56/76 Tube Line Stage

PabloL

PabloL

Active Member
Just finished this tube line stage from parts I had laying around in the shop. The I did buy some cheap Radio Shack enclosures to house them in. The circuit is a simple Resistance Coupled Amplifier from the chart in the RC-15. The heaters are DC, I used some LM317's and can select both 2.5v for the 56 tube and 6.3 for the 76 tube. The boxes were small so I put the PSU in one and the Line Stage in another. The PSU is a simple bridge rectified 120v winding to a C-LC-RC (30uf - 6H/45uf - 10ohm/45uf). The line stage has a 300ohm grid stopper, 100k Rp, 4500ohm Rk, 100uf Ck, 4.5uf coupling cap, and 100k Rg.

It sounds great! A little "warm" which tones down my speakers which are a little "bright."

I might have to make some wood enclosures to class it up a bit...
 

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soundmotor said:
Nice work, is it microphonic at all?
Click to expand...

Yeah, if you knock it around you can hear it, and the location of the knobs makes it a bit fiddly. But I got a boat load of 56's from a different project, I plan on working through them to find the best ones.
 
Very nice! I've been wanting to build something with the 56 and 76 tubes I have.

Good choice on the Solens. I really like those caps.
 
dsndblm said:
Very nice! I've been wanting to build something with the 56 and 76 tubes I have.

Good choice on the Solens. I really like those caps.
Click to expand...

Me too, I like how they have a wide selection of high voltage film caps, as well as being widely available. I have used them in PSU's as cathode bypasses, everywhere really. I usually get the Xicons and Orange drops for general use though.

I buy my resistors in bulk from Hong Kong on Ebay, however, many of my chokes and power transformers, and WW power resistors, come from old organs and broken electronics bought on the cheap. I recently found a bunch of good terminal strips in an old audio generator.

Pablol
 
PabloL said:
Yeah, if you knock it around you can hear it, and the location of the knobs makes it a bit fiddly. But I got a boat load of 56's from a different project, I plan on working through them to find the best ones.
Click to expand...

I built a 56 LS years back but only had a few tubes to choose from. I never got it close to usable and gave up on it.

(You've got the ideal situation where you have many tubes to choose from.)
 
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