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Old 14th December 2001, 07:12 PM   #1
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Default EL34 vs. 6L6GC for 1ST DIY Tube Amp?

Hello a friend and I are starting to layout our first tube amp, we've built several SS Amps, and want to try tubes. Neither of us have particularly efficient speakers so we're leaning Push-Pull, 25 to 40 W. For the output stage, any sonic/practicality opinions on the EL34 vs. 6l6gc and/or are there other tubes (similar price range and commonly available) that should be looked at? The plan is to rig the amp to allow switching between triode/ultralin./pentode-tetrode just to allow us to learn a little more and hear some differences. Thank you for your advice, its appreciated!
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Old 14th December 2001, 11:53 PM   #2
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EL34 vs 6L6

Pete,

Given a choice between EL34 and 6L6, I would have no hesitation in selecting 6L6.

At the risk of being shot down to pieces, I have to say that EL34 is not a good design from the start. This tube was favoured by many manufacturers because you could apply 800 volts on the Anode; and this means more watts per dollar in a commercial sense. The only good EL34 that I have respect for is the old GE 6CA7 manufactured in USA. If you want long (3-5 years) trouble free operation do not apply more than 400 volts on the screen and anode of current production tubes.

6L6 on the other hand is a more robust design. Philips ECG STR-318 (STR stands for Special Tube Request and please note that I am not crash hot the 318 number… I am just quoting from my ROM…..rusty old memory) 6L6GC is very good tube if you can find some somewhere. Markings are in Blue colour on the envelope. This is a true 35 watt dissipation tube. This tube can take some abuse from a beginner to tube audio.

My approach to DIY is to achieve performance at a level higher than most if not all commercially available designs. DIY enthusiast should not compromise, if possible. Price is not the object.

Since you are willing to experiment, I would recommend you to start with a 250 volt power supply and a 4200 ohm (load for two tubes in PP) primary PP transformer. You will need to apply feedback in the tetrode mode. The lower voltages will help you to try the different configurations that you propose.

You will also need a flexible output transformer. Have four 1 ohm secondaries that you can configure in many ways. These are separate windings and not taps.

You will also need two separate B+ windings on your power transformer with three taps (perhaps 220V, 160V, and 110V) on each winding. You may connect these taps to obtain various voltages. You may also consider 150VA for each B+ winding.

Personally, I do not like tube rectifiers. I use solid state devices in all of my designs.

If your goal is for high quality sound, then use choke input filter. Two stage filter is recommended.

The above are recommendations to get you started with a range of flexibility that beginners need. I presume that your experiments will continue over a period of time to warrant custom made transformers. Always be careful when dealing with high voltages. An occasional zap may be good for the heart but a few in succession can be lethal.

Mohan
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Old 15th December 2001, 12:20 AM   #3
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Pete,
I use 6550s (a push-pull pair will give you about 75W, class AB), but I can give you some feedback on the 6L6 from my musician's viewpoint, crossed with the stereo viewpoint.
I have not used the 6CA7, and have no opinion as to sonics. There have been some well-reviewed amps that use the 6CA7, but I haven't heard any of them, myself.
The 6L6 is generally regarded as being somewhat more oriented towards mids and highs (a lot of guitar amps use them--this in contradistinction to bass amps, which tend to use 6550s).

Grey
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Old 17th December 2001, 02:37 AM   #4
TJ is offline TJ
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Hi there,
i've been using valve amp for many year and this is own MY opinion about this two tube. The EL34/6CA7 i like it most b'coz it sound warmth and more power . 6L6GC tonal balance good and clear in hi freq ! BUT if u change it with GEC KT66 (If u still can found the brown base ) it sound fabulous ! im using GEC KT66 with my Sansui AU111. If u want something cheaper and can learn more i think u should stick with EL84/6BQ5/N709/7189 . Parallel push pull in ultraline. 2 pair u can get a healty ~30w , pppse ~ 15w , pentode ~ 35 w ! ?? Good luck !
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Old 17th December 2001, 02:51 AM   #5
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Default EL34 vs 6L6

Given the choice I would go with the 6L6 just because the options on good tubes are much better. If you can buy used/test good old stock matched quads you won't spend a lot of money and with the new ones that are out there you can really put together a nice library for a lot less than EL34s. EL34s might be more interesting in that I think there is a wider range of qualities but for myself the prices of NOS EL34s are way out of line. I have a few 6L6 amps and I am particularly fond of my Bogen DB20DF which I have a pair of the old coke bottle Sylvanias in. I have a pair of Allen 20s and I have a matched quad of GEs in them. The old RCA Black plates are very good. All these tubes I pulled from old consoles or salvaged out of ruined Conn organs etc. I haven't listened to any of the new ones yet but understand that the quality is good. Another tube that is very good, low priced, large variety and too often overlooked by the tube audio group is the 6V6. Might want to play with some of those too.
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