New project on HHH http://sm0vpo.altervista.org/ (www.sm0vpo.com later)

Hi Ivan, Yes! yes! YES!!!  
I remember the old telephone "baretta" lamp used in telephone exchanges. PYE Telecom used them in the 600 Ohms line controllers for remote radios. They were really common, but today you never hear of them  

I remember the story of a Boston telephone engineer who tried impress a telephone operator, around 1920, or so. He strung a few of them in series, plugged them into the wall socket, and the first christmas-tree lights were born.

... and the more recent 28V 50mA telephone lamp https://uk.rs-online.com/web/p/filament-indicator-lamps/2945191/

As you say, the modern replacement LED lamps are not at all suitable.

But my project uses just those bicycle rear lamps you mentioned. They have a small enough mass to allow temperature changes.

Very best regards from Harry

Hi Harry,
a tungsten filament lamp has certainly has much less persistence, but it breaks more easily than a thermistor. It may be hard to get now too. I remember two sources of suitable lamps, both are obsolete now: "telephone lamps" used in status lights of phone exchanges and E10 lamps for rear bicycle lights (6V 50mA). LEDs are used on these positions now.

VBR from Ivan

Hi Ivan,
Thank you very much for the info. When I made the original design (30 years ago) I tried several thermistors.

The 10mW in the glass envelope work great, but when you change frequency, the output level varies up and down, then settles in about 3 seconds to a constant level. I used a 6v 40mA lamp (from my Philips EE kit) and the lamp stabilised the temperature a lot faster. I tried a carbon-block thermistor (like the one in my 10W HF Linear Amp) and that took up to a 30 seconds to stabilize, but that one used discreet transistors.

For general lab use it should be ok, and will make a useful test tool, but one should be aware of the limitations. I shall buy a pack of those from the link you gave and give them a try, then add the results to the article when I photograph the built prototype.

Thank you once more for the info. Much appreciated.

VBR Harry

Hi all,
if you want to replicate the original design with a thermistor, it can be still available for fair prices e. g. here  They are 50 mW rated and packed in epoxy.

VBR from Ivan

Hi Guys,
Just added another new project on HHH. The same as before, I have only been able to add it to http://sm0vpo.altervista.org/ because I don't have FTP access to www.sm0vpo.com.

The "new" project is an old design Audio Frequency Generator. All the design is complete. I built this project about 30 years ago (or was it more?). I had it for years, but it went in the house moving, downsizing and such. But I am really missing it.

Some of the older components were difficult to get 30 years ago, but today you have to throw money at them. There is an alternative :-)

See: http://sm0vpo.altervista.org/audio/af-gen_01.htm

Sorry it is a bit long-winded. It was planned and designed while I was in Spai, but I hope to build it shortly. I will post the pictures/photos and any possible corrections.

I bought a piller drill today, so I can now drill holes in PCBs   The only other drill I had access to was at work, costs US$60,000 and the interlocks will not let me hold a PCB in my hand!!

Enjoy -  BR Harry SM0VPO