Uploaded May 2018 | Updated September 2026, 2 weeks ago
NOTE number 1 THE WRONG HOLE WAS SHOWN FOR ADJUSTING THE VFO COIL THE CORRECT HOLE IS IN THE FRONT OF THE VFO AT THE COIL ITSELF WHERE IT IS MOUNTED WITH THE 1/2 INCH NUT .NOTE number 2 In the VFO where I installed 2 of the 10PFN750 capacitors I had to reduce the capacity of one of the 3 33 PFN75 capacitors by series connecting it with a 330 PF NPO capacitor this reduced the capacity by 10 PF as measured on the capacity meter and allowed 2 10 PF N750 capacitors to be installed and this VFO was very stable then drifting 37 HZ in one hour . Here are tips to Improve the stability of the Heathkit analog VFO . These VFO's were stable enough back in the 70's but today we need something better and also these VFO's are over 30 years old or more and in need of a little TLC . Note That I commented on using two 56 PFN75
capacitors and a 10 PF NPO for temperature compensation this is for the SB104 ONLY the analog dial rigs will not calibrate using this capacitor combination in the LC circuit . LC meaning L is the COIL or Oscillator Coil and C is the combination of the variable capacitor and the temperature compensating disk capacitors . To me getting really good VFO stablity has always seemed to be a type of magic . There are formulas etc. to use for stability BUT getting the compensating capacitors and other parts can be an exercise in futility . Each VFO has shown to require a little different small value temperature compensating capacitors this is due to parts tolerances but with a lot of patience and perseverance a workable solution was arrived at . Those hard to find capacitors 33pfN75 are Ebay number 222874986351 just copy and paste the number in the Ebay search box .
Heathkits Forever 73 Bob
NOTE number 1 THE WRONG HOLE WAS SHOWN FOR ADJUSTING THE VFO COIL THE CORRECT HOLE IS IN THE FRONT OF THE VFO AT THE COIL ITSELF WHERE IT IS MOUNTED WITH THE 1/2 INCH NUT .NOTE number 2 In the VFO where I installed 2 of the 10PFN750 capacitors I had to reduce the capacity of one of the 3 33 PFN75 capacitors by series connecting it with a 330 PF NPO capacitor this reduced the capacity by 10 PF as measured on the capacity meter and allowed 2 10 PF N750 capacitors to be installed and this VFO was very stable then drifting 37 HZ in one hour . Here are tips to Improve the stability of the Heathkit analog VFO . These VFO's were stable enough back in the 70's but today we need something better and also these VFO's are over 30 years old or more and in need of a little TLC . Note That I commented on using two 56 PFN75
capacitors and a 10 PF NPO for temperature compensation this is for the SB104 ONLY the analog dial rigs will not calibrate using this capacitor combination in the LC circuit . LC meaning L is the COIL or Oscillator Coil and C is the combination of the variable capacitor and the temperature compensating disk capacitors . To me getting really good VFO stablity has always seemed to be a type of magic . There are formulas etc. to use for stability BUT getting the compensating capacitors and other parts can be an exercise in futility . Each VFO has shown to require a little different small value temperature compensating capacitors this is due to parts tolerances but with a lot of patience and perseverance a workable solution was arrived at . Those hard to find capacitors 33pfN75 are Ebay number 222874986351 just copy and paste the number in the Ebay search box .
Heathkits Forever 73 Bob
