Tag: 4-65a DHT

4-65a Triode Curves

Tracing the transmitter valve curves

20131102-171745.jpgI posted several times about my 4-65a SE Amplifier and also traced in the past the curves using my analogue curve tracer to get a view of the loadlines of this fantastic DHT in triode mode.

Now that I have the uTracer I traced again the curves including grid current and A2 anode curves which are very handy for this type of transmitter valve.

My tests were conducted with the following heating and bias setup:

  • DC heater using Rod Coleman regulator @ 6V and 3.5A
  • Cathode connection to the negative filament terminal of the regulator and valve.

Continue reading “4-65a Triode Curves”

Upgrading the DHT filament regulators

I upgraded the DHT filament regulators to version 4. Rod has released a new kit which introduces temperature compensation for high current filaments. This is a key feature in my 4-65a design and I shall explain why:

Continue reading “Upgrading the DHT filament regulators”

4-65A SE Amp: first tweaks

As discussed previously, I replaced the gyrator’s polypropylene caps with better ones I had at hand which are 1uF 450Vdc Mundorf Mcap EVO Silver Gold Oil Cap (EVOSGO-080). I should look at lower value. A 220nF or even 100nF one should provide a 1Hz -3dB point with the 4M7 resistor. Anyway, the sound is a tad better in the bass I would say. Nice upgrade but should listen to it more to find what other changes has this capacitor made to the amp:

Replacing the capacitors
Mu-follower gyrator boards finished

4-65a THD

Quick test on a EIMAC JAN-8165/4-65a NOS. Here is the THD response at output level of +22.22dBu:

4-65a THD

Artefacts at 50Hz and above are all a result of a poor filament power supply 🙂

Nice to see this valve providing 0.14% THD at a low operating point: Ia=85mA, Va=246V. At least this is a nice test to show how linear this valve it is.

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