#102 died yesterday :( how,why?

[donvan]

Very interesting read and learning. For my last amp, which uses the 40-18042 classic tone PT I didn't use the balancing resistors on the heaters because the PT already has a central ground. Would it be advisable to use the 100R (1/2W) regardless of the PT having that central ground? I think I will add it to my amp...

that's a good question and I'd be interested in people views on this too. I've always used the CT if it's there.



M

I was really hoping someone would weigh in on this. What would Dumble do? Are there any examples of Dumble's amps where he used a PT that that had a central ground? If so, did he still use balancing resistors?

[pompeiisneaks]

I've heard a bit of debate on that. Some (I think Jelle and a few others) say that the resistors perform a 'cheap fuse' function if you somehow get high voltages on the rail, they blow and the amp then doesn't draw the current w/o the center tap, but then others told me that the amp still will draw current and can damage things because the heaters still work w/o a center tap, and will just be way noisier.

I'm still of the opinion that the center tap, if it exists, is super easy to use, use it

~Phil

[Guy77]

I was finishing up a 102 build while this topic of the 1/2 watt 100 ohm resistors was going on. I ended up not using the heater center tap and used the 1/2 watt resistors for the heater grounds and so far its been just as quiet as using the center tap on a previous 102 build I did a few months earlier. This was a 22 watt build so things maybe different noise wise with a 100 watter.
I will burn in the amp for 8 hrs tonight and see how it sounds in the morning.

I do agree with Phil that it is so easy to just use the center tap and I was so tempted to do that but wanted to try something different this time.


Cheers

Guy

[mojotom]

The artificial center tap is by design well balanced and could yield a quieter amp. The CT from the transformer could be off balanced (not exactly on the middle of that secondary).

[ijedouglas]

Very interesting read and learning. For my last amp, which uses the 40-18042 classic tone PT I didn't use the balancing resistors on the heaters because the PT already has a central ground. Would it be advisable to use the 100R (1/2W) regardless of the PT having that central ground? I think I will add it to my amp...

I just used the 100R on the center tap to ground as described here: http://www.valvewizard.co.uk/heater.html