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Author Topic: Biasing DC30 clone/Tube trouble  (Read 6688 times)
scottlwilson
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« on: April 20, 2009, 03:16:30 AM »
Hello Everyone

I'm new to the forum.  I built a DC30 clone about a year ago.  Great amp that I am very happy with.

Unfortunately, I am having an issue with it causing a tube problem on the right side circuit (rotary tone switch side).  I am wondering if this is because I have not biased the amp and should, or if there is a fault that needs addressing.  Essentially, one tube became microphonic and in the second set of replacement tubes it became quieter and noisy.  I'm guessing it might be a power cap that's gone bad, but I wanted to hit you folks to see if there is a simple issue that requires attention, such as biasing (and the need to be biased).  I have yet to dive into tech'ing the issue, but appreciate any advice up front.

Thanks very much for your insight!!

Scott Wilson
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alwalt
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« Reply #1 on: April 20, 2009, 03:55:59 PM »
I'm not tech at all, but as long as I know there is no need to bias this amp, you just use a matched quad of powertubes (I have already changed my powertubes once, and it only improved the sound!). The EF86 tube is prone to be microphonic, this was my first questión to Nik about the rubber ring that came with that valve.  Did you try another EF86 instead the one you replaced?
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scottlwilson
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« Reply #2 on: April 21, 2009, 04:10:38 PM »
Thanks for the reply!

I replaced the entire set of power tubes, but at this point I'll need to find out which one is the issue and see if there is a fault in that area or if it is just tube quality.  The first set I put in were Ruby and they lasted about a year before one going bad.  The thing that concerns me is the new set has popped one of them as well and now output is lower on that channel.

Thanks

Scott


Quote from: alwalt on April 20, 2009, 03:55:59 PM
I'm not tech at all, but as long as I know there is no need to bias this amp, you just use a matched quad of powertubes (I have already changed my powertubes once, and it only improved the sound!). The EF86 tube is prone to be microphonic, this was my first questión to Nik about the rubber ring that came with that valve.  Did you try another EF86 instead the one you replaced?
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alwalt
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« Reply #3 on: April 21, 2009, 04:51:37 PM »
Well, my first set of JJ's were faulty from the start, but I had asked Nik to include an spare set, so I just replaced them and nothing wrong happened, but the amp came alive. So at that point, I ordered another set from www. eurotubes.com as a new spare set.  I have not test it, I will test it to make sure they're not faulty.

Another thing you can do is to swap the two outer tubes by the two inner tubes, and test the amp on lo power/hi power. If I remember well, this option "cuts out" the two outer tubes on 15 watt setting (you can verify this by looking at the tubes as they go off when you change the power switch).

What is funny is that if your problem is related to powertubes, both channels should be affected, not only the EF86 I believe. That's why I was asking about the EF86 tube...
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hywelg
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« Reply #4 on: April 21, 2009, 08:03:43 PM »
alwalt is right, both channels use the EL84 poweramp tubes. If you get a problem with an amp its good practise to try and find out what is causing it and you can't do that if you change all the tubes at onces.

Pound to a pinch of snuff its the EF86. Channel 1 uses V1 and V2 (ecc83's) and Channel 2 uses v3 alone (EF86). Both channels combine to use all the remaining valves. V4 is the PI (ecc83) that splits the signal to the two pairs of EL84's (v5-v8).

Trial and error with replacement new valves will tell you whats wrong, but you need to do it in stages.
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scottlwilson
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« Reply #5 on: April 22, 2009, 03:03:55 AM »
Excellent.  Will do.  Thanks for your insight!!!  Looking forward to teching it tomorrow sometime.

Thanks very much everyone for your help.

Scott


Quote from: hywelg on April 21, 2009, 08:03:43 PM
alwalt is right, both channels use the EL84 poweramp tubes. If you get a problem with an amp its good practise to try and find out what is causing it and you can't do that if you change all the tubes at onces.

Pound to a pinch of snuff its the EF86. Channel 1 uses V1 and V2 (ecc83's) and Channel 2 uses v3 alone (EF86). Both channels combine to use all the remaining valves. V4 is the PI (ecc83) that splits the signal to the two pairs of EL84's (v5-v8).

Trial and error with replacement new valves will tell you whats wrong, but you need to do it in stages.
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