[FLBOATANCHORS] My 1st AM QSO w/Knight T150

[Brian Carling]

Hi Norm - I have a T150 too - a busted one... ah but it ws very 
cheap, he he!

Well, those rigs have a major reputation for two things:
VERY bad audio, and VERY bad TVI.
I am not sure what you can do about either.
Most of these rigs have been dumpsterized or shot long ago.
I DO think the problems can both be fixed with the judicioous 
use of some better capacitor values, and additional chokes etc.

The thing about the modulator is that it needs to become more 
like the DX60 circuit. Perhaps a 6DE7 tube could swing the final 
screens sufficiently.
I am not sure.

I LOVE what the manual says:
"THIS KIT MUST BE PROPERLY SOLDERED!" right at the 
beginning. I gues that gives them an "out" if something is not right:
You will think - "Ah ha! I must not have soldered it right!"

Anyway I digress...

Page 32 of the DJVU manual shows the schematic of this brute,
ftp://bama.edebris.com/bama/knight/t150full/t150full.djvu

At 300% you can read it...
Looks like a 6DR7 (V5) is doing the job for screen mod them...
Does that really say it has 540V on the plate? Hmmm.

It's rated for 275 max volts:
http://tdsl.duncanamps.com/sheets/6dr7/6dr7-1.gif

So we had better hope the screen grid of either of the 6146 
finals never shorts to earth!

Are there ANY articles out there on improving the T150 
modulation?

I would think if it is "muffled" audio, that you could decrease the 
capacitance of C39 and / or C43 perhaps...

I would think that if it lacks bottom end you could increase the 
capacitance of C40 and C42.  R47 could be tweaked just a little 
too, I think.

These are just guesses. In any case, I bet a D104 would 
IMPROVE the audio considerably.

Has anyone run across any articles describing improvements in the 
T150 audio?

One of the keys to getting this kind of screen grid mod to work well, 
is that you need low resting current and plenty of peak current.
It is "reduced carrier" AM (compared to conventional plate mod)
and so the resting power out is relatively low.

The operating instructions say nothing about what the resting 
current for the 6146es should be during AM operation.
It would have been smart to include some kind of adjustment.

Is this a hopeless case? I like my T150 - it's a pity someone
smashed it up... I might get it going some day, but then 
there are the T50s and the T60 here that need  attention
too!

On 12 Jan 2005 at 6:41, Norm Palin K7NCR wrote:

> 
> 
> Hi All!
> Had my first AM qso with a CA station this afternoon on 20M. I cleaned
> the band switch contacts on my T150, and tuned up. I still have no
> output on 6M, and the audio is poor, according to my returned signal
> report, either with my amplified Turner SSB mic (lowZ) or a couple of
> crystal hand mics from my tube CB radios. Then after operating for a
> while, the power output fell off, but the plate current whent WAY up!
> Buffer output indication was low also. Time to recheck the
> buffer/multiplier I guess. Any other thoughts? I still had a GREAT
> time on the air with this rig! My other problem is "talk-back" from my
> R100A, even with the receiver on standby with the receive muted by my
> DOW relay contacts. Possible overloaded AF circuit from the T150? Have
> fun everyone!!
> Norm K7NCR
> 
> 
> 
> 
> 
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