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Post by Boomzilla on Apr 10, 2013 18:05:20 GMT -5
My Rogue Audio Tempest tube integrated amplifier has switches to change the tubes from ultralinear mode to triode mode. I listened to the amp for awhile this afternoon in triode mode. I then turned off the amp and waited for about a minute and a half. I then switched the amp to ultralinear mode.
When I turned the amp on again, I got a low frequency from the right loudspeaker only. This is not a 60 Hz. hum but rather a moderately loud noise that starts at about 100 Hz. and descends rapidly in frequency. Sounds almost like a doppler shift as if a vehicle was moving away from you.
Any idea as to what's happened? I've not previously seen this behavior from a tube amp. The outputs are two KT88s per channel.
I don't have a tube tester, but I do have a spare tube set. I'm reluctant to put known good tubes in the amp until I'm certain that the amp won't damage the good tubes (KT88s aren't cheap).
Thanks - Boomzilla
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Post by garbulky on Apr 10, 2013 18:16:03 GMT -5
You're tube thought it was an xpa-1 L? Hehe. Sorry. Anyway, I know nothing about tubes but does it mean it's losing it's bias or loose?
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Post by Boomzilla on Apr 10, 2013 18:57:26 GMT -5
Plan A - Switch it back to triode mode and see if the problem persists.
Plan B - Swap a known good tube for the existing output tubes - one at a time
Plan C - Replace the entire output set
Since I know of nobody who has a working tube tester, substitution may be my best option.
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Post by AudioHTIT on Apr 10, 2013 19:33:55 GMT -5
Well I have a tube tester, if you post a picture I'll check it out ... sorry, Garbulky humor.  Your plan sounds ... sound. Reevaluating at each step. |
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Post by Boomzilla on Apr 10, 2013 19:51:42 GMT -5
Curioser and curioser... When I switch the amp back to triode mode it works perfectly and sounds its usual awesome self. Maybe one of the slider switches has gone bad?
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Post by AudioHTIT on Apr 10, 2013 23:37:34 GMT -5
Seems like it could still be a bad tube (though I don't really understand how triode / ultralinear switch works). Do you have a separate switch for each channel? Seems unlikely it would go bad, it was working before you tested triode right?
What about swapping the two tubes within the bad channel to see if there's any difference, or go to your plan B.
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Post by Boomzilla on Apr 11, 2013 2:38:07 GMT -5
The ultralinear switch doubles the gain for the output tube by using intermediate grids on the tube to increase amplification. The amp produces 60 watts per channel in ultralinear mode, 30 in triode mode. There is one miniature slider switch per tube.
Because all tubes appear to work properly in triode mode, I'm thinking that the tubes themselves are fine, but this isn't yet a proven conclusion. Because the unused grids are simply "turned off" by the slider switches for triode mode, those grids may not be completely "turned back on" by a defective slider switch. Alternately, one of the internal grids may be physically or electrically damaged inside the tube. If the latter is the case, then using the tube in triode mode may be the only available option until the tube itself is replaced. The latter, however, seems somewhat unlikely.
Plan B has now shifted a bit; I'll call around town to see if any repair shop (Bob & Ronnie's Live Music, for example) has a tube tester. If the tubes appear to be OK after testing, then checking continuity on the switches will be in order. If a switch has gone bad, I'll see about replacement with better-quality switches. Since the newer Rogue products have a relay switch and can be changed from ultralinear to triode mode via the remote control, I may just put in a similar arrangement for this amp.
The reason I got the fully-tubed amp in the first place was to try it with the Klipsch Cornwalls. Because the DefTech SM65 speakers seem a bit dull with the tubes, I may just eBay the Rogue and go back to my Emotiva gear with the DefTechs. I listened for a while last night with the Mini-X and the DefTechs. Once warmed up, the Mini-X sounded really, really good. Another alternative may be the Rogue Sphinx. That integrated uses a tube preamp with a class-D power amp section. With 100 wpc, the Sphinx would easily drive the DefTechs. I'd really like to wait and see what Emotiva comes out with, though...
Cheers - Boomzilla
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Deleted
Deleted Member
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Post by Deleted on Apr 11, 2013 4:04:07 GMT -5
Maybe this might help. You usually fine one of these at the local family owned drug store or grocery store. There can be quite a learning curve but look for the operations manual usually hanging by a string on the side of the machine. Good luck!  |
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Post by Boomzilla on Apr 11, 2013 4:57:56 GMT -5
I've not seen one of those since I was in high school!
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guitarforlife
Sensei
Just another busy day in Northern Wisconsin.
Posts: 947
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Post by guitarforlife on Apr 11, 2013 5:23:25 GMT -5
Boom, I could be 100% wrong on this.
But from playing tube amps(guitar amps) for the 35years.
when they would buzzz I would switch the polarity and that would do the trick. Or I would change outlets. It was always a ground problem.
I always had spear tubes and I would test them in the amp but that was never the trouble.
But that was guitar amps.
And to tell you the truth when my tubes would go they would just go.
Like the amp would just stop working.
Just my 2 cents. good luck.
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Post by Boomzilla on Apr 11, 2013 6:40:21 GMT -5
Thanks, guitarforlife -
Since this isn't a typical hum or buzz, I'm thinking it's not a polarity problem. Also, since the amp plays perfectly in triode mode, and through the same outlet, I'm also not thinking polarity. I appreciate the suggestion, though. I can't change the power supply polarity since the amp uses a three-pin, grounded IEC cable.
Thanks again for your suggestion, though; I really appreciate it. Boom
PS: I will get to the bottom of the problem and will post the solution when I have one.
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Post by mgbpuff on Apr 11, 2013 7:38:11 GMT -5
Swap both left channel tubes with the right channel tubes. If the hum switches channels, the tubes are the problem. If the hum is still in the same channel, then the switch for that channel or a grid resistor for that channel my be defective. The switch may have a tendency to oxidize, thus the reason for relays in later products by Rogue.
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Post by Boomzilla on Apr 11, 2013 7:48:53 GMT -5
THANKS, mgbpuff - Great suggestions. I'll implement them pronto & see what happens.
Boom
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Post by Boomzilla on Apr 11, 2013 8:34:57 GMT -5
Well, I swapped the tube pairs and the noise stays in the original channel, so the tubes aren't to blame. It's either a switch problem (my best guess) or one of the resistors has toasted.
Unfortunately, the circuits aren't on a single-plane board. There is a daughter-board that is mounted above the main board and I'm just tempted to have it done by a shop. If I felt ambitious, I'd disassemble it myself and go to town, but my time is limited.
I've about had it with tube power amp sections. I'm zero for two on recent purchases. The VTL monoblocks are STILL at the shop (shop's trying to find new transformers) and the Rogue (supposedly a pretty reliable design) has now flaked out.
I'm thinking a hybrid design would offer most of the advantages of tubes with far better reliability. Come on, Emotiva - help me out!
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KeithL
Administrator 
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Post by KeithL on Apr 11, 2013 8:47:11 GMT -5
You are getting some sort of oscillation. In ultralinear mode the additional active grid is tied to a separate winding on the output transformer; in triode mode it is tied to B+ through a resistor (usually). Tying that grid to the transformer gives you more power and lower distortion (which is why its there). It could be that the tube, the switch, or one of the few components is bad. It could also be that, since an ultralinear connection uses the transformer for feedback, and so is a bit more critical of other circuit design parameters, there is some other problem which is simply being exposed in that mode. Check the tubes first (couldn't hurt), slide the switches back and forth several times each (in case the contacts are dirty); if one switch is dirty it certainly could cause something like that to happen. If those aren't it, then have someone look at the amp - problems like this can be tricky to locate but shouldn't involve anything expensive to fix. The ultralinear switch doubles the gain for the output tube by using intermediate grids on the tube to increase amplification. The amp produces 60 watts per channel in ultralinear mode, 30 in triode mode. There is one miniature slider switch per tube. Because all tubes appear to work properly in triode mode, I'm thinking that the tubes themselves are fine, but this isn't yet a proven conclusion. Because the unused grids are simply "turned off" by the slider switches for triode mode, those grids may not be completely "turned back on" by a defective slider switch. Alternately, one of the internal grids may be physically or electrically damaged inside the tube. If the latter is the case, then using the tube in triode mode may be the only available option until the tube itself is replaced. The latter, however, seems somewhat unlikely. Plan B has now shifted a bit; I'll call around town to see if any repair shop (Bob & Ronnie's Live Music, for example) has a tube tester. If the tubes appear to be OK after testing, then checking continuity on the switches will be in order. If a switch has gone bad, I'll see about replacement with better-quality switches. Since the newer Rogue products have a relay switch and can be changed from ultralinear to triode mode via the remote control, I may just put in a similar arrangement for this amp. The reason I got the fully-tubed amp in the first place was to try it with the Klipsch Cornwalls. Because the DefTech SM65 speakers seem a bit dull with the tubes, I may just eBay the Rogue and go back to my Emotiva gear with the DefTechs. I listened for a while last night with the Mini-X and the DefTechs. Once warmed up, the Mini-X sounded really, really good. Another alternative may be the Rogue Sphinx. That integrated uses a tube preamp with a class-D power amp section. With 100 wpc, the Sphinx would easily drive the DefTechs. I'd really like to wait and see what Emotiva comes out with, though... Cheers - Boomzilla |
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KeithL
Administrator
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Post by KeithL on Apr 11, 2013 8:51:27 GMT -5
How about a hybrid SYSTEM...... In other words, use a tube preamp and a solid state power amp..... Well, I swapped the tube pairs and the noise stays in the original channel, so the tubes aren't to blame. It's either a switch problem (my best guess) or one of the resistors has toasted. Unfortunately, the circuits aren't on a single-plane board. There is a daughter-board that is mounted above the main board and I'm just tempted to have it done by a shop. If I felt ambitious, I'd disassemble it myself and go to town, but my time is limited. I've about had it with tube power amp sections. I'm zero for two on recent purchases. The VTL monoblocks are STILL at the shop (shop's trying to find new transformers) and the Rogue (supposedly a pretty reliable design) has now flaked out. I'm thinking a hybrid design would offer most of the advantages of tubes with far better reliability. Come on, Emotiva - help me out! |
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Post by Boomzilla on Apr 11, 2013 11:02:04 GMT -5
Thanks, KeithL -
The ultralinear mode worked fine about a week ago. I'll exercise the switches a bit to see if I can get them functioning. If not, I'll have the switches replaced with physical jumpers.
I agree that a hybrid integrated sounds like what I want. I'm hoping Emotiva will offer one soon. If not, then the Rogue Audio Sphinx or the (Chinese) Yaqin VK-2100 may suffice.
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emovac
Emo VIPs 
Saeed al-Sahhaf
Posts: 2,456
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Post by emovac on Apr 11, 2013 20:07:09 GMT -5
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