New TWXpress build

[paulster]

I did note in the 0539 picture from 6/1/10 that it looked like your PI coupling caps were "backwards". All of the other pictures that I have seen show those with the black line facing the front of the amp.

Not sure how important that really is....but....thought it worthy of note nonetheless.

The black line on the PVC caps does not indicate the outer foil (despite doing so on many brands of capacitor), so you actually have to test and mark each cap yourself if you want to orient them 'correctly'.

[loupy31]

Thanks for that info, ok,
1/ how do I test them,
2/ which direction do they have to be placed and
3/ does it make a difference to the sound of the amp.

Regards Peter

[paulster]

1/ how do I test them,
2/ which direction do they have to be placed and
3/ does it make a difference to the sound of the amp.

1) You need an oscilloscope (ideally) or you can try using a phase switch and the input to an amp to see which way round is quieter. A few people have used this method successfully but I haven't tried it since I just use a scope.

2) The outer foil should go to the lowest impedance side of the circuit, so in the case of a cap coming off a plate then the outer foil would go to the plate side. In tone stacks and the PI you need to look at what's going to present the lowest impedance.

3) It shouldn't make any difference whatsoever to the sound, but may impact the ambient noise levels and possibly the susceptibility to external noise sources.

[PlinytheWelder]

This is a good read.
http://www.aikenamps.com/OutsideFoil.htm

[loupy31]

Just a few More pics

Cheers

[Cliff Schecht]

This amp looks well built, very neat and tidy inside. Did you test it yet?

[loupy31]

Hi, No I have not tested it yet, I am waiting for parts to make a bias tester, should be able to test soon

[Big Jim]

I'm keeping an eye on your thread Loupy. I'm hoping the testing and startup phase go well for you. Your build looks really good. Keep us posted, I'm sure you will have that baby roaring in no time!

[Cliff Schecht]

Bias tester? Turn on the amp with no tubes, check voltages and set bias to about -30V, plug in the tubes and BAAAM! I admire your patience in wanting to do things right though .