6HS5 triode

More than 8 years ago, I played with this valve after Thomas Mayer wrote about it here. It seemed like a good option but despite a few bench tests, I never got around building an amplifier with it.

I’m preparing for ETF.19 and will be bringing my eTracer to the event so I built a few socket adaptors. It was the time for the 12-pin Compactron to come to life.

Through my few Compactron valves, I bumped into the 6HS5 again, so I decided to put it to the mercy of the tracer. I wanted to see the positive grid current behaviour, as haven’t seen curves around with it:

6SH5 triode with positive grid bias.

What can we say of the above curves? Well this triode could do 7-8W easily as Thomas says. It has an anode power dissipation of 30-35W. The anode slope is between 7 to 10K so local feedback will be needed. You will need to aim for 600-700V bias at least, probably higher with slightly negative bias. However, you will need a hefty source follower to drive the grid. Look at the grid current. It can be 50mA at 5V and creeps up the higher the grid voltage it goes.

Interesting valve with a 6.3V/1.5A heater, and the high-mu (80-100) can work out as a SPUD amplifier with local feedback. Driver should be able to handle the grid current and low impedance. Not an easy task though.

814 SE Amplifier: Custom Output Transformers

 Improving the 814 SE Amplifier

photo 3After more than a year listening to this fantastic amplifier, it was time to do the first significant improvement to it despite I resisted to modify it after so much work and effort put into the design and build. The evident upgrade was the output transformer. When frequency response was measured, it was evident to see that the HF response was lower than expected. This is the result of the transformer and its configuration in this circuit. The LL9202 is a better OT for higher impedances and in this circuit, it is used in the 6KΩ /8Ω mode.

Continue reading “814 SE Amplifier: Custom Output Transformers”

4-65a SE Amp building process

Some drilling and mounting work done this morning on the 4-65a SE amp breadboard:

During the afternoon, I managed to wire a filament supply for one channel 46 driver. Tested and working ok, now can move to the next one: