Converting a class C FM PA to AB or AB1 'linear'

Post new topic   Reply to topic

View previous topic View next topic Go down

Cannot upload pictures

Post by jomac on Sat Jan 04, 2014 5:34 pm

Hello,
       I dont know what im doing wrong, but i cannot upload pictures, they are jpegs and are less then 200K in size. I select the file and hit ok, then i get a small menu with 3 file addresses i can select one or none, hit upload and then nothing, where am i going wrong?

If i can post the pictures, you can clearly see the circuit layout on the PCB.

Regards

jomac

Posts : 11
Join date : 2013-08-26

View user profile

Back to top Go down

Re: Converting a class C FM PA to AB or AB1 'linear'

Post by Ivan on Sat Jan 04, 2014 12:15 pm

Hi Jomac,
it is hard to give a sure advice with no schematics, but it is well possible to move the transistors into the AB class by proper biasing. Some PAs are even switchable between the SSB and CW/FM mode, simply by switching a resistor in the bias network. The network from Harry's amp may do.

BR from Ivan

Ivan

Posts : 176
Join date : 2012-11-25
Location : Praha, Czechia

View user profile

Back to top Go down

Converting a class C FM PA to AB or AB1 'linear'

Post by jomac on Fri Jan 03, 2014 10:16 pm

A little while ago, i bought a couple of vintage 4 metre PA boards made by Wood & Douglas in the late 70's early 80's Despite some pretty long searches, ive not managed to find any information about these on the internet.

The type number on these PA's is 70FM8/30 From this im assuming that these amps are FM, 6 metres, and with an 8 watt drive will produce 30 watts out. With these amps, i also bought a small transmitter strip, again marked 8 watts, presumably to match these PA's

Now what i want to do is to convert them if i can for SSB use as well as AM/FM The boards use the MRF646 transistors which are capable of a lot more then 30 watts. Is it feasable to convert these for 'linear' SSB use by just adding a bias stage? I was thinking of copying the bias network from Harry's 10 watt HF amp. Would it work?

The set im building will be for 6 metres as well as 4 metres and having a pair of these, would be ideal if it could be done.

Ive tried uploading a couple of pictures, but nothing happens?

jomac

Posts : 11
Join date : 2013-08-26

View user profile

Back to top Go down

Re: Converting a class C FM PA to AB or AB1 'linear'

Post by Sponsored content


Sponsored content


Back to top Go down

View previous topic View next topic Back to top

- Similar topics

Post new topic   Reply to topic
 
Permissions in this forum:
You can reply to topics in this forum