Hi Pierre,
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- Yes please put a resistor in place as per data sheet advice as this will limit surge/peak current and extend the life of the tube cathode
- I'd use 47uF if I was just using a C filter or CRC as that will be the optimum value. However... as you are using CLCLC, it's a specific circumstance that might benefit from a smaller value. If you have C1 L1 C2 L2 C3, it's good for C1 < C2 and C2 < C3 as this will help to prevent ringing in the system
Some tips that might help you with all of this:
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- You can simulate the anode resistor by working out the source impedance using one of the transformer calculators, then simply add the value of a single anode resistor to this value. For example if you have calculated 110 ohms source impedance and have a 230 ohm protection resistor for each anode, use 110+230 = 340 ohms
- Check out the tube data as advised by others, my TDSL site has links to data sheets which you may find useful
- Check the peak current in the rectifier and compare with the data sheet. Try different capacitor values and you can see the effect of changing the value. Lower peaks are likely to translate into longer tube life
- Experiment with a smaller capacitor value at the start of the filter chain, it's really easy to try different ideas with PSUD to get to where you need quickly, look at the effects on filter ringing
- If your filter is left with a small amount of ringing, use the soft start feature in PSUD to simulate that the tube conduction will slowly rise; that should make it go away
- Sonic differences will always be subjective, and for that reason it's a topic I generally avoid, however you may want to consider a couple of items:
- Lower ripple is generally better. Single ended amps will end up with ripple in the output so less ripple will translate to less hum out of the speaker. Push-pull amps should cancel the hum, however they will be affected by intermodulation distortion so they still benefit from lower ripple. As your target is a line stage, this would be treated the same as single ended
- Power supply impedance - there are two things to consider, one is "sag" from the power supply which is where it runs out of steam at high load and the voltage will reduce, potentially resulting in quieter periods after transients. The other is the impedance to AC variations in the load which can affect the sound output at different frequencies. PSUD will check for sag; the stepped current load is great for assisting with this. It doesn't currently allow for output impedance vs. frequency to be plotted
Hope the above is of some help to you.
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Regards,
Duncan
