Category Archives: tube

Tube Amp

I have other loves in life other than cycling – some of them being electrical projects. I’ve been working on this baby for a while – but, only recently has it recieved its power transformer. I pulled the transformer from an old ceiling fan; 120v to 24 volts, with ~ 1/3 amp supply capability. And that voltage happens to be *almost* exactly what I need for the heater filament of the single 25EH5 tube that comprises the amp. However, measuring the wall voltage at an actual level of 126 volts, the voltage coming out of the transformer is actually above 25 volts (ie. 120/24=5, 126/5= 25.2 volts). This is well within the 10% tolerance of  the vacuum tube’s operational voltage range, being only .9% off of ideal. Right now, until I find/build a proper wooden cabinet for it, the entire amp resides in an old margarine container.

Fire hazard: kids at home, never mount a transformer to anything
using tape. Even if the tape is electrical tape.

The rest of the amp’s circuit is very basic; it is “single-ended”, has a simple solid-state bridge rectifier (although I was contemplating a tube rectified version…), and uses random bits and bobs for its other electrical organs. Yes, low-fi, but still should have that “mellow”,  interesting tube-based sound.

The dark (and tangled) underbelly of the beast….

I’m still waiting for a cheap 1 watt resistance-matched output transformer, from the 5000 ohms of the tube’s plates to 8 ohm for the speakers. As this has only cost me $15 for all the parts so far, I’d rather not pay $30 for a single part if it can be had otherwise!

Crappy 15-sec B&W exposure of the tube in operation

The Frugal Man’s Patch Kit

Because of all the punctures I’ve had to patch, I came up with a use for the beyond-use tubes I have lying around…. I made them into new patches! Turns out you can use strips of the butyl rubber from old inner tubes to patch other inner tubes quite reliably. The extra stretch compared to regular patches may also be a bonus for high-pressure tubes, or for tubes in really wide tires. At the current price of $2.50 for a patch kit with 10 patches  and two tubes of rubber cement, that’s $.25 every time I patch. However, the glue usually lasts longer than the ten patches, and so I can use about 10-15 more strips of inner tube as patches, halving the cost to ~$.12 per patch.

Complete inner tube first-aid kit

However, if I were to buy just the glue and inner tubes, the price would drop further. Rubber glue is ~$2 for a large tube, and a whole inner tube is $3.00 at my LBS, meaning I could patch about 50 tubes  for $5 dollars. I estimate each inner tube would make 100 patches, so the real cost is in the glue…. maybe I can buy the rubber cement by the jar?

1/2 tube left; just enough for 5 patches!