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Old 31st July 2007, 12:52 AM   #1
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Default Orientation of EL34 Tubes

Hi,
Simple question (I hope!). Is there a correct/preferred orientation for the EL34 tubes. By orientation I mean what part of the tube should face the front of the amp. I have bought the JJ's and they have the logo stencilled over the part of the tube with the little slots in the grid directly behind but I have seen some amps with these little slots facing the side of the amplifier. Is there a technical reason favouring one orientation or another (keeping in mind also that I may substitute other tubes in future) or is the orientation simply cosmetic. Common sense would seem to dictate that the stencilled logo should face forward but it appears that different tubes (particularly NOS) have the logo stencilled on other parts of the tube. Any thoughts either technically or aesthetically based?
Cheers,
Rob
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Old 31st July 2007, 01:54 AM   #2
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Hi Rob,

Whenever I build an amp my first consideration is the orientation of the tube socket in relation to the other parts connected to it, and also where they are on the chassis. This includes filament and power wiring and to a lesser extent smaller componets. There is no technically correct orientation from a fuctional standpoint. This is provided the tubes are vertical. Horizontal mounting does have rules and constraints.

Cosmetics and aesthetics are just that, and they are governed by personal taste. I pay more attention to those if the tubes are big outputs like 845s or 300Bs. I like the plates to be square and perpendicular to the chassis line. I also like them forward where I can see them and not hidden behind transformers. Remember that when the amp is done, and you're sitting several feet away, you can't see the labels anyway. You'll be watching the warm glow more then anything.

Victor
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Old 31st July 2007, 03:19 AM   #3
Colt45 is offline Colt45  Serbia
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Just cosmetic.


Although I like to have all the keys pointing the same direction.
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Old 31st July 2007, 03:43 AM   #4
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Heater pins facing the chassis wall, unless you like hum or are exceptional with layouts (doubtful and doubtful if you have to ask).
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Old 31st July 2007, 04:33 AM   #5
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Rob,
You need the Morgan Jones "Building Valve Amplifiers" book. It discusses these sorts of issues.

One good piece of advice above is to keep the heater wiring (pins 2 and 7) away from the feed to grid 1 (pin 5). I like pin 5, the input grid to be toward the driver circuitry.

I try to stick to that BUT I also try to arrange for the anode sides (the flats on the outermost box structure) which throw off the most heat, to be directed outward or at least to areas of least density of other components AND particularly not toward electrolytic capacitors which don't like heat.

Hope this helps.
Cheers,
Ian
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Old 31st July 2007, 10:07 AM   #6
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Hi,

Thanks for the replies. Good recommendation Gingertube, I do have the Morgan Jones book - I find it useful but I must admit I find this forum a little more helpful for specific issues. Morgan Jones seems more concerned about heat dissipation than hum which is not mentioned in his book (as far as I can see) with respect to valve orientation except perhaps for the inference that the orientation of the heater pins outward allows for a more direct route for the heater wiring to follow the chassis.

Judging by the varied opinions, this issue is perhaps not quite as straightforward as I hoped. In my particular design, the output tubes are aligned in a row in the mid line of the chassis (in front of the transformers) with adequate space between them for heat dissipation.

I will stay tuned with interest.

Cheers,

Rob
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