开云体育

However, during the 9-years when Bill Fisher, W4AN, was among the living, AMPS did a fairly good job of providing a venue where old farts could pass on what we knew to the new crew.
cheerz

On Nov 4, 2006, at 7:23 PM, renn0vati0 wrote:

Good to be HERE.

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

indeed. Byte bye Tom Rauch.

On Sep 14, 2006, at 8:41 AM, k6kwqdm04 wrote:

This is great! No censorship here.

...

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

On Nov 5, 2006, at 2:06 AM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 3, 2006, at 5:10 PM, pentalab wrote:

Gent's

Some poor fellow on the 'other' amp reflector smoked the 25

ohm 25

watt wire wound glitch R on his Henry 3K .

What was not mentioned was that Henry installs the glitch R in
the B-..... NOT the B+.... no big deal... cept the glitch R +

all

wiring in/out of the glitch R has to use 10 kv wire.. and
glitch R well insulated from chassis... on stand offs.

RICH SEZ.... Not only that, but the filament transformer must to

be able to withstand the full anode V. This is why Henry Radio
amplifiers need circuit improvements before they are fired up --
sometimes quite literally.

### Point well taken !! I drew it out on paper... ur right...
the fil xfmr will spike to full B+.... with the glitch R.. in
the B- lead. What were these guys thinking ?

They probably weren't.

Easy to fix.

indeed

Another problem is that this particular resistor usually has an
adjustable tap / slider -- and that makes it not suitable for
glitch service.

### Why install an adjustable wirewound ?? Plane nuts.

It was part of the over-current relay ckt. -- something that
thoriated-tungsten filament tubes do not need because their emissive
layer (di-tungsten carbide / W^2C) can not be damaged by too much
cathode current - as is the case with oxide cathode tubes such as the
8877.

Try
this for an experiment... if u are brave enough. Install a 25 ohm-
25 watt wire wound wound... in a metal bomb proof box... fed
with 10 kv Red /Black Belden HV wire.... Hook the other ends of
the HV wire DIRECTLY to the B+ and B- of ur favourite HV
supply..... like a 3-K, etc....[NO HV fuse installed] Install a
heavy duty vac relay or better yet.. a vac contactor in the B+
lead. Turn on the HV supply.... stand back... and activate the
vac relay..... applying 3-8 kv across the glitch R...... then
lemme know IF the glitch R remains intact.

A 25W ww resistor is c. 2" long. 3000v is on the ragged edge of too
much V-gradient for a 2" resistor. Since 10w ww resistors are also
c. 2" long, it would be preferable to series two of them for glitch
service at 3000v or greater. The ultimate solution is to use a surge-
rated - in Joules - type resistor. The glitch resistors we current
supply with our low-Q suppressor retrofit kits are rated at 120J,
which is slightly more than what a SB-220 HV-PS is capable of during
a serious glitch.

He also smoked the safety diode between chassis and one end of
the glitch R. He shoulda
also had safety diodes across both the grid + plate meter. On a
8877... it really needs electronic fast grid overcurrent
protection.....

RICH SEZ.... The problem with 8877s is not grid damage from too
much HF grid-I, it's gold-evaporation from the grid caused by
occasional UHF parasitic oscillations that causes large bursts of
UHF grid-I that evaporates off thin layers of gold, which in turn
forms gold melt balls that create leakage paths in the vacuum. It
is my opinion that the way to stop gold sputtering is to limit peak
discharge current from the HV filter C with a sturdy glitch R in the
HV+ lead. As I see it, 8877s have so much UHF gain that they can be
a pain.

which I doubt would even work with the safety
diode shorted between chassis and his glitch R/ B-

agreed

### Here's the deal..Now this IS important. . A buddy of mine
brought over a QST article a few yrs back... in the stray's
dept... it depicted ur typ "electronic grid overcurrent"
protection scheme.... seen in many handbook projects... and also
used in many commercially produced linears. In many handbook amp
designs.... you will see a pair of diodes REVERSE connected...
between the chassis and B- Only one diode is really needed...
the worse thing that can happen usually.. is a B+ to chassis
short.

... which would be the case if the glitch-R was not capable of
limiting I-pk to the diode's peak-current ability. (typ. 200A-pk in
3A diodes or 400A-pk in 6A diodes)

### The tech note went on to show what really happens... IF
reverse connected diodes are installed from chassis to B- AND
electronic grid protection is used. They re-drew the entire
schematic.... and what is now depicted is the 2nd diode [not
needed].... ends up DIRECTLY in parallel... with.. u guessed it....
the small value resistor installed between grid shunt and
chassis. This small value resistor, [typ 5-15 ohms] has DC grid
current flowing through it all the time. It also has a V drop
across it.. typ 1-3 volts... which is fed to the wiper of a
pot... used as a V divider... then applied to a transistor...
activates a relay.. etc.. kicks amp offline, lights LED...
latches... etc. Trbl is... If the un needed 2nd safety diode
is used.... the V drop across the resistor is directly in parallel
with it... and turns on the diode !!!! DC Grid current is then
partially or fully diverted through the un-needed safety diode....
and u guessed it... the dc grid meter is now reading too low !

Use a 0.5Ω grid-current meter shunt-R and one can read up to 1A of
grid-I without exceeding a Si diode's 0.5v threshold point.

### The fix is... to remove the un-needed safety diode.

### On my 3000/6000A7 designs... NO electronic grid overcurrent
protection is used.

Does the 3cx6000A7 have a gold-plated grid?

A simple fast 3agc fuse is installed
between neg of grid meter and chassis. [with nothing across the
fuse either].

I would put a transient suppressor diode across the fuse. They are <
a dollar.

RVS connected 6 A diodes ARE used [I use 2-3
6A diodes in EACH direction... 4-6 in total].. wired between
chassis and B- I don't install any 10-1000 ohm resistor
between B- and chassis in either RF deck.... OR HV supply.

good

The
RVS connected diodes will never allow the B- to float more than
+/- .7v from chassis potential[grnd]...(grid fuse open). With
the grid fuse intact... the B- ends up at chassis potential
anyway... since the neg of the grid meter is fed via grid fuse...
to chassis.

### Originally, we installed a 100 K 3 watt resistor across the
grid fuse holder... thinking IF the grid fuse opened up... the V
drop across the 100 k resistor would bias the amp off.... it
doesn't ! With 800 w of drive applied on a 3x6... and the grid
fuse OPEN... all of a sudden you get 60 w reflected power on the
input of the amp [normally zero]... and abt 20% of normal power
output... [2500w instead of normal 12 kw]. We removed the 100 K
resistor... leaving a wide open (if fuse opens up).... and now with
drive applied.. and an open grid fuse.... u get ZERO watts
output.... and of course... ZERO DC grid current. [desired effect]

### The BIG question is.... WHERE the hell does this 800 watts of
drive end up ??? It's still being fed to cathode. Does it
just sit there and cook the cathode ??

How can you measure P if the input Z goes bananas?

## In any event the grid fuse concept works superbly..
everytime. Some reason's for the grid fuse blowing are.. excess
drive with a dead cxr... HV fuse blown... underloading, etc. I'm
now thinking that since all bugs are out... and all steady state
grid/plate current/ fil V/ plate V measurements have been done....
.. and now we just pulse tune it... then talk.... OR just dial up
the vac tune load caps... "by the pre-set numbers".. we can
probably REDUCE the size of the fast grid fuse from the current
750 Ma... down to something like 400-500 ma.

If it works, why fix it?

### Also.. my scheme of paralleling a PAIR of 50A magnetic-
hydraulic breaker to make one big 100A breaker's works quite
well.... one such assy is installed in EACH leg of the 240V line.
The kicker here is... we removed the tie bar on each assy. With
steady state dead cxr stuff... all 4 x poles are turned on.... with
ssb.... u can safely shut one pole off per assy. [now it's a 50 A
breaker] THEN.. if something goes amuck... with a lower value
grid fuse.. and pri breaker [ HV fuse remained same value.. 3
A] ... while on ssb.... both the pri breaker and lower valued grid
fuse will blow even faster.

Is faster better?

Later... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

--- In ham_amplifiers@..., "pentalab" <jim.thomson@...>
wrote:

### Here's the deal..Now this IS important. . A buddy of mine
brought over a QST article a few yrs back... in the stray's
dept... it depicted ur typ "electronic grid overcurrent"
protection scheme.... seen in many handbook projects... and also
used in many commercially produced linears. In many handbook amp
designs.... you will see a pair of diodes REVERSE connected...
between the chassis and B- Only one diode is really needed...
the worse thing that can happen usually.. is a B+ to chassis
short.

### The tech note went on to show what really happens... IF
reverse connected diodes are installed from chassis to B- AND
electronic grid protection is used. They re-drew the entire
schematic.... and what is now depicted is the 2nd diode [not
needed].... ends up DIRECTLY in parallel... with.. u guessed

it....

the small value resistor installed between grid shunt and
chassis. This small value resistor, [typ 5-15 ohms] has DC grid
current flowing through it all the time. It also has a V drop
across it.. typ 1-3 volts... which is fed to the wiper of a
pot... used as a V divider... then applied to a transistor...
activates a relay.. etc.. kicks amp offline, lights LED...
latches... etc. Trbl is... If the un needed 2nd safety

diode

is used.... the V drop across the resistor is directly in parallel
with it... and turns on the diode !!!! DC Grid current is then
partially or fully diverted through the un-needed safety

diode....

and u guessed it... the dc grid meter is now reading too low !

### The fix is... to remove the un-needed safety diode.

########### Here's the MISSING note. Even IF the un -needed diode
is removed on an electronic grid over current scheme.... and the
remaining WANTED safety diode [between chassis and B-] ever
shorts out [typ on ALL Ameritron amps..cuz they use TOO small a
surge rated diode], your fancy electronic grid overcurrent
protection scheme is NO longer gonna work until that safety diode
is replaced ! With the diode shorted, the small value drop
resistor that's part of the above mentioned grid overcurrent
scheme... is now directly in parallel with the shorted diode !!
ALL DC grid current will simply flow through the shorted
diode.. through the PLATE meter... back to cathode.

### Wait, it gets worse! With the safety diode shorted
out... the plate and grid meter are now directly in parallel with
each other. The grid meter however, will still have a 5-15 ohm
resistor in it's neg leg... the plate meter does NOT. The Pos
terminals of both meter's are tied together of course..... so plate
meter will now read the SUM of the plate current AND grid
current.

### Left in that above config... the amp will still work... except
the grid meter will not function... and the grid overcurrent will
not function. IF a HV fuse is used.... and say blows at the
same time the safety diode shorts... you are now in bigger trbl !
With drive applied, and NO plate V.... you will send the grid
current into orbit... and with NO functioning grid over current
protection.... u can kiss the tube goodbye.


### On my buddy's Ameritron amps..[he has since gotten rid of
em].... the manual tells you to .. "check for a shorted safety
diode"... "after an event" !! Now if the bozo who designed it had
used a bigger surge rated diode.. and a glitch R... this would never
happen.

### Beware... some pundits on the "other reflector" have
suggested using a standard pre-packaged bridge rectifier 4-25 A
50V diode assy... like the typ sealed type.. with 4 x wires
protruding out.... as a "safety diode". Now this will work....
PROVIDED u strap the TWO AC input's together.... THEN grnd em to
chassis.... and then wire the + output of the rectifier assy...
to the B- of the HV supply. The neg output of the bridge
rectifier assy is NOT used.

#### On the other reflector.. it was stated to simply wire the
AC input's between chassis and B- !! Draw that config out on
paper.. and u will see that u end up with opposing pairs of
diodes.. and the PIV of 2 of the diodes will be exceeded... and
those two diodes will blow clean in 1/2..... leaving two
paralled open circuits... and now an open loop. Unless u got
more safety diodes installed across each meter.. AND 3-4
more...wired in series in the grid overcurrent circuit.... u will
smoke the meter's and the grid overcurrent assy.

### PIV rating for a safety diode is not an issue... it's
strictly the SURGE rating. 6A diodes are cheap... so are
paralled 1N5408's [3A] .

Later... Jim VE7RF

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 3, 2006, at 5:10 PM, pentalab wrote:

Gent's

Some poor fellow on the 'other' amp reflector smoked the 25

ohm 25

watt wire wound glitch R on his Henry 3K .

What was not mentioned was that Henry installs the glitch R in
the B-..... NOT the B+.... no big deal... cept the glitch R +

all

wiring in/out of the glitch R has to use 10 kv wire.. and
glitch R well insulated from chassis... on stand offs.

RICH SEZ.... Not only that, but the filament transformer must to

be able to withstand the full anode V. This is why Henry Radio
amplifiers need circuit improvements before they are fired up --
sometimes quite literally.

### Point well taken !! I drew it out on paper... ur right...
the fil xfmr will spike to full B+.... with the glitch R.. in
the B- lead. What were these guys thinking ? Easy to fix.


Another problem is that this particular resistor usually has an
adjustable tap / slider -- and that makes it not suitable for
glitch service.

### Why install an adjustable wirewound ?? Plane nuts. Try
this for an experiment... if u are brave enough. Install a 25 ohm-
25 watt wire wound wound... in a metal bomb proof box... fed
with 10 kv Red /Black Belden HV wire.... Hook the other ends of
the HV wire DIRECTLY to the B+ and B- of ur favourite HV
supply..... like a 3-K, etc....[NO HV fuse installed] Install a
heavy duty vac relay or better yet.. a vac contactor in the B+
lead. Turn on the HV supply.... stand back... and activate the
vac relay..... applying 3-8 kv across the glitch R...... then
lemme know IF the glitch R remains intact.

He also smoked the safety diode between chassis and one end of
the glitch R. He shoulda
also had safety diodes across both the grid + plate meter. On a
8877... it really needs electronic fast grid overcurrent
protection.....

RICH SEZ.... The problem with 8877s is not grid damage from too

much HF grid-I, it's gold-evaporation from the grid caused by
occasional UHF parasitic oscillations that causes large bursts of
UHF grid-I that evaporates off thin layers of gold, which in turn
forms gold melt balls that create leakage paths in the vacuum. It
is my opinion that the way to stop gold sputtering is to limit peak
discharge current from the HV filter C with a sturdy glitch R in the
HV+ lead. As I see it, 8877s have so much UHF gain that they can be
a pain.

which I doubt would even work with the safety
diode shorted between chassis and his glitch R/ B-

agreed

### Here's the deal..Now this IS important. . A buddy of mine
brought over a QST article a few yrs back... in the stray's
dept... it depicted ur typ "electronic grid overcurrent"
protection scheme.... seen in many handbook projects... and also
used in many commercially produced linears. In many handbook amp
designs.... you will see a pair of diodes REVERSE connected...
between the chassis and B- Only one diode is really needed...
the worse thing that can happen usually.. is a B+ to chassis
short.

### The tech note went on to show what really happens... IF
reverse connected diodes are installed from chassis to B- AND
electronic grid protection is used. They re-drew the entire
schematic.... and what is now depicted is the 2nd diode [not
needed].... ends up DIRECTLY in parallel... with.. u guessed it....
the small value resistor installed between grid shunt and
chassis. This small value resistor, [typ 5-15 ohms] has DC grid
current flowing through it all the time. It also has a V drop
across it.. typ 1-3 volts... which is fed to the wiper of a
pot... used as a V divider... then applied to a transistor...
activates a relay.. etc.. kicks amp offline, lights LED...
latches... etc. Trbl is... If the un needed 2nd safety diode
is used.... the V drop across the resistor is directly in parallel
with it... and turns on the diode !!!! DC Grid current is then
partially or fully diverted through the un-needed safety diode....
and u guessed it... the dc grid meter is now reading too low !

### The fix is... to remove the un-needed safety diode.

### On my 3000/6000A7 designs... NO electronic grid overcurrent
protection is used. A simple fast 3agc fuse is installed
between neg of grid meter and chassis. [with nothing across the
fuse either]. RVS connected 6 A diodes ARE used [I use 2-3
6A diodes in EACH direction... 4-6 in total].. wired between
chassis and B- I don't install any 10-1000 ohm resistor
between B- and chassis in either RF deck.... OR HV supply. The
RVS connected diodes will never allow the B- to float more than
+/- .7v from chassis potential[grnd]...(grid fuse open). With
the grid fuse intact... the B- ends up at chassis potential
anyway... since the neg of the grid meter is fed via grid fuse...
to chassis.

### Originally, we installed a 100 K 3 watt resistor across the
grid fuse holder... thinking IF the grid fuse opened up... the V
drop across the 100 k resistor would bias the amp off.... it
doesn't ! With 800 w of drive applied on a 3x6... and the grid
fuse OPEN... all of a sudden you get 60 w reflected power on the
input of the amp [normally zero]... and abt 20% of normal power
output... [2500w instead of normal 12 kw]. We removed the 100 K
resistor... leaving a wide open (if fuse opens up).... and now with
drive applied.. and an open grid fuse.... u get ZERO watts
output.... and of course... ZERO DC grid current. [desired effect]

### The BIG question is.... WHERE the hell does this 800 watts of
drive end up ??? It's still being fed to cathode. Does it
just sit there and cook the cathode ??

## In any event the grid fuse concept works superbly..
everytime. Some reason's for the grid fuse blowing are.. excess
drive with a dead cxr... HV fuse blown... underloading, etc. I'm
now thinking that since all bugs are out... and all steady state
grid/plate current/ fil V/ plate V measurements have been done....
.. and now we just pulse tune it... then talk.... OR just dial up
the vac tune load caps... "by the pre-set numbers".. we can
probably REDUCE the size of the fast grid fuse from the current
750 Ma... down to something like 400-500 ma.

### Also.. my scheme of paralleling a PAIR of 50A magnetic-
hydraulic breaker to make one big 100A breaker's works quite
well.... one such assy is installed in EACH leg of the 240V line.
The kicker here is... we removed the tie bar on each assy. With
steady state dead cxr stuff... all 4 x poles are turned on.... with
ssb.... u can safely shut one pole off per assy. [now it's a 50 A
breaker] THEN.. if something goes amuck... with a lower value
grid fuse.. and pri breaker [ HV fuse remained same value.. 3
A] ... while on ssb.... both the pri breaker and lower valued grid
fuse will blow even faster.

Later... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

Good to be HERE.

ORIGINAL MESSAGE:

On Sat, 04 Nov 2006 00:27:50 -0000, "pentalab" <jim.thomson@...>
wrote:

I found 38 mistakes in it so far.. mainly typo's....

------------ REPLY FOLLOWS ------------

The plural of typo is typos.

Sorry, couldn't resist. :-)

Bill, W6WRT

So, is the equation wrong? Jim's answer implies an inverse square equation.

-J

On Nov 3, 2006, at 5:10 PM, pentalab wrote:

Gent's

Some poor fellow on the 'other' amp reflector smoked the 25 ohm 25
watt wire wound glitch R on his Henry 3K .

What was not mentioned was that Henry installs the glitch R in
the B-..... NOT the B+.... no big deal... cept the glitch R + all
wiring in/out of the glitch R has to use 10 kv wire.. and
glitch R well insulated from chassis... on stand offs.

Not only that, but the filament transformer must to be able to withstand the full anode V. This is why Henry Radio amplifiers need circuit improvements before they are fired up -- sometimes quite literally.
Another problem is that this particular resistor usually has an adjustable tap / slider -- and that makes it not suitable for glitch service.
A friend named Jim who repairs and builds amplifiers once asked Henry why they use VHF parasitic suppressors that exhibit a high-Q (c. 5.5 @100MHz) . The answer: Because we have always used them.

He also smoked the safety diode between chassis and one end of
the glitch R. He had an arc between base of plate choke and
chassis.

Which is another reason why the glitch R needs to go in the HV+.

Fault current simply flows from chassis up through under rated
puny glitch R.... through the glitch R... back to B-...... whereby u
guessed it.... the safety diode shorted out [wouldn't handle the
surge]... then the 4 kv is sitting right across the 25 ohm glitch
R... blowing it to Kingdome come !

The fellow replaced the glitch R... amp works.. BUT his grid meter
is off the scale ! As u can see if u trace it... with a shorted
safety diode.... the plate AND grid meter are now directly in
parallel ! [neg of grid meter bonded to chassis... flows along
chassis... through shorted safety diode back to B-... then to neg
of plate meter] 1/2 plate current flows through EACH meter..
then the grid meter get's smoked.

The fix is of course.. 2-3 x 6A diodes in parallel between
chassis and in his case.. glitch R.... OR B-.... if glitch R is in
the B+ lead ["normal amp"]

IF he had a HV fuse in the B+.... he would NEVER have smoked the
glitch R. The slow breaker in his 240 V line is just that... way
too damned SLOW.


Also... IF he had a FAST grid fuse between chassis and neg of
grid meter/shunt... u would not smoke the grid meter. He shoulda
also had safety diodes across both the grid + plate meter. On a
8877... it really needs electronic fast grid overcurrent
protection.....

The problem with 8877s is not grid damage from too much HF grid-I, it's gold-evaporation from the grid caused by occasional UHF parasitic oscillations that causes large bursts of UHF grid-I that evaporates off thin layers of gold, which in turn forms gold melt balls that create leakage paths in the vacuum. It is my opinion that the way to stop gold sputtering is to limit peak discharge current from the HV filter C with a sturdy glitch R in the HV+ lead.
As I see it, 8877s have so much UHF gain that they can be a pain.

which I doubt would even work with the safety
diode shorted between chassis and his glitch R/ B-

agreed

...

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

On Nov 3, 2006, at 3:36 PM, pentalab wrote:

--- In ham_amplifiers@..., jmltinc@... wrote:

In the VHF/UHF Handbook, chapter Receivers, Transmitters And

Transceivers ,

section, 'Tuned Circuits'; the author writes: "If discs are used,

the

capacitance varies in a very non-linear manner with the distance

between them.

It is: C(pF) = 0.00885 x Area (sq mm) / Spacing (mm)"

The equation for capacitance vs area vs spacing is linear. What's up?

John, N9RF

### You double the spacing between any two plates... and C drops
to just 1/4 of the original. [ V rating doubles].

### conversely... u reduce the spacing by 1/2 the original... and C
increases 4 x [V rating drops in 1/2]

Correctomundo, Jim. Congrats

later... Jim

Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

On Nov 3, 2006, at 4:53 PM, jmltinc@... wrote:

Hey Jim,

No, the book is ARRL's VHF/UHF Handbook. The formula is correct, as it is
found elsewhere, including Orr's book (p 2-6, 23rd Edition). He includes the term
for inclusion of a dielectric.

He states (correctly, as the equation illustrates), that C is proportional to
the area of the plates and inversely proportional to the spacing between
them. Halve the spacing -- double the C.

My problem is the statement of Dick Bidulph, M0CGN, author of the ARRL
publication regarding the "nonlinear manner". Unless, of course, he is using a
nonlinear screw!

Guffaw!!

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

On Nov 3, 2006, at 2:17 PM, jmltinc@... wrote:

In the VHF/UHF Handbook, chapter Receivers, Transmitters And Transceivers ,
section, 'Tuned Circuits'; the author writes: "If discs are used, the
capacitance varies in a very non-linear manner with the distance between them.
It is: C(pF) = 0.00885 x Area (sq mm) / Spacing (mm)"

The equation for capacitance vs area vs spacing is linear. What's up?

More taurine feces, John, Cheerz

John, N9RF



Yahoo! Groups Links

R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org

Gent's

Some poor fellow on the 'other' amp reflector smoked the 25 ohm 25
watt wire wound glitch R on his Henry 3K .

What was not mentioned was that Henry installs the glitch R in
the B-..... NOT the B+.... no big deal... cept the glitch R + all
wiring in/out of the glitch R has to use 10 kv wire.. and
glitch R well insulated from chassis... on stand offs.

He also smoked the safety diode between chassis and one end of
the glitch R. He had an arc between base of plate choke and
chassis.

Fault current simply flows from chassis up through under rated
puny glitch R.... through the glitch R... back to B-...... whereby u
guessed it.... the safety diode shorted out [wouldn't handle the
surge]... then the 4 kv is sitting right across the 25 ohm glitch
R... blowing it to Kingdome come !

The fellow replaced the glitch R... amp works.. BUT his grid meter
is off the scale ! As u can see if u trace it... with a shorted
safety diode.... the plate AND grid meter are now directly in
parallel ! [neg of grid meter bonded to chassis... flows along
chassis... through shorted safety diode back to B-... then to neg
of plate meter] 1/2 plate current flows through EACH meter..
then the grid meter get's smoked.

The fix is of course.. 2-3 x 6A diodes in parallel between
chassis and in his case.. glitch R.... OR B-.... if glitch R is in
the B+ lead ["normal amp"]

IF he had a HV fuse in the B+.... he would NEVER have smoked the
glitch R. The slow breaker in his 240 V line is just that... way
too damned SLOW.


Also... IF he had a FAST grid fuse between chassis and neg of
grid meter/shunt... u would not smoke the grid meter. He shoulda
also had safety diodes across both the grid + plate meter. On a
8877... it really needs electronic fast grid overcurrent
protection..... which I doubt would even work with the safety
diode shorted between chassis and his glitch R/ B-

To stop the arcing between base of plate choke and chassis...
install a teflon /plastic disc or square, between chassis and
bottom of plate choke. On a Henry.. with a choke in it... make
sure the bypass caps at the base of the plate choke are good for
10 kv. .... in case a wirewound let's go in the bleeder string...
otherwise.... no load plate V will skyrocket... as the HV supply
now looks like a C input filter.

later... Jim VE7RF

--- In ham_amplifiers@..., "pentalab" <jim.thomson@...>
wrote:

--- In ham_amplifiers@..., jmltinc@ wrote:

In the VHF/UHF Handbook, chapter Receivers, Transmitters And

Transceivers ,

section, 'Tuned Circuits'; the author writes: "If discs are

used,

the

capacitance varies in a very non-linear manner with the distance

between them.

It is: C(pF) = 0.00885 x Area (sq mm) / Spacing (mm)"

The equation for capacitance vs area vs spacing is linear.

What's up?

John, N9RF

########### Congrat's... u just found ur 1st mistake. If this is
orr's latest blue book..... which page is it on ??? I found 38
mistakes in it so far.. mainly typo's.... have not got to the
vhf/uhf stuff yet.

Jim

### You double the spacing between any two plates... and C

drops

to just 1/4 of the original. [ V rating doubles].

### conversely... u reduce the spacing by 1/2 the original...

and C

increases 4 x [V rating drops in 1/2]

later... Jim

--- In ham_amplifiers@..., jmltinc@... wrote:

In the VHF/UHF Handbook, chapter Receivers, Transmitters And

Transceivers ,

section, 'Tuned Circuits'; the author writes: "If discs are used,

the

capacitance varies in a very non-linear manner with the distance

between them.

It is: C(pF) = 0.00885 x Area (sq mm) / Spacing (mm)"

The equation for capacitance vs area vs spacing is linear. What's up?

John, N9RF

### You double the spacing between any two plates... and C drops
to just 1/4 of the original. [ V rating doubles].

### conversely... u reduce the spacing by 1/2 the original... and C
increases 4 x [V rating drops in 1/2]

later... Jim

--- In ham_amplifiers@..., "pentalab" <jim.thomson@>

wrote:

--- In ham_amplifiers@..., "zerobeat40"

<zerobeat40@>

wrote:

### When I look at the 2 x tone on the scope.... the

envelope varies from zero to full pep.

Z SEZ.... At what rate? The rate of the diff between the tones.

So, if your two tones are, say, 3Hz apart, then the power supply is
having to feed out current that varies at a 3Hz rate. Not a prob
with a bridge-cap power supply, but can cause wild fluctuations in
voltage for a choke-input supply.

### I get it now... at 3 hz... this would be like slowly turning up
the drive to the linear.. when on say cw mode... with a dead cxr...
up down up down.. etc. So what.... any HV supply should be able
to handle that.... esp a resonant choke set up???

### IOW... what u are saying is with a 3-20 hz rate... u are in
effect MODULATING the HV supply... at an AUDIO rate ???




On my bias
supplies... they are just a string of 6 A diodes with a 5000-
10,000 uf cap across em.. end to end.... and some .01 uf discs
between each end of string.... and chassis for bypass.

### Maybe for the bias... we need bigger bypass caps on each end
to chassis... like 1-10uf non polarized ... as well as the
usual .01 uf disc caps ??? [stagger tuned]

Z SEZ.... And, it's to test all the power supplies. The p-supply's
job is to feed out a fixed voltage, but let the current vary all
over the place, at any rate, without the voltage changing.

You can test it with CW pulses, then you have to use a scope to

watch power supply behavior.

### a scope across the last HV lytic [cold end] in a HV supply
should work... or the last two x lytics. A battery operated
digital fluke storage scope would be ideal... even for ssb.. or cw.





Or you can feed it two-tone IMD sigs, and measure the IMD coming
out to see if the power supply behavior is impacting the amp
performance.

### I have wondered about that.... Voice IMD vs HV
regulation... esp a C input HV supply. Well, I can easily add in
100uf and 50uf banks of caps... up to a whopping 450 uf of filter
cap [11 kv rated]

Z SEZ... No problem with a well-designed power supply, which has

low source

impedance from DC to high audio freqs.

### OK.. will big lytics in a HV supply handle high audio
freqs ??? Same question on my variable bias supply ??

Z SEZ....Maybe with modern PS design, it's a moot point. But, the

point is to test the PS regulation under dynamic load - varying
pulse rates.Z

### agreed... which is why I like putting loads of uf into my HV
supplies... kills 2 x birds at once.... results in superb dynamic
regulation.... and <1 % ripple. [ripple freq is of course 120 hz]

### since I mess with ESSB... and can easily put out 1.5 kw with
20 hz sine wave, voice etc... going into the analog BM... maybe
I should base stuff on down to say at least 30-50 hz.

### Right now.. I have several 2 x tone generators... none will
allow close spaced tones...they are all fixed.

Tnx Z... U answered my question.

later....... Jim VE7RF

Hey Jim,

No, the book is ARRL's VHF/UHF Handbook. The formula is correct, as it is
found elsewhere, including Orr's book (p 2-6, 23rd Edition). He includes the term
for inclusion of a dielectric.

He states (correctly, as the equation illustrates), that C is proportional to
the area of the plates and inversely proportional to the spacing between
them. Halve the spacing -- double the C.

My problem is the statement of Dick Bidulph, M0CGN, author of the ARRL
publication regarding the "nonlinear manner". Unless, of course, he is using a
nonlinear screw!

-J

--- In ham_amplifiers@..., "pentalab" <jim.thomson@...> wrote:

--- In ham_amplifiers@..., "zerobeat40" <zerobeat40@>
wrote:

###> The 2 tone test is flawed, and isn't used anymore in the

commercial world. By juggling the spacing of the 2 x tones,

you can hit a .."sweet spot" and come up with really good IMD
numbers.

Z SEZ... That's usually with very wide spacing. At very narrow

spacing, you challenge the power supply bypassing, so the worst
numbers often occur at that test condition.

### Rauch sez the same thing....verbatim on his site...with no
explanation of course.


### OK... what am I missing here ??? I don't "get it". Why
would narrow two tone spacing... "challenge the power supply
bypassing" ??????

### Which supply.... the bias supply and or the HV supply???
What do you mean by "power supply bypassing"..... my giant 100 uf
C filter in my C input HV supply... or something else... like
bypass caps at the base of the plate choke ???

### When I look at the 2 x tone on the scope.... the envelope
varies from zero to full pep.

At what rate? The rate of the diff between the tones. So, if your
two tones are, say, 3Hz apart, then the power supply is having to feed
out current that varies at a 3Hz rate. Not a prob with a bridge-cap
power supply, but can cause wild fluctuations in voltage for a
choke-input supply.

And, it's to test all the power supplies. The p-supply's job is to
feed out a fixed voltage, but let the current vary all over the place,
at any rate, without the voltage changing.

You can test it with CW pulses, then you have to use a scope to watch
power supply behavior. Or you can feed it two-tone IMD sigs, and
measure the IMD coming out to see if the power supply behavior is
impacting the amp performance.

No problem with a well-designed power supply, which has low source
impedance from DC to high audio freqs.

In my early days in RF amp design (the amps were then being used in
the telephone system, to multiplex many long-distance phone calls onto
a single twisted pair), we made the mistake of a too-large plate
choke. That plate choke, when forced to dole out current pulses that
were fairly slow (several Hz), rang and resonated with the PS filter
caps (microfarards were a precious commodity in the 30s) and caused
arcing in the tubes.

Maybe with modern PS design, it's a moot point. But, the point is to
test the PS regulation under dynamic load - varying pulse rates.Z

I wrote:

In the VHF/UHF Handbook, chapter Receivers, Transmitters And Transceivers ,
section, 'Tuned Circuits'; the author writes: "If discs are used, the
capacitance varies in a very non-linear manner with the distance between them.
It is: C(pF) = 0.00885 x Area (sq mm) / Spacing (mm)"

The equation for capacitance vs area vs spacing is linear. What's up?

My question is perhaps not clear. The author states that "capacitance varies
in a very non-linear manner...". Yet the equation is linear. Now, what's up?

-J

In the VHF/UHF Handbook, chapter Receivers, Transmitters And Transceivers ,
section, 'Tuned Circuits'; the author writes: "If discs are used, the
capacitance varies in a very non-linear manner with the distance between them.
It is: C(pF) = 0.00885 x Area (sq mm) / Spacing (mm)"

The equation for capacitance vs area vs spacing is linear. What's up?

John, N9RF

--- In ham_amplifiers@..., "zerobeat40" <zerobeat40@...>
wrote:

###> The 2 tone test is flawed, and isn't used anymore in the

commercial world. By juggling the spacing of the 2 x tones,

you can hit a .."sweet spot" and come up with really good IMD
numbers.

Z SEZ... That's usually with very wide spacing. At very narrow

spacing, you challenge the power supply bypassing, so the worst
numbers often occur at that test condition.

### Rauch sez the same thing....verbatim on his site...with no
explanation of course.


### OK... what am I missing here ??? I don't "get it". Why
would narrow two tone spacing... "challenge the power supply
bypassing" ??????

### Which supply.... the bias supply and or the HV supply???
What do you mean by "power supply bypassing"..... my giant 100 uf
C filter in my C input HV supply... or something else... like
bypass caps at the base of the plate choke ???

### When I look at the 2 x tone on the scope.... the envelope
varies from zero to full pep.

### What's supposed to happen... if say the two tones are
a multiple of each other... like 1000 hz and 2000 hz..... or 500
hz + 1000hz? This is supposed to be a big 'no-no'. Looks to
me like they would still be .."in phase" regardless of spacing ?

### What 'bad' is supposed to happen if the two tones are say
1000 hz.... and 1120 hz..... or 1000 hz and 1060 hz ??? Is
the 120/60 hz difference freq supposed to modulate the linear
at an audio rate or something ???

I'm completely lost.

later.... Jim VE7RF