WDØHCO wrote in message
...
Hola Amigo's...

Biz Wichy here ( WDØHCO )

Hi Bill and Thermo

He's talking about the VFO in the RX section and to answer your question
Thermo - NO - that's not normal. I have 3 HW-16's and none have ever done
that.

So lets fix her...

First step is to switch V3 6EA8 with the Het Mixer V2 6EA8 and see if the
problem goes away. There's one chance in a million the tube is the
problem... if that's it then you really should be playing the lottery!!!

Second step - try swapping the 6EW6 V4 IF AMP with 6EW6 V1 RF AMP and see
if
the problem goes away. This one stage away from VFO/MIX but it's worth
tryin
cause it only takes a second and well who knows...

Third Step - possible cold solder joint. Give a good going over all the
joints in the that part of the circuit board. Pay particular attention to
wire "X" that connects L7. Make sure it's as short as can be and no other
wires come near it. Make sure the copper island on the board where it
lands
is clean ( i.e No Rosen crap ).

Fourth Step - check all the entrances and exits of the VFO circuit. In
this
case there is only two. Check R33 47K 1W resistor to see if its within 20%
of the 47K value. Just left up one leg and check with a VOM. This little
guy
connects the +310 VDC bus and drops it to +95 to the plate of the triode
section of the VFO 6EA6. Hook the resistor back up and check the +95
voltage
with a ANALOG VOM. Tune in a strong signal and see if it dips as you rock
the tuning knob. Next - lets check C56 cap which goes into the cathode of
the VFO MIX. If you have a cap checker - fine and dandy - if not remove
C56
and solder 2 2" 20 gauge vinyl coated wires and twist them together loosly
three times. That should be near 680 Puff. Turn on the set and see if the
problem went away. If not - put C56 back in place.

At this point - we can conclude that VFO might not be the problem. A
likely
suspect could be the BFO Circuit - V5B which uses a 12AX7. since the '16
only has one 12AX7 you can't sub unless you have a spare 12AX7 - then try
it.

The fixed freq BFO is directly mixed with the IF sig at T3. R51, C72 and
C77
could be troublemakers. The best way to check it is with a FREQ Counter.
If
you don't have one - use a good shortwave rcvr. Attach a wire antenna and
bring it near T3 and tune it to the BFO freq on 3396.4 KC. Turn on the
Shortwave Rcvr's BFO and get a good whistle. Now tune the HW-16 to a
strong
station and see if the HW-16's BFO shifts around.

Well that should be a good start. Please post what your results were.

Biz WDØHCO




Again, thanks for your helpful words. I have not found anything wrong
yet except for a bad solder on V1. I won't get into everything that I did,
but the tubes are good, C56 is good, I can't find any other bad components,
and for sure its the main VFO that is being affected. I tuned it in on
another rx. The freq shift is small, maybe 50 cycles at its worst, but thats
enough to be a problem. I tried other values for C56 and find that the shift
is less with less C and larger with more C. There is a slight voltage
variation of about 1/2 volt on the screen of V3 that can be detected when a
strong signal is present, and a change of a couple hundredths of a volt on
the cathode. I think next I will remove C56 entirely and see if the VFO is
still shifting. Will let you know what happens! Thanks.......T

Hello Again Thermo-man and everyone else. Well your on the right track.

There is a slight voltage variation of about 1/2 volt on the screen of V3 that
can be detected when a strong signal is present, and a change of a couple
hundredths of a volt on the cathode.

There should be no voltage changes. Oscillators are very fragile things -
doesn't take much to get an amp to oscillate but keeping it on an exact freq
is an art. Most military receivers have buffer amps after various
oscillators to keep things steady. This is why they have so many tubes ! Any
little change will affect frequency. SOMETHING is causing this voltage
change. What could it be ??

I tried other values for C56 and find that the shift is less with less C and
larger with more C.

Big clue! What your doing is adjusting the amount of coupling from the VFO
RF into the cathode circuit of V3A mixer tube. Well DUH!

But what most folks forget is that a cap is a two way RF door. Part of the
Main sig is coming back to the VFO the other way...

It travels down to the Colpitts circuit of C59 and C61 (both 1000 puff). The
idea is to attenuate the main sig to ground (C61) while coupling the VFO RF
to C56. If C59 or C61 values have changed then the main sig will couple into
the VFO tube Cathode circuit (V3B) and cause all sorts of problems. It could
also couple into the control grid -and- VFO LC circuit if C58 has changed
value (100 puff). You can also check resistors R34 and R32 but I really
don't think that's the problem.

I think next I will remove C56 entirely and see if the VFO is still shifting.

This will prove that it's not a power supply problem. Your not coupled to
anything so the VFO should not shift frequency.

NOW FOR SOME FUN...

You can couple the VFO to other parts of the Mixer tube. Heath has it
coupled to the Cathode of V3A but you don't have to have it that way....

What happens if you run a wire from C56 and plug it into the Plate ? Well
since an equal number of electrons are emitted from the Cathode as they are
arriving at the Plate - I would expect no change in VFO performance/problem.

What happens if you run a wire from C56 and plug it into the Grid Leak
circuit (Pin 3 6EA8 V3A)? Now your more isolated from the main sig but your
VFO drive level is too high! You can compensate by using less cap in C56.

What happens if you run a wire from C56 and plug it into the Control Grid
circuit (Pin 2 6EA8 V3A)? Now your VFO is mixed with the main sig but at a
much lower level. Again, your VFO drive level is too high! You can
compensate by using less cap in C56. T2 bandpass limits the amount of VFO
passing back up to the V2A Het Mixer. The main sig level is too low to
bother the VFO unlike the Cathode injection point. This might be a good
alternative solution to your VFO problem.

So now your can change the VFO mixer level.

What if you could adjust the BFO and 1st HET oscillator levels too ? Well
you would have one heck of a receiver customized for present band
conditions, DX or local QSO's and even individual tubes! Lets face it - all
factory circuits are a compromise of performance, tube values and conditions
and operator likes and dislikes.

Actually this is a pretty good idea for a project if you don't mind butching
up a set. And since you can find 16's for $25 to $50 bucks you wouldn't be
out by much if you blew it up.... hmmm when's the next hamfest???

-B

WDØHCO wrote in message
...
Hello Again Thermo-man and everyone else. Well your on the right track.

There is a slight voltage variation of about 1/2 volt on the screen of
V3 that
can be detected when a strong signal is present, and a change of a couple
hundredths of a volt on the cathode.

There should be no voltage changes. Oscillators are very fragile things -
doesn't take much to get an amp to oscillate but keeping it on an exact
freq
is an art. Most military receivers have buffer amps after various
oscillators to keep things steady. This is why they have so many tubes !
Any
little change will affect frequency. SOMETHING is causing this voltage
change. What could it be ??

I don't know, but I tried jumping a different value resistor at this
circuit thereby greatly changing the voltage on the screen and there was no
freq shift.


I tried other values for C56 and find that the shift is less with less C
and
larger with more C.

Big clue! What your doing is adjusting the amount of coupling from the VFO
RF into the cathode circuit of V3A mixer tube. Well DUH!

But what most folks forget is that a cap is a two way RF door. Part of the
Main sig is coming back to the VFO the other way...

It travels down to the Colpitts circuit of C59 and C61 (both 1000 puff).
The
idea is to attenuate the main sig to ground (C61) while coupling the VFO
RF
to C56. If C59 or C61 values have changed then the main sig will couple
into
the VFO tube Cathode circuit (V3B) and cause all sorts of problems. It
could
also couple into the control grid -and- VFO LC circuit if C58 has changed
value (100 puff). You can also check resistors R34 and R32 but I really
don't think that's the problem.

I thought that was a good idea, so checked it out. Those caps are
ok, so no luck there.

I think next I will remove C56 entirely and see if the VFO is still
shifting.

This will prove that it's not a power supply problem. Your not coupled to
anything so the VFO should not shift frequency.

Removing C56 absolutely clears up the freq shifting alright.


NOW FOR SOME FUN...

You can couple the VFO to other parts of the Mixer tube. Heath has it
coupled to the Cathode of V3A but you don't have to have it that way....

What happens if you run a wire from C56 and plug it into the Plate ? Well
since an equal number of electrons are emitted from the Cathode as they
are
arriving at the Plate - I would expect no change in VFO
performance/problem.

What happens if you run a wire from C56 and plug it into the Grid Leak
circuit (Pin 3 6EA8 V3A)? Now your more isolated from the main sig but
your
VFO drive level is too high! You can compensate by using less cap in C56.

What happens if you run a wire from C56 and plug it into the Control Grid
circuit (Pin 2 6EA8 V3A)? Now your VFO is mixed with the main sig but at a
much lower level. Again, your VFO drive level is too high! You can
compensate by using less cap in C56. T2 bandpass limits the amount of VFO
passing back up to the V2A Het Mixer. The main sig level is too low to
bother the VFO unlike the Cathode injection point. This might be a good
alternative solution to your VFO problem.

So now your can change the VFO mixer level.

What if you could adjust the BFO and 1st HET oscillator levels too ? Well
you would have one heck of a receiver customized for present band
conditions, DX or local QSO's and even individual tubes! Lets face it -
all
factory circuits are a compromise of performance, tube values and
conditions
and operator likes and dislikes.

Actually this is a pretty good idea for a project if you don't mind
butching
up a set. And since you can find 16's for $25 to $50 bucks you wouldn't be
out by much if you blew it up.... hmmm when's the next hamfest???

-B


So I can't find anything wrong, its just bad design and it needs a
buffer. I live pretty close to W1AW and it is the main source of this rigs'
problem. None of my other rigs are bothered by strong signals except maybe
for the old S-38. So I built up a little source follower circuit with a
MPF-102 on a terminal strip, played with circuit values a bit and it stops
the freq shift just fine, BUT the output of the follower is too low. The
mixer does not give full output. So I guess I build an amp for that circuit,
or maybe put a tube cathode follower in there or throw the radio out the
window....................the saga continues...........