I've found the MSP2222, PN2222, 2n2222A to be interchangeable
assuming good parts. However, depending on the source and how
they got in to the product stream they can be out of spec devices.
A good 2N2222a has an Ft of not less than 350mhz and good gain
at 5ma Ic. The 2n3904 however is a little quieter and slightly
better gain even though the Ft is the same. A 2n5179
or other VHF device will not achieve much more gain as the
amplifiers are of RC feedback type and component values set
the gain not the transistor used unless the transistor is
poor quality or simply not reasonable for the frequency
I have some bad commercial experience with parts that just were
not up to spec. I had this once back around '78 with MPS1764s,
bought a bag of them from Motorola and tested them with 100%
yeild to spec. Purchasing bought another 1000 from a cheaper
source and the failure rate was 25% to spec. Showed Motorola
and they wanted to know where they came from. Seems they were
purchased as known offspec for a non critical app the excess
were being resold as full spec. I've been similary burned with
2n3866s and 2n5109s (low Ft and beta), 2n5179s (noisy and low Ft)
to name a few.
So when talking parts like transitors simple DC tests do not tell
all. Measured in an RF test circuit it's easy to spot.
--- In BITX20@..., Arv Evans <arvevans@e...> wrote:
Hito be quite
low. After substituting a handfull of 2N3904s my gain became muchbetter.
a 2N2222 with a 2N3904.the IF & RF
sections of the BITX. There seems to be some merit in that idea.2N2222s that
were purchased from DigiKey were all good in the BITX but those thatwere
purchased from another source (100 each 2N2222s for $1.50 USD) showvery poor
HF gain, but they are just fine for audio applications.so I
filter.put it back.
schematic as I>
RX the> > was doing it, every trace is accounted for.
> same? It could be possible one transistor is shorted collector to