[TMC] pal-350

Mon May 8 09:03:05 EDT 2006

Hi Mark.
I think that the information you have provided, is important to all So, with 
your permission, I am posting it on the TMC net so it will be for the 
benefit of all.

The PAL 350 is stable inherently stable but in the name of technical 
perfection I thought that there must be a way to adjust it without taking 
covers off etc.
As to the ALDC I don't like TMC's procedure and as you have said it is 
pretty useless, on the other hand I don't want to drill any holes. What I am 
thinking of doing is mounting a small planetary drive  1-2 rpm motor on the 
pot shaft at the rear and a momentary switch on  the front to control it, 
w/o any mechanical/wiring  mods.
As to the 6.0V fil, I have externally marked the correct point with a fine 
marker  on the multimeter glass (easily erasable,) using calibrated DMM and 
that part is solved.
Thanks for sharing your knowledge.
Ira.
CE3AM,,,,,,4X4SW

----- Original Message ----- 
From: <night-ops at worldnet.att.net>
To: <kch at tie.cl>
Sent: Sunday, May 07, 2006 7:56 PM
Subject: Fw: [TMC] pal-350

> Ira,
>
> My name is Mark, KI0PF, and I live in Colorado, USA.
>
> I'm not a member of the TMC List but one of my friends
> who watches it sent me this post of yours.
>
> I have two complete PAL-350 setups, one of which is
> on the air almost every night on 40m.  I've had a lot
> of experience addressing the issues you're asking
> about.
>
> See my comments at the "***"
>
> --Mark
>
> -----------------------
>>----- Original Message ----- 
>>From: "Ira Curtis" <kch at tie.cl>
>>To: <tmc at mailman.qth.net>
>>Sent: Sunday, May 07, 2006 6:09 PM
>>Subject: [TMC] pal-350
>>
>>
>>Hi  All
>>Can anyone tell me the exact procedure for adjusting the ALDC in the
>>PAL-350?
>>Read the manual over and over again -no trace.
>
> ***It's in there all right, but it's pretty useless.
>
> "While the unit is still fully tuned at some frequency, turn ALDC
> adjustment potentiometer slowly clockwise (from fully CCW) until
> output will just begin to drop off."
>
> What they're asking you to do here is introduce a little RF
> compression, which will keep the amp from overdriving too easily.
> Two problems with this:
>
> 1) Overdo it and you introduce a LOT of distortion.
> 2) The ALDC setting VARIES with frequency, often enough to cause
> #1 above, especially when switching bands.  Or it may not be
> ENOUGH ALDC on the new freek and you'll overdrive the amp.
>
> I relocated the ALDC control to the front panel on both my amps,
> substituting a 50K pot with a longer shaft, and re-routing the
> three pot wires through the chassis access tube.  Now I can
> adjust the ALDC easily from the front panel.
>
> I tune up for 350W carrier then advance the ALDC until the power
> just starts dropping.  With no speech processing you'll probably need more
> ALDC.  You've probably found the mike input on the SBE is *very* touchy.
> There is NO compression in the SBE at all and it's very easy to
> overdrive the amp, as I'm sure you've found out already!
> I use a homebuilt speech processor with a lot of compression/clipping
> and a 600ohm output connected directly to Channel 1.  The audio level is
> kept very uniform, which is what you want for a linear amp anyway.
>
>>What would be the best way to connect the SBE-2 to the Pal 350  ALDC?
>
> ***There's no provision to do that.  Unlike the bigger SBT-1K and GPT-10K,
> etc., there's no way I know of to directly connect the ALDC to an exciter.
> That's why I moved the control.  Believe me, if you don't adjust the
> ALDC correctly on your amp, you'll either be unable to get full power
> or you'll be tripping the HV breaker constantly.
>
>>I have found out that PAL-350 neutralization  changes with the top  cover 
>>on
>>or  off.Not much though, but it changes. Any idea as to how can I 
>>neutralize
>>the amplifier with the covers installed and preferably the amplifier
>>installed in it's  rack?
>
> ***Are you actually seeing instability?  If not, leave the neutralization
> where you found it.  I've tried fiddling with it on both my amps and it
> made very little difference.  I think these amps are very stable to
> start with.
>
> Also, the 4CX250Bs need to have 6.0V on the filaments +/- as close
> as you can adjust it.  Voltage too far away from that is not good
> for the tubes.  Do NOT trust the red mark on the meter -- I've
> never seen an accurate reading on these amps yet.  After removing the
> airbox cover for many years to adjust the voltage, I finally mounted
> a test point on the back panel -- makes it much easier, and keeps
> cooling air on the tubes all the time.
>
> Hope this helps.
>
> --Mark
>  KI0PF
>
> ----------
> From CQ Communications,
>
>            "MIL SPEC RADIO GEAR"
>                   by Mark Francis, KI0PF
>
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>
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>
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>
> ----------
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