• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6V6 line preamp

diyAudio Chief Moderator
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To use the most waste heat efficient approach is the priority I think. That would be a low drop out voltage regulator with mains worse case drop kept in mind and a sink that will keep it long term reliable. Each time we halve the temp we quadruple life expectancy in electronics.
 
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This is a wonderful line amp, have been listening to it for the past week.
But it seems to have a bit too low a gain, I crank it all the way up and it's still bearable. Was the gain at 15? Must have lost it some where?

The gain was measured as 15dB with 5K load and informed here. 15dB or ~5.5 times and you get 7 times because you ended up with more load due to less B+. So all is normal.
 
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Ok, found it, the gain is 7, no wonder it's has the same feel as my(once upon a time) 01A preamp.

Salas or anyone,
have tried cascade DN2540 CCS on the plate? And Schottky diode at the cathode?

I had tried other Mosfets, enhancement mode ones in cascode, the gain went up to 10 times or something don't remember exactly it was long ago. But I remember I did not like it better and I put the resistor back. Your mileage may vary.
 
Hi all, Yassas Salas,

I have a paire of OPT (5:2) that would be good for preamp and was looking for tube that could feat them.
I found the 6V6 interesting and had a look on GG with "6V6 pre amp" wording and found this 112 pages thread that is runnning since 2007. Wow.

So, as I do not plan to read all this pages, sorry for that, what is the latest schematic of this pre amp?
Do you think that my transfo with 5:2 (2,5Kohm/400ohm) would be good for the 6V6?

Thanks,
Vincent
 
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You would need a primary around the 8K mark to load a 6V6 well for THD, certainly no less than 5K. The schematics are linked from post#1 either for normal gaining preamp or impedance buffer type. The only further comment is 7.5K load resistor and 300V can be used if the 330-340V aren't handy. Voltage gain is 15dB with 5K resistive load or 17dB with 7.5K.
 
Hi Salas,
thanks for the fat answer and sorry, I´ve been to fast and did not saw the link on the first page. shame on me.
I was thinking to have a 800ohm resistor on the output to fix the working resistance to 5Kohm on the tube side. That would feet with your advice.
the only doubt I have is about the impedance of 800ohm on preamp output.

How to know if it will be good calculated for my amp?

Vincent

Vincent
 
diyAudio Chief Moderator
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As it is with 5K resistive load it has 1650 Ohm output impedance in gain mode or 250 Ohm in buffer mode, still its vigorous subjectively.
It runs 20mA+ bias current though, not a common line pre config for tubes and bias choices.
So your 800 Ohm halves that gain version's Zo figure already. Check point should be where you go for voltage gain at secondary and OPT ratio.