Friday, February 11, 2011

Love Grandfather Tube Radios? DIY


The first time i've seen a radiotube was when i was about 8 or 9 years old. On my way home from school there was an old radio on the sidewalk and i ran home to get a little trolley and i went back to pick up the radio.
It immediately caught my interests although i had no idea what to expect. Of course the radio did not work and my father removed the powercord for my savety before i started fiddling around in it.

At the same time i probably came into contact with a solder iron ant there's the point where it all started.
In the same year i got my very first electronic lab for kids from my aunt for christmas and it was HUGE with tons of cool electronic experiments. I propbably built all these experiments within 1 week.

Today, about 35 years later i decieded to build my very first own tube radio. Not that i've never built a radio, in fact i have built many but all of these were modern style transistor radios. I do have a good knowledge about tubes today but so far i have only built guitar or HiFi amplifiers which is cool but im stuck in it and i need something new. So, last month i started to gather informations and schematics of tube radios and other peoples projects. One very good resource i came across is the website of an australian guy named "john"
He has lots of extremely well documented and accurate schematics and building plans of tube related electronics such a radios and amplifiers.

The radio i will build is based on his pulse counter superhet FM reciever

The only difference will be the amplifier part. I will not build the audiopart as shown here in the bottom half of the schematic but will use a 6V6 tubeamp solution with a ECC82 preamp stage.

First i need a good chassis, such as i have previously used for guitar amplifiers. Here i prefer high quality chassis from hammond. My chassis is a aluminium 16 x 8 x2 inch type 1444-26 which is very good to work with. Another product from hammond will be the power transformer and the audio output transformer.

As i know that i will need about 250 volt i will use the Hammond 260C power transformer which has secondary output of 250-0-250 for the application and 5Volt and also 6.3 Volt for the filament (heaters) of the tubes.
Btw. i always prefer power transformers with 5V / 6.3V filament output because sometimes use rectiver tubes that need 5V on the filament. As you might know different type of rectiver tubes output a different DC voltage as example, the 3Y5 (octal socket) gives less output than a EZ80 (noval socket) on the same transformer but the 3Y5 needs 5 Volt for the filament and the EZ80 needs 6.3Volt

Here are some of the pictures i did today from the chassis, trannies and tubes etc. 

On the lefthandside you can see the Hammond 269C Power Transforner, far left is a 3 watt 5k 4/8R output transformer. The rectiver tube is a EZ80 and as "smoother" i am using a 500Volt dual 32uF electrolytic capacitor. The variable capacitor in the front with the extended shaft is a 15pF handmade by Jan Phillip Wuesten

In the back are the four 6AU6 as well as the ECF80 and the EAA91. On the left from the OT (output transformer) near the yellow wire is a ECF82 which will be used as audio amp driver.

While i am waiting for a special drill for the tubeholes i will cut some aluminium sheets and bend them into forms to hold the other hardware such as a "lift" where the VaCap (variable capacitor) will be fitted. etc...
Pictures of this will follow these days.

The Doc  11/02/2011