My new JE Labs Simple 2A3/45 amp

If cleaning the hum pots doesn’t work you might want to try these. Are you thinking about selling it? Or trade?

Dennis


Would be nice if it's just the hum pots and/or a DC supply were to fix the problem. However the Redboy 45 here is really close if not the exact circuit and I'm perfectly happy with it's level of hum. I'm afraid it's more of the transformer alignment like @paulbottlehead noted. Do you recall it having a hum when you had it?
 
Sadly, I've shelved this amp and have gone back the Redboy 45.

As @paulbottlehead noted, it does have quite a bit of 60hz hum. Lived with a quite a while, going back really made me realize how bad it was. Not sure what I'm going to do with it at this point.

Wondering if there might be an easy fix, or what steps to take to try and reduce or eliminate it. First step when I get a chance I'm going to clean the hum pots. They were pretty scratchy and did reduce the hum, but not enough.
The only way to reduce the hum entirely is to go with DC filaments.

If it is being induced by the power transformer, you could rotate the output transformers 90 degrees.
 
The only way to reduce the hum entirely is to go with DC filaments.

If it is being induced by the power transformer, you could rotate the output transformers 90 degrees.
Was also going to suggest just rotating the output transformers 90 degrees and see if that helps.

Should be a quick and easy fix.
 
Would be nice if it's just the hum pots and/or a DC supply were to fix the problem. However the Redboy 45 here is really close if not the exact circuit and I'm perfectly happy with it's level of hum. I'm afraid it's more of the transformer alignment like @paulbottlehead noted. Do you recall it having a hum when you had it?
The system I had at the time had 2 Altec 288 CD which are 115db efficient so almost every amp had a bit of hum. However unless the hum is very sever the hum disappears when the music starts.
 
I’ve built SE amps with AC filaments mainly to see how severe the hum is. A DHT with filament voltage below 2.5V is acceptable for AC, depending on how sensitive you are to hum. However, it is so easy to use modern 3 terminal regulators, there is almost no excuse not to have DC filaments.

Don’ t believe the BS that AC filaments sound better. It is hard to hear the 60Hz modulating the audio signal, but it is there…
 
Was also going to suggest just rotating the output transformers 90 degrees and see if that helps.

Should be a quick and easy fix.

Unfortunately, the transformers are not square and eyeballing it, there does not appear be enough room on the chassis to turn them 90 degrees.
 
Could you slip a piece of steel or Mu-metal in between and see if that changed the hum?
 
I have a square of my-metal on a stick with a wire soldered to it with a clip on the end. I slip it between parts when looking for hum.
 
Thought about a piece of metal as a shield to test. Don't have any MU here. May have to order some. Thought about maybe a cover for the power transformer to shield it. I've also thought about making a new larger plate and chassis and moving all the components over. Also thought about using different output transformers. Free time to do all this is constantly a problem.
 
Thought about a piece of metal as a shield to test. Don't have any MU here. May have to order some. Thought about maybe a cover for the power transformer to shield it. I've also thought about making a new larger plate and chassis and moving all the components over. Also thought about using different output transformers. Free time to do all this is constantly a problem.
IMG_1281.jpg
I just measured 1-1.1mV of hum from my Simple 45.

My PS configuration Hammond 272DX >5Y3 > 100 ohm > 20uf > 7H choke > 50uf + 50uf > split rail to each channel with another 50uf each. If memory serves me right, that goes up to about 2mV with 2A3s, at least that's what I measured from the recent Radiotron SE2A3 I built and my other 2-stage SE2A3.

I hardly hear any hum from my listening position when I drive my Altec 753Cs using this Simple 45 or SE2A3 amps with AC filaments. Hum was also not an issue when I brought them to a friend's listening room with 604-8Gs.

Since you're stuck with that chassis and can't rotate the choke, could the hum be caused by a ground loop? Since @Redboy's amp is significantly quieter, maybe you can use that as a reference for rewiring the grounding scheme?

I wish I could help further but I'm really bad at remote sleuthing.

Good luck!
 
Thought about a piece of metal as a shield to test. Don't have any MU here. May have to order some. Thought about maybe a cover for the power transformer to shield it. I've also thought about making a new larger plate and chassis and moving all the components over. Also thought about using different output transformers. Free time to do all this is constantly a problem.

I have a chunk of Mu metal you can have Mike. Pm your address.
 
I wish I could help further but I'm really bad at remote sleuthing.

I get it. I'm the same way. Guess I really need to put it on the bench and measure the hum. I've haven't set to up the to run 45. The Redboy amp is 45 only.

Really can't hear it when playing music. What was concerning me, was the left channel seemed to have more hum. It is closer to the power transformer. Then when I started playing around with a electronic crossover and adding a amp and set of subs seem to make it worse.
 
The coil axis of the power transformer is perfectly aligned with the coils of the output transformers; this build is a bit scratched from the start.
 
Ok so I did an actual hum measurement while adjusting the Redboy 45 and got about 2.3mV with it in my system. I cleaned the hum pots on George's 2A3. While I was at it, cleaned the tube sockets. Adjusted by ear as I had been doing and measured about 10mV. Using a meter for the adjustment and noticing that there was some interplay between the two sides got both down to 4.7mV. I can live with the 4.7. Would love if it were less. Really figured out that 7 to 8mV is where I find it unacceptable. I'll play with with some shielding later and see it has any affect.
 
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