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Pa Drivers Biasing

 

Changed the bias on the PA drivers ...Q90 - R 81 changed to 2700 ohms
Q911,912 - R85 changed to 220 ohms, R 86 changed to 2200 0hms
Q 92,93 - R 90 changed to 220 ohms, R 92 changed to 2200 0hms
Q 96,97 - R 93 changed to 220 ohms, R 95 changed to 2200 ohms

All this to redistribute Emitter current across the drivers ..Q90 now has 8,5 ma current , each Q911,912 have 10 ma, each Q 92,93 have 10 ma. and Q 96,97 now have 10 ma each..? stage 1= 8.5 ma, stage 2 20 ma, stage e 40 ma ...to keep each stage progressively amplifying without overloading from the previous stage.

Ran some scans of overall passband from input to the low-pass filter (after the last mixer) through to dummy load as well as individual band output...I'll put the bulk of the pictures in a Photo Folder called PA MOD ..

80 meter before pa bias and T11 change.jpg

 

Jim,

Good work.? Back in May I was writing about that problem nutty high bias.
I had the basic board with most of the 3904s in the TX running at 25 to 29ma!

However, you need to bridge those with .01, 2.7uH, 1k(or less) all in series
to tame the gain at 80m and balance power from 3-30mhz.? This is colletor
to base negative feedback to control the gain soar at low frequencies.

IF a stage is to high a gain that R can be as low as 330 ohms...

Allison
 

What I did find is at 13.8V all on the 2n3904s in the power chain run very hot
with no signal.? How hot 125-130 degrees.? Measurements had the first Q90
running at 38ma and for a low level sage thats very high and for a 3904 its?
near excessive.? From #49731 May 19.

I was only warming up to dig in.? If you found lower that goes to the wide
variations?I've seen in these using the HFE on 3904s is in the 8:1 range
depending on what vendors' datasheet you read.

The other problem is most of the amp stages go into current limiting due to
high emitter resistance used.? This leads to serious levels of compression
before the irf510s hit the wall.? IT tends to be worse at 10M than 80m.



Here is the full bore change list of june-6, I stopped there mostly when I
realized the level of spurs at the high end were prohibitive.
========================================================
Full bore change list:
?
IF all goes well 6w on 10M when RV1 is set for 14W on 80m.
IF it doesn't, I'm not accepting complaints.
?
==================== first amp q90 ========================?
Replace Q90 with BFR106.? (Mouser about 18cents each)
Reset bias OF Q90 with BFR106 ,Set bias for less than 12ma (r86 2.7K for mine).
Make C81 470pf, and R83 8.2ohms. (lower power at 80m improves 10m)
?
To set bias and measure simple measure across the devices emitter resistor
voltage/resistance=current? so 100ohms with 1Volt is .01A or 10ma.
?
Change C82 to 470pf?
(peaking for 10M and less power at 80m, optional if your not playing at more than 20mhz.)
?
remove T8, remove wire and wind with 8 turns #28 Bifilar, pay attention
to wiring.? Ignore pins 1 and 6 as they are not used.
?
==================== Pre-driver ========================?
All the 2n3904s in the predriver replaced with 2n2222A or better (5109).
Hint I mounted them from the underside with very short leads as it makes?
the top less crowded.??
IF 2n5109 is used add a ferrite bead on the collector lead. the part if FB61-unknown
as I had a few handy they are 4.5mm long and the hole is large enough to pass a?
transistor lead.
?
R87, R88 emitter resistors for pre-driver reduced to 11ohms (add parallel 22ohm).
R86 replaced with 1.5K ohm in series with 2.7uh SMT choke.? (resets bias?
and adds peaking.)
?
Remove t9 and take one turn trifilar off of the 10.? Reinstall, pay?
attention of lead placement.? IF available 6turns #28 trifilar?
on BN43-302
?
==================== Driver? ========================
All the 2n3904s in the driver replaced with 2n2222A or better.
Hint I mounted them from the underside with very short leads as it makes?
the top less crowded.? IF 2n5109 is used add a ferrite bead on the collector lead.
?
R911,r96, R941, R942 emitter resistors for driver reduced to 11ohms (add parallel 22ohm).
R92, R95 replaced with 1.5K ohm.? (resets bias)
?
Remove t10 and take two turns trifilar off of the 10.? Reinstal pay attention?
of lead placement.
?
==================== final amp? ========================
?
Replace T10 with FB43-202 4 turns bifilar #26.
There are several variations including larger ferrite?
and differnt turns ration such as 2turn primary and 3 turn secondary.
NOTE: this only use two of the three windings so ignore pins 4 and 3 (unused).
?
Ferrite heating here is likely due to two possible causes:?
Inefficient transformer due to how its wound, not enough ferrite?
(more than 12W) or wrong material (43 or 61)

Bias on finals at that time was 180ma per for best power and soso IMD.

Despite claims the RD16HHF is NOT a panacea and does not materially?
help 10M result.? At 10$ its your fun.? I tried them and have used?
them elsewhere with good result but not that much better.
?
====================? ?end? ?========================
?
?
Allison
 

Just for fun and to try some different output transformers on the PA chain, I built (dead bug) the Q90 and associated components test circuit ..Some will recognize it as part of Fig. 6.154 from EMRFD ..Photos show gain rolloff due to emitter bypass network ...

Jim
Q90 Ckt 2n3904 C81-R83 in circuit (emitter bypass).jpg
Q90 Ckt 2n3904 power on.jpg
Q90 Ckt 2n3904 power off.jpg

On Thu, Sep 6, 2018 at 11:48 AM ajparent1/KB1GMX <kb1gmx@...> wrote:
Jim,

Good work.? Back in May I was writing about that problem nutty high bias.
I had the basic board with most of the 3904s in the TX running at 25 to 29ma!

However, you need to bridge those with .01, 2.7uH, 1k(or less) all in series
to tame the gain at 80m and balance power from 3-30mhz.? This is colletor
to base negative feedback to control the gain soar at low frequencies.

IF a stage is to high a gain that R can be as low as 330 ohms...

Allison

 

6.154 is a 6M PA to about the 300mW level using 2n5109s.
The Fedback and bias is 2.2k, base to ground is 470 and the emitter degeneration is 3.6ohms.

I have a radio using that exact circuit and it drives a irf510 to about 6W at 6m.
used 5109s and got the book gain.? Tried 3866s and it was not as good.

If you use a 3904 it goes down by nearly 7 db(depending on how good it is, some worse)
by 10m.??If you make the emitter bypass cap 470pf the low end (3.5mhz) gain falls off
to about 12-13db and the high end (30mhz) is about 11db.? However at 14mhz it peaks
a little at 14db.? The problem with that is the amp was designed to 16-18db of gain
which is not possible with 3904 at 10m.? Best I've seen is about 11(+-1db)DB at
30mhz from 3904.

Try a better device.? 2n2369, MPSH10, 2n5179 as is you see flatter gain from 3-30
not flat but flatter.? The 2n5179 should be nearly flat.


Allison
 

Allison, to clarify your "full bore" list:

===q90 stage
R86 should be R81

===Pre driver
When using 2N5109, is that one device replaces the two 2N3904's?

For those us in Metric countries, #28 is about 0.3mm although no doubt non critical.

===driver
if using 2N5109's is that all 4 devices or a pair.

===final amp
T10 should be T11
#26 wire is about 0.4mm, again no doubt non critical.

In VK, 2N2222a's are about $2.30 each, 2N5109's are near unobtainable, although i have a few in my stocks, hence the above query re numbers.

glenn -vk3pe-



On Fri, Sep 7, 2018 at 06:30 AM, ajparent1/KB1GMX wrote:
What I did find is at 13.8V all on the 2n3904s in the power chain run very hot
with no signal.? How hot 125-130 degrees.? Measurements had the first Q90
running at 38ma and for a low level sage thats very high and for a 3904 its?
near excessive.? From #49731 May 19.

I was only warming up to dig in.? If you found lower that goes to the wide
variations?I've seen in these using the HFE on 3904s is in the 8:1 range
depending on what vendors' datasheet you read.

The other problem is most of the amp stages go into current limiting due to
high emitter resistance used.? This leads to serious levels of compression
before the irf510s hit the wall.? IT tends to be worse at 10M than 80m.



Here is the full bore change list of june-6, I stopped there mostly when I
realized the level of spurs at the high end were prohibitive.
========================================================
Full bore change list:
?
IF all goes well 6w on 10M when RV1 is set for 14W on 80m.
IF it doesn't, I'm not accepting complaints.
?
==================== first amp q90 ========================?
Replace Q90 with BFR106.? (Mouser about 18cents each)
Reset bias OF Q90 with BFR106 ,Set bias for less than 12ma (r86 2.7K for mine).
Make C81 470pf, and R83 8.2ohms. (lower power at 80m improves 10m)
?
To set bias and measure simple measure across the devices emitter resistor
voltage/resistance=current? so 100ohms with 1Volt is .01A or 10ma.
?
Change C82 to 470pf?
(peaking for 10M and less power at 80m, optional if your not playing at more than 20mhz.)
?
remove T8, remove wire and wind with 8 turns #28 Bifilar, pay attention
to wiring.? Ignore pins 1 and 6 as they are not used.
?
==================== Pre-driver ========================?
All the 2n3904s in the predriver replaced with 2n2222A or better (5109).
Hint I mounted them from the underside with very short leads as it makes?
the top less crowded.??
IF 2n5109 is used add a ferrite bead on the collector lead. the part if FB61-unknown
as I had a few handy they are 4.5mm long and the hole is large enough to pass a?
transistor lead.
?
R87, R88 emitter resistors for pre-driver reduced to 11ohms (add parallel 22ohm).
R86 replaced with 1.5K ohm in series with 2.7uh SMT choke.? (resets bias?
and adds peaking.)
?
Remove t9 and take one turn trifilar off of the 10.? Reinstall, pay?
attention of lead placement.? IF available 6turns #28 trifilar?
on BN43-302
?
==================== Driver? ========================
All the 2n3904s in the driver replaced with 2n2222A or better.
Hint I mounted them from the underside with very short leads as it makes?
the top less crowded.? IF 2n5109 is used add a ferrite bead on the collector lead.
?
R911,r96, R941, R942 emitter resistors for driver reduced to 11ohms (add parallel 22ohm).
R92, R95 replaced with 1.5K ohm.? (resets bias)
?
Remove t10 and take two turns trifilar off of the 10.? Reinstal pay attention?
of lead placement.
?
==================== final amp? ========================
?
Replace T10 with FB43-202 4 turns bifilar #26.
There are several variations including larger ferrite?
and differnt turns ration such as 2turn primary and 3 turn secondary.
NOTE: this only use two of the three windings so ignore pins 4 and 3 (unused).
?
Ferrite heating here is likely due to two possible causes:?
Inefficient transformer due to how its wound, not enough ferrite?
(more than 12W) or wrong material (43 or 61)

Bias on finals at that time was 180ma per for best power and soso IMD.

Despite claims the RD16HHF is NOT a panacea and does not materially?
help 10M result.? At 10$ its your fun.? I tried them and have used?
them elsewhere with good result but not that much better.
?
====================? ?end? ?========================
?
?
Allison
 

also, I guess a typo, in ===final amp====

FB43-202 should be BN43-202 core.

vk3pe


On Sat, Sep 8, 2018 at 09:48 AM, Glenn wrote:
Allison, to clarify your "full bore" list:

===q90 stage
R86 should be R81

===Pre driver
When using 2N5109, is that one device replaces the two 2N3904's?

For those us in Metric countries, #28 is about 0.3mm although no doubt non critical.

===driver
if using 2N5109's is that all 4 devices or a pair.

===final amp
T10 should be T11
#26 wire is about 0.4mm, again no doubt non critical.

In VK, 2N2222a's are about $2.30 each, 2N5109's are near unobtainable, although i have a few in my stocks, hence the above query re numbers.

glenn -vk3pe-



On Fri, Sep 7, 2018 at 06:30 AM, ajparent1/KB1GMX wrote:
What I did find is at 13.8V all on the 2n3904s in the power chain run very hot
with no signal.? How hot 125-130 degrees.? Measurements had the first Q90
running at 38ma and for a low level sage thats very high and for a 3904 its?
near excessive.? From #49731 May 19.

I was only warming up to dig in.? If you found lower that goes to the wide
variations?I've seen in these using the HFE on 3904s is in the 8:1 range
depending on what vendors' datasheet you read.

The other problem is most of the amp stages go into current limiting due to
high emitter resistance used.? This leads to serious levels of compression
before the irf510s hit the wall.? IT tends to be worse at 10M than 80m.



Here is the full bore change list of june-6, I stopped there mostly when I
realized the level of spurs at the high end were prohibitive.
========================================================
Full bore change list:
?
IF all goes well 6w on 10M when RV1 is set for 14W on 80m.
IF it doesn't, I'm not accepting complaints.
?
==================== first amp q90 ========================?
Replace Q90 with BFR106.? (Mouser about 18cents each)
Reset bias OF Q90 with BFR106 ,Set bias for less than 12ma (r86 2.7K for mine).
Make C81 470pf, and R83 8.2ohms. (lower power at 80m improves 10m)
?
To set bias and measure simple measure across the devices emitter resistor
voltage/resistance=current? so 100ohms with 1Volt is .01A or 10ma.
?
Change C82 to 470pf?
(peaking for 10M and less power at 80m, optional if your not playing at more than 20mhz.)
?
remove T8, remove wire and wind with 8 turns #28 Bifilar, pay attention
to wiring.? Ignore pins 1 and 6 as they are not used.
?
==================== Pre-driver ========================?
All the 2n3904s in the predriver replaced with 2n2222A or better (5109).
Hint I mounted them from the underside with very short leads as it makes?
the top less crowded.??
IF 2n5109 is used add a ferrite bead on the collector lead. the part if FB61-unknown
as I had a few handy they are 4.5mm long and the hole is large enough to pass a?
transistor lead.
?
R87, R88 emitter resistors for pre-driver reduced to 11ohms (add parallel 22ohm).
R86 replaced with 1.5K ohm in series with 2.7uh SMT choke.? (resets bias?
and adds peaking.)
?
Remove t9 and take one turn trifilar off of the 10.? Reinstall, pay?
attention of lead placement.? IF available 6turns #28 trifilar?
on BN43-302
?
==================== Driver? ========================
All the 2n3904s in the driver replaced with 2n2222A or better.
Hint I mounted them from the underside with very short leads as it makes?
the top less crowded.? IF 2n5109 is used add a ferrite bead on the collector lead.
?
R911,r96, R941, R942 emitter resistors for driver reduced to 11ohms (add parallel 22ohm).
R92, R95 replaced with 1.5K ohm.? (resets bias)
?
Remove t10 and take two turns trifilar off of the 10.? Reinstal pay attention?
of lead placement.
?
==================== final amp? ========================
?
Replace T10 with FB43-202 4 turns bifilar #26.
There are several variations including larger ferrite?
and differnt turns ration such as 2turn primary and 3 turn secondary.
NOTE: this only use two of the three windings so ignore pins 4 and 3 (unused).
?
Ferrite heating here is likely due to two possible causes:?
Inefficient transformer due to how its wound, not enough ferrite?
(more than 12W) or wrong material (43 or 61)

Bias on finals at that time was 180ma per for best power and soso IMD.

Despite claims the RD16HHF is NOT a panacea and does not materially?
help 10M result.? At 10$ its your fun.? I tried them and have used?
them elsewhere with good result but not that much better.
?
====================? ?end? ?========================
?
?
Allison
 

Glen,

Generally I used one 5109 for ever pair of 3904 due to what I had on hand.

However there are a raft of other parts in the CATV class of 1-3W, 800ma Ic,
and FT greater than 1200mhz.

Did not say copy this so like I said your on your own.??

BN 43-202? typo, old stiff fingers.

Allison
 

Thats ok on parts.? Although getting them might be another story. I have? a pretty good 'junque box' from years of playing radio, but never deep enough with whats 'wanted'.

And typos.

glenn

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