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Vintage threads from the first ten years

Another Construction Question

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4/3/2000 5:28 PM
Mathew S	Another Construction Question Anyone give me a figure on how far apart to space the EL34's on the chassis?     What is the minimum distance for these valves?.

 

4/3/2000 7:42 PM
ken gilbert	generally, it depends, but given the following:     ---bases down   ---run at moderate plate dissipation (about 20Wpa)   ---no forced air cooling   ---good convection airflow     i would say 1.5" at their closest point. that means about 2.25" center to center. you can mount 'em closer than that if you need to, but there are compromises.     kg

 

4/3/2000 11:27 PM

MBSetzer

Traditionally, the EL34 has a smaller diameter bulb than the base of the tube. The base of these is usually about the same diameter as the octal tube socket.     The historical US equivalent 6CA7 has a bulb larger in diameter than the base, so maybe that needs to be taken into consideration.     Or if anyone might be thinking about rebiasing and trying the bigger octal tubes like KT88 or 6550A, not only are the bulbs bigger yet, but the bases are also larger in diameter than the socket itself, they just overlap onto the chassis.     If Marshall had made their EL34 sockets too close together, they would not have been able to use 6550's in the US-distributed amps back when their amp popularity was gaining faster than the availability of EL34's in the US. Of course some people would think that's a good thing . . . but I like my 6550's     Hope this helps,   Mike

 

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