Saturday, January 23, 2010

I'm making a transistor radio from scratch using only 2N4124's

I have a box full of 2N4124's. I also have a box of RCA IF
transformers of various Q's. So i have decided to make a transistor
radio from scratch using parts from my scrap parts collection.

Today i built a 2 stage IF amplifier, where, each stage provided
about 30 dB of gain. Circuit Q was very high, set by the IF
transformers which coupled each stage together.

I built a full-wave envelope detector using one of the IF
transformers and two germanium diodes.

I injected a tone into the base of the first stage and sucessfuly
used it as a mixer.

I successfully tuned in AM broadcast bands by injecting an LO into
this mixer, listening to local sports and talk stations.

Next steps:
1. need to build a VFO that can swing a couple of volts on the output.
2. modify the IF amps so that they are adjustable gain
3. build a front-end that is band-limited with a bandpass filter or
adjustable resonator transformer of some kind.
4. look into using this at short-wave frequencies, might have to
build an RF amp and pre-selector.

Tuesday, January 12, 2010

video of the Olympic 6-606, a 1946 retro boom box in action


video

The Olympic 6-606 in action with Ipod connection. Lots of fun with this radio over the weekend. Planning to use it frequently at parties and other gatherings. Bring vintage tube sound anywhere you go!

Wednesday, January 6, 2010

There exists another Colin B. Kennedy Model 20B

Casper's CBK Model 20B:

My CBK Model 20B:

A fan of the blog, Casper, has written to me about his Colin B. Kennedy Model 20B. He was searching the web for some info on his radio and found my web page dedicated to the restoration of my CBK 20B.

It was very interesting to see another CBK 20B because the chassis was very different and the only schematic that exists for this radio actually matches Casper's radio better than mine. For example; Casper's 20B has a push-pull output with two triodes, whereas my 20B has one pentode in a single-ended configuration. There are a few other differences too.

Casper has successfully implemented a simple modification to the AF stages to increase the AF bandwidth by placing caps in strategic locations in the AF circuitry. Nice work! I might try the same thing with mine someday because of his success.

Both CBK Model 20B's continue to play music to this day. I use mine about 4 hours daily, and his is on just as much. It is true what was said on the front of the model 20B, Colin B. Kennedy is the "Royalty of Radio."



Sunday, January 3, 2010

Olympic model 6-606 portable tube radio, now running off batteries, and playing a vintage playlist off of an ipod




Now i have my tube 'boom box' ready for music anywhere.

I had to build a replacement battery pack for the two type B and the two type A battery packs (90V and 9V respectively). This battery pack contains 16 batteries total; 10 9V's and 6 size C. It costs about $30 in batteries alone to run this radio! lol



But it is worth it because now we are ready to rock with tube sound anywhere....

Cheers! Thanks for following,
Greg


Friday, January 1, 2010

1946 Olympic Model 6-606 portable tube radio, restoration complete, with IPOD doc




I just completed the restoration this beautiful 1946 Olympic model 6-606 portable/AC powered tube radio.

This radio runs off of line voltage or high voltage batteries.

In addition to this I have modified (or as some might say hacked) this radio so that it can be used as an ipod doc. This was difficult to do safely because this is a 'hot chassis' radio. On the rear panel you will see a small quarter-inch toggle switch where you can select either radio or ipod mode. The ipod is fed through an audio isolation transformer and into the grid of the first AF stage.

This was the most difficult radio restoration I have done to date because of the strange 1 series tubes and the difficulty in maintaining proper bias with old resistors and modern (higher) line voltages.

I plan to build some battery packs for this radio and use it as a vintage 'boom box.'

More later on this...