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Old 4th October 2006, 07:51 AM   #1
felixx is offline felixx  Romania
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Default silicon or tube rectifier?

So...I ask .....silicon or tube rectifier...for a line preamplifier?
This question came up on my mind often because both ways have some issues.
That who experimented both ways,please describe the suitable way.
Thx.
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Old 4th October 2006, 08:13 AM   #2
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This topic was discussed recently, in this thread, so you might like to see if it answers your question.
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Old 4th October 2006, 08:28 AM   #3
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Since I never commented in that thread.....

When each circuit is on the breadboard, I try tube, regular SS and fast recovery diodes and go with the ones that sound best for it
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Old 4th October 2006, 12:58 PM   #4
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My latest (SE power) amp has both, with a switch. You can switch on the fly. So:

Loud rock at high volumes ----- silicon, there is more headroom due to 25 more volts. The sound is punchier and a little more dynamic. Again this may be due to the higher voltage.

Female vocals, and generally simpler "quiet" music ----- Tube (5AR4). It just seems do be slightly more detailed. May be psychoacoustic (I know where I put the switch). I have not yet conducted random blind testing, but it is coming.

For average listening at far less than full throttle, it doesn't seem to matter much. The FFT analyzer shows NO change in the noise floor or hum level. There is a 2 or 3 db change (SS is worse) in the level of residual 180 Hz, but this is 85 db down, so it really doesn't matter.

PS circuit is: Transformer ----- rectifier (either one) ----- 47uF cap ----- 12 Hy choke ----- 120 uF electrolytic in parallel with a 100 uF motor run cap.

How do you switch on the fly. Leave the tube rectifier in the circuit at all times, wire the diodes (usual full wave CT circuit) to the transformer. Wire a switch (SPST) between the junction of the 2 diodes and pin 8 of the rectifier. With the switch open the tube rectifier functions normally. With the switch closed the diodes are in parallel with the tube, their low forward voltage drop will totally take the tube out of the circuit. If you really want you can pull the rectifier from its socket in the SS mode. This gives me 2 more B+ volts due to the fact that the power transformer doesn't have to light the rectifier filament.

I use an appliance switch that is rated for 230 volts AC at 10 amps. These seem to live at the higher voltages and lower currents found in tube amps. I also have a switch for triode - UL switch on the fly, and CFB on - off. When I finish packaging this amp there will be a few more switches, including a couple that do nothing. They will only be marked with numbers. I plan to loan the amp out and ask for feedback as to the reviewers favorite switch positions, and why. This should get some interesting (and potentially useless) feedback.

I think that in a preamp, with GOOD grounding and layout, there would be even less difference.
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Old 4th October 2006, 01:02 PM   #5
SY is offline SY  United States
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Quote:
I think that in a preamp, with GOOD grounding and layout, there would be even less difference.
Bingo.
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Old 4th October 2006, 01:43 PM   #6
jlsem is offline jlsem  United States
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Quote:
I think that in a preamp, with GOOD grounding and layout, there would be even less difference.
But a difference nonetheless...
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