Tag: 300B Amplifier

300B SE Amp: build part V (Fixed Bias)

Last year I developed a voltage reference using an HV LED. Unfortunately these devices from OSRAM seem to be discontinued. I managed to buy enough parts for my own use though. What is interesting from these LEDs is that the dynamic resistance is low. About 150Ω with good current, or between 300Ω to 500Ω.  Tempco is very low and with such a low dynamic resistance, they are great for creating a voltage reference with a stable CCS:

The LEDs are extremely bright and found that with a 1mA current are dim enough whilst retaining the stability needed. I have a cap multiplier arrangement and the LED array is fed by a stable CCS. Jumpers on the board allow bypassing LEDs and there is also the option to use a trimmer for variable voltage adjustment. Very handy for screen grid supply and phono stages. The reference voltage is extremely quiet with more than 100dB PSR.

OSRAN 67V LED curves

Continue reading “300B SE Amp: build part V (Fixed Bias)”

300B SE Amp: build part IV (Board 1 finished)

Board 1 completed

Wiring job is done. The fixed bias supply delivers from +50V to -300V. It has more voltage capability as am planning to use this same supply for future builds (e.g. 845 SE). The filament supply set to minimise power dissipation on the filament regulators for the 300B. All working fine, so am happy with this board. Filament noise is 0.3mV.

300B SE Amp: build part II

Slowly making progress during the lockdown period. Over the past few weeks I managed to achieve quite more than I was expecting. The fixed bias and 300B filament supply board (board 1) needs to be wired. On the other hand, the driver filament supply plus the HT supply board is completed (board 2):

Board No. 2: HT Supply and DHT driver filament supply

I tested the HT supply and can deliver over 430V. It has more voltage capacity, however the filtering capacitors are 450VDC.  The DHT filament supplies can do 8V to 15V to accommodate different filament requirements (including some level of filament bias). It works beautifully!

Continue reading “300B SE Amp: build part II”

300B SE Amp – here we go

A Brave New World

Surely you’re as tired as I’m with COVID-19. One of the best things I can do to distract my mind is to keep myself away from social media. Every stone you turn, there is COVID or a statement about it. I won’t moan as I have a job for now and a healthy family. Some members of my family were infected but nothing major. I can only say is that the world has change. And so my day to day life looking after the young family whilst working is a real challenge. Starting my fifth week of lockdown, I have to distract somehow my mind at times, otherwise will go mad.

A New Concept

Continue reading “300B SE Amp – here we go”

Flexible HT Power Supply (Part II)

Here are some picture of my slow progress on this flexible power supply.  I started with the layout of the parts before any marks were made on the top plates:

Working out the layout of the top plates
Working out the layout of the top plates

 

Once I was happy with the layout, I submitted myself to the mercy of the most dreadful job on earth which is metalwork!

Continue reading “Flexible HT Power Supply (Part II)”