EMRFD Message Archive 1826
Message Date From Subject 1826 2008-07-22 10:09:40 Stan push pull amplifier output questiion
transistor is rated at 1 watt then two of them can be used in a push
pull circuit for 2 watt output.
I can not verify this - can anyone point me to the answer?
Thanks, Stan1829 2008-07-22 15:44:15 Allison Parent Re: push pull amplifier output questiion 1833 2008-07-24 08:34:15 Ashhar Farhan Re: push pull amplifier output questiion
conducts when the first is off, the linearity is much better. the odd
harmonics are attenuated due to this behaviour and it is the
cross-over distortion that will dominate the harmonic distortion.
emitter degeneration and keeping the input drive low will make
push-pull a far better performer than a single ended amplifier.
I am investigating a push pull amplifier QRP gallon with four ordinary
2N2218s to deliver 5 watts. Our earlier experiences with the BITX
power chain left much to be desired in terms of stability, linearity
and reproducibility. I will post the results soon.
- farhan
On Wed, Jul 23, 2008 at 4:14 AM, Allis1834 2008-07-24 19:40:39 Allison Parent Re: push pull amplifier output questiion
A push pull amp usually is cleaner with lower crossover distortion
when there is bias applied to the devices running a small current
and a a small emitter degeneration for DC stability. A stiff bias
source is always a good thing with bipolar transistor amps. A pair
of 2218s I'd set the bias to around 10mA per device.
If you need lower IMD a reasonable amount of negative feedback will
work well. Balance is always a good thing.
I've run two 2218s PP for about 2.5W clean and fairly flat from
5mhz to 30mhz with the binocular transformers. Using a pair of
3866s gave 2W but flat to 55mhz. The problem with both is they
didn't like high SWRs and the TO5 case does not easily heatsink
well. A pair of 2sc2166 proved most robust and good for over
6W plus the tab mount case made cooling easier than the TO5 can.
There is a long list of 10 to 20W transistor types that perform
well. An over sized device will more likely withstand all forms of
antenna mischief without failing. For a lot of applications
the ability to withstand abuse is a desirable trait.
FYI a pair of 2n2222A will drive a pair of 2SC2166 easily for
HF through 6M and a push pull driver can be very clean and higher
efficientcy than class A with high standing current.
Allison
1837 2008-07-26 21:46:20 Hari G Re: push pull amplifier output questiion
Could you plase share the shematic or design details on the stages(like
the last post on driver amp), what was the input signal level.
73
Hari
On 7/25/08, Allison Parent <kb1gmx@arrl.net> wrote:
>
> Farhan,
>
> A push pull amp usually is cleaner with lower crossover distortion
> when there is bias applied to the devices running a small current
> and a a small emitter degeneration for DC stability. A stiff bias
> source is always a good thing with bipolar transistor amps. A pair
> of 2218s I'd set the bias to around 10mA per device.
>
> If you need lower IMD a reasonable amount of negative feedback will
> work well. Balance is always a good thing.
>
> I've run two 2218s PP for about 2.5W clean and fairly flat from
> 5mhz to 30mhz with the binocular transformers. Using a pair of
> 3866s gave 2W but flat to 55mhz. The problem with both is they
> didn't like high SWRs and the TO5 case does not easily heatsink
> well. A pair of 2sc2166 proved most robust and good for over
> 6W plus the tab mount case made cooling easier than the TO5 can.
> There is a long list of 10 to 20W transistor types that perform
> well. An over sized device will more likely withstand all forms of
> antenna mischief without failing. For a lot of applications
> the ability to withstand abuse is a desirable trait.
>
> FYI a pair of 2n2222A will drive a pair of 2SC2166 easily for
> HF through 6M and a push pull driver can be very clean and higher
> efficientcy than class A with high standing current.
>
> Allison
>
>1838 2008-07-27 06:38:42 Allison Parent Re: push pull amplifier output questiion
Once I have them scanned right now work has way too much of my time.
The basics and good detail are in EMRFD. I plowed no new ground
on this. If anything the real work is building input and output
transformers that perform well. The topology for a RF PP power amp
looks much like the audio versi1839 2008-07-27 11:35:06 yo8can Re: push pull amplifier output questiion
It is true, also in some cases the transistors may be connected in
parallel, but this works only using low power bipolar transistors
which have high enough input impedances in RF, or are MOSFET's. Else,
only push pull schemes are required, which can give twice power than
one single transistor, with also some benefits in linearity and even
harmonic suppresion.
Romi YO8CAN
1843 2008-07-28 06:33:32 Ashhar Farhan Re: push pull amplifier output questiion
behaving as RF amplifiers. The LM386 has quite a shame, though I
managed to get something out of an LM380, but not enough to drive a
PA. Let me check if the 2SC1226A is available locally... it should be
an interesting experiment.
The BD137s are probably not common across the pond, my personal
experience is that they are unable to give repeatable, stable
performance.
allison is quite right about the 2N2218s being unable to take a lot of beating.
I have an observation to make about the EMRFD. I find myself going
back to SSD as a reference for power amplifier design. the treatment
of power amplifiers, design of matching networks, heat sinking etc. is
more elaborate in the SSD as compared to EMRFD.
- farhan
1844 2008-07-28 18:55:30 Allison Parent Re: push pull amplifier output questiion 1845 2008-07-29 11:35:21 Hari G Re: push pull amplifier output questiion
reliable and very repeatable amps i have ever seen.I have two working in my
shack.
73
Hari
http://www.radio-kits.co.uk/
On 7/29/08, Allison Parent <kb1gmx@arrl.net> wrote:
>
>1850 2008-07-30 19:06:16 Allison Parent Re: push pull amplifier output questiion