[Milsurplus] Use of an external VFO with a BC-610 transmitter?

[Roger Basford]

Hi All,

I posted on the BC-610 Yahoo group recently asking about the use of an 
external VFO with a BC-610 transmitter. I got some helpful feedback but 
no-one I think had actually used the same VFO as me. I've a pair of Heathkit 
HG-10B VFOs here, both working and stable. I have checked their RF outputs 
on 3.6 Mc and both produce about 3 volts of RF into a 75 Ohm load, falling 
to about 1.5 volts when connected to the crystal socket on the BC-610 tuning 
unit. Now, I feel 1.5 volts isn't going to be enough to drive the 6V6 
oscillator and so what I'm wondering is, has anyone tried this particular 
VFO with a '610 and if so, what matching arrangements did you use?

For info, the HG-10B uses a single triode-pentode 6CH8 with the triode 
section connected as a cathode follower with a 100pf isolator capacitor to 
the RF-out socket. The Heathkit spec gives a 50K Ohm load impedance with an 
output of 5 volts RMS into an open circuit. I'm using an old BC-500 crystal 
holder with a BNC socket mounted on the plastic case to connect the VFO to 
the crystal socket. If I monitor the VFO signal on the shack HQ-170A I can 
see a 40dB increase in signal when the local key switch is thrown on the 
'610, that's with the HT supply to the PA off as the tuning unit door is 
open.

Any advice appreciated!

73 for '08,

Roger/G3VKM





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