The 300B are Sophia mesh plate that I bought at good deal about 10 years ago. Went in the stash and finally had a chance to use them. Also tried some EH gold grid, gold pin to that I bought about 2 years ago. Both sound good. EH a bit darker but a good full sound, Sophia a bit airy and lighter but a good detailed sound. EH don't look like much, the Sophia light up beautifully at night.
Only two caps off board. One is paralleled with 100R resistor to "lift" the signal ground off the chassis and main earth ground - that's the little dark square one in the back. Other one is on the tiny pcb with a diode to take the 7vac from a junk box filament transformer I had and give me 9vdc to run the little fan. No motor run in the actually amp ps, only what's on the TSE-II board.
Me too!! very nice. I think you need a GZ37 rectifier...would go good with those tubes.....haha
Looks like Sophia makes a ST glass 5AR4 equivalent rectifier ....
https://www.ebay.com/itm/115225444395?hash=item1ad3f8c02b:g:Y1AAAOSwET1h83UD
https://www.ebay.com/itm/115225444395?hash=item1ad3f8c02b:g:Y1AAAOSwET1h83UD
From what I understand, the 274 has a very low first capacitor limit... something like 10uf and a lot less current ability. I thought about them since I like the look, but when I did the math I realized that I would need to parallel two them and get a higher voltage PT to keep the B+ up.
Attempting to fuse a high voltage circuit carrying DC can often lead to an arc over or an explosion, especially when an inductor (the OPT) is in the path. This can only be done if a fuse rated for DC and the highest possible voltage seen in the circuit is used. This would require a low current (100 to 250 mA) high voltage (500+ DC volts) fuse which is rare and expensive. An ordinary 250 volt glass fuse can explode, I have seen it happen.
A fuse blows by burning a thin metal conductor in half. As it blows the metal is designed to burn away making the gap wider. Any arc attempting to jump the gap will be extinguished at the next zero crossing on AC, but this cannot happen on DC, so the arc continues spraying metal ions into the surrounding air and onto the glass, providing a path for continued current flow. This path is resistive causing extreme power dissipation and excess heat. If the arc continues for a few milliseconds, the fuse will explode, and the arc may then jump to some neighboring parts. I have a couple burnt PC boards that demonstrate the power in a DC arc.
DC fuses are filled with a compound or gas that will extinguish the arc when used within their ratings. Using a DC fuse beyond its voltage rating can also make it fail.....spectacularly.
It is possible use an AC fuse in the Center tap of the HV winding on the power transformer to protect against a severe or long term high current condition. I have done this in some high powered amps, but I have not tried it on the TSE or TSE-II. Again, the voltage rating on the fuse should be higher than the secondary voltage of the power transformer. I have used 250 volt fuses in amps with 500+ volt B+ voltages without any explosions, but I cannot recommend this course of action. My work was just short term test amps that never got built into anything left turned on unattended.
And the first "test" involved electrolytic capacitors and the wall outlet!
I attended a technical high school where I took a 3 year program in electronics totaling 1080 hours of education. It was "equivalent to an associate's degree in electronics technology" but not accredited since it was a high school. This was 1967-1970, and in Florida where education was not a priority, so the test books came from the US Navy and were all about vacuum tubes. Yes, this is where I really learned how to make them glow. Blowing stuff seemed to be an acceptable practice in the lab, as long as I could present a proper explanation to the class as to what happened and why. Once the teacher bet me that I could not make the outer metal envelope of a metal 6L6 tube glow red. I won that one, but it stunk up one entire wing of the school. This was the vocational wing where metal shop, welding, auto shop, woodworking, electronics, commercial art, and cosmetology were taught. Smoke, stink, and loud noises were expected. I made my share of all three. We played crazy games like get everybody in the class to hold hands in series, connect us up to a Variac, and crank it up to see who the wimps were. Was it a coincidence that the two best players at that game went on to have long careers at Motorola?
When my career at Motorola in Florida ended and I moved 1200 miles north, I began looking for employment. There isn't much work in rural America for a cell phone / two way radio designer, but I did visit the two colleges, two tech schools, and one community college that had an electronics or computer related curriculum within a reasonable driving distance from here. Only one seemed even remotely interested, but they needed a PHD to satisfy an accreditation requirement. A master's degree in electrical engineering and a bachelor's degree in computer engineering was not good enough. After 5 years of job hunting, I got one offer. It was for a general maintenance person in a prison paying $12 / hour in a place where someone could kill me for my ring of keys. No, I didn't go for it. Now there are several jobs for 5G cellular work, but a 69 year old person who has been out of the work force for 8 years isn't going to get hired either.
You can stick an ordinary 2 amp 32 volt fuse in the current measurement socket of a Fluke if you are using it on low voltage. We did that at the Motorola plant where everything we built worked on 3.7 to 15 volts.