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KT88 and 6SN7 tube spacing and aligment
KT88 and 6SN7 tube spacing and aligment
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Old 14th May 2018, 10:29 AM   #1
Mission720 is offline Mission720  United Kingdom
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Default KT88 and 6SN7 tube spacing and aligment

Hi - I've a question regarding physical layout of KT88 and 6SN7-G valves/tubes.

Reading a KT88 data sheet it mentions that KT88 centres should be not less than 100mm (4 inches) apart, plus that pins 4 and 8 should be aligned for each valve.

For 6SN7-G, there should be no less than 5mm between glass but I can find no other comments about base centre spacing or pin alignment.

Any comments or further guidance would be appreciated. Thanks in advance.
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Old 14th May 2018, 10:42 AM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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The sole reason for KT88s to be 4" apart is air flow. Alignment of the pins makes it easier to wire and keeps the valves the same way around.
6SN/L7 need 1/2" for air flow and it is usual practice to align the pins for aesthetics.
Always wire the heavy heaters first to minimise voltage drop. Running the 6SN/L7 heaters at raised DC voltages is not requires nor is a DC heater supply.
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Old 14th May 2018, 10:52 AM   #3
Burnedfingers is offline Burnedfingers  United States
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It depends on the manufacturer.... some equipment will align pins so everything looks pretty and others will set up socket orientation so that heater wiring is maximized. It would seem that English equipment favors the pin alignment from what I have seen.
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Old 14th May 2018, 11:30 AM   #4
Mission720 is offline Mission720  United Kingdom
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Guys - thanks for the quick response and contents noted...

Should I also look at seperating KT88 and 6SN7 by 100mm (4 inches) as well? I have the PSVANE-UK versions which are full coke-bottle shape.

So for my PP amp I would have a valve base centre square of 100mm x 100mm. This is a PCB based design with a single PCB per channel so two indetical PCBs for stereo.
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Old 14th May 2018, 01:30 PM   #5
kodabmx is offline kodabmx  Canada
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KT88 and 6SN7 tube spacing and aligment
The KT88 pins are aligned so that the coolest side of the bulbs face each other, and the hottest away from each other.

The KT88 is taller than the 6SN7, and most of the heat goes "over the top" of the 6SN7. I have then about 1 inch from the KT88 (KT120) in my build. Here's the GEC datasheet with the supplementary: https://frank.pocnet.net/sheets/084/k/KT88_GEC.pdf

Last edited by kodabmx; 14th May 2018 at 01:32 PM.
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Old 14th May 2018, 02:52 PM   #6
Kay Pirinha is offline Kay Pirinha  Germany
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Doesn't physical alignment of some tubes, KT88's in this case, only apply to horizontal mounting? The purpose of it is that the long axis of the internal system comes perpendicular, due to avoid unwanted bends of the grid wires.

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Old 14th May 2018, 03:06 PM   #7
Mission720 is offline Mission720  United Kingdom
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Quote:
Originally Posted by kodabmx View Post
The KT88 pins are aligned so that the coolest side of the bulbs face each other, and the hottest away from each other.

The KT88 is taller than the 6SN7, and most of the heat goes "over the top" of the 6SN7. I have then about 1 inch from the KT88 (KT120) in my build. Here's the GEC datasheet with the supplementary: https://frank.pocnet.net/sheets/084/k/KT88_GEC.pdf
Hi Kodabmx - yes, the datsheet confirms spacing and pin alignment. I suspect you have GT versions of 6SN7. I have PSVANE-UK versions which are 9.8cm height (without pins).
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Old 14th May 2018, 03:12 PM   #8
kodabmx is offline kodabmx  Canada
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KT88 and 6SN7 tube spacing and aligment
I'm using 6N8S actually, but yes, they're T10 tubular.
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