Blowing NE602s.Why?
 

I'm using an NE602 as a balanced modulator in a simple DSB transmitter.
The circuit is similar to that of the K2.
My problem is that in the course of debugging the TX, I've somehow
destroyed three NE602s. At first I thought it was voltage spikes
from the T/R relay, so I put a diode across the relay coil to knock that
down. Then I blew another one. Now I suspect that somehow the problem
is related to parasitics that I'm trying to eliminate in the PA: There is
an impednce transformer in the 602's output circuit that would look like
a big step up transformer to any RF that that nasty oscillating PA might
send back down to the modulator.

What do guys think? Is this a likely suspect? Anyone know of other causes
for this kind of 602 carnage? Stop me before I kill again!

73 from London
Bill M0HBR N2CQR CU2JL
http://planeta.clix.pt/n2cqr

Bill Meara wrote:


What do guys think? Is this a likely suspect? Anyone know of other causes
for this kind of 602 carnage? Stop me before I kill again!

Hmmmmm.....don't know about the xfmr idea, but what supply voltage are you
applying to the chip? I was faced with a similar situation once till I
realized I was feeding it 12VDC when it's max rating is 9VDC.

Good luck.

Bob WB0POQ

Bill Meara wrote:


What do guys think? Is this a likely suspect? Anyone know of other causes
for this kind of 602 carnage? Stop me before I kill again!

Hmmmmm.....don't know about the xfmr idea, but what supply voltage are you
applying to the chip? I was faced with a similar situation once till I
realized I was feeding it 12VDC when it's max rating is 9VDC.

Good luck.

Bob WB0POQ

Bob: Thanks, but I don't think its that simple. I have a zener diode
regulating the supply voltage, keeping it at around 6 volts. 73 Bill


Bob Liesenfeld wrote in message ...
Bill Meara wrote:


What do guys think? Is this a likely suspect? Anyone know of other causes
for this kind of 602 carnage? Stop me before I kill again!

Hmmmmm.....don't know about the xfmr idea, but what supply voltage are you
applying to the chip? I was faced with a similar situation once till I
realized I was feeding it 12VDC when it's max rating is 9VDC.

Good luck.

Bob WB0POQ

Bob: Thanks, but I don't think its that simple. I have a zener diode
regulating the supply voltage, keeping it at around 6 volts. 73 Bill


Bob Liesenfeld wrote in message ...
Bill Meara wrote:


What do guys think? Is this a likely suspect? Anyone know of other causes
for this kind of 602 carnage? Stop me before I kill again!

Hmmmmm.....don't know about the xfmr idea, but what supply voltage are you
applying to the chip? I was faced with a similar situation once till I
realized I was feeding it 12VDC when it's max rating is 9VDC.

Good luck.

Bob WB0POQ