I've been trawling the internet for some views on the EL34 vs the 6L6GC but all I can find is guitar amps.
The 6L6GC is supposed to be more linear but how do they really compare in the Hi-Fi world ?
The 6L6GC is supposed to be more linear but how do they really compare in the Hi-Fi world ?
I too noticed that too but I have various search engines -smaller but more independent searching .
Personally I prefer the original KT range which were designed for audio but when comparing the two you mentioned you can get opposite views from guitarist websites and audio websites .
IE- "6L6 smoother but lacking in mid-band "/ "EL34 more forward mid-band etc " .
The guys here will have views on this .
Personally I prefer the original KT range which were designed for audio but when comparing the two you mentioned you can get opposite views from guitarist websites and audio websites .
IE- "6L6 smoother but lacking in mid-band "/ "EL34 more forward mid-band etc " .
The guys here will have views on this .
Quite simply put, beam tetrodes have more IMD, as well as higher odd harmonic THD when used in PP amps.
(the 807 is a good example, which is basically a high voltage 6L6).
Pentodes are fundamentally less efficient because of the non aligned grids and high g2 emissions, but have lower IMD values, which makes them sound less dissonant.
The beam tetrode became king, because of the higher outputs, but the IMD spectra of both KT66 and KT88 are absolutely horrible even in Keroes "ultralinear".
I imagine these modern Russian made, KT90-120 are a whole quantum leap worse.
Read the data sheets, you will be suprised to see typical IMD values around 5% from GEC for the KT88.
The 807/5B254M straightens out, the closer you get to it melting, as does the TT21 (the high voltage version of KT88).
That is perfectly logical when you hear how much better they sound when running at high quiescent current to within 90% of max Pa at idle, at or above theoretic max Va, and with the loadlines optimised.
(You can see the TT21 running well at 1-1.2kV, like the 807 at 800-900V).
(the 807 is a good example, which is basically a high voltage 6L6).
Pentodes are fundamentally less efficient because of the non aligned grids and high g2 emissions, but have lower IMD values, which makes them sound less dissonant.
The beam tetrode became king, because of the higher outputs, but the IMD spectra of both KT66 and KT88 are absolutely horrible even in Keroes "ultralinear".
I imagine these modern Russian made, KT90-120 are a whole quantum leap worse.
Read the data sheets, you will be suprised to see typical IMD values around 5% from GEC for the KT88.
The 807/5B254M straightens out, the closer you get to it melting, as does the TT21 (the high voltage version of KT88).
That is perfectly logical when you hear how much better they sound when running at high quiescent current to within 90% of max Pa at idle, at or above theoretic max Va, and with the loadlines optimised.
(You can see the TT21 running well at 1-1.2kV, like the 807 at 800-900V).
I've been trawling the internet for some views on the EL34 vs the 6L6GC but all I can find is guitar amps.
Some EL34s are built as pentodes, others are built as beam power. Another way to confuse us!😕
Some EL34s are built as pentodes, others are built as beam power. Another way to confuse us!😕
I am not sure whether this applies to P-P like the 5-20, but in my SET the typical anecdotes about EL34 vs. 6L6GC ring true. In other words, the EL34 is more midrange-forward than the 6L6GC and the 6L6GC has fuller/richer bass (but nothing missing in the mids and highs). Grain of salt, and all that...
To further muddy the waters, consider the beam power tetrodes that are purported to be "equivalent" to the true pentode EL34: the 6CA7 and KT77.
FWIW, I think this is yet another case of what amp, which speakers, whose ears, etc. ad infinitum.
If you want to maximize open loop IMD performance in full pentode mode, regulate g2 B+ at some fraction of anode B+.
FWIW, I think this is yet another case of what amp, which speakers, whose ears, etc. ad infinitum.
If you want to maximize open loop IMD performance in full pentode mode, regulate g2 B+ at some fraction of anode B+.
Originally EL34 were all Pentodes. Had a Suppressor Grid, g3; which is pin 1, and must be connected by the circuitry (outside of the tube). Do not let g3 float.
Originally KT77 were all Beam Power tubes, had Beam Formers. The KT77 Beam Formers are connected internally in the tube.
The EL34 and KT77 have very similar specifications, so there may be some that are built as one type, and labeled as another type.
Confusing, Yes.
Another set of very similar specification tubes:
6BQ5 was originally a Beam Power tube.
EL84 was originally a Pentode
There are many tubes that are dual marked: 6BQ5/EL84.
Confusing, Yes.
Originally KT77 were all Beam Power tubes, had Beam Formers. The KT77 Beam Formers are connected internally in the tube.
The EL34 and KT77 have very similar specifications, so there may be some that are built as one type, and labeled as another type.
Confusing, Yes.
Another set of very similar specification tubes:
6BQ5 was originally a Beam Power tube.
EL84 was originally a Pentode
There are many tubes that are dual marked: 6BQ5/EL84.
Confusing, Yes.
Last edited:
Since this is essentially a mildly tweaked mullard 5-20, it has a decent chunk of negative feedback. I have tried pentode EL34, beam former 6CA7 and KT77 in my tweaked 5-20 and can state, there is basically no detectable difference to my ears. Even trying different input pentodes between EF86, E80F and 6BR7 barely registered a difference.
Kei,
Did you also do some "Coupling Capacitor" rolling in that amplifier?
It might prove to be an interesting study.
Did you also do some "Coupling Capacitor" rolling in that amplifier?
It might prove to be an interesting study.
I did change the capacitors that couple the phase splitter to the output valves a few times. Same story, not one iota of audible difference to my ears. That included changing the value from 0.47uF to 0.1uF to help with feedback. I wasn't trying anything really fancy though, just some various MKP parts from nichicon, kemet and vishay.