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I'm resurrecting this thread to post an update on a couple of observations on the overall performance of the construction experiment.
First, due to circumstances surrounding the covid-19 pandemic, I've really very little access to the shop I use for personal projects, until fairly recently.
This particular amp build, was one of several projects I've been getting back into. So, putting the amp up on the bench again brought, I decided it was a good time to finally change something which had been bothering me for a while.
When I decided to install Belton noval sockets to replace the earlier 9-pin sockets, I (for some reason) replaced all the preamp sockets, but used ceramic sockets for the output tubes. (see below).
The quality of the Belton sockets was so much better that these ceramic sockets in nearly every way, with the exception that thermoplastic can melt. The ceramic sockets would not secure the EL84s to any acceptable degree. The EL84s could be moved or dislodged without much torque at all, and it became clear pretty quickly that these output sockets needed to go to.
Retrofitting and rewiring the sockets was a bit of work, but I probably shaved a 1/3rd of the time off the project since there was no longer any need to drill out and machine my own base plates. I just needed to source M20 machine washers, and drill out the mounting holes. For the preamp tubes (photographed in earlier posts), I used Zinc plated steel for the mounting bases because they were readily available, and easy to machine. But they were already beginning to show quite a bit of oxidization.
Because the silicone gasket provided galvanic isolation between the aluminum chassis and mounting plate material, I decided to use A2(18-8) stainless steel for the output tubes. So, I called Boltdepot, to see if they had M20 size washers. They only carried up to M16 (I believe), but referred me to another supplier in MA called Belmetric (https://www.belmetric.com). Belmetric carried several types of M20 washers, and the price was right for 18-8 at $0.39 a piece.
The interesting thing I learned about Austenitic stainless steel, is that it cannot be hardened by heat/tempering, but it can be work hardened. With types 304 & 316, the process of drilling alone will harden the steel significantly along the cutting edge and tip of the drill. So, care must be taken in setting the speed of the cutter, or you can wear them out quickly.
After drilling out the bases, I cut small grommets in halves to add some further isolation for the machine screws during the install.
Unfortunately, it was a pretty big improvement over the first attempt on the preamp sockets. So, I couldn't help myself from redoing the rest of the sockets. The fact that the zinc plated washers were showing corrosion already was a big factor as well. You can see the difference below.
here are the finished sockets.
First, due to circumstances surrounding the covid-19 pandemic, I've really very little access to the shop I use for personal projects, until fairly recently.
This particular amp build, was one of several projects I've been getting back into. So, putting the amp up on the bench again brought, I decided it was a good time to finally change something which had been bothering me for a while.
When I decided to install Belton noval sockets to replace the earlier 9-pin sockets, I (for some reason) replaced all the preamp sockets, but used ceramic sockets for the output tubes. (see below).
The quality of the Belton sockets was so much better that these ceramic sockets in nearly every way, with the exception that thermoplastic can melt. The ceramic sockets would not secure the EL84s to any acceptable degree. The EL84s could be moved or dislodged without much torque at all, and it became clear pretty quickly that these output sockets needed to go to.
Retrofitting and rewiring the sockets was a bit of work, but I probably shaved a 1/3rd of the time off the project since there was no longer any need to drill out and machine my own base plates. I just needed to source M20 machine washers, and drill out the mounting holes. For the preamp tubes (photographed in earlier posts), I used Zinc plated steel for the mounting bases because they were readily available, and easy to machine. But they were already beginning to show quite a bit of oxidization.
Because the silicone gasket provided galvanic isolation between the aluminum chassis and mounting plate material, I decided to use A2(18-8) stainless steel for the output tubes. So, I called Boltdepot, to see if they had M20 size washers. They only carried up to M16 (I believe), but referred me to another supplier in MA called Belmetric (https://www.belmetric.com). Belmetric carried several types of M20 washers, and the price was right for 18-8 at $0.39 a piece.
The interesting thing I learned about Austenitic stainless steel, is that it cannot be hardened by heat/tempering, but it can be work hardened. With types 304 & 316, the process of drilling alone will harden the steel significantly along the cutting edge and tip of the drill. So, care must be taken in setting the speed of the cutter, or you can wear them out quickly.
After drilling out the bases, I cut small grommets in halves to add some further isolation for the machine screws during the install.
Unfortunately, it was a pretty big improvement over the first attempt on the preamp sockets. So, I couldn't help myself from redoing the rest of the sockets. The fact that the zinc plated washers were showing corrosion already was a big factor as well. You can see the difference below.
here are the finished sockets.
.
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