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Help with Hybrid Design

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I got back to this project and got it working on a breadboard.  I'm transferring that design to terminal strips and when I get that working I'll post some audio samples.  I'm not much of a guitarist, but I should be able to give some examples of the tone.   Initially, it was pretty noisy, but I'm currently rebuilding it using a shielded heater run and shielded input wiring.  The tone is never quite clean, and the amp has a very interesting distortion at full bore.  It is never really loud, so it would only work as a practice amp.

Here is a photo of the amp near its final configuration, re-mounted in the phenolic board "chassis"  I re-worked the tube mount using a piece of aluminum to remove flammable material from the build.

Well, I "finished" my first junkyard amp project.  I decided to make this a small combo with an external speaker jack that will bypass the internal speaker.  I goofed on the dimensions of the cabinet cross pieces.  Where there is a triple thickness of wood on the sides, I only planned for a double thickness.  My idea was that a three-inch tall strip attached to each side would support the top board of the cabinet and the middle board of the cabinet which served as both the shelf for the amp innards and the top of the sealed speaker enclosure.  The bottom, front, and back of the "chassis" are pieces of phenolic board salvaged from computer floor tiles.  This was salvaged from floor purchased new around 2006, so it probably doesn't contain asbestos but I wore a respirator when I cut it, just in case.

The speaker is an Oxford 6x9 speaker from an old Chrysler complete with a high-tech whizzer cone. :lmao:  I know these trunk speakers pretty much operated in an infinite baffle environment, but I tried the amp both ways and I liked the sound better with the back sealed.

All in all, I have about 45 dollars in parts.  The PT was $10, the OT was $3 and the tube was less than $2.  Speaker was junk, the floor tiles were junk, wood was lying around the shop.  The biggest expenses were the filter caps and the grill cloth.

Modifications to the original circuit included a couple of high-frequency shunt capacitors to prevent oscillation in the SS preamp, two cathode bypass capacitors (one in all the time, the second put in circuit by the right-hand switch),  a bright capacitor around the volume control, and a tone control pot between the 1st and 2nd stages.  I played around with values for all of these but ultimately the differences in tone are all very subtle, the volume pot has more impact on the "tone" of the amp.  Turning down the amp to where it plays cleanly makes it really quiet but the tone is warm and round.  About half-way up, things get interesting, and running full-tilt there are bizarre things happening to the low frequencies that may or may not be musical, depending on your personal taste.

I truly hope to have sound samples soon.


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