[HBR] troubleshooting an HBR 16-help appreciated

[hbr@mailman.qth.net]

Lew asked:

> Any other suggestions most appreciated. I do have a signal gen, vtvm,
> and a scope. 

Oh boy -- I love these pop quizzes!   

Have you looked at the set in a darkened room to see that all the 
tubes light?   Filament wiring problems, maybe even a dead fil., are 
possible.

The local osc should tune 5400-5700 on 40, i.e., *below* the 40 
meter band.

Check to be sure that you really have a 6BH6 in that socket -- 
fleamarket finds often have scrambled or 'equivalent' tubes.  Next 
check the connections on the tube socket -- swapping wires is easy 
to do. Substitute another 6BH6 for the HF oscillator.   Since the 
marker osc. works, you could use that one.   Internal grid-cathode 
shorts (can be pretty high resistance) are fairly common.

Then measure the voltages.  Here are the answers for the Deluxe 
HBR in Bill Orr's handbook, which has exactly the same osc. circuit 
and uses the same tube -- pins 1-7, in order.  These are per VTVM.

-4.1, 0, 6.3 VAC, 0, +50, +88, 0

If the -4.1 is there (anything upwards of -1.5 is probably okay) then 
the stage is oscillating and may just be way off frequency; you can 
get a rough idea with the scope (couple as loosely as you can and 
still count the cycles on the screen) and then perhaps find it with a 
general coverage receiver.  

What to do next, depends on what you know.  If you know the set 
has ever worked on 40, then you can skip checking winding of the 
coil.  If you don't know (fleamarket 'find') the check that the coil is 
wound correctly, in particular that if you start at the end that goes to 
the screen and follow the wire, you get to the screen supply and then 
the other winding continues *in the same winding direction* with the 
connection to ground.  It should be wound just as if the nearest two 
coil connections were a tap, except they're separated for DC 
purposes.  Reversing one winding (or the connections to one winding) 
is a common fault when building oscillators.  Make each coil 
connection goes to the right pin.  Check the soldering to each pin -- 
all should have continuity to at least one other pin and will read ~0 on 
a VTVM.  Go into the set and check the coil connections there.   

If you can borrow a GDO, then 'dip' the coil.   It should be somewhere 
in the osc. tuning range, should tune as you tune the receiver, and 
should have a pretty sharp dip.   Try the test out of the receiver too -- 
the dip should be significantly higher frequency.   Shorted turns or 
crummy caps will often show up at this stage.   

If no GDO or you don't like the answer, count the turns on each 
winding; I don't have the #s for the HBR 16 but the 40 meter coil for 
the 'deluxe HBR' in Bill Orr's handbook has 6-1/2 turns on the control 
grid winding and 10-7/8 turns on the screen winding; those should be 
approximately right.   Check spacing -- Deluxe HBR is 3/32"

Inspect for shorts between plates or in wiring to the three variable 
caps/trimmers in the oscillator circuit.   

If all of that checked out, then you're down to parts faults.   Retrace 
the wiring before getting too deeply into it, particularly check how 
everything connects to the coil and within.   When you've done this, 
then get someone else to do it for you -- you may be overlooking a 
mistake.   Disconnect C7 (coupling cap to the mixer -- that 
eliminates it as a fault.   Replace the .001 screen bypass cap.   
Replace the 100 mmf grid coupling cap.  

By now it should be working.   Good luck with your project!

Walt Hutchens
KJ4KV