View Single Post
  #4   Report Post  
Old September 30th 06, 10:24 PM posted to rec.radio.cb
Frank Gilliland Frank Gilliland is offline
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 432
Default Griffey changes his mind...derates to 322 watts PEP

On 30 Sep 2006 13:32:13 -0700, "Telstar Electronics"
wrote in
. com:

Premium Quality PC Board, Components and Chassis
13.8VDC
10 Meter Amateur Radio Band Coverage
All Mode (CW, AM, FM, SSB)
Toshiba 2SC2879 Push-Pull Configuration with Beta/Gain Matched
Transistors
Regulated Class-AB Biasing
High Output Power
High Efficiency Heat Sink
Polarized Detachable Power Cord
Fuse Protected
Extremely Low Stand-By Power
Remote Operation Ready
Carrier Operated Relay (COR) or Multiplexed Keying†
SSB Delay to Eliminate Relay Chatter
High Reliability Design
Low Harmonic Content
90 Day Limited Warranty
† Contact Telstar Electronics for details on using this feature

www.telstar-electronics.com



Hey Brian.....

Since the transistors you are using are rated for a typical gain of
15.2dB, and you are using two of them, why is your amp rated for only
15dB instead of 18.2dB?

And at 18.2dB, if you shove in a typical 4 watt carrier from a CB,
doesn't that put your AM "RMS" output about 264 watts? (And your PEP
output at 1056 watts?)

Now assuming you have a magical amp that can achieve 55% efficiency
irrespective of the 35% collector efficiency of the transistor, when
you 100% modulate this 264 watt carrier (giving an AVERAGE power 396
watts), doesn't that mean you are going to be drawing 720 watts from
your power supply?

Just in case I missed something in 3rd-grade math you better check my
work he 720 watts / 15 volts = 48 amps. You also have a base-bias
current of 1 amp for each transistor, so 48 + 2 = 50 amps. Right?

But who uses a 15 volt power supply? Heck, we'll use the more common
automotive standard of 13.8 volts. So 720 / 13.8 = 52.2 amps, plus 2
amps = 54.2 amps.

HOLD ON A SEC.... Your amp only has a 30 amp fuse!!!

So after I get this all hooked up, wired directly to my battery and
everything, plug in my favorite little 4-watt CB, this amp is going to
blow a fuse every time I yell "A-U-D-I-O" into the mic.

Ok, I bypass the fuse and switch my CB on SSB with 12 watts PEP.
What's going to melt first -- the transistors or the power leads?

And you call this a "High Reliability Design"....."LOL"!!!