• 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.

assembling a LITE LS-69 Hybrid Balance pre-amp

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#2
I have exactly the same problem with my LS 69. Seems to be a general fault. It is probably easier to just reverse the polarity on the output side of the preamp. Some day I may actually rewire the output. Nice sounding amp but perhaps a bit on the dull side. I had to eventually switch to EH6992 Gold tubes to get the right balance between the registers. Tried NOS Siemens E88CC. Eventhough they had a very very nice midrange there was a total lack of information above c:a 6kHz (according to a test record) and the whole set sounded like an old tube radio. Would have liked a bit deeper bass as well but it is a tube amp, you na´t have it all. My LS 69 is driving a Krell 250a through the balanced connections. Fantastic holographic performance. The LS 69/Krell combination seems to be a perfect match, especially on CD/SACD.
 
#3
finally:

ls69.gif
 
#7
so is it better to quadruple the supply (i dont have enough space in the case)

double the supply + 2 glow tube that power 2 preamp tube each

or one supply ton of capacitor that ends with one glow tube that power 4 preamp tube (more money for capacitor of big value 450 volt dc bypass with expansive mica)

should i bought a bigger case to do all the above hihihi

thanks for the answer of people with more gray matter than me

Martin
 
#10
the transformer that i use is a antek that gives me 180 volts ac
it rectify to 251 volts dc with no load
when i hook it up to the regulator tube that is hook up to the preamp pcb i get 152 volts dc (HV only)
and when i start the drain (-24 voltd dc) and the filament (2x6.3 volts dc)
the hv supply sags to 146 volts dc

and my dc power supply is running hot, you see the 300 ohm resistor

hot.gif
 
Last edited:
#17
yilingcheng said:
seems that it is reversing polarity...

why is that? and what's the consequence of using it with different switching amp like Red Dragon M500MkII and class d audio SDS-258?

its a bummer if i have to reverse loudspeakers polarity...

([FONT=Verdana, Arial, Helvetica, sans-serif]Hybrid tube balance pre-amp using FET input, tube cathode follower output)[/FONT]

http://www3.telus.net/gagnonma/LS69.jpg
Click to expand...

by the way the polarity need to be reverse to get the sound to float between the my KEF speakers
 
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