SB400 - Low Grid Drive on 40 Meters

[Guy G. Giacopuzzi]

Ok, Ray's 401' is  easy...look at the circuit that gives the meter it's 
grid indication....I'm at my 2nd home, so I don't have a schematic 
handy...concerning the 400', it seems like something in the 40 meter 
circuit....and sometimes, the hetrodyne xtal goes south...


Guy,
WA6OQQ

RAY FRIESS wrote:
>  
>
> I have the same, but not exact same, problem with my Sb401, which I've paired with and SB 303.  In my case, I show practically no grid current on the meter on any band, yet I am getting full output on all bands and good reports on the air.
>
> So, I havent really paniced because I know I'm getting output because my meter works fine on relative power output position and I can tune for max with it..
>
>  
>
> So .. I'd be interested in anyone's comments and solutions too.  Mainly so I can make the twins work like they were supposed to ... in this case, meter readings.
>
>  
>
>
>  
>   
>> Date: Wed, 12 Aug 2009 17:41:49 -0400
>> From: mvjohn at SYMPATICO.CA
>> Subject: SB400 - Low Grid Drive on 40 Meters
>> To: HEATH at LISTS.TEMPE.GOV
>>
>> Heath Team;
>>
>> I've got an interesting problem on an SB-400. The transmitter is paired up with an SB 300 receiver.
>>
>> I had the exact problem on an SB300/400 pair a few years ago and never resolved it to my satisfaction. I happened to find this pair a few months ago and thought I'd bring them back to life as I always enjoyed using the Heath twins. Upon nearing completion and doing the final tuning tweaks, I ran across this problem again. 
>>
>> The net of the issue is there is no,or very little, grid drive showing on the meter when tuning up, or when the rig is in operation. I get full output into a dummy load and a nice clean CW/SSB signal on the SB-610 scope, but there is no grid drive showing on the meter. The rig has great output on all bands and on air signal reports are good. 
>>
>> I know the 8.65 mhz trap setting can be tricky and cause 40 meter output problems so I adjusted mine my feeding the transmitter, through attenuators, into my spectrum analyzer and I adjusted the trap variable cap for minimum. It adjusted fine. 
>>
>> The LMO, Het Osc and BFO cables from the SB300 to the SB400 are proper RG-62 and cut to exactly 24 inches. 
>>
>> The SB300 Het Osc coils are peaked OK. 
>>
>> I changed out the meter dropping resistor, 4700 ohms, for the grid circuit as it was high. All other voltages are OK.
>> ,
>> As mentioned, I had this exact same problem years ago on a previous pair. Output on 40 meters is a nice 95 watts into my dummy load, just not showing any grid current on 40. All other bands, there is grid current showing. 
>>
>> Any ideas?
>>
>> Many thanks
>>
>> Mark V Johnson VE3DJU/VE3DDI
>>
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