[Amps] Centurion cooling improvement ideas for AM service

Wed Aug 25 15:03:43 EDT 2004

On Aug 25, 2004, at 11:48 AM, Joe Isabella wrote:

> 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"
>
Thanks, Joe.  So this means that if adopted, 10m FM as well as AM will 
be illegal.
>
> 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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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org