[heathkit] Heathkit SB400 low output

[G3OOU@aol.com]

Hi Robin

 

I would check that the components in the oscillator circuit are still within tolerance, particularly the resistors. Carbon composition resistors go high over a long period of time and I threw out my "new old stock" of carbon resistors as they were 30+% high. Check the oscillator coils for dry joints etc and if you have a Q bridge measure the coils on that. Also make sure that the valveholder sockets are not oxidised.

 

If you disconnect the HFO lead to the SB400 does the SB300 oscillator work correctly? I found it useful to monitor the HF oscillator grid current with a test meter when I did my rebuild, re-alignment and subsequent tests with an SB401.

 

You need to keep the interconnecting lead as short as possible to minimise loading the SB300 oscillator.

 

It was designed to work in this mode so it should be possible to make it work correctly. However, in my particular case, I installed a buffer in my SB301 as I needed to use longer interconnect leads in my station console.

 

73

Bob
G3OOU
G-QRP 6907
www.g3oou.co.uk