Hi everyone, I thought I'd share with you my most recent tube amp build.
I'd been going through all my junk and came across an old Philips EL3541D reel-to-reel/radio that I'd picked up years ago and forgotten about. It was in very poor condition, the plastic case was turning to dust and was cracked everywhere, and there had literally been a wasps nest in there at one point, so this was definitely a salvage job, not a restoration.
So I pulled it apart, salvaged the power and output transformers, the voltage selector switch and the tubes - ECC83 dual triode, EF86 signal pentode, ECL82 dual triode/power pentode, EZ80 rectifier and EM84 magic indicator tube, then set to drawing up a schematic. I came up with a bom and ordered parts about half an hour later.
When all the parts arrived, I decided to try an experiment, and rather than planning a layout as I normally do, I decided to follow my intuition and wing it, and see how it turned out - I could always start again. About 4 hours later it was making sound, but I decided to try some tweaks, the first was an LND150 source follower to bootstrap the input gain stage, which I liked, and then I tried another LND150 source follower to replace the cathode follower and repurpose the triode as another gain stage, but after playing with different bias points and the interstage attenuation, I decided I wasn't a fan and returned the circuit to the earlier iteration.
The layout came out ugly, but quite functional - the amp is dead silent despite being quite high gain. And I'm very pleased with the sound, which is the most important thing of course.
It's single-ended, fixed bias, puts out around 4-1/2W. The EM84 is hooked up as a VU meter. It has a "squish" control - variable screen bypassing on the EF86, and a "shift" control - variable slope resistance in the tone stack to move the center frequency up or down. With the shift at 12 o'clock the tone stack matches a JCM800 2203/4 tone stack. Everything else is normal - gain, bass, mids, treble and master. There's an inbuilt dummy load, and line output, so I can crank it and run it into a bigger amp for more volume (or to add reverb or something on top of power amp distortion, that sounds great, like post-processing but live!), or equally, to run it into a smaller amp/a big amp turned down to get the cranked tone at bedroom/nighttime levels.
Here's a
video demoing it. Sorry for the poor lighting and picture quality, it's all my potatophone can manage. Also note the audio recording came out darker than in person due to mic placement.
Please go easy on my playing, I'm very out of practice, I had DVT in my right leg a couple of years ago which I wouldn't have survived if it had happened a couple of months earlier before they'd introduced new treatments, and I damn near lost my leg anyway, so I've spent most of my time convalescing. And I'm only 31, so pretty traumatising I'm sure you'll understand.
Note that I've left the schematic as built, there are some redundant parts in there (the cathode bypass caps on the input gain stage).
So thanks for reading, hope you enjoyed!
