Owen Y Posted September 15, 2009 Share Posted September 15, 2009 Dudes, 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... http://www.vt4c.com/shop/program/main.php?group_id=2&cat_id=1033#678 Link to comment Share on other sites More sharing options...
Owen Y Posted September 15, 2009 Author Share Posted September 15, 2009 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 Link to comment Share on other sites More sharing options...
enzedone Posted September 16, 2009 Share Posted September 16, 2009 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.......... What would something like these cost to build Owen, and could an idiot build one...:confused: Maybe I should stick to op-amps..... Brett. Link to comment Share on other sites More sharing options...
Owen Y Posted September 16, 2009 Author Share Posted September 16, 2009 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. Link to comment Share on other sites More sharing options...
Owen Y Posted September 16, 2009 Author Share Posted September 16, 2009 Pics of the linestage 'on the bench'...new transformer covers being fitted... (Woohoo!... AudioEnz Forums now automatically resizes attachments!) Attached files Link to comment Share on other sites More sharing options...
Owen Y Posted September 16, 2009 Author Share Posted September 16, 2009 Ugly underside shot. Have learnt a bit about Grounding over the past yrs so rewired the ground busses & tidied the whole wire-up. Yup, 129 plate volts... passed the 'smoke test' last night Attached files Link to comment Share on other sites More sharing options...
paul300b Posted September 16, 2009 Share Posted September 16, 2009 Nice copper plate Owen. What do your power amps look like? I'm building the JElabs FF preamp at mo, 6sl7 phono and 6sn7 line. Outboard power supply chassis. Paul Link to comment Share on other sites More sharing options...
Owen Y Posted September 16, 2009 Author Share Posted September 16, 2009 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 ) Link to comment Share on other sites More sharing options...
Jon1553552729 Posted September 16, 2009 Share Posted September 16, 2009 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! Link to comment Share on other sites More sharing options...
Owen Y Posted September 16, 2009 Author Share Posted September 16, 2009 Yes Jon, the bases are provided w holes, but I have left them unbolted for the moment while I experiment with best orientation to minimise hum pickup :rolleyes: Link to comment Share on other sites More sharing options...
Owen Y Posted September 16, 2009 Author Share Posted September 16, 2009 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 Link to comment Share on other sites More sharing options...
Owen Y Posted September 16, 2009 Author Share Posted September 16, 2009 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.) Link to comment Share on other sites More sharing options...
Recommended Posts