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
