In my #26 preamp I use 0.22uF 200V FT-3 too .... paralleling with 100nF V-Cap.
Yes, I would be interested too. I have played with bypassing in speaker crossovers with mixed results, and in fact I removed a polystyrene bypass cap yesterday as it was worse! But not tried it in the 26.
As I wrote earlier I use (quasi parafeed) TVC on the output. Parafeed capacitor quality is very important, and I like (good) teflon capacitors, especially V-Cap (I use its for almost a decade).
220nF is a little, 470nF too much, 330nF enough, but I don't have such value V-Cap (450 USD/pair !! ).
FT-3 is a good capacitor (and damned cheap), but some enhancement is not a bad solution. I own -spare- 100nF V-Cap, so I used them as bypass.
In my experience 5-10% bypass with very good quality capacitor hides main coupling capacitor weaknesses. IMHO.
Ah, of course! And using the V-Cap coupling cap calculator, into a 33k power amp input, I get a -3dB point of 10.26 Hz with 0.47uF. And 24.11Hz with 0.2uF! So I need more capacitance, if that is correct. I have more 0.1uF FT2s, so I could parallel another 1 or 2.
But have I worked that out correctly, and would it filter the DC adequately?
EDIT. But hang on a mo! I have a TVC in between, so where am I now? Why is life so complicated? 🙂
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Hi!
I'm using a AVC(300ohm) at the output of my 26 transformer couple (LL 2745) preamp without any hum or noise problem.
I also own a 01a preamp with Gyrator output. I'm using S&B TX-101 TVC(50k ohm) at the output. Also without any problem. However, if a 300ohm impeadence AVC being used here, the 01a preamp will show some problem.
I'm using a AVC(300ohm) at the output of my 26 transformer couple (LL 2745) preamp without any hum or noise problem.
I also own a 01a preamp with Gyrator output. I'm using S&B TX-101 TVC(50k ohm) at the output. Also without any problem. However, if a 300ohm impeadence AVC being used here, the 01a preamp will show some problem.
My Sowter 9335 TVC quotes 10k ohm. Which would suggest that increasing the output capacitor on the gyrator would be a good idea. If my conclusions are wrong please feel free to jump in here. 😀
For me "300 Ohm" is uninterpretable.
TVC/AVC is a huge inductance (S&B about 400H, my nano core AVC 110H). Impedance changes as frequency changing.
I have changed to Cardas hookup wire in my 26 preamp. Very nice improvement. Just like changing from a mediocre polypropylene to a very good paper in oil capacitor. Hookup matters. It's confirmed. Case closed.
Just signal. Cardas must be making some very good litz wire (or my old unbranded hookup wire must be quite bad).
Another difference however is that this time I've done it with no screening except between volumpot and grids. Maybe too much screening can be a bad thing.
Another difference however is that this time I've done it with no screening except between volumpot and grids. Maybe too much screening can be a bad thing.
Or too little! I will have to try some screening on the 01A signal wires; the 26 with output transformer doesn't seem to need it.
Only natural as the LL2745 is 5.6:1. You know that there is an elephant in the room? Built a new power amp with lower gain and TUBES! 😛
My 26 line amp (and my 10 line amp) is cap output.
What is the lowest voltage rating output cap that I can safely use please ?
What is the lowest voltage rating output cap that I can safely use please ?
if you want to test your caps, solder cap into preamp output and bias with 1m to output.
then measure the dc voltage accross the resistor till it stabilizes. compare results with 200 , 400 or 1000v caps.
AC test would be to run 10khz into a 1k ohm load and measure voltage drop accross capacitor.
Awkwardbydesign, you can lower the gain of your amp just by placing a resistor divider at the amp input. eg. 15k / 3.3k would yield about 4.5v input for 250w.
check amp input resistor to maintain input impedance. if amp is 27k then use 22k / 5.6k as your divider
then measure the dc voltage accross the resistor till it stabilizes. compare results with 200 , 400 or 1000v caps.
AC test would be to run 10khz into a 1k ohm load and measure voltage drop accross capacitor.
Awkwardbydesign, you can lower the gain of your amp just by placing a resistor divider at the amp input. eg. 15k / 3.3k would yield about 4.5v input for 250w.
check amp input resistor to maintain input impedance. if amp is 27k then use 22k / 5.6k as your divider
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Thank you. Unfortunately I am one of those who dislikes added resistor attenuation. Anyway, the TVC attenuator on the output of the 01A is working well, it's just the hum issues I need to deal with if I want to use it without that.
I over kill on the voltage rating of the PSU caps with 630V.
If I do not want to go over kill with the out put cap, what is the lowest voltage rating that I could use please ??