78`s produce big sonic swings. Maybe the recording gear or the speed which would or should carry more info.
I`ve still got an old wind up in a cupboard that I bought at a boyscout jumble sale. My dad had a small collection of 78`s. Issy Bon kind of stuff. Ah, the old valve gramaphone player & radio in one.  :)
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Re: Troubleshooting
Reply #11 - 02/23/13 at 01:18:41
 
I got my new matched pair of JJ E34L's yesterday. Just installed them, exact same problem is still there. I then switched out the input tubes, turned the amp back on and the problem was there for a few seconds then disappeared, which of course made no sense to me. But I test the attenuator, everything looks fine now both meters reading around 42 mills with the higher gain input tubes, start playing one of my perfect condition 78's, sounds beautiful with pre-amp and Rachel almost at full volume like I'm used to, then half-way through the song I hear what sounds like laser beams shooting out of my speaker. Scared the s*&! out of me, never heard anything like it. I turned the amp off immediately after that. I truly hope this didn't destroy my relatively new speaker.  :'(

Steve,

Any ideas what's going on here? The only tube I haven't switched is the rectifier. It's dark and cloudy here today so I turned the room light off for the two minutes Rachel was doing ok to see the tubes glow. The rectifier tube only had glow at the top, can't remember but is there no glow in the middle or lower part of the tube?


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Re: Troubleshooting
Reply #12 - 02/23/13 at 01:22:00
 
marky,

Not sure what you mean by "big sonic swings" but I can assure you there's nothing wrong with 78s.
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hifitubes
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Re: Troubleshooting
Reply #13 - 02/25/13 at 11:09:47
 
Wow, crazy Decware lasers. Def switch out the rectifier imo.

I think he just meant HDR on your 78s, High Dynamic Range which I'm sure lend a lot of realism to the recordings.

I have one Rachel and considering going Open Baffle. Midrange is creamy but ACCURATE (e.g. John Prine's voice sounds incredibly there).

I would like to consider adding a 2nd Rachel someday.
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marky
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Re: Troubleshooting
Reply #14 - 02/25/13 at 13:49:43
 
Yes good way of putting it. I was hoping for any comments into `how it was` to when 33 & a 1/3rds started up. Any adjustments..or relaxations in the recording and cutting. When researching for a phono there were some phonos that offered several equalisation `curves` for the older discs.
I`m using just one SE341 at the moment. Valve failure. Ordered two more of same  so will have a spare.
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