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EL34 or 6L6g
EL34 or 6L6g
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Old 12th February 2019, 02:03 AM   #1
santitrucco is offline santitrucco  Argentina
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Default EL34 or 6L6g

Hi guys.

Iam going to do a tube amplifier single ended. I need about 10 watts. 6L6g tetrode or EL34 pentode could do a good job ? How they sound compare to triodes like 300B ?

Thanks
Santiago
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Old 12th February 2019, 02:35 AM   #2
6A3sUMMER is offline 6A3sUMMER  United States
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Without some form of negative feedback, both the 6L6G and EL34 will have a damping factor less than 1. And the distortion will be high at 10 Watts, unless (even if) you use negative feedback.

You may need to use a 6L6GC instead of a 6L6G, or use an EL34 to get 10 Watts. Plate dissipation of the 6L6G is 19 Watts, 6L6GC is 30 Watts, and EL34 is 25 Watts. You will not get 50% efficiency out of a single ended amp. (you will really be pushing it to get near to 10 Watts single ended with only one of those tubes). You need to go parallel single ended, or get less than 10 Watts.

Otherwise, you need to go with Push Pull (and that is two output tubes per channel; so if you want single ended with those tubes, go to a parallel single ended circuit).

Single Ended 6L6G or EL34 without negative feedback:

The output impedance of the 8 Ohm tap will be higher than 8 Ohms. 4 Ohm tap impedance > 4 Ohms, etc. The amplifier will not damp the Woofer.

And the frequency response of the amp output will be according to the varying impedance of the speaker versus different frequencies.

Even with an 8 Ohm resistor on the 8 Ohm tap, the amp frequency response will be dependent on: the output transformer inductance the output transformer distributed capacitance the output transformer leakage reactance.

You will need some form of negative feedback: Global including the output and driver stages Schade feedback 16 Ohm output tap to the 6L6G / EL34 cathode (make sure the phase is correct so that it is negative feedback, not positive feedback) Ultra Linear (may need to go with 50%, 60%, or 70% UL tap). A primary 40% UL connected backwards gives 60% (but reverses phase at the output). Triode wiring of the beam power tube / pentode tube

Trying all those circuits, and asking how the sound is compared to a 300B that may not need or have negative feedback is quite a task. And of course the sound is dependent on how well each of those negative feedback designs are carried out, and how good the output transformer is. Beam power tubes, pentodes, and real triodes need good output transformers.

Last edited by 6A3sUMMER; 12th February 2019 at 02:54 AM.
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Old 12th February 2019, 03:07 AM   #3
carlthess40 is offline carlthess40  United States
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Default EL34 or 6L6g

If your looking for a diy. I have the el34 Baby Huey boards and the parts kit from the group buy
But the shipping may be high as Iím in the USA
This pic is not my boards but itís the same thing. I have all the parts but the tubes, transformers and tube sockets
IMG_3255.jpg
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Old 12th February 2019, 12:08 PM   #4
santitrucco is offline santitrucco  Argentina
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EL34 pentode with some NFB ( 12db ) could work fine?
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Old 12th February 2019, 01:40 PM   #5
azazello is offline azazello  Bulgaria
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Using EL34, You will have no more 4-5 W clear sound. 10 W is not serious for HiEnd, and sound will be sharp and distorted /EL34, 6L6 are, IMO, for guitar amps/. Better choice is 300B, that will give You real 6-7 W with clear, warm sound and deep and detail sounding. /using FB will press the scene of sound/.
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...

Last edited by azazello; 12th February 2019 at 01:44 PM.
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Old 12th February 2019, 01:56 PM   #6
santitrucco is offline santitrucco  Argentina
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Ok , thanks azazello.
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Old 12th February 2019, 06:28 PM   #7
multi is offline multi  Australia
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Do you want to spend hundreds of dollars for short lived 300B?
KT88/6550 wired as triodes are excellent single ended
The kt88/6550 have similar plate impedance to a 300b, so just as good damping factor. More power than 300B's. Easier to drive. warm sound and deep and detail sounding. is a matter of opinion Better to put the money saved using 6550 instead of 300B into better output Transformers
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Old 12th February 2019, 06:58 PM   #8
H713 is offline H713  United States
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10 watts, I might suggest an EL84 push-pull, but I get that's not everyone's cup of tea.

As for SE, I second the suggestion for the KT88. A 300B is going to be a very expensive 8 watts. I haven't heard one so I can't comment on their performance. I have heard a P-P EL84 amp (similar to a Dyna ST35) that made 15 very, very sweet watts. I'd be inclined to go in that direction.

If you're set on SE, I'd either do parallel 6L6GCs or a KT88. Anything run in pentode or tetrode mode will need negative feedback to get a reasonable damping factor. No need to fear this. Lots of great amps use negative feedback to lower distortion and flatten out the frequency response.
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Old 12th February 2019, 07:15 PM   #9
GUNFU is offline GUNFU  Russian Federation
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300B unnecessarily expensive, or rather, they are artificially inflated demand. If you want to use direct-glow radiators, a good solution is the 811A, as well as the Russian and Chinese counterparts. 811 is a feature, they are the right characteristics and require a thoughtful driver, and there are also a lot of ready-made circuits for them.
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Old 12th February 2019, 09:36 PM   #10
azazello is offline azazello  Bulgaria
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Cheep tubes, cheep sound....better expensive sound, than cheep...
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...
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