CarlA
373 posts
Jul 13, 2013
4:27 PM
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This happens when I power on one of my tube amps. Lasts a few minutes then the noise ceases. What does this mean, and does it need to be fixed??
Thanks!!
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Rick Davis
2108 posts
Jul 13, 2013
4:56 PM
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LOL... that's a new one.
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-Little Rick Davis
The Blues Harp Amps Blog
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Harpaholic
288 posts
Jul 13, 2013
5:27 PM
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That is a new one! First thing is try a different cord/mic, second swap all the tubes one by one to see if it goes away, if not try a different speaker. If none of the above helps the amp most likely has a problem internally and will need to see an amp doctor.
Last Edited by Harpaholic on Jul 13, 2013 6:54 PM
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nacoran
6926 posts
Jul 13, 2013
6:20 PM
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Oh, that's an easy one! Just turn the volume knob down to a low simmer and add the pasta!
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Nate
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SuperBee
1306 posts
Jul 13, 2013
6:23 PM
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Maybe "motorboating" is the more common term.
Used to have a valve radio did that
I found this:
""In an amplifier that has ever worked correctly once, motorboating is almost always a signal that the decoupling capacitors in the B+ lines of the preamp section are going high impedance, not decoupling properly. Replace the B+ decoupling capacitors at least for the preamp. Since the other capacitors are old, also, consider replacing ALL of the electrolytic capacitors in the amp (doing a cap job - see the Tube Amp FAQ at http://www.eden.com/~keen for info on the what and why of cap jobs.)"
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JellyShakersTipJar
Last Edited by SuperBee on Jul 13, 2013 6:27 PM
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Tuckster
1299 posts
Jul 13, 2013
6:37 PM
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I've had this problem,but it didn't go away on warm up. Turned out to be a bad preamp tube. Maybe one of yours is going south,but not there yet.
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Harpaholic
289 posts
Jul 13, 2013
6:55 PM
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what amp is it?
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CarlA
375 posts
Jul 13, 2013
6:56 PM
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@ MJ
@Superbee
Thanks for the info. It was interesting reading
@Tuckster
I will try changing the preamp tubes. Thanks!
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Greg Heumann
2266 posts
Jul 13, 2013
11:11 PM
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Sounds like a bad tube.
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***************************************************
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BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
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Kingley
2882 posts
Jul 14, 2013
12:55 AM
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Try changing the valves first and see if that cures it.
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CarlA
376 posts
Jul 14, 2013
7:14 AM
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@ Greg
@ Kingsley
It's was a bad 12AY7 tube! It corrected the problem immediately!
I don't know much about amp circuitry, but to me the amp seems to sound MUCH BETTER! Is this possible or is it just my perception?
Either way, thanks to everyone for their input/advice.
-Carl
Ps. At least now my amp doesn't sound like a $1600 dollar kettle-lol
Last Edited by CarlA on Jul 14, 2013 7:15 AM
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Kingley
2884 posts
Jul 14, 2013
7:19 AM
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Glad you got it sorted out. Yes it's very possible that the amp sounds better. Different brands of preamp valves in this case the 12AY7 can have a very noticeable effect on the tone of an amp.
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CarlA
377 posts
Jul 14, 2013
7:28 AM
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@kingsley
Thanks! I like the tone so much that this will probably be my go to amp. Really pleased!
-Carl
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Greg Heumann
2268 posts
Jul 14, 2013
8:54 AM
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The tube was probably failing slowly for a long time and tone suffered. You might not have noticed.
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
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CarlA
378 posts
Jul 14, 2013
8:57 AM
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@ Greg
This is most likely the case! I never really liked the tone of the amp (I bought it second hand) but now that the tubes have all been replaced, this amp really COOKS!!
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Harpaholic
290 posts
Jul 14, 2013
9:43 AM
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Carl, the suspense is killing me! What amp is it?
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CarlA
379 posts
Jul 14, 2013
11:28 AM
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@harpaholic
Sorry I missed your earlier question earlier. The amp in question was my HG 1210. I was planning on selling it earlier on, but I am now elated that I kept it. It was owned by several previous owners, so I should have had the sense to replace all the tubes when I first received it.
Don't get me wrong, the amp sounded GREAT when I first received it, but now it's sounds SUPER! This will definitely be an amp I will by no means sell.
-Carl
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The Iceman
1001 posts
Jul 14, 2013
11:34 AM
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Always carried a 12AX7, 12AU7 and 12AY7 with my amp when I was into that amp sound/stuff.
It was always interesting to switch them out and hear the difference in the amp.
Finally settled on 12AU7 as my favorite.
Why do these different tubes have different effects on the sound?
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The Iceman
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MP
2835 posts
Jul 14, 2013
12:41 PM
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Boiling water?! Love it! :-) i'm used to terms like 60 cycle hum. Glad you got it fixed. cheers!
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MP
affordable reed replacement and repairs.
"making the world a better place, one harmonica at a time"
click user name [MP] for info-
repair videos on YouTube.
you can reach me via Facebook. Mark Prados
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CarlA
380 posts
Jul 14, 2013
12:54 PM
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@MP
My amp knowledge is dreadful, so I was stretching to find a relatable adjective-lol
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Harp2swing
102 posts
Jul 14, 2013
5:52 PM
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Curious to know why you have a 12ay7(45 gain factor) instead of the 12ax7 (100 gain) that normally comes with this Amp. (I have the 4x10 version and it also Cooks. Glad yours is back on track.
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CarlA
381 posts
Jul 14, 2013
6:11 PM
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@harp2swing
It's funny you mentioned that, because I just noticed that on the HG website about 10 minutes ago! Like I stated earlier, it was purchased second hand and previously owned by several members of this board(or so I was told).
Odd thing is, I had the amp sent to Brian Purdy about 4 months ago for a complete inspection, etc and it was sent back with the original tubes which came with it when I bought it(ie: 12at7 and 12 ay7).
Since I replaced those two preamp tubes this morning the amps tone has been vastly improved.
The million dollar question at this point is should I leave it as is, or should I change the preamp tubes to 12ax7???
Any input or opinions???? Now I am a bit confused
-Carl
Last Edited by CarlA on Jul 14, 2013 6:12 PM
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Greg Heumann
2270 posts
Jul 15, 2013
9:10 AM
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Don't change a thing!!! If you like the way it sounds and performs - leave it as is!
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
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MP
2838 posts
Jul 15, 2013
12:27 PM
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CarlA,
i really don't know much about amps other than certain amps i've tried sounded good to me, or not good. I'm in the dark compared to 5F6H and others. What little tech knowledge i've acquired was accidental as i worked in a buy and sell music store once. Used gear tends to have problems. 60 cycle hum was one of them.
as an aside, some older tube amps have 60 cycle hum no matter what you do. Even if you have humbucking pick-ups on your guitar.
i thought the boiling water comment was funny because that is how i would explain something noisy. heh, heh. :-)
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MP
affordable reed replacement and repairs.
"making the world a better place, one harmonica at a time"
click user name [MP] for info-
repair videos on YouTube.
you can reach me via Facebook. Mark Prados
Last Edited by MP on Jul 15, 2013 12:30 PM
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CarlA
383 posts
Jul 16, 2013
10:06 AM
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@ Greg
I agree! I think I will probably just leave it as is.
But just out of curiosity, what general effect do higher gain preamp tubes make on amps (ie: 12Ay7 changed to 12 Ax7)???
I am completely ignorant about amps and their insides
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HawkeyeKane
1887 posts
Jul 16, 2013
10:30 AM
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12AX7 will add more gain, which can do a number of things. Your overall volume can increase...your tone can become more overdriven (some might say harsh)...and your feedback threshold will be much lower in relation to your volume. Try one out in there and see how it sounds. That's the only way you'll know if you like it or not.
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Hawkeye Kane
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barbequebob
2305 posts
Jul 17, 2013
8:09 AM
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Different brands of tubes of all types are going to sound different for reasons like the way tubes are made in terms of the glass, glass thickness, the component design, the grade of the components (military grade means heavy duty everything) and every brand by design is ALWAYS going to sound different and may work well in one amp, and not so good in others, based on the circuit design and what tubes they were originally designed to use. This is true with both newer production as well as NOS tubes.
Sometimes tubes will be microphonic right out of the box regardless if it's new or NOS production.
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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