UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio 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.

Reply
 
Thread Tools
Old 8th Nov 2018, 10:41 pm   #21
Miguel Lopez
Heptode
 
Miguel Lopez's Avatar
 
Join Date: Dec 2011
Location: Mayabeque, Cuba
Posts: 533
Default Re: Playing with valve oscillators

This is an oscillogram of the LC oscillator output at 25 kHz. Sweep is set at 20uS/div and amplitude is set at 20V/div. What seems to be a crossover distortion is in fact a flaw of the oscilloscope that I've been too lazy to solve.
Attached Thumbnails
Click image for larger version

Name:	DSCN1194.JPG
Views:	41
Size:	158.3 KB
ID:	172484  
__________________
When electrons move, things happen.
There's nothing you can do that can't be done.
Miguel Lopez is offline   Reply With Quote
Old 9th Nov 2018, 6:43 pm   #22
TrevorG3VLF
Octode
 
Join Date: Apr 2011
Location: Matlock, Derbyshire, UK.
Posts: 1,108
Default Re: Playing with valve oscillators

Passive circuit with gain greater than one.
I assume that the phase shift is zero.

There is an old book by Dean (p197) which I cannot find. This used a pair of pnp transistors in a Darlington pair to get high input resistance and low output resistance.

There were three capacitors in series, two were driven by 47k resistors, the third went to the transistor base.
With C=80microF, 1cycle/minute
With C=100nF, 11Hz
I believe this low frequency system was used to generate vibrato in electronic organs.
TrevorG3VLF is offline   Reply With Quote
Old 10th Nov 2018, 6:32 pm   #23
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 4,631
Default Re: Playing with valve oscillators

Quote:
Originally Posted by Miguel Lopez View Post
Quote:
Originally Posted by kalee20
You need an RC network with a gain >1 at a particular frequency
With passive components only? Doesn't that opposes the law of conservation of energy, or even more isn't that a "perpetum mobile"
No, you can have a voltage gain >1 with just RC components (though power gain is of course less than 1).

See photo below, which'll make things clearer. So with a cathode follower having a gain > 29/30, you can make it oscillate!
Attached Thumbnails
Click image for larger version

Name:	image.jpg
Views:	30
Size:	29.4 KB
ID:	172572  
kalee20 is offline   Reply With Quote
Old 19th Nov 2018, 6:36 pm   #24
Miguel Lopez
Heptode
 
Miguel Lopez's Avatar
 
Join Date: Dec 2011
Location: Mayabeque, Cuba
Posts: 533
Default Re: Playing with valve oscillators

An update for today.

Both oscillators are already mounted and running. I will need to apply some decoupling as signal are appearing on each other.
Attached Thumbnails
Click image for larger version

Name:	DSCN1199.jpg
Views:	12
Size:	80.2 KB
ID:	173107  
__________________
When electrons move, things happen.
There's nothing you can do that can't be done.
Miguel Lopez is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 8:51 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 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.