D09: guitar tube amplifier from a turntable

I've found a junked turntable, it's not in good condition, plate is broken and enclosure has some crack. But the front cover is pretty, and also it's powered by tubes, so I've decide to convert it in a small practice tube guitar amplifier.

The most of the time I found something in the dumpster it works, it's just a matter of cleaning it. Sometimes, when it does not works, it's something simple to fix. Taking a look at this turntable makes me think someone threw it away cause the plate has something broken.

WARNING! - The project described in these pages utilizes POTENTIALLY FATAL HIGH VOLTAGES. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

Most important thing to notice when building tube guitar amplifier from old devices is to check that they don't use an autotransformer https://en.wikipedia.org/wiki/Autotransformer, cause you don't want to get a shock plaing your electric guitar :) And this player has a standard transfromer.

This turntable has two tubes:

• rectifier tube: 
• preamplifier + amplifier tube: ECL86

Checked this, I've removed the tubes and connected it to power plug. If you have a Dim-Bulb Tester it's better to use that. But I've not build it yet.

Once connected I have to test the voltage output. First I've checked the heater voltage for the two tubes pinout, and that's 6.3V AC, so right. Then I've checked the high voltage and that's good enough.

So I've started putting the rectifier tube in. It works, the high voltage DC came out without problems.4 Then I've connected the ECL86. Heater works, and tube output too. Checking a sine wave input in the input wire from the old turntable needle yield to a sound output. It means also the output transformer works. That's great! Now it's time to rebuild the circuit to make it works for guitar input.

I've take a couple of reference:

- Magnatone 411

- Radio Tone by Guilhem

Rebuild the circuit was pretty easy, I just changed a few values from the reference circuit. Also I've add a switch to change from triode to pentode mode output.

This amplifier has a single volume control, which is also the power one switch. This makes the front grid so minimal and pretty.

Back to woodworking, I cut the enclosure back, where the turnatable plate was installed, keeping just the front grid. Then I removed the original faux leather cover and do some woodwork with wood putty and grind paper.

I've tweeded it using vinylic glue and one of my grandmother nightgown.

Final enclosure looks pretty good.

Time to check the audio output. This amplifier it's really clean. The original speaker sounds good even if it was not built for guitar. It starts with a little overdrive at 5 to 10 volume, ending up in a nice tube overdrive sound at max volume.

Even if it's just a 4W amplifier it's loud enough for a quiet jam session.

Notes

• read risk disclaimer
• excuse my bad english