Tube Amp distortion over time. Help needed ...
Jul 14, 2008 at 8:32 PM Thread Starter Post #1 of 22

epaludo

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Hey guys,
I own a Mapletree Audio Design Ear+ Purist HD2. I always enjoyed it, but a while ago it started to distort the sound after some time playing (about 10 min.). Don't know what that could be, but i'd shoot some of the tubes problem. Apparently the amp adds distortion after the tubes (or some other component) warms up.
I'd love to get this issue fixed once i really enjoy the HD2 sound and wanna be able to listen to it with no problems again.
Thanks in advance, any thoughts will be highly appreciated ...
 
Jul 14, 2008 at 10:43 PM Post #3 of 22

Uncle Erik

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If it takes some time before distorting, that sounds like an issue with heat. It could be a tube, so I would suggest ordering another set to see if that fixes it. If you have access to a tube tester, then check them out.

It is possible for components (resistors, caps, etc.) to drift when they get hot. That shows up as distortion and can be tricky to hunt down because you usually test components cold. You have to be very, very careful, but there is a way to find the component that's acting up. Open up the amp and let it get to where it distorts. Take a can of compressed air/coolant and hit each component with it. This should cool it off enough to stop distorting. When you spray the one that stops distortion, that's the one to replace. This involves a live chassis, so you have to be super careful.
 
Jul 14, 2008 at 10:52 PM Post #4 of 22

sacd lover

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Quote:

Originally Posted by Nick 214 /img/forum/go_quote.gif
how long have you had the same tubes in the amp?

They may need re-biased...




The tubes in the Mapletree amps are self-biasing. So there is no bias adjustment.

The amp uses a single ECC99 for output duty. The ECC99 is a new production tube that is prone to section mismatches and the tubes life is much shorter than a nos tube. If you are using a new production 12ax7/5751 that tube will also have a shorter lifespan. I would try some new tubes ands see if that corrects the problem.
 
Jul 14, 2008 at 11:09 PM Post #5 of 22

M0T0XGUY

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Have you mentioned the problem to Dr. Peppard of MAD yet? Even if you bought your unit used or have run out of warranty, I think he'd be willing to offer a helpful suggestion or two concerning the matter. Either way, the majority of sonic issues with tube amps originate in the tubes themselves (with the other majority lying in output transformers); so I'd look into buying a full set of new tubes and go from there.
 
Jul 14, 2008 at 11:22 PM Post #6 of 22

Pricklely Peete

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Unlce Eriks advice is spot on. Visually inspect the parts, look for bulging tops on the electrolytic caps, leaking, discoloration, the resistors might show some discoloration or nothing at all, that's why Erik's suggestion of active spot cooling during operation is an effective method for nailing down the culprit.

First off.......The obvious place to start is with new tubes known to be working properly. Try that before the internal inspection, if it solves your distortion problem...then that's great
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Peete.
 
Jul 15, 2008 at 3:04 AM Post #8 of 22

Pricklely Peete

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Quote:

Originally Posted by olblueyez /img/forum/go_quote.gif
Wouldnt it be better to use Uncle Eriks compressed air trick before you invest in new tubes?


Not if the tubes in question are old (have been in use for quite a while). Besides having extra tubes for your tube amp is a necessity IMO, otherwise how do you narrow down certain easily cured issues ? Swapping out tubes is far easier than opening the case up, poking around and exposing yourself to potentially lethal voltages
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Best to test tubes first.....that's rule no 1 (IMHO) with any tube based gear.

Peete.
 
Jul 15, 2008 at 3:24 AM Post #9 of 22

M0T0XGUY

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Quote:

Originally Posted by olblueyez /img/forum/go_quote.gif
Wouldnt it be better to use Uncle Eriks compressed air trick before you invest in new tubes?


The EAR+ HD2's tubes really aren't that expensive, and UncleErik's testing method is quite dangerous when you consider the voltages involved in these electronics. Plus, since all of the MAD's components are fixed to the underside of the casing, you'd have to flip the amp upside to test for any malfunctions.
 
Jul 15, 2008 at 6:15 AM Post #11 of 22

Pricklely Peete

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Quote:

Originally Posted by olblueyez /img/forum/go_quote.gif
And when you replace the tubes and the problem is still there?


It's called Plan B.
rolleyes.gif


Peete.
 
Jul 15, 2008 at 9:27 PM Post #13 of 22

Skylab

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When there is an issue of that sort with a tube amp, it really is almost always the tubes. But one free thing you can try first - take the tubes out, clean the pins with some contact cleaner, and then re-insert and fire it up. Sometimes that is all that is needed.
 
Jul 16, 2008 at 5:55 PM Post #14 of 22

epaludo

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Quote:

Originally Posted by Skylab /img/forum/go_quote.gif
When there is an issue of that sort with a tube amp, it really is almost always the tubes. But one free thing you can try first - take the tubes out, clean the pins with some contact cleaner, and then re-insert and fire it up. Sometimes that is all that is needed.


That's a good tip, i'll try that later. Is there a way to clean the tube pin socket on the amp itself?
 
Jul 16, 2008 at 6:36 PM Post #15 of 22

Pricklely Peete

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Quote:

Originally Posted by olblueyez /img/forum/go_quote.gif
Sounds like wasting money on tubes to me.


Do you happen to have extra light bulbs at home or are those a waste of money as well ?

How about a positive contribution towards the OP's problem...just a thought...
rolleyes.gif


Peete.
 

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