Salora Tube Radio Project

This is a description of a project of rebuilding an old tube radio into a functional guitar amplifier.
© Hannu-Pekka Poikonen 2009

Getting Started

It took a pretty long time to finish the project. The radio in it's original condition was purchased already a few years ago. Here's how it looked:

This radio was a product from the brand Salora from Finland. I believe it has been manufactured here some time in the 50s. The radio was bought at a flea market. It was already broken and as the images show, not in a great external condition:

Thus, we decided that it's not worth it to rebuild it as a radio. Instead it would serve as a rather suitable base for guitar amp project.

Electronics

This picture was taking after rebuilding the electronics of the radio:

We got started by taking off all the old components that were not necessary for a guitar amp. Not much was left - only the chassis, transformers, and a tube socket (see a pic from the inside at the further down the page). The electronics for the new amp were designed and built by Matti Kari. The preamp is based on old Fender designs and the power amp was Matti's own design based on using the original transformers of the radio. There is a single ECC83 preamp tube and a single 6V6 power amp tube for about 6 W output power. The controls are Gain, Master, Bass and Treble.

Unfortunately we couldn't preserve the original glass front panel, because it wasn't quite suitable for the new purpose. It had holes for only 2 pots and it would have been quite uncomfortable to have some of the controls in the back. However, for practical reasons the power switch was placed in the back in the end.

When Matti had finished the electronics, it was time to test the amp. At that time the plan was to keep using the original 6" bass speaker of the radio. The treble speaker is still in the cabinet, but it isn't in use. However, I ran into an unpleasant surprise: the bass speaker had a hole in the cone. It was still working, and actually sounding nice and smooth, but began to break down quickly. The hole seemed to be caused by some sharp object that had broken the grille cloth ass well. Too bad!

After some consideration I bought a new Weber Alnico Signature 8S speaker. There is just enough space for an 8" speaker in the cabinet. It would have been nice to go for 10" but the space just isn't enough. So, after I got the speaker it was finally time to work on the cosmetics.

The Externals

Even if I wasn't trying to make it look shiny and new there was a bunch of things to do:

I got the grill cloth from Weber tobether with the speaker. Unfortunately it isn't quite as beautiful as the original one, but it was the best that I could find. It does look nice though, I think. I used some patent band and additional pieces of plywood to keep the cabinet together.

For some reason the front of the cabinet has a very large hole for the speaker. Perhaps it was originally used in different models of radios. It was necessary to add a piece of plywood to have the speaker fit in properly. Also the original speaker was fit in by using a similar solution. The handle is a new addition, which makes it possible to carry the amp around. This makes sense now, that the bottom won't fall off. I got the handle and the Marshall style knobs at Uraltone.

The front and back panels are made of hardboard. I chose this, because I don't have tools for working with more durable materials. And actually some similar materials were actually originally used in the radio, so it wasn't such a bad choice. The artwork is hand painted and drawn by Anna - thanks, you're a true artist!

So here's where we ended up:

The Sound

First of all: 6 W is plenty! Especially at home. Even if the 8" speaker isn't terribly loud, it still isn't an amp that you could just crank up without disturbing somebody. This kind of an amp might even be useful in a band context if you don't need 100% clean sounds. With 4 X 12" cab it really rocks. Of course the single 8" sounds smaller but at home it gives nice tones as well. According to Matti it should also work with higher power tubes (such as EL34) in the power amp section. That hasn't been tested, but it might really make the amp even more useful for not-too-loud band activity.

Anyway, you'll judge for yourself. Here's some audio samples:

If flash doesn't work for you, download the mp3s here.

The recording setup: