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Tube Linestage mods

Owen Y

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Been quiet chez mois for a while, too much 'real 'work to do but good to see that the DIY dept on here is active.


Sometime ago (yr 2000) I built a linestage based on a published design employing the 5687 twin triode... a fairly common, not too boutique, tube introduced ~1950. Very simple design, single tube, 20dB (10x) gain, but employing an output transformer (ie. transformer coupled to the power amp). It was my first scratch build & in my naivety I didn't attend to some basic precautions... namely, small signal transformers are prone to noise pickup & should be shielded.


It's time I fixed this, so I spotted some nice Chinese made 'transformer covers' on Chung's vt4c site...


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This was the finished WOT(with output transformer) linestage, alongside a 'Phi-42' phonostage (42dB MM gain, on RHS, built later) - both published designs by Diego Nardi in Italy.


The boxes, in Jarrah, were made by Henry (recomm by Phil at Smith Sound) & as you can see, I was taken by the Audio Note aesthetic at that time ;)


The output trannies are the 2 plastic encased boxes at the rear.

Attached files =-phi&wot~1.jpg
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They are extremely nice looking


I have always wished for something like this, but my skills don't extend that far I'm afraid.

I wouldn't know one end of a valve to another. And I've heard that that are extremely expensive to build and they don't last long? Is this correct? no idea..........:o


What would something like these cost to build Owen, and could an idiot build one...:confused:


Maybe I should stick to op-amps.....;)




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Hi Brett,


A valve/tube linestage is extremely simple, circuit-wise, as a single valve is all that's needed to amplify a signal the req'd 10x for a line preamp.


The hard part, as with all DIY amps, are the PSU & chassis. So, I always suggest starting with a 'kit'.


Can't remember if we had a DIY Tube (Line) Preamp thread... maybe we should start one.

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Power amps are presently 2A3PPs... see this earlier thread in Feb.


Don't ask how I found the time ;)


Joe Esmilla is a cool dude, been around the 'underground' tube community a while... I'd like to see your preamp schematic, esp battery biased phono, naturellement!

(Open a thread for your build, I'd like to follow a JE Labs project :) )

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Lovely looking job!


How are you going to mount the new covers? Stupid me... I just saw you already have them mounted! So final pics please!


I forgot, Valves will last for a long time... and as long as you treat them with respect they will give fine service.


They also give you the opportunity to tube roll and change the sound for not a lot!

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Incidentally, the underside looks rather busy cos the 2 cylinders on the RHS are a later addition...vol control TVCs & the 2 big caps on the LHS are humungous electros specified by the designer to provide a 'quasi battery' supply.


Whilst the signal cct is extremely simple (just a single tube), the PSU is rather (over?) complicated!


Also, against the (top of pic) side is a bd with a reg'ed 12vdc heater supply, which also contains a 5v supply for input relays - the latter eventually disabled when I discovered that the relays were significantly detrimental to the sound.


You can see a bit better what's going with the big caps removed...

Attached files 103164=3149-DSC04690.jpg
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The idea of input relays is cool in theory (input switching located right at the input sockets instead of taking rear input wiring all the way to a front selector switch) but in practice, relays (Omron GSV-2) are sonically less desirable than an old fashioned silver contact switch!


YMMV of course.


(You can see the bank of black relays stacked on a pc of veroboard at top RH cnr right next to the input RCAs.)

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