One Last SET Driver Check

I took some time yesterday to perform a performance check on the driver for the 6AS7 SET. As some may recall, this driver was developed and prototyped back in 2015, and brass boarded in 2016, as a driver for the 6336 SET Amplifier. In the 6336 design it uses a 300v B+ to produce a swing of 82V peak to fully drive the big triode. However, in the unique power supply topology of the 6AS7 SET, there are some additional considerations.

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About That Bias Point

Back in June, in the Competing Priorities post when talking about the 6AS7 SET, I made the following statement:

I also had another idea this morning which may lead to a little more prototyping work to check out a theory I have (another potential delay). But if the experiment turns out well, I may move bias points around a little on the 6AS7.

Well, I spent this morning with some prototype circuits and a stack of tubes investigating the bias points for the 6AS7 SET power stage. And I learned a couple of important lessons.

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Another Option

This last week I was thumbing through my very dogeared copy the RCA RC-30 Receiving Tube Manual. I was not looking for anything in particular but just browsing and a data sheet for a particular tube caught my eye; the 6DQ5 Beam Power Tube. The only description was “Glass octal type used as horizontal-deflection amplifier in color and black-and-white television receivers”. As I began looking through the specifications I began to wonder how I had missed this tube up to now.

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In Praise of the “Album”

For me, it really started about six years ago. I had been using an iPod for a while before that, but the real transition took place sometime in 2015. I had been notified that I was moving cross country for work and things were getting boxed up and ready. All my CDs and vinyl were carefully packaged up for the move. I was left with an iPod and my computer for playing music. That was when I started my slide into bad musical habits.

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Back to Work

The Christmas break saw me very busy with tasks other than amp building. So the new SET is a little behind schedule. In spite of it supposedly being a “quiet” Christmas with just immediate family, I ended up tackling several small projects which I had been putting off and I helped my daughter move. And of course I was back at work this week as well. Now that doesn’t mean that I got nothing accomplished, it just means that things are progressing slower than anticipated. This is where I’m at:

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