300B completion

[Erik Mandaville]

It's like an old house with new furniture. I'm using AC, centertap grounded heaters on the 6SN7s, with an external regulated DC filament supply on the 300B. All power is controlled by a new DPDT switch. I included brand new filter caps, as well.

What I have been thinking about for the driver stage turned out to be what is probably the heart of this particular design, and I am pleased with very good FR, perfect gain characteristics with the Lexicon, and quiet overall performance. Even with AC on the input driver stage, the amps are very satisfactory, and I'm pretty picky about noise. The Moondogs used DC in that application, but in removing basically everything from before except two resistors, I tried AC heaters and was happy with the performance. It's simple, and works well. All AC carrying leads are of course twisted to minimize hum, and it's not a problem.

This isn't a make-do 300B amp. I was given the tubes as a gift, and wanted to make the effort to make the best of them, and I think that's the case, at least for right now!

The space toward the bottom of the picture is reserved for a possible ultrapath capacitor in the future, but I want to listen to how things are right now before I make anymore changes.

Keep in mind these amps have been the basis of many experiments, revisions, and modifications, and the basic chassis shows its age a little. The caps and resistors are not cost-no-object components, either. They are reasonably priced and are doing the job.

I've very, very happy with how things have worked out. I listened to one channel late in the evening, with the great Teac on the other side. It was surprising, actually, how well the two worked together. I've been working on this almost non-stop for two days, and both amps are now done.

[Erik Mandaville]

Here's a picture from earlier on, where, for troubleshooting a small hum in one channel, I'm using the power supply from the completely hum-free amp to help diagnose the source of noise in the other.

Note: Don't even think about doing something like this if you have children or pets nearby, or if you're not familiar with working around dangerously high voltages. This is more involved than what might appear to be the case at a first glance.

Erik

[jcmusic]

Hello Erik,

Looks nice, to bad I don't know what I am looking at. I only know what I read and more importantly what I hear. Your descriptions are very informative therefore I like to read your post. Free knowledge I can not get enough of, so keep it coming.

Jay

[Travis In Austin]

Erik,

Looks like it is coming along fine. Are your plans still the same for the beginning of June? If you are not going to be laid up would love to have you bring those baby's up to Austin. We are going to have another 300B's (Western Electric's no less), that just looks beautiful. I beleive Wardsweb posted photos of it under his Texas bottlehead post.

By the way, how much voltage is comming out of the bottom of those things. (I hope this does not start another debate about whether it is the volts or the amps that kill you)

Let me know what I owe you for shipping, parts, etc for that center channel box.

Travis

[Guest " "]

awesome.

[lwhaples]

Cool! I also enjoy your posts,but need to learn more. Thanks for sharing Eric!

Larry