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Old 13th Jul 2020, 7:35 pm   #24
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 367
Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Well no advance today, I was hoping to build a variable current load for the PSU just to map how it performed Volts against Current, I have a few devices such as BU508 or a S2000AF which should deal with up to 50 Watts on a decent heat-sink and cope with the HT voltages, but as the hfe of the devices are typically very low I need something else to drive them with that could also cope with several hundred volts and in that I seem to be lacking in the spares box. I continue to look.

So for now I have been having fun with my CV4014 or EF91 Valves for most of the day. I could not find any curves with a screen voltage less than 250 Volts so have been mapping them out myself. Then picking an operating point based on and selecting the anode load and grid values etc.

For small signal inputs to the grid, I have picked 250 Volts, 47K Ohm anode load, 200 Volt on g2 and control grid around -2.3/2.4 Volts gives around 3mA Ia and 1mA Ig2. So a 600 Ohm Cathode resistor probably called for.

This would have been an excellent task for one of the valve tracer projects!

Anyway at the end with the settings I had selected I mapped out Va against Vg and plotted it in a spreadsheet to provide what I have below.

It is all a bit of fun for me as it was something to do and helped me understand things a bit better than just reading about Pentode curves. I get Vout/Vin of 175 but would imagine that would be loaded with the input resistance of any following stage and capacitance.

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