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theoman

Moth Audio 45

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the amp sounds great but it has a hum and the guys on AK sent me over here. I don't know the how or what the bias should be?

I can't find and info on them. I tried Craig but no reply. IMG_7381.thumb.JPG.3c6e282da59cad0d2d35c09b44d86899.JPG

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56 minutes ago, theoman said:

the amp sounds great but it has a hum and the guys on AK sent me over here. I don't know the how or what the bias should be?

I can't find and info on them. I tried Craig but no reply. IMG_7381.thumb.JPG.3c6e282da59cad0d2d35c09b44d86899.JPG

 

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What brand are those output tubes? Do you have a way to test them?

 

I'm taking a guess that it sounds like 120Hz hum, from what could be the filaments...maybe power supply related?

Another guess that the amplifier doesn't have bias adjustment. But it should or might have hum adjustment pots.

 

If it does, did you try adjusting for least hum?

 

Nice amp. Those are some good sized output transformers.

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Some things you might try.

 

If it has a Hum/Buzz control try adjusting it.

 

If you remove the input cables to the amplifier do you still hear the buzz..? It's actually best to use RCA shorting plugs on the input for this test if you have any. 

 

Is all the equipment plugged into the same AC outlet ..?

 

Any AC plugs that are non-polarzed (ie: 2 prongs of equal size) can be reversed in the ac receptacle to see if that reduces the buzz.

 

Another thing to check for would be if you are using any light dimmers try turning them totally off and see if the buzz goes away.

 

miketn 

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4 minutes ago, mike stehr said:

What brand are those output tubes? Do you have a way to test them?

 

I'm taking a guess that it sounds like 120Hz hum, from what could be the filaments...maybe power supply related?

Another guess that the amplifier doesn't have bias adjustment. But it should or might have hum adjustment pots.

 

If it does, did you try adjusting for least hum?

 

Nice amp. Those are some good sized output transformers.

here's the tubes. that would be great if it is. what brand is this? is it cheap?IMG_7393.thumb.JPG.186f1520a5808e5ac0d85fe8b36216d4.JPG

 

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2 minutes ago, mikebse2a3 said:

Some things you might try.

 

If it has a Hum/Buzz control try adjusting it.

 

If you remove the input cables to the amplifier do you still hear the buzz..? It's actually best to use RCA shorting plugs on the input for this test if you have any. 

 

Is all the equipment plugged into the same AC outlet ..?

 

Any AC plugs that are non-polarzed (ie: 2 prongs of equal size) can be reversed in the ac receptacle to see if that reduces the buzz.

 

Another thing to check for would be if you are using any light dimmers try turning them totally off and see if the buzz goes away.

 

miketn 

buzz at all volumes with nothing connected. heres the buzz

 

 

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Been trying to fix.... anyway Google 

 

JJ 2A3-40 data sheet to learn about the tubes and you will find the 6 moon review as well. 

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1 hour ago, theoman said:

no buzz when the when I pull the rectifier tube outs it have to be a ground

 

Could be ground or capacitor or design issues. 

 

If you can find a schematic and/or comfortable working with amplifiers you can take pictures of it's internal construction then we might can help more.

 

CAUTION:  Be careful it's possible if not designed with power supply bleeder resistors to have 250v to 400v stored in the pwr supply capacitors. 

 

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Is the Moth 45 an amplifier for 45 type output tubes, or is a convertible amp which can also use 2A3 or 300B?

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9 hours ago, mike stehr said:

Is the Moth 45 an amplifier for 45 type output tubes, or is a convertible amp which can also use 2A3 or 300B?

It also can take 45B's

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9 hours ago, mikebse2a3 said:

 

Could be ground or capacitor or design issues. 

 

If you can find a schematic and/or comfortable working with amplifiers you can take pictures of it's internal construction then we might can help more.

 

CAUTION:  Be careful it's possible if not designed with power supply bleeder resistors to have 250v to 400v stored in the pwr supply capacitors. 

 

I can't find a schematic.

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