Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Archives of favorite topics => Topic started by: tubenit on August 06, 2014, 06:50:35 am
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I have had to look this up several times over the years and it's somewhat challenging to find the information. So, I will post this for consideration.
I found posts that suggested the "center to center" spacing be 1.5 times the diameter of the tube.
I found a chassis template for a Dumblish chassis that used 1&1/8" spacing for preamp tubes and 1&1/2" for power tubes.
I found a chassis template for Trainwreck type amp that used 1&1/4" spacing for preamp tubes and 2&1/4" for power tubes.
With respect, Tubenit
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To add for possibly debate of things to consider, from TUT3, Kevin O'Connor, page 4-19;
Socket Spacing - center to center (min.);
6V6 - 1.75"
6L6 - 2"
EL34 - 2.5"
6550 - 2.5"
KT88 - 4"
He also talks about the 'hottest part of the tube' being the plate seems * and that it's best to not align the tubes plate seems facing each other. (* For some reason the Sovtek 6V6EH plate seems are the coolest point in those tubes.)
It would be interesting for guys with classic amps to post the C/C measurements of the power tube sockets with tube type.
Brad :icon_biggrin:
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The old M-O Vlave Company / Genalex KT77 data sheets recommended not less than 3.5" and, when vertical, all keyways to line up along the centre line of all the valve centers. If horizontal mounted the spigots should be in the vertical plane.
And here is a photo of the implimentation in a very well respected British amp of that time:
half the recommended spacing at 1.75" and the keyways are all at 90° to the center line of the valves.
These things get really, really hot. Even though the amp is more than 27" wide, the massive iron left little room for the KT77s.
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Looking at the picture they have all the KT77 plate seams in line with each other.
What brand amp is it? (Hi-Watt?)
Brad :think1:
Willabe, the brand is Burman and pretty much unknown outside of the 70s / 80s session musician circle in England.
You are fairly close with Hiwatt, our old member KT77 once described these as being like a rabid Twin or a Hiwatt on steroids. They were handmade in Newcastle as a development of a respected PA company and guitar amps could do absolutely anything except Marshall buzz :-)
The image above shows the rare as hens teeth bass amp. The few that have used it say it knocks out an SVT. That is quite a claim, I think it sounds very fine, but I'm biased having grown up with these things.
The military build quality took the best ideas of both Hiwatt and the Twin, but that put the price way off the radar of anyone except professionals. They were tracked on many albums during late seventies, early eighties. Today they are virtually unkown and too rare to ever crop up on internet chatter. So they stay a well kept secret by default of hardly anyone getting the pleasure of using them.
OK I checked the keyway - when i wrote before it was from memory - but it turns out correct:
they are indeed at 90° to the valve center line. The spigot is at 90° to the plate welds on both these GEC branded 77's and the M.O.-V Golden Lion 77s.
tony
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Sluckey's 6V6 Plexi with 1.75" centers