UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Closed Thread
 
Thread Tools
Old 12th Dec 2022, 7:10 pm   #1
pmmunro
Octode
 
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,797
Default LM199/399 application

I am working on a Standard Cell replacement based on a Linear Technology data sheet circuit which I have also found to be very similar to TI's data sheet.

This all seems fine, but during some research, I found a reference in "The Art of Electronics" 2nd Edition, (Horowitz and Hill). The second last paragraph on page 339 states "One caution when using the LM399: The chip can be damaged if the heater supply hovers below 7.5 volts for any length of time". Apparently this does not appear in the third edition of H & H, although I have not been able to check myself and I haven't found anything to support this caution on the internet.

Could anyone who has detailed experience of the LM399 offer any clarification please? I am not at all sure what is meant by hovering nor what constitutes "any length of time" or why a low heater voltage should damage the IC.

PMM
Attached Files
File Type: pdf Linear Technology App Note Page 5 .pdf (29.2 KB, 39 views)
pmmunro is offline  
Old 12th Dec 2022, 7:23 pm   #2
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,803
Default Re: LM199/399 application

I've not used it, but I have been involved with precision, ovened quartz oscillators.

Some early generation ones used a nichrome resistive heater with a transistor circuit switching on and off, as directed by a thermostat. Small variations in the oscillator frequency could be traced to the switching.

The replacement was a linear temperature controller. The heat from the power transistor was not wasted, its heatsink was the oven mass. I wondered why they retained a resistive heater section. They could have used just the power transistor alone, and had faster heat-up. The answer I got was that if the heater supply was low, there needed to be something to limit the current to a non-damaging level.

I think that is what may be going on in the LM399, it the heater is all-transistor. It could be at risk of over-current.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 2:21 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.