开云体育

OK... I'll bite. What exactly is Orr's... "super cathode driven"
circuit all about ?? Is this simply semi floating the grids on a
3-500Z.... or something else ?

25 years ago.... there was this circuit for a 4CX-1000.... and I
thought it was called "super cathode driven".... might be wrong...
believe it was in either cq or 73 rag. If I remember correctly...
Drive was applied to both the cathode and the control grid at the
same time... and the screen grid was grndned for RF. I still know
of two of those 4CX-1000 amps that are still round.. within 200
miles of me. The kicker was.... it required 160 watts to drive
it to 1200 w out. At the time it was no big deal... since the
xcvr's used were FT-DX-400/401's.

### a local across town from me in the 80's built one.... took
out 100 khz of 20m with it.... not imd... but shot noise. My
Drake R4C noise-blanker took it right out on RX... and I could then
get real close to him... within 15 khz. We both had yagi's up
70'.... and only 2500' apart. He subsequently found the problem...
never was told what the problem actually was. His xcvr at the
time was a 101ZD...with 6146W finals.

## The guy's with the FT-DX-400/401 xcvr's had clean sigs on
75m... so the concept worked... albeit... not a lot of gain ...
8.75db

Later... Jim VE7RF

A CV transformer is uneffected by RF. An active regulator will have to be properly shielded so RF doesn't modulate it. I saw it as a cool idea but the failure modes could be a problem. gfz

pentalab wrote:

--- In ham_amplifiers@..., "badgerscreek" <qrp73@...>
wrote:

There is a nice article published in the latest QEX. Its for a
filament voltage regulator. Its Titled " A high Efficiency

Filament

regulator" K8LV. It uses a PIC and some pass resistors. It seems

any size tube is accomodated by increasing pass transistor sizes,

including bumping up heatsink sizes. It also has a ramp up

feature. My guestimate suggests that it would be cheaper building
this regulator than buying 2 X 50 or 100 watt rheostats.

Greg

### Greg.... how would 2 x 50/100 w rheostats regulate fil
V ?? Or are they using pass transistor's in a regulator ?

### Fil V can be of concern...esp when sucking vast amounts of
current for the plate xfmr. On a set up where the fil xfmr pri V
is derived from the same 240 V source as the plate pri.... under a
full bore load... the fil V can be affected.

### One way out of this mess, is to run a separate, smaller 240 V
line... just for the fil xfmr pri. That might not solve all the
fil sag problems... but at least the separate fil 240 v supply...
will only have the v drop on your drop wires coming into your
home, to contend with. If anybody goes this route... make sure
you label.. "more than one live circuit present". You are gonna
have to kill TWO sets of breakers to completely kill all 240 v
coming into the amp. In cases where the RF deck is totally
separate from the HV supply, it may not be an issue.

### I have the fil xfmr, and associated variac for it.. + a
sola constant V xfmr.. in a shelf... below RF deck.... so RF deck
is in top of rack... fil stuff is below... in same rack. HV supply
is in a separate rack.


### another method is to use a sola constant V xfmr. These are all
of the ferroresonant type. Mine has input taps for
118....208....236 v. The output side is a constant 236 /118 V
It regulates very well. You can swing the input Voltage a huge
amount on either side of a particular input tap... and output side
remains constant. These things are HEAVY though.... my 750Va unit
weighs 65lbs. I have seen em in 250-500-750-1000-2000 va. Fair
radio had tons of em.... some brand new in the box.... dirt cheap.

### A SS regulated method might be the ticket....would be lighter.
How much fil POWER can these things handle ? Are they RELIABLE ?
The last thing anybody needs is a regulator to crap out... and fil
V increase... even a few percent.

### Another related issue is seasonal line V regulation. I have
seen mine as high as 247.2 V at 1 AM in the summertime [122.2 +
125 =247.2] Usually , in the dead of winter, at dinner time,
it's 240v, or 239.9v. Last week, it's 234V [117+117]... and that
was at 2 pm on a sunday afternoon... go figure.

Point here is the variation is from 247.2 v... down to 234V... and
that's just measuring the V with HV supply OFF... no big load.
With a big load on thr plate xfmr.. it's going to get sucked down
even more. Changing taps on a plate xfmr is one thing... having to
constantly be tweaking a fil variac is a real pain... and impossible
to do between RX/TX. I don't use the variac for step start
either. The variac.. once set.. stays put. A 25 ohm 100/150 w
metal finned resistor in one leg of the 240 V, feeding the fil xfmr
primary.. and a 8 second delay, is used.

Later... Jim VE7RF

On Nov 8, 2006, at 11:48 PM, Rick xxxx wrote:

Just looking around.

Hi to Rich!

Longtime no hear!

Remember that excursion to Mt Pinos for the VHF contest in the 70's?

My last VHF Contest was a few miles East of Mt. Pi?os on Frasier
Mountain. What is your callsign?

73/Rick

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

Reid Brandon at Eimac phoned me today. Reid passed this important
info along.

The correct phone number for Arnold Howell [KB8JCY] of Howell Tube
Sales is 330-744-7582. Make sure to *82 1st... to shut OFF your
call block [if u have auto block]. Arnold returns calls fairly
promptly. Also, Arnold Howell's CORRECT e-mail
address is ... KB8JCY @ AOL.com His snail mail address is PO
Box 5842, Youngstown, OHIO, Zip- 44504 He has NO website.

Also had Arnold Howell himself, phone me this afternoon. Howell had
Eimac build a... "hot rod" version of a 3CX-1200.... called a YU-
120. This is the 1500w anode dissipation version... with a 6.3 V
@ 26 A filament. There is also another version... called a 3CX-
1500D7. The 1500D7 version is the same 1500 w anode
dissipation.... EXCEPT the fil is 5.0 V @ 30 A. BOTH versions of
these tubes are thoriated tungsten fils, instant on, and both use a
SK-410 [or any version of a 3-500Z socket, like the Johnston] socket.
He also has the custom Teflon chimney's for them.

Howell also tells me, he has 20-24 x YC-179's available... $400.00
plus shipping. He also has access to hypersil pole pigs... most
in 4160+ 4800 V taps.... and also 7200 V...... all in 5-10-15-25
Kva... with, OR without the oil. He also has some 4CX-10,000D's,
and 4CX-5000A's available. Also available, are blowers for 3CX-
10,000A7's, etc.

The story on the YC-243 [socketless version of the 3CX-6000A7 /YU-
148] is... he needs a minimum order of 10 [TEN] to justify a small
production run by Eimac. Apparently,[no surprise], costs go down,
with volume... and tubes are bought in either quantities 1-4.... 5-
9.... 10-49..... 50-XXX.

The YC-243 is ONLY available from Howell.. not anyone else.. like
Richardson. The "YC" designator means it's a custom made tube for
a client. The YC-243 rebuild process is done by Freeland.[Way
better price than Econco... both are 2 x biggest tube rebuilder's
about].... so it can be rebuilt over and over again.

The tube has identical electrical specs to a 3CX-6000A7. Reid Brandon
e-mailed me the official Eimac PDF document on the YC-243. This
version contains ALL the 'typ' operating parameter's for AB2
operation... like Cathode Driven AM operation.... Cathode Driven AB-
2 SSB..... And Class C, Cathode driven CW operation. [The
Eimac 3CX-6000A7 literature is for AB-2 FM broadcast..... the
Svetlana specs also include Class C FM broadcast, with loads of bias]

The biggest feature of the YC-243, is the expensive socket [now
$375.00 from RF parts] is NOT required.... being a socketless tube.

Per the Eimac spec's... the input Z is 50 ohms. I found some minor
discrepancies and typo's between the YC-243 spec sheet + the 6000A7
sheet... and these will be corrected.

Told Reid about the increase in anode diss, that's possible with a
lower intake air temp... AND increased airflow.... AND described the
9.5" square box built around the tube.... with a solid teflon top.
He agreed any TAPERED cone shaped chimney, should be at LEAST 8"
diam... and pref even bigger. Both Howell and Economy Electronics
make straight up/down chimney's for this tube.[6.3" ID]... but Reid
agreed... both those versions restrict the airflow way too much.
I'm going to forward him my finding's.. and measurements, of what
our 'typ' operation is.

So the short of it...a min of 10 x tubes [in total], needs to be
ordered by Howell...from Eimac. Contact Howell, if you are
interested.

Later.... Jim VE7RF

Just looking around.

Hi to Rich!

Longtime no hear!

Remember that excursion to Mt Pinos for the VHF contest in the 70's?



73/Rick

I often order HV transformer from a local shop. price: RMB2 per VA(25C/VA),
a 1000VA CCS HV xfmer =$253(TYPE R or C iron core), if it is "EI" type iron core,
the price is $150.
73! Hsu

Try this again since it claimed to post it then didn't.

That transformer looks somewhat familiar. There's a company just
outside of LA named WTS which is short for Woodys Transformer Service
that wound transformers for most 11 meter tube amps made in
California and the surrounding states. I bought them also since the
cost was low enough that after paying higher shipping, I still came
out. I don't have a URL for them.

Most down south (amplifier alley) building amps use Galaxy
Transformer in New Jersy. They make a custom transformer to work with
an alternator that has the rectifiers removed making it an AC 3 phase
generator. In other words it has a 14 Vac 3 phase primary. That was
an old way to run tube mobile amps.

Their URL is;

www.galaxytransformers.com

Best,

Will

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

Gent's

Check this out..... plus it's an interesting site worth
bookmarking.



Then, after u have added it to ur shopping buggy.... all u gotta

do

is get ur local power co to upgrade the pole pig + drop wires in
front of ur home!

A real steal... compared to that $8750.00 Alpha.

I'd suggest using the 7073 vac tap... which will give you 10 kv
dc under load. This is the perfect xfmr ...for a pair of 3CX-
20,000A/C7's. Also suitable for a pair of 4CX-15/20 K's. All

those

tubes are rated at 10 kv @ 6 A. Now I'd highly recomend a Buss

10-

kv HV sand-filled fuse [10" long] Dunno about a "glitch
R"...perhaps a paralleled pair of those 50 ohm 1 kw globars

[2"diam

x 24" long]


Later.... Jim VE7RF

That transformers construction looks familiar. Several of us used a
transformer manufacturer just outside of LA which was called Woodys
transformer at the time. They wound about all the transformers for
the 11 meter amps made in California and surroundng states. Woody
retired and his son now runs the company. I think it's now called
"WTS" which is short for Woodys Transformer Service. They had some of
the best prices available for HV transformers. They were so cheap
that I could pay the shipping to Ohio and still come out ahead. That
was buying like 10-20 transformers at a time. There single lot price
is almost as cheap. I don't have a website for them though.

Some of the other builders down south (amplifier alley) who are still
in business use Galaxy Transformer in New Jersey. They make some
special transformers to be used with an alternator less the
rectifiers/voltage reg. making it a 3 phase generator. The primary
then is about 14 Vac, 3 phase. The secondaries can be any voltage
needed. That's an easy way to run a big tube mobile.

Their website is;



Best,

Will




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

Gent's

Check this out..... plus it's an interesting site worth
bookmarking.



Then, after u have added it to ur shopping buggy.... all u gotta

do

is get ur local power co to upgrade the pole pig + drop wires in
front of ur home!

A real steal... compared to that $8750.00 Alpha.

I'd suggest using the 7073 vac tap... which will give you 10 kv
dc under load. This is the perfect xfmr ...for a pair of 3CX-
20,000A/C7's. Also suitable for a pair of 4CX-15/20 K's. All

those

tubes are rated at 10 kv @ 6 A. Now I'd highly recomend a Buss

10-

kv HV sand-filled fuse [10" long] Dunno about a "glitch
R"...perhaps a paralleled pair of those 50 ohm 1 kw globars

[2"diam

x 24" long]


Later.... Jim VE7RF

That transformers construction looks familiar. Several of us used a
transformer manufacturer just outside of LA which was called Woodys
transformer at the time. They wound about all the transformers for
the 11 meter amps made in California and surroundng states. Woody
retired and his son now runs the company. I think it's now called
"WTS" which is short for Woodys Transformer Service. They had some of
the best prices available for HV transformers. They were so cheap
that I could pay the shipping to Ohio and still come out ahead. That
was buying like 10-20 transformers at a time. There single lot price
is almost as cheap. I don't have a website for them though.

Some of the other builders down south (amplifier alley) who are still
in business use Galaxy Transformer in New Jersey. They make some
special transformers to be used with an alternator less the
rectifiers/voltage reg. making it a 3 phase generator. The primary
then is about 14 Vac, 3 phase. The secondaries can be any voltage
needed. That's an easy way to run a big tube mobile.

Their website is;



Best,

Will




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

Gent's

Check this out..... plus it's an interesting site worth
bookmarking.



Then, after u have added it to ur shopping buggy.... all u gotta

do

is get ur local power co to upgrade the pole pig + drop wires in
front of ur home!

A real steal... compared to that $8750.00 Alpha.

I'd suggest using the 7073 vac tap... which will give you 10 kv
dc under load. This is the perfect xfmr ...for a pair of 3CX-
20,000A/C7's. Also suitable for a pair of 4CX-15/20 K's. All

those

tubes are rated at 10 kv @ 6 A. Now I'd highly recomend a Buss

10-

kv HV sand-filled fuse [10" long] Dunno about a "glitch
R"...perhaps a paralleled pair of those 50 ohm 1 kw globars

[2"diam

x 24" long]


Later.... Jim VE7RF

On Nov 8, 2006, at 12:47 AM, pentalab wrote:

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

RICH SEZ.... In my experiences, the G2DAF design is c. 11db

cleaner
with a 2-tone modulation test than it is with voice modulation.
With voice modulation, total IMD is c. 21db below pep.

### I have a 2 x 4-400 G2DAF linear. About 900w out with 75
w
of drive... and only 2700 V. Any more than 75 w of drive... and
it
won't do any more than 900w.

### The secret with the g2DAF design is selcting the PRECISE values
of screen caps to charge up. Too small... and u are outa luck....
too big... and all the energy gets diverted into charging em up. A
friend here in town built several 4 x hole 4CX-250B linear's..
and
also several 2 x 4-1000 linears... all in G2DAF. The 4CX-250B
design came straight from G2DAF himself... back in 1968/69. You
can't just take the original 813 design... and stuff any tetrode
into it. It has to be tweaked just right... for a specific tube.

### My 2 x 4-400 was built by the local RI here in town... uses a
4:1 un-un to step up the Z to 200 ohms... then terminated into
200
ohms.

### IMD on ssb is better than I thought. We ran several tests here
in town.... NOBODY bitched about IMD. I could switch it with a GG
linear in under 1 second... and nobody heard the difference. Not
one
of my favourite designs.... but done exactly right... it works
good. Done wrong... and it's not as clean as could be.

## It changes class as drive cycle increases. The whole thing
hinges on charge rate of the screen caps.... get em wrong.. and IMD
will go to hell.

### I have heard several 4-1000 G2DAF linears on ssb.... also
switched to 4-1000 GG [2nd linear] in mid sentence.... while a few
of us monitoring off freq [some up.. some down]. Damned if we could
hear any diff on or off freq. I have also heard some 4-400 G2DAF
linears that were nothing but problems. They are a trick to get
just right.... so u just can't right em all off as.. "bad".

### With no drive applied... no screen V is developed... and no
idle
current... tube cut off..... it saves a complicated, possibly
failure prone regulated screen supply.. + 2 x bias supplies, [RX +
TX].... + NO tuned input required... since it's terminated in a
globar. They look + sound very good on CW too..

On CW, Class C sounds delightsome.

.. so it DOES
have
some merits. Somebody In EU.. thought SM land... has a 4CX-10,000
in G2DAF.... who swears by it IMD wise.

Those who operate 5kHz from a G2DAF swear at the IMD. Here in the land of fruits and nuts (California) I have listened to three of them on 40m and 80m. All were ok with a 2-tone test, but with a human voice they definitely did not cause others to rejoice.
As I understand it, G2DAF did not know how to go about building a regulated screen supply, and that's why he came up with his cockamamie idea of a virtually Class C linear with Class C levels of efficiency.

Dunno what gain it
has.....
a lot less than if a real screen supply used..... and a bit better
than GG.

### My 1st choice would still be a hi MU triode in GG.

The 8160 high-Mu triode requires c. 1500w to drive it nicely. An 8171 or 8281 tetrode in AB1 can be driven with 170w . However the g- g triode is cleaner, but OTOH the input circuitry for AB1 grid-driven is easier to build.

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@..., R L Measures <r@...> wrote:

RICH SEZ.... In my experiences, the G2DAF design is c. 11db

cleaner
with a 2-tone modulation test than it is with voice modulation.
With voice modulation, total IMD is c. 21db below pep.

### I have a 2 x 4-400 G2DAF linear. About 900w out with 75
w
of drive... and only 2700 V. Any more than 75 w of drive... and
it
won't do any more than 900w.

### The secret with the g2DAF design is selcting the PRECISE values
of screen caps to charge up. Too small... and u are outa luck....
too big... and all the energy gets diverted into charging em up. A
friend here in town built several 4 x hole 4CX-250B linear's..
and
also several 2 x 4-1000 linears... all in G2DAF. The 4CX-250B
design came straight from G2DAF himself... back in 1968/69. You
can't just take the original 813 design... and stuff any tetrode
into it. It has to be tweaked just right... for a specific tube.

### My 2 x 4-400 was built by the local RI here in town... uses a
4:1 un-un to step up the Z to 200 ohms... then terminated into
200
ohms.

### IMD on ssb is better than I thought. We ran several tests here
in town.... NOBODY bitched about IMD. I could switch it with a GG
linear in under 1 second... and nobody heard the difference. Not
one
of my favourite designs.... but done exactly right... it works
good. Done wrong... and it's not as clean as could be.

## It changes class as drive cycle increases. The whole thing
hinges on charge rate of the screen caps.... get em wrong.. and IMD
will go to hell.

### I have heard several 4-1000 G2DAF linears on ssb.... also
switched to 4-1000 GG [2nd linear] in mid sentence.... while a few
of us monitoring off freq [some up.. some down]. Damned if we could
hear any diff on or off freq. I have also heard some 4-400 G2DAF
linears that were nothing but problems. They are a trick to get
just right.... so u just can't right em all off as.. "bad".

### With no drive applied... no screen V is developed... and no
idle
current... tube cut off..... it saves a complicated, possibly
failure prone regulated screen supply.. + 2 x bias supplies, [RX +
TX].... + NO tuned input required... since it's terminated in a
globar. They look + sound very good on CW too.... so it DOES
have
some merits. Somebody In EU.. thought SM land... has a 4CX-10,000
in G2DAF.... who swears by it IMD wise. Dunno what gain it
has.....
a lot less than if a real screen supply used..... and a bit better
than GG.

### My 1st choice would still be a hi MU triode in GG.

Later.... Jim VE7RF

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

--- In ham_amplifiers@..., "Robert B. Bonner"
<rbonner@...> wrote:

Yeah who needs fuses?

Current limit with the power company.

Hello? Yes this is NUKE STATION #6, yes this is SM2EKM I'm coming

on line, pull the rods out.

### Yeah ! Pull the rods ALL the way out ! ROFLMAO

### Later... Jim VE7RF

Hee hee.

Thanks Bob, nice to start the day with a nice laugh.

73 Jim SM2EKM
--------------

Robert B. Bonner wrote:

On Nov 7, 2006, at 1:34 PM, Peter Voelpel wrote:

Peter,

It might be a good idea to contact SM2CEW



If it costs already a lot of time and money I would invest 100 more Euros
(for new Parts)
in a well regulated screen supply.
Otherwise I am shure you are asking for trouble with an output >4KW.
The data for the screen in HF class B is 800V at 100-120mA, where will that
derive from?

73
Peter

________________________________

From: ham_amplifiers@... [mailto:ham_amplifiers@...]
On Behalf Of Peter
My PSU being about ready, I await comments before whether deciding
going on with my G2DAF design or changing to stabilized g2 / g1
suplies ( the G2DAF option being the more attractive to me as far as
construction is concerned ).

In my experiences, the G2DAF design is c. 11db cleaner with a 2-tone modulation test than it is with voice modulation. With voice modulation, total IMD is c. 21db below pep.

My project costs me much time, efforts and money and I therefore need
all available information before deciding what to do.





Yahoo! Groups Links

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

Yeah who needs fuses?

Current limit with the power company.

Hello? Yes this is NUKE STATION #6, yes this is SM2EKM I'm coming on line,
pull the rods out.

--- In ham_amplifiers@..., "Robert B. Bonner"
<rbonner@...> wrote:

--- In ham_amplifiers@..., "Robert B. Bonner"
<rbonner@> wrote:

Jim,

## A 500 ohm 10-25 watt resistor across it is a throwback to
Orr's books.["low Z across cathode fuse"] We already tried that

on

the 3x6 amp.. and other amps. We removed the 800 ohm 10 watt

R...

and replaced it with a 100 K 3 watt MOF. IF Cathode fuse
blows... the V-drop across the 100 k resistor will bias the tubes
to cut off ASAP. Dissipation across the 100 K R is virtually zero
watts.

***You would be surprised how little it takes to bias off an amp.

Currently

on one project I have a 3000 ohm 10 watt resistor biasing the tube

during

standby. If you lose a fuse do to some reason other than a HV arc

the 500

Ohm resistor does a sort of controlled slow shut down. 100,000 is

way up

there, to high in my opinion. You already used a 1000 ohm, and

mine is

playing with a 3000 ohm, and Hank uses 10K to bias the tube in

just about

everything.

### Anything from 500 ohms to 2 megohms works just fine. Rich's
electronic bias scheme used 1 meg. Depends on what tube u are
trying to cut off... and plate V. A 3x3 needs 45v to get it down
to just 1 ma idle current. [zsac] A lot of eimac specs will say
XXX V will produce 1 ma of zsac. IMO... somebody found a 25 k-
25 watt in their junk box... used it in a linear for cut off
bias.... on RX.... then it got copied into the next 25 hand books.

### IMO a 100 k or any value of MOF will be more reliable than a
wire wound.

However I have a 5 OHM 100 watt in the B+

You should also have a 100-200 Ohm 25 watt B- lead to ground in
the power supply and the 1 ohm grid metering resistor in the head.

### The grid meter in my case is a separate meter 0-1000Ma... shunt
is built into it... abt .82 ohm I think. Can't stand
multimeter's. I want to be able to see all the metering all the
time.. all at once... including fil V and current, plate V, grid
I.. plate I.. plate xfmr pri v and I... etc.

The 100-200 ohm resistor is for WHEN the fuse blows, anything over

10X the meter resistor doesn't effect the meter calibration. A 100
Ohm keeps the B- close to ground if the fuse blows. That's what its
for.

### That 100-200 ohm resistor from B- to chassis just keeps B-
from straying to far. IF ur cathode fuse BLOWS in the CT of a
thoriated tungsten fil tube like 3-500Z or a 3x3.... the B- is
STILL at chassis potential... via the grid shunt !!! A better
method is to just use RVS connected diodes between chassis and B-
.... then B- can never float more than +/- .7 V Dunno abt oxide
tubes like a 8877... with a separate cathode.

### IF u got a B+ to chassis short.... and u didn't have diodes
across ur meter's... and only a 200 ohm r between chassis and B-
...... u would smoke both meter's.... IF the meter's blew wide
open.... the only other alternate path is through ur 200 ohm
resistor from chassis to B-. IF the meter's were protected,
the B+ would come out of the chassis.. thru both meter'... back
to B-.... shorting out the B+ supply.

*** That way things don't "run wild" if the fuse opens. Yes

without a resistor or if that resistor opened up there could be a
safety issue.

### agreed. IMO the MOF resistor would be less likely to open up
than a wire wound. For redundacy... a PAIR of 100 k 2-3 w mof's
across the fuse... or a pair of wirewounds would be the ultimate
answer... problem solved.

There are many ways to design and or build amplifiers all are just

fine and values can be variable within reason.

### Partially agreed. some designs are flawed... some are just
outright dangereous. Some older ARRL designs put the HV meter
between B+ and chassis... instead of B+ and B- ... no R between
B- and chassis.. and no meter protection. IF grid shunt ever
opened up... or no connection via multi meter switch... HV meter
would drop to zero.... when in fact.. HV is still present... and
lethal.

I use 1 ohm grid shunt. A 100 Ohm in the PS B- to chassis,

Usually 10K to bias the tube during standby and have used as little
as 3000. A pair of 20 OHM step start resistors and 100K bleeder
across the power supply.

### You only need step start resistance in one leg of the 240 v
line... and only one spst relay/ contactor to short it out. Only
thing of interest in a HV step start is loop resistance in the
primary. Having said that... I tried 50 ohms... and also 25
ohms. 50 ohms will limit 240 v inrush to 4.8 A 25 ohms will
limit 240 v inrush to 9.6 A I found with 50 ohms... that plate
V would not rise as high as 25 ohms.... and when shunted, the
secondary surge was WAY higher. That was with 6800Vdc supply...+
100 uf filter cap.... and 14 second delay. A 0-50 A ameter in one
leg of the 240 V primary will give one a real eye opener...esp that
sec surge.

### 25 ohms works great.. and any relay/contactor will handle
9.6A. Plate V starts at zero.... just sails right uo.... then
slowly keeps climbing... then it jumps that last little bit. Energy
in joules goes to the square of the voltage. A cap that only
has 1/2 V on it.... is only 1/4 charged up..... u want the V up as
high as u can get... b4 shunting... and a 25 ohm resitor works
better than a 50 ohm. [for a 6.8 kv + 100 uf filter]

I have always placed 500 across the cathode fuse, however the bias

size would also work. The 500 will drop amp gain to nothing almost
instantly and you've still got power applied at that point. That RF
needs to go somewhere.

I haven't experimented with my expensive tubes by removing the

cathode fuse and applying power... I've only had 1 cathode fuse
POP in 35 years, and that was during power up for some reason.

### Try it... tube shuts down.... works great.

I have never used a 100K for a standby resistor. I would

personally prefer to just cut off the tube rather than bury it in
cutoff.

### Anything from 600 ohms to 2 megs works fine for the RX cut
off... and no, u are not burying it into cutoff. IF it actually
was really toatally 100% cut off.... and no current flow... u
would also have NO v drop... and NO cut off bias developed. Fact
is...it reaches equilibrium.... it's never quite cut off..... just
enough current flows to almost cut it off ... but not quite. EG: to
get 45 v of cut off bias.... you will have .45ma of current flowing
through the 100 K resistor. [diss =.02 W]

#### Haven't tried anything above 2 meg.... I'm sure even 10 meg
would work.... u just don't EVER want a wide open.... so a PAIR
of resistors... either MOF OR wire wounds would be better... then
u have redundancy.

later... Jim VE7RF

I have two linear power amplifier units for sale:
4XSD1427(THX15-C) in parallel push-pull in each unit, with driver stage and large heat sink.RF output power( each unit):400W, freqence range:1.8-30MHz, it was used in a 400W solid state SSB transmitter, not for RF power generator.I have test all transitors,they are all OK.You can add a combiner to build a 800 or 1kW linear amplifier.
I ask $400 for two unit, include shipping cost( surface mail).
73! Hsu

Peter,

It might be a good idea to contact SM2CEW



If it costs already a lot of time and money I would invest 100 more Euros
(for new Parts)
in a well regulated screen supply.
Otherwise I am shure you are asking for trouble with an output >4KW.
The data for the screen in HF class B is 800V at 100-120mA, where will that
derive from?

73
Peter

________________________________

From: ham_amplifiers@... [mailto:ham_amplifiers@...]
On Behalf Of Peter
My PSU being about ready, I await comments before whether deciding
going on with my G2DAF design or changing to stabilized g2 / g1
suplies ( the G2DAF option being the more attractive to me as far as
construction is concerned ).

My project costs me much time, efforts and money and I therefore need
all available information before deciding what to do.

Good afternoon List !

I'm new to the list.
Today I got a tip G2DAF experts might be around here.

From various sides I got incompatible advices on the G2DAF concept
for a HF linear ( SSB speech ) PA with a Philips QBL 5/3500 ( @ Va 6
Kv and @ Ia 1.1 A , very heavily cooled... ).

It seems the contrary opinions are all about the IM3 distortion ( and
to a lesser extent the efficiency ).

I'd be grateful for unbiased reviews or ( even better ) real life
experiences on this subject.

Maybe even one of you did build yourself a QBL 5/3500 HF linear PA on
basis of the G2DAF concept ?

My PSU being about ready, I await comments before whether deciding
going on with my G2DAF design or changing to stabilized g2 / g1
suplies ( the G2DAF option being the more attractive to me as far as
construction is concerned ).

My project costs me much time, efforts and money and I therefore need
all available information before deciding what to do.

Thanks for input.
Peter, PE1E.