[Amps] Centurion cooling improvement ideas for AM service

Wed Aug 25 14:48:44 EDT 2004

Here's the scoop, straight from the League:
------------------
Note: forwarded message attached.

Subject: RE: One more question
Date: Wed, 25 Aug 2004 14:02:35 -0400
From: "Sumner, Dave, K1ZZ" 

Also -26 dB, because that's how 97.3(a)(8) defines bandwidth.

Dave
------------------

So there you have it: SSB is slated to be defined at 3 kHz @ -26dB.

Joe,
N3JI

--- Joe Isabella <n3ji at yahoo.com> wrote:

> It doesn't say anywhere that I can see, even though it does specify 6kHz @ -26dB for ISB, and
> 9kHz at -26dB for DSB AM.  I asked -- I'll let you know what I find out.
>  
> Joe,
> N3JI
> 
> "R.Measures" <r at somis.org> wrote:
> 
> On Aug 25, 2004, at 6:56 AM, Joe Isabella wrote:
> 
> > I take that to mean 650W PEP, 50% duty cycle for 10 mins. To equate 
> > that to AM, 650W PEP is about
> > 150W carrier. But since you have a 150W carrier 100% of the time, 
> > does that require further
> > derating?? All I know is that the TL-922 or SB 220 would do 300W 
> > carrier AM (or about 1200W PEP)
> > for a "normal" AM transmission. I added the auxiliary cooling to my 
> > Kenwood to keep things cooler
> > in the power supply since the fan pulls air mainly over the tubes and 
> > did little for the supply.
> > I would add the extra fan and start at 150W carrier and see how it 
> > does for a while. if all is
> > well (and I'm sure it will be), take it to 200W carrier. If that's 
> > okay, go to 250W, then 300W.
> > I would guess that you'll be fine running it at 300W -- it's beyond 
> > that that I started having
> > problems (PS got too hot).
> >
> > BTW, read your QRZ bio -- glad you're getting into AM. I run ESSB as 
> > well and find AM even
> > better!! Seems that if the League's proposal of 3kHz wide SSB goes 
> > through, there won't be any
> > other place to run extended audio!! Let's see how it goes...
> 
> Joe -- 3kHz wide at how many db down?
> 
> >
> > Joe,
> > N3JI
> >
> > --- Ed Briggs wrote:
> >
> >> I contacted the manufacturer on a related topic some time back. Their
> >> official response (contained in the manual) is for keydown operation, 
> >> 650W
> >> max, 50% duty cycle, 10 minutes max transmission time (as you know 
> >> from the
> >> manual)
> >>
> >> I inquired how to derate this for a longer transmission time (say 30
> >> minutes). I speculated that since when operating bias is applied (no 
> >> rf
> >> drive) the amp idles at appx 160 ma yielding a dissipation of 450w,
> >> representing just under 50% of the combined dissipation of the two 
> >> tubes,
> >> and I asked, is it 'safe' to let the two tubes run with at this level 
> >> of
> >> dissipation for 30 minutes (the key is up after all).
> >>
> >> They responded " In theory 450 watts should be safe for key down 
> >> operation
> >> but we could not guarantee the tubes would survive this operation."
> >>
> >> How does this apply to your AM question. The manufacturer seems to 
> >> have
> >> some reservations about cooling at 450w steady state so, although I'm 
> >> not
> >> sure whether they mean 450 w output or 450 w dissipation (possibly the
> >> same).
> >>
> >> Others on this reflector may be able to use this data point from the
> >> manufacturer to predict.
> >>
> >> Ed
> >>
> >> ----- Original Message -----
> >> From: "Rob Atkinson, K5UJ" 
> >> To: 
> >> Sent: Tuesday, August 24, 2004 10:13 AM
> >> Subject: [Amps] Centurion cooling improvement ideas for AM service
> >>
> >>
> >>> Hi folks,
> >>>
> >>> I am the owner of a 3 year old Ten Tec Centurion amp. This unit 
> >>> employs
> >> two
> >>> 3-500ZGs on an elevated socket platform in the rear right side of the
> >>> cabinet (when facing the front panel). On the rear left side is the 
> >>> h.v.
> >>> power supply with a Dahl model 422 transformer which delivers 3.2 kv
> >> (around
> >>> 2.9 under load) to the plates. Between the p.s. and rf deck is a rf
> >> shield
> >>> running down the middle of the chassis. A square hole is cut in this
> >>> between the tubes and p.s. and over that is mounted a Bi-Sonic tube 
> >>> axial
> >>> muffin fan, model 4E-115-S21, sleeve bearing, 115 v. 220 ma 20 w. 
> >>> 2200 RPM
> >>> moving 82 CFM. The fan is on the tube side of the shield, and draws 
> >>> air
> >> in
> >>> through the left side of the cabinet, over the p.s. and exhausts it
> >>> horizontally over the h.v. plate choke and tubes, including the pins 
> >>> and
> >>> anode heat sinks, which are the flat type extending out 
> >>> horizontally. As
> >>> most of you know, this has become the standard cooling method for 
> >>> these
> >>> tubes in amateur amps since Heathkit began using it for the SB220.
> >>>
> >>> This cooling is adequate for low duty cycle modes for which the 
> >>> Centurion
> >>> was designed, but I would like to use mine for brief transmissions 
> >>> (5 to
> >> 10
> >>> minutes or less) of dsb carrier AM running a carrier of 200 to 250 
> >>> watts.
> >> I
> >>> have done this for a couple of minutes and the amp gets pretty darn 
> >>> hot.
> >> I
> >>> would therefore like to boost cooling so as to avoid seal failure.
> >>> Increased noise is not a problem for me.
> >>>
> >>> Bi-Sonic manufactures a fan that is identical to the stock fan but at
> >> higher
> >>> rpm, and 20 more ma, 22 w. and 105 CFM, around a 25% improvement over
> >> stock.
> >>> Is this an increase worth pursuing? Another possibility would be 
> >>> to add
> >> a
> >>> fan to the external surface of the cabinet over the grill on the 
> >>> right
> >> side
> >>> of the rf deck to speed up the draw of air to the right, out of the
> >> cabinet.
> >>> Again, is this an improvement, and would it be worth pursuing?
> >>>
> >>>
> >>>
> >>> Overall, :
> >>> A. Are these mods necessary
> >>> B. Are there any comments on these methods
> >>> C. Perhaps most important, is operating this amp on AM beyond its
> >> efficiency
> >>> and heat dissipation design capability and should I keep it for SSB 
> >>> and
> >> CW,
> >>> and look for something with higher plate voltage and/or tubes with 
> >>> higher
> >>> plate dissipation / more cooling?
> >>>
> >>> Tnx,
> >>>
> >>> Rob Atkinson
> >>> K5UJ
> >>>
> >>> p.s. to save you time and trouble, please no comments to run a plate
> >>> modulated boat anchor.
> >>>
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> >
> >
> >
> > 
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> >
> Richard L. Measures, AG6K, 805.386.3734. www.somis.org
> 
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