Need help in tracking down issue with Heath SB102 on 40 meters

[W5EUQ]

I've fixed several SB and HW rigs Bernie. 
One suggestion is the alignment of the rig.  Are you sure it is aligned 
properly?   Are you using 6146A's? See discussions re 6146A vs 
6146B's... also neutralizing. 
Two: Check the RF choke for the 6146's.  If it is discolored then 
replace it.  Swap it with a known good one to see if it makes a 
difference. 
Three: Have you measured the frequency of the signal feeding the 
6146's?  It sounds like it may be a parasitic or a signal off freq that 
is actually feeding the output tubes.  Tuning could be similar but 
produce a low output. 
Four: I have found in FM broadcast transmitters, when I could not 
achieve 100% out, that I was putting out parasitics that were "eating 
up" the power.   Check for parasitics.  Do you have a spectrum 
analyzer?   I do,,, if you can get the rig to me, I will look at its 
output.
Five: I'm still thinking... will let you know if I think of anything else..
HOPE this helps some... you seem to be a knowledgeable engineer or 
technician.  I hope I haven't "insulted" you in any way.   Glad to help. 
Bob

Bernie Murphy wrote:
> I am at a loss to figure out why my SB102 has about 5 db loss on 
> receive and won't transmit at full power on 40 meters.
>
> I am not sure of the original status of this radio as I just purchased 
> it recently; the seller claimed he did not test it.. It may have never 
> worked properly when it was assembled; the challenges of kits.
>
> Using my signal gen with 100 uv into the antenna jack, the meter reads 
> S-9+5dB or better on all bands except for 40 meters where the signal 
> reads S-8.5 or so.
>
> On transmit, the rig will not load beyond 160 ma and only puts on 
> about 30 watts on 40 meters into a dummy load. All other bands, the 
> rig puts out double that power or better, except for 10 meters (which 
> is to be expected). On all other bands, the transmiter loads to 250 
> ma.  Power ouput readings where taken with a Collins Wattmeter (there 
> have been reports that these meters read low as they age).
>
> There is no grid drive reading on 40 or 80 meters according to the 
> SB102 meter. Lots of grid drive on all other bands.
>
> I've tried the following:
> 1. Cleaned all the switch wafer contacts and in particular the driver 
> grid and driver plate wafer switches. These are really hard to clean 
> as the clearance is minimal.
> 2. Using an ohmmeter, metered the driver grid and driver coils and all 
> looks well
> 3. Resoldered the traces involving 40 meters on the driver grid and 
> driver plate boards going to the 40 meter coils
> 4. Resolderd the 40 meter driver grid and driver plate coils where the 
> windings are soldered into the coil holder
> 5. Swaped another 6HS6 RF amp tube from another working SB102; got a 
> bit more gain on receive (about 5 dB)  on all bands but of course, did 
> not fix the transmit issue.
> 6. Tried another set of 6146s (should not make a difference) and it 
> did not.
>
> Anyone run into this type of issue with the HW100/SB100 series radios?
>
> Any suggestions would be most welcome.
>
> Sounds simple to fix but this one has me stumped ...
>
> 73, Bernie
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parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

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