[TMC] SBT-1K ramblings

[telegrapher at att.net]

I've been doing some testing with the big rig.  Hooked the GPE exciter 
into the amp to see how it would perform.  Think i've got the tuning of 
the amp figured out as i can get about 400w out of it on CW.  I set the 
power out to 250W when testing in AM mode.

I've noticed that about all i can get out of it is 370 Ip.  no matter 
where i set the Plate overload pot, the main power CB trips when i go 
over that value.  Keep in mind that this tube is pretty flat.  But if i 
run it at about 360 ma Ip i can drive it in CW mode real easily to 400W 
out.  Isg is around 23 ma which i think is pretty good.  Lots of room 
for increase.  However if i try and drive it to get more out, all it 
does is increase the screen current with no appreciable out power 
increase.  So therefore we keep the power down.  ALl this btw is into a 
dummy load as i don't have an antenna line into the garage where all 
this work is going on.

Now when i tried it on voice, AM specifically as that's all the GPE-1A 
will provide, just barely cracking open the modulation control would 
trip the main power CB.  I couldn't believe that it took such a small 
amount of drive to drop this thing off line.  I did notice tho watching 
the multi meter that if the indications on Ip or Isg flickered to much 
it would kick off the main CB.  Driving me nutso.....

Finally put the Heathkit SB-610 in line to see what the output envelope 
looked like while talking into it.  Turning the drive way down to the 
bottom i keyed up the tranny and started talking.  Ever so slowly 
bringing up the mod control on the GPE-1A.  It took a couple of trys but 
i've found a setting of the Mod control that will give me a pretty good 
envelope with closure at the baseline.  Have to be careful tho that i 
don't hit any syllables with hi peak power or it'll dump the Main power 
CB and then i have to wait for the 3 minute timer to reset before 
bringing the HV back up.  Trials and tribulations.

I think that a new 8295/PL-172 will do wonders for this beast.  Maybe 
then i'll be able to get the proper output power and perhaps it won't be 
so sensitive to voice peaks.

The D-104 mic i'm using, well i'm wondering if maybe the output on it 
isn't to hot for the exciter.  Don't know what type mic they spec'd for 
the transmitter originally but i've never been able to do more than just 
barely open up the Mod control on it and it would drive the pants off of 
the amp.  It also might be that since the GPE-1A has no ALDC provisions 
that i need to get the SBE unit fixed and online as it does use ALDC or 
have the provision for it.

Any other users out there with any experience with this transmitter?

This is so much fun!

Larry
W0OGH