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


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.

Thread Tools
Old 3rd Mar 2021, 6:20 pm   #1
G6Tanuki's Avatar
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 9,815
Default Regen HF receiver supply stabiliser.

Over the last 5 decades I've always been fascinated by regenerative HF receivers, and have built loads [valve, FET, bipolar] with varying degrees of success.

One of the underlying issues is that to receive CW/SSB stations you need to have the receiver gently oscillating - but being able to get a receiver to slip gently into and out-of oscillation without there being undue hysteresis in the regen control, or the poor thing 'squegging', is always tricky. Part of this is due to the DC conditions of the valve/transistor changing between oscillating and non-oscillating states.

My latest toy is a 2N3819 receiver for 5MHz; it uses a Hartley configuration, with regeneration controlled by varying the supply-voltage. It's rebuilt-from-memory of a design first published in 'Practical Electronics' sometime in the 70s.

To minimise the change-in-DC-conditions issue I've focussed on minimising the DC resistance in the supply-feed; I replaced the design's original 10KOhm drain-feed resistor/regen-control with the primary-winding of a 'LT44'-type driver-transformer [whose secondary feeds a BC109C followed by a LM384 IC audio-amplifier] - the DC resistance of this transformer's primary is a twentieth of the originally-specified drain-load resistor.

Then, I added a BC109C and Zener to provide an emitter-follower-voltage-regulator [again, that low-source-resistance thing]. This allows me to control the drain-voltage from 6V up to 12V with a 10KOhm pot; the result is wonderfully-smooth and hysteresis-free regeneration. I'm currently 'optimising' the capacitors either side of the transformer-primary, in order to provide decent cutoff of signals above 3KHz.

Experimentation continues - now I know rather more-accurately the voltage-range I need to cover for the regen-stage I will consider replacing the Zener and 10K pot with different values - 9.1V for the Zener and 1K for the pot look likely trial-values.
Attached Thumbnails
Click image for larger version

Name:	reg.jpg
Views:	52
Size:	57.6 KB
ID:	228178  
G6Tanuki is offline   Reply With Quote

Thread Tools

All times are GMT. The time now is 11:54 am.

All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at
Failure to heed this warning may result in death or serious injury to yourself and/or others.

Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.