Paul -
The resistor is ok, but you need to calibrate (with R38) to get the BIAS
setting of 0.07A correct on the meter. Obviously the idle current needs
to be set correctly for linearity. The 1/4W is a little small, but as
long as you keep the final dipped it may be ok. Typical plate current
of 0.340A is just a little over a quarter watt in the resistor. The
concern is that as the resistor is overheated it will go up in value.
You never know where you are!
I like to use 1W or, even 2W if I can find them, "flameproof" metal
oxide resistors. They don't change value so once calibrated you don't
have to worry about it any more. The finals can easily draw an amp or
more of current off-resonance, which would leave 2.2W in your resistor!
Even a half amp is over a half watt in the resistor.
But at least now you know HOW to fix it
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Paul Gerhardt wrote:
Garey
Thanks for the help on this one. The meter shunt on the vertical
board behind the three power resistors was open! Yea...
I replaced it with another 2.2 it is probably too small at 1/4 but it
seems fine for now and I can order a higher wattage one for later.
May still need to get the resistor on the slide switch changed as I
think the meter is now reading a bit low but the output is way up from
yesterday. I was able to load it up to 100 watts out and it may go a
bit so it still needs work but yesteray it was 7-8 watts so it is up a
LOT!
Will try to get a pix of the 'bad' part up on my blog.
73's
Paul K3PG
If I screw the bias back I see up to 80 watts with the plate meter
pegged hard over.
With the bias set 'properly' I only see power output if I turn the RF
Gain up to where the meter is again pegged to the right. When it hits
the pin I am getting 5 - 7 watts.
When the modulation 'looks' right on the meter I am getting 5-10 watts
pep out but the plate meter is kicking up all the way.
I am hearing anti vox coming out the speaker while in SSB is this
normal? I would think not?
The R4B seems to be working well.
The two VFO are transceiving using either or both with the inj cable connected.
I am going to start 'dusting, cleaning and visual inspection'
Paul Gerhardt
K3PG
http://pgerhardt.blogspot.com
QRP ARCI 6674
FP 274
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