Look at what a friend brought to me so I look at it, because when it heats up the trebles fade away…
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Damn, those stacked vactrols need a NSFW tag
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I wonder what is it part of?
B.t.w. wouldn’t it be a cool name for a new electro/rock/punk/new-wavy/old/medium-large band: “So many Vactrols” ?
Or should that be "Too many Vactrols! " ?
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It’s part of an Mesa/Boogie TriAxis guitar preamp.
That’s a CPU controlled tube preamp with MIDI (what a mix !), from the 80’s or early 90’s.
There are even more vactrols on the daughter board (which is all blurred in the first pic) :
Here the Z80 CPU with RAM, ROM and DART serial port for MIDI :
And the whole thing :
While I didn’t really find something, taking it appart, giving it a good cleaning, looking in every corner seems to have fixed it.
Let’s see how it goes in a few weeks…
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I see some 500V caps, and some large coils probably for an SMPS-circuit.
Are the vectrols meant to ensure a good separation between the low voltage control circuit and the high voltage tubes ?
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I can only guess it’s the case.
The configuration of the tubes also seems to be configurable by the CPU, some vactrols look like they are used as a routing “grid” for the signal path.
More info here :
http://guiguijones.free.fr/Electronique%20&%20Bouine/electronique/Schema%20Amplis%20Effets%20etc/Amplis/Mesa%20Boogie/triaxis.htm
with a link to the schematics (but they are all over the internet).
Ok so I’ll relate this with a pinch of salt… (English for not sure I believe it myself.)
An ex military ferranti engineer tells me that old vactorol kit can crack and absorb moisture which can condense and vary the response with temperature.
I called BS but now have an idea for a smoke LFO.
Any thoughts?
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I have no idea, I discovered the existence of vactrols last years…
But if it’s true (and it can well be) it may be the real cause of the problem.
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If in doubt… Swap them out.
If it was so easy 
But with the number of them, and the way it is build…
And this thing is worth $2000+ … I pass and let a pro check it out
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Years ago I ordered a large amount of memory for a Novell server running a Gupta database. The memory cost over £4000. When it arrived I rang the vendor and asked if an engineer would be coming to install this expensive chip. Their response, which has stuck with me all these years was “Go on! Be a Man!”
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If it was mine, I would probably try to do it (probably… )
But it’s not mine…
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