Sunday, May 23, 2010

Repair and restore your own antique radio equipment

Interested in repairing an old tube radio that you purchased at a garage sale? How about connecting your ipod to it?

Read this briefing to see how it is done.

(this briefing is for vacuum tube radios that use power supply transformers. it is not for 'hot chassis' or transformer-less radios. i suggest staying away from these or using an isolation transformer when working on them)

The author is not responsible for any injury or death that may occur due to working on antique radio equipment. Antique radios are dangerous because of the high voltages inside of the radio equipment. Do not work on antique radios unless you have proper training or experience. Serious injury or death can occur. These briefings are for reference only.

Wednesday, May 19, 2010

another Colin B. Kennedy Model 20B as emerged

A fellow fan of the CBK model 20 has sent me this photo (photo 1) of
another model 20B that he has purchased. This one is much different
than mine, where, there are no front doors and the output tubes are
push/pull type 45's rather than my single ended variant (photo 2).
In addition to this, it does not have doors on the front.

A great find! Can't wait to see it working.

Sunday, May 9, 2010

low phase noise VFO

Here is my low phase noise VFO. It is the differential transistor
pair VFO from the 2010 ARRL handbook, scaled to a frequency range of
10-10.5 Mc and combined with a surplus VFO chassis/vernier dial gear
reduction that i salvaged out of an old FAA modulation tester.

Photos from the top:
1. VFO
2. insides
3. connected to the rest of the modules that make up my 20 M SSB
radio project.

Works great! I found that cheaper 2n4124's (or equivalent) NPN
transistors work better than UHF low-noise transistors. This was
indicated in the ARRL handbook, but, i chose to ignore it and hoped
to improve phase noise performance by using the low-noise UHF
transistors. The problem with the UHF transistors was that they
would output broad-band oscillations on occasion causing instability
in the VFO. So, best approach is to follow the directions from the
handbook and go with the cheap transistors for this type of VFO.

Saturday, May 8, 2010

a low phase noise crystal oscillator BFO

I developed a crystal oscillator based on Rhode's low-phase noise
reference oscillator from his 1997 book on PLL synthesizer design.
In this i used a new low-noise NPN transistor, with an NF=1 dB.

Oscillator signal chain includes: oscillator circuit -> mmic
amplifiers -> LPF -> RF out at 10 dBm.

Photos (from top down):
1. inside of the oscillator
2. outside of oscillator
3. oscillator connected to SSB radio signal chain. works great!

Monday, May 3, 2010