[Gradofan2]

Based on the foregoing "meadering" and speculation... we can draw the following conclusions:

1. Both the WA6 and the WA6 SE use a CAP INPUT SUPPLY - not a choke input supply.

2. The PSU filter cap, must not be of too great a value, or must have a resistor after the inductor too avoid stressing the 274B tube.

3. The WA6 and WA6 SE both use a PSU filter cap, which is too large to safely allow the use of 274B tubes, without stressing them and shortening their life... and... must either have the value of the PSU filter cap reduced, or a resistor added after the inductor, to allow safe use of the 274B tube.

4. That is the case for both the WA6 and WA6 SE.

5. One person has reduced the size of the PSU filter cap value to resolve this issue... and... it is a better solution than inserting a resistor after the inductor.

6. Reducing the value of the PSU filter cap, or adding a resistor after the inductor, can reduce the current output so much that it will reduce the amps ability to drive low impedance phones well - so you must be careful.

7. This is only an issue when using the 274B tube, and is not an issue with other rectifier tubes such as the 5U4G, 5AR4, GZ30, GZ32, GZ37.

So, you don't have to worry, if you don't use the 274B - its best not to use a 274B tube, unless you make these modifications.

I'll forward this to Jack and adivse him to change the design of the WA6... at least for mine.

 

[sclamb]

I think it would be better to wait until we hear from Jack on this rather than sending a message to Jack 'advising' him on how he should change his amp design. He is talking to Sophia Electric and I am sure will come back with a statement of what has to be done (if anything) to use the 274B tube.

 

[atbglenn]

Quote:

Originally Posted by sclamb /img/forum/go_quote.gif I think it would be better to wait until we hear from Jack on this rather than sending a message to Jack 'advising' him on how he should change his amp design. He is talking to Sophia Electric and I am sure will come back with a statement of what has to be done (if anything) to use the 274B tube.

Probably the best idea. I'm sure Jack with figure it out and take whatever steps are necessary to correct this issue.

 

[sclamb]

I removed the top plate from the transformer and switched the amp on and there was hardly any hum at all. I had to get my ear right next to the transformer and even then it was only just audible.

I then placed the top plate back on and the hum re-appeared. It seems that on my amp the top plate is closing the enclosure sufficiently to act as an amplifier for the hum and it makes it sound louder.

So, the transformer is actually pretty silent, it is just the enclosure that is acting like a speaker cabinet and amplifying the sound. Now I know I guess it is just something to live with as it appears to be the casing that is causing the hum to be louder.

Is it worth putting some sound deadening material on the inside of the top plate? Would this be dangerous being next to the transformer?

 

[jamato8]

In the above information I haven't seen where reducing the cap or adding a resistor will reduce the ability to drive a headphone. This isn't true unless you are reducing the voltage by using a resistor and not adjusting the other ones to allow for the correct voltage drop. I don't think anyone is suggesting just adding a resistor without compensating.

I have stated I don't think the SE is a cap input supply. And more than one person has reduced the first cap. A few have made the first cap a 22uf, which when considering the voltage used in the amp at approx 200 volts and a little more for the SE, should work fine.

 

[Gradofan2]

Quote:

Originally Posted by sclamb /img/forum/go_quote.gif I think it would be better to wait until we hear from Jack on this rather than sending a message to Jack 'advising' him on how he should change his amp design. He is talking to Sophia Electric and I am sure will come back with a statement of what has to be done (if anything) to use the 274B tube.

I would agree... except... I want this issue resolved before he ships mine (scheduled for next week - short timeframe)... and...

... we need for Jamato8 and Jack to confront this issue directly... between the two of them... and to fully and finally resolve it.

I'd like to use the 274B... but... I'm not going to invest $150 in a tube that may only last a few weeks, or months... unless... Jack is going to warrant it for the life of a normal tube. Since... he only warrants it for 30 days... he must not be too confident about the tube in his circuit either.

And... I want the amp to drive both Denons and Grados, as well as Senns... without any compromise - meaning, I don't want to reduce the current output so much, that it won't drive low impedance phones well.

There's no point in continuing to "talk around the issue" and "speculate" about the implications and options - I want it brought to full and final closure.

 

[jamato8]

Quote:

Originally Posted by sclamb /img/forum/go_quote.gif I removed the top plate from the transformer and switched the amp on and there was hardly any hum at all. I had to get my ear right next to the transformer and even then it was only just audible. I then placed the top plate back on and the hum re-appeared. It seems that on my amp the top plate is closing the enclosure sufficiently to act as an amplifier for the hum and it makes it sound louder. So, the transformer is actually pretty silent, it is just the enclosure that is acting like a speaker cabinet and amplifying the sound. Now I know I guess it is just something to live with as it appears to be the casing that is causing the hum to be louder. Is it worth putting some sound deadening material on the inside of the top plate? Would this be dangerous being next to the transformer?

Something placed on the top enclosure plate of the transformer housing would be fine. Dampening material is often used. You could even ad a very thin piece of something between the top plate and the rest of the housing before you replace the top. This would dampen vibration and if 1/64 th or 1/32 or so thick it would also allow the top to vent heat from the transformer if not continuous, which is fine and it would break the acoustical coupling.

 

[takezo]

yeah, like putting a gasket between two metal pieces... just make
sure you don't interfere with the venting holes on the sides...

 

[takezo]

Quote:

Originally Posted by Gradofan2 /img/forum/go_quote.gif ...There's no point in continuing to "talk around the issue" and "speculate" about the implications and options - I want it brought to full and final closure.

yes, you'd want to go thru jack directly for that... good luck.

 

[sclamb]

Quote:

Originally Posted by jamato8 /img/forum/go_quote.gif Something placed on the top enclosure plate of the transformer housing would be fine. Dampening material is often used. You could even ad a very thin piece of something between the top plate and the rest of the housing before you replace the top. This would dampen vibration and if 1/64 th or 1/32 or so thick it would also allow the top to vent heat from the transformer if not continuous, which is fine and it would break the acoustical coupling.

Thanks. Would it matter if the dampening on the underside of the top plate touched the top of the transformer? I am not sure if it gets hot in there, although the enclosure is cold to the touch even after hours of on-time.

Great idea about something between the top plate and the side casing

As an amp builder, do you recommend anything for sound dampening such as this?

 

[jamato8]

There are special dampening materials but for this I would put it between the side of the transformer housing and the top plate. It isn't going to touch the transformer as it is down in the housing and there is no reason for it to touch the transformer if it is between the top and sides of the housing. You could even use a few pieces of the sticky material left over from the press on feet used for small amps. Experiment.

 

[sclamb]

Quote:

Originally Posted by Gradofan2 /img/forum/go_quote.gif I would agree... except... I want this issue resolved before he ships mine (scheduled for next week - short timeframe)... and... ... we need for Jamato8 and Jack to confront this issue directly... between the two of them... and to fully and finally resolve it. I'd like to use the 274B... but... I'm not going to invest $150 in a tube that may only last a few weeks, or months... unless... Jack is going to warrant it for the life of a normal tube. Since... he only warrants it for 30 days... he must not be too confident about the tube in his circuit either. And... I want the amp to drive both Denons and Grados, as well as Senns... without any compromise - meaning, I don't want to reduce the current output so much, that it won't drive low impedance phones well. There's no point in continuing to "talk around the issue" and "speculate" about the implications and options - I want it brought to full and final closure.

I agree that you need to speak to Jack directly to make sure you get the correct specification in the amp you want.

Please let us know the result of your conversation with Jack with regard to running the 274B tube and the agreed specification for your own amp.

Would you believe I have not had any sparking for the past two days!

 

[sclamb]

Quote:

Originally Posted by jamato8 /img/forum/go_quote.gif There are special dampening materials but for this I would put it between the side of the transformer housing and the top plate. It isn't going to touch the transformer as it is down in the housing and there is no reason for it to touch the transformer if it is between the top and sides of the housing. You could even use a few pieces of the sticky material left over from the press on feet used for small amps. Experiment.

Ah, a project

Thanks again. I shall see what I can come up with.

 

[Gradofan2]

Quote:

Originally Posted by sclamb /img/forum/go_quote.gif I agree that you need to speak to Jack directly to make sure you get the correct specification in the amp you want. Please let us know the result of your conversation with Jack with regard to running the 274B tube and the agreed specification for your own amp. Would you believe I have not had any sparking for the past two days!

I guess I'd leave the "transformer cover" off - if you haven't had any vibrations, or sparks... since you removed it....

 

[sclamb]

LOL

That would definitely ruin the sleek asthetics and fabulous build quality of my black beauty.

I will try and find some very thin gasket type material and sit that between the casing and the top plate. The smallest gap should be enough to cut the amplification of the transformer sound.