[AMRadio] 6146Bs in Globe rigs?


Jim Wilhite w5jo at brightok.net
Sat Oct 20 11:11:00 EDT 2007


Ellen does the Scout have neutralization?  I don't know so am being a 
bit generic here.  If it does, then neutralize it and you probably will 
find the cap will be at minimum.  You may be inserting capacitance where 
it is not needed.  I have two rigs designed around the 6146 and one is a 
B&W 5100B.  I am using 6146Bs in it and it works fine except on 10 
meters.  Up there the tuning is a bit dicey but does work.

There is a way to neutralize a transmitter without ruining the finals.
1. Tune up the transmitter into a dummy load on what ever band you want 
to neutralize.

2. Turn off all power and attach a signal generator to the output 
connector of the transmitter.

3. Attach a scope that will show the frequency you are doing the 
neutralization to the grid of the final(s).  If you are doing this on 10 
meters you should use a scope that has a bandwidth of 50 Mcy.

4. Move the signal generator frequency until the scope shows the signal. 
The horizontal display should get wider as you come on frequency where 
the transmitter is tuned.

5. With the widest display possible, adjust the neutralizing cap until 
the display shows no or the least amount of signal on the grid(s).

Now give it a try.  If it is still dicey, then you may have to modify 
the neutralization circuit.  That was the issue with the 32S series of 
radios.  Collins modified their neutralization circuit to accommodate 
this but I don't know if Heath ever published a service bulletin.

Have fun.

Jim/W5JO





> Hi Everybody,
>
> The 6146 final in my Globe Scout 680 is toast (it won't even dip or 
> load anymore). I don't have any spare 6146s or 6146As, but I do have a 
> couple of Chinese 6146Ws (today's 6146W is rougly equivalent to a 
> 6146B) lying around, collecting dust (my Kenwood TS-820 didn't like 
> them, so I had to put in a set of NOS Phillips 6146Bs in it instead), 
> that I wouldn't mind putting to use.  But, as you know, using a 6146B 
> in a 6146/6146A rig can be a dicey affair.  Some 6146/6146A rigs have 
> no problem with the tube, other rigs (especially certain Collins and 
> Heathkit radios) can have bigtime problems with the 6146B (such as not 
> neutralizing out, or suffering runaway parasitics that can nuke them 
> out).  I have no data on how well Globes (especially my Scout 680) 
> handle the 6146B.  Does anybody have this info.?  I'd sure hate to 
> find out the hard way (while trying to neutralize one of my 6146Ws), 
> that Globes don't take too kindly to the 6146B/614W.
>
> 73,
> Ellen - AF9J



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