Crawls Backward (When Alarmed)

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'42 Tube Amp DIY Project - Finished

After making sure it works, it's just a matter of mounting the chassis in the frame.  I slipped the chassis down into it and ran #8 wood screws through the holes in the side of the chassis and into the frame.

Here's some pictures of the completed final amp:

I went with the tubes lined up in a row to be able to admire their art-deco-ness.

The color combination of the painted chassis and the maple frame came out ok I think.

The input jack is next to the volume pot.  I insulated the jack from the chassis with nylon washers.  The ground side of the jack goes to the input side star ground.

The knob for the volume control came from my stash of vintage knobs.  It was probably on some kind of communications radio originally.

The speaker outputs are next to the output transformer.  You can see the exposed wiring - I will put some sleeving over the terminals at some point.  The side facing the camera is the speaker side.  The other side is the high-voltage side - I'll insulate that too.

Who woulda thunk you could get a decent piece of flame maple at Home Depot?  Came out pretty well.

More detail.  The switch came from my junk box of old switches.  Just polished it up and put it back into service.

You can also see the pop rivets I used instead of screws for the tube sockets and the terminal strips.

Engraved base 42 tube.  I have a small stash of 42s - I plan to experiment with different ones for the heck of it.

The amp runs about 285 volts on the plate of the 42 and about 160 volts on the plate of the 6J5 input tube.  I'm probably getting about 3.5 - 4 watts out of it. 

Here it is in operation.  I almost put a pilot light on it, but I'm glad I didn't.  It's pretty easy to tell when it's on :-)

I'm using it in a bedroom driven by a Dynaco FM-3 into an old Boston Acoustics speaker (not shown).  It's ok volume-wise.  I am planning some full-range speakers and I'll use the amp with one of those eventually.

The amp is dead quiet.  No discernable hum or noise.  It was a good test bed for my future 2A3 I can experiment with different coupling caps and output transformers.  The circuit is so simple that any change should be readily noticeable.

The station I was listening to was playing some string quartets which sounded nice...and somehow appropriate for this little amp to be playing.

It sounds good - the mids and highs sound pretty good, and as expected, there is a lack of bass that I'll try to address.  But it's not too bad right now with the 125E output transformer in it.

One last look at the wiring.  I tried to keep it as tidy as possible.  


Post a Comment 2 comments:

  • Toy Making Dad said...
    June 4, 2010 at 1:13 PM
    Outstanding. Looks great. You should be really proud of how the maple finish came out. It looks amazing. The "glow in the dark" aspect of the tubes is cool. Very classy.
  • Anonymous said...
    June 29, 2013 at 1:00 AM
    That is a Japanese-made "Sato" brand knob which was manufactured from the mid-1960's on. Sato made a lot of OEM and replacement components and were considered a high-quality parts manufacturer. I fitted lots of them on valve-based audio mixers where they looked very professional. I can't agree on your use of pop-rivets though - I would have used pan-head machine screws to maintain that vintage look. Also, lots of products used "hammerglaze" or crinkle/crazed/baked paint on metal chassis and cabinets all through the valve era.

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