sBitx #sBitx PA MOD Plan #sBitx


John
 

Which message number is best to read to understand the plan for a PA mod?

John


WP3DN
 

https://groups.io/g/BITX20/message/97318


This is working very well in my radio.

WP3DN


WP3DN
 

Just to #3. Not using the diode switch yet.


ajparent1/kb1gmx
 

Maybe someone can write that up and put it in the wiki.  



Allison
------------------
Please use the forum, offline and private will go to bit bucket.


John
 

I am waiting to hear from Ashhar that he has the hot switching diode issue solved.
I assume that there may be a kit of parts and a board made available for those of us
with a junk box + 30 years old or who operate in a parts desert, 
Some visually challenged my need to purchase a finished new mainboard.
My sBitx sits on the shelf until changes are confirmed.

J
TI4JWC


Ashhar Farhan
 

The T/R switching has survived 15 days of FT8 and an ssb contest. The t/r add on board is being assembled and tested. They will be posted this week.
I will post the PA mods in the next 24 hours.

On Sun, Nov 6, 2022, 8:17 PM John via groups.io <n0ure=yahoo.com@groups.io> wrote:
I am waiting to hear from Ashhar that he has the hot switching diode issue solved.
I assume that there may be a kit of parts and a board made available for those of us
with a junk box + 30 years old or who operate in a parts desert, 
Some visually challenged my need to purchase a finished new mainboard.
My sBitx sits on the shelf until changes are confirmed.

J
TI4JWC


ajparent1/kb1gmx
 

The TR as I've built (similar) it is running well in another radio at 50W
and also in the SBITX.
I'd expect few issues with it.

The layout and modification for the TX as WP3DN need a fpit ure or two,
schematic for that section and a few words for those that are not following
closely.

FYI the diode heating of the LPF switching, check the schematic used 
as you may have a error there.  I believe but unconfirmed the diodes
that are heating are the active (selected ones). But since there are two
(input and output side) which one or both.


Allison
------------------
Please use the forum, offline and private will go to bit bucket.


Gerald Sherman
 

Yours is on the shelf.  So is mine

Gerry Sherman

Sent by the Linux Thunderbird

On 2022-11-06 14:47, John via groups.io wrote:

I am waiting to hear from Ashhar that he has the hot switching diode issue solved.
I assume that there may be a kit of parts and a board made available for those of us
with a junk box + 30 years old or who operate in a parts desert, 
Some visually challenged my need to purchase a finished new mainboard.
My sBitx sits on the shelf until changes are confirmed.

J
TI4JWC


Ashhar Farhan
 

Allison ,
Hans cracked it for me. They were 1n4001s relabelled as 1n4007s. Now, the LPFs run very cool.

On Sun, Nov 6, 2022, 8:54 PM Gerald Sherman <ve4gks@...> wrote:

Yours is on the shelf.  So is mine

Gerry Sherman

Sent by the Linux Thunderbird

On 2022-11-06 14:47, John via groups.io wrote:
I am waiting to hear from Ashhar that he has the hot switching diode issue solved.
I assume that there may be a kit of parts and a board made available for those of us
with a junk box + 30 years old or who operate in a parts desert, 
Some visually challenged my need to purchase a finished new mainboard.
My sBitx sits on the shelf until changes are confirmed.

J
TI4JWC


ajparent1/kb1gmx
 

I built a similar diode switched LPF for testing and 
using FT817 and 100W amp at 60W using WSJTx ft8 as
test signal at 13.99Mhz Into the dummy load results after
3 days 72 hrs sustained the diodes get warm.  Warm is
less than 40C measured using IR thermometer.

For 80M they get hotter 50C as as that's getting near the
lower limit for them.  Still an acceptable temp. 

160M, forget that.  Diode switching below 2MHZ requires
exotic stuff as recombination time has to be very long.

Measured loss suggests about .5 db per pair depends on band
but its hair splitting.

The SBITX still has its relays for band selection with wetting current
added (8ma) and they have not caused a moments grief but the
only time the are active is band change.  I'm mixed as to the need 
change.

Allison
------------------
Please use the forum, offline and private will go to bit bucket.


ajparent1/kb1gmx
 

1n4001 though 1n4005 will not work, they have a pin structure but
thinner!

Only the 800 and 1000PIV parts have that thicker PIN structure.

That great news.  Fire the supplier or at least let them know
those were frauds!

You can see from my testing I found little issue.  The temps I
got were at measured 60W sustained to a load back off to 40W
then cool a fair amount.  But 50C is not too hot.

Allison
------------------
Please use the forum, offline and private will go to bit bucket.


Jerry Gaffke
 

I'm curious, how do you know they are 1n4001's?
Scrape the paint off and saw 1n4001?
Have you determined they go into zener or avalanche mode due to excessive reverse voltage?
Or have you determined they don't have persistent charge carriers like a PIN diode?

The spec for the 1n400x series differentiates between the various flavors only 
by max reverse voltage.  https://www.vishay.com/docs/88503/1n4001.pdf
It's possible to build a 1n4007 that complies with the spec but doesn't work as a PIN diode.

Here's a quote from a guy who says spec compliant 1n4007's that don't work as PIN diodes could be quite common:
    https://groups.io/g/BITX20/message/32099

So get your 1n4007's from a reputable source, and stick with one manufacturer.

Jerry, KE7ER


On Sun, Nov 6, 2022 at 07:41 AM, Ashhar Farhan wrote:
Hans cracked it for me. They were 1n4001s relabelled as 1n4007s. Now, the LPFs run very cool.


ajparent1/kb1gmx
 

Jerry,

The prime characteristic is the 1n400x series are controlled recovery diodes
and that is to help with parasitic effect for power supplies.  Most common
datasheets usually for get Trr for rectifiers but include it for so called fast
diodes like 1n4148.   My old Moto book (1988) lists Trr at 2us, really slow.

The acid test is try to use a 1n4001-7 as a rectifier at greater than 1mhz.

Also 1N4001 is a 50V diode so fobbing it off as 1000V part would cause
any AC supply at 100V or more to emit smoke.  As the voltage exceeds
its breakdown.  IT can be seen non destructively  on a curve tracer that
has a voltage source high enough.  The reverse current will be really low
(nanoamps) until you hit the reverse avalanche where it goes sharply
higher.

So if it fails there its not a 1n4007 pin or not.


Allison
------------------
Please use the forum, offline and private will go to bit bucket.


ajparent1/kb1gmx
 

Trr is easily tested, Cj is usually specified.

What's funny is any diode in glass package may be a "1n4007" but it
never behaves as its light sensitive.

The complete spec is hard to find but Trr is a real thing.
YOu drive some forward current though the diode and then
switch it off (very fast fall time) to a reverse voltage,  watch
the forward current into a resistive load with a really fast
scope.  The current continues to flow in the reverse direction.

Why is it important... for a power supply at 60hz or 400Hz
and you need say 3000V at milliamps sides that do not
switch (stop conducting) predictably have to be loaded
with R and C to keep the voltage across them.  Especially
with really sluggish diodes for higher currents.

Look at any decently engineered supply for any of the
big tube amps. 


Allison
------------------
Please use the forum, offline and private will go to bit bucket.


Jerry Gaffke
 

As I was suggesting, it probably meets spec as a 1n4007
but happens to fail as a PIN diode. 

However, I can easily believe somebody out there is selling a 50V part as a 1n4007.

Jerry



On Sun, Nov 6, 2022 at 09:11 AM, ajparent1/kb1gmx wrote:
The prime characteristic is the 1n400x series are controlled recovery diodes
and that is to help with parasitic effect for power supplies.  Most common
datasheets usually for get Trr for rectifiers but include it for so called fast
diodes like 1n4148.   My old Moto book (1988) lists Trr at 2us, really slow.

The acid test is try to use a 1n4001-7 as a rectifier at greater than 1mhz.

Also 1N4001 is a 50V diode so fobbing it off as 1000V part would cause
any AC supply at 100V or more to emit smoke.  As the voltage exceeds
its breakdown.  IT can be seen non destructively  on a curve tracer that
has a voltage source high enough.  The reverse current will be really low
(nanoamps) until you hit the reverse avalanche where it goes sharply
higher.

So if it fails there its not a 1n4007 pin or not.


ajparent1/kb1gmx
 

Jerry,

Therein rests the problem, LIES.  ITs a fraud and some get away with it.
That diode would fail in a 300V supply with likely a resounding BANG!
Some however the markings are really indecipherable.
Its also a significant problem when a part has a known spec does not
meet it.  Industry plague.

Forensic engineering.

Keep in mind the circuit used puts greater than 90V reverse bias on
the diode if it avalanches the 470K resistor is a current limit but in the
avalanched state is essentially on to some degree and that's bad. 
High losses and heat.  If all else was OK the 50V diode never had
a chance.


Allison
------------------
Please use the forum, offline and private will go to bit bucket.


Gordon Gibby
 

Sounds like progress!

Gordon KX4Z


On Nov 6, 2022, at 12:53, ajparent1/kb1gmx <kb1gmx@...> wrote:

Jerry,

Therein rests the problem, LIES.  ITs a fraud and some get away with it.
That diode would fail in a 300V supply with likely a resounding BANG!
Some however the markings are really indecipherable.
Its also a significant problem when a part has a known spec does not
meet it.  Industry plague.

Forensic engineering.

Keep in mind the circuit used puts greater than 90V reverse bias on
the diode if it avalanches the 470K resistor is a current limit but in the
avalanched state is essentially on to some degree and that's bad. 
High losses and heat.  If all else was OK the 50V diode never had
a chance.


Allison
------------------
Please use the forum, offline and private will go to bit bucket.


John Clark
 

So...... from a non-engineer, we must hope that Farhan can build a test gig to find the GOOD 1N4007

that service the high speed 300V reversal?  What is the cost of a true listed diode switch?

John



--
John
TI4JWC


ajparent1/kb1gmx
 

Actually its easier than that.
A basic curve tracer that hits more than 600V will cull low voltage diodes,
That and knowing your source.

One you have the signature for the real thing its easy to spot a fraud.

FYI a 1n4001 works IF the voltages are less that 50V peak.  That would
be around 22W.  But it also must be above 5mhz.  To do that when a higher
voltage part exists is kinda nuts.

A PIN diode for this power class and for lower HF use if you can find them
is likely over 20$ each.  For VHF and UHF use there are plenty of parts
and cheap but they do not work at all well at HF.  I use them at 6M and up 
and the usual parts available are a 1$ each for the .25W and less range
and up to maybe 10W under 3$.  Parts for 300W, well a good coaxial
relay was more appealing (and not cheap).


Allison
------------------
Please use the forum, offline and private will go to bit bucket.


Gordon Gibby
 

Put quite a few megohms in series with a tube transmitter’s power supply and just measure the back voltage across the diode with a few micro-amp or two of reverse current


On Nov 6, 2022, at 15:28, ajparent1/kb1gmx <kb1gmx@...> wrote:

Actually its easier than that.
A basic curve tracer that hits more than 600V will cull low voltage diodes,
That and knowing your source.

One you have the signature for the real thing its easy to spot a fraud.

FYI a 1n4001 works IF the voltages are less that 50V peak.  That would
be around 22W.  But it also must be above 5mhz.  To do that when a higher
voltage part exists is kinda nuts.

A PIN diode for this power class and for lower HF use if you can find them
is likely over 20$ each.  For VHF and UHF use there are plenty of parts
and cheap but they do not work at all well at HF.  I use them at 6M and up 
and the usual parts available are a 1$ each for the .25W and less range
and up to maybe 10W under 3$.  Parts for 300W, well a good coaxial
relay was more appealing (and not cheap).


Allison
------------------
Please use the forum, offline and private will go to bit bucket.