KT66 biasing in SLO ?

G

Giga

New member
Hey all, just for the hell of it I've been experimenting a bit with Gold Lion KT66's in my SLO.
Much to my surprise I liked them biased to 20-25 mA each where normally I'd be running my JJ 6L6's much higher.

It seems that running the KT66 high adds some really nasty artificial harmonics and clouds the bass somewhat. The lower bias gives a much cleaner tone with snappy bass.

Anyone else ran into this ?

Giga
 
I try to stay in the range of 50%-70% when biasing.
Getting to cold or to hot is not good for the ears or amp.
But there is really no perfect setting.
 
KT66's are true kinkless 6L6 tubes whereas 6L6GC's are beam powered tetrodes. they are essentially the same tube and can be ran in the same manner in triode mode but the major difference is the current requirements. KT66's will pull more plate current if they are a true kinkless tetrode design. they will also pull more heater current - .9 amps on the datasheets for 6L6 bottles and 1.3 amps for KT's. this greater pull of heater current and plate current can cause the PT to become warmer and also effect your preamp tube voltages if a seperate filament transformer is not used.

if the PT cannot supply enough current you'll see an excess drop in voltage.

this could be one reason why your increase in bias does not sound as good - it stresses the PT and/or is effecting other areas of the amplifier in a negative manner.

it is also quite common to bias amplifiers a little on the colder edge for those that actually play with volume for better bass response and efficiency whereas those who do not play at high volumes would prefer a higher bias for better high end efficiency. there is no real set of standards for tubes though - some will sound better at lower or hotter bias - it all depends on the tube and the circuit design.
 
glpg80":nhfth54r said:
if the PT cannot supply enough current you'll see an excess drop in voltage.

this could be one reason why your increase in bias does not sound as good - it stresses the PT and/or is effecting other areas of the amplifier in a negative manner.
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The SLO100 PT is more than capable of handling KT66 bottles according to Mike himself.
 
J.B.":2x9imnvc said:
glpg80":2x9imnvc said:
J.B.":2x9imnvc said:
Doesn't the SLO require a resistor change when going from EL34's to the KT66's?
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KT66's to EL34's you mean?

yeah they do.
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I meant 6L6/5881 to KT66's. Not EL34's. My bad..
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no, not required, although recommended if it is a true kinkless tetrode tube and not a beam powered triode.
 
johnnyjellybean":1vahij4f said:
glpg80":1vahij4f said:
if the PT cannot supply enough current you'll see an excess drop in voltage.

this could be one reason why your increase in bias does not sound as good - it stresses the PT and/or is effecting other areas of the amplifier in a negative manner.
Click to expand...

The SLO100 PT is more than capable of handling KT66 bottles according to Mike himself.
Click to expand...

sure it can handle it. but to say increasing current supplies does not drop other voltages is ignorant. only when it drops your DC supply more than ~20VDC is where you are loading the PT too much and going to cause problems with heating the windings of the PT too much. but i can guarantee that the loading of the PT will change with power tubes regardless of what tube is being used - ill bet your career on it :thumbsup:

if a seperate filament transformer is not used you will affect other areas on the amplifier. Basic thevenin equivalent theory being applied here.
 
Giga":8yqwe3wg said:
According to Soldano I could safely drop in the KT66's.

Giga
Click to expand...

safely of course - will it work yes. designed around that tube? possibly. will it affect other areas of the amplifier? yes. the same can be said for 6550's, KT88's, etc
 
Bottom line is whether it drops voltage in the pre, changes the sound, affects the amp in any which way.............. the SLO100 sounds considerably better with KT66. That is not just my personal opinion but the opinion of pretty much anyone who has ever tried KT66 in an SLO including Mike Soldano himself. Of course sound is a subjective thing and your opinion may be different.
 
johnnyjellybean":3mbshjvr said:
Bottom line is whether it drops voltage in the pre, changes the sound, affects the amp in any which way.............. the SLO100 sounds considerably better with KT66. That is not just my personal opinion but the opinion of pretty much anyone who has ever tried KT66 in an SLO including Mike Soldano himself. Of course sound is a subjective thing and your opinion may be different.
Click to expand...

question, KT66's vs SED =C='s?
 
glpg80":35jyhjt4 said:
johnnyjellybean":35jyhjt4 said:
Bottom line is whether it drops voltage in the pre, changes the sound, affects the amp in any which way.............. the SLO100 sounds considerably better with KT66. That is not just my personal opinion but the opinion of pretty much anyone who has ever tried KT66 in an SLO including Mike Soldano himself. Of course sound is a subjective thing and your opinion may be different.
Click to expand...

question, KT66's vs SED =C='s?
Click to expand...
I don't know the SED's or the C's. I do like the Gold Lions myself.
 
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