[Amps] Can I cool too much the tubes or ants?

Roger sub1 at rogerhalstead.com
Mon Aug 23 20:06:46 PDT 2010 


On 8/23/2010 10:03 PM, Charles Harpole wrote:
> Melting antennas is a very good sign.   If u have never done so, ur ham ticket is in jeopardy.
Yah, but QRP operators seldom see the ends of the driven element(s) and 
directors dripping fire. <:-))
> Charles Harpole k4vud at hotmail.com
>
>
>
>
> Could it be the antenna heating up and causing it to click off-line?
Unlikely it'd be the antenna heating, but OTOH the typical balun sold to 
hams is quite susceptible even at less than the legal limit. On low 
bands like 160 and 75 it's easy to fracture the ferrite inside.  A few 
weeks back when we were having temps in the lower 90's and bright 
sunshine I was operating on 40 meters using the AV640.  The bands needed 
a bit of readjusting since I rebuilt the matching unit, but I'd not 
gotten to that yet.  The AV640 uses a current balun for isolation 
followed by a 4:1 balun with both using 2 cores each IIRC.  Although not 
recommended when using baluns I was keeping the SWR down to the amp 
using the Palstar AT5K tuner.

I was running the legal limit and had been on for a while when the amp 
(Emtron DX-2sp) kicked off due to high SWR.  And it was high...on the 
order of roughly 6:1.  I was mulling this over wondering what had gone 
wrong when I hit the key to check the SWR again.  It was showing 1.0:1!
I switched and made a short transmission at the legal limit on SSB 
before the amp kicked off due to high SWR *again*. So, this time I 
waited 5 minutes and again the SWR had dropped back to 1.0:1.  This time 
I managed about a 30 second transmission before the SWR again went high.

I have the AV640 down, but I've not had a chance to open the tuning unit 
yet.

I finished welding up the 25G base last night with the addition of the 
hinges that use half inch bolts. I hope to get the priming done with 
self etching primer tonight, at least in the cracks and crevices where 
rust is likely.  Tomorrow is to be the painting day.  Hopefully I'll get 
the Ham IV along with the 2" DOM masting ready for painting as well.

With the designs listed in Jim Brown's (K9YC) RFI tutorial I use an 
antenna tuner at the legal limit and very high SWR at the band edges on 
both 160 and 75 with no problems of overheating. 6 turns of LMR-400 or 
Davis BuryFlex(TM) on 5 or 6 2.4" cores seems to work quite well.
I had some misgivings about not having both sides of the wire antennas 
at DC ground for precipitation static build up, but "so far" it's not 
been a problem.

OTOH I think I need to add a remote tuner at the feed points to keep the 
voltages down on the feed lines to the 6-pack and the remote antenna 
switches.

73

Roger (K8RI)
>   I
> don't know if the amp has any VSWR or Over Current Protection but I have
> had antennas heat up, catch on fire or melt from time to time. My amps
> would protect themselves and go to stby when that happened.
> N9FUT
>
> Original Message:
> -----------------
> From: Jeff Blaine keepwalking188 at yahoo.com
> Date: Fri, 20 Aug 2010 11:20:53 -0500
> To: ranchorobbo at gmail.com, apolloeme at live.com, amps at contesting.com
> Subject: Re: [Amps] Can I cool too much the tubes?
>
>
> Gentlemen,
>
> You should take a look at the plate dissipation at the reduced power levels.
>
> In my amp, as the power output drops back, the efficiency drops at a faster
> rate on some bands. Which means that running the amp at half power, for
> example, as is the current rule of thumb for RTTY operation, may not
> actually reduce the effective plate dissipation very much.
>
> Of course, one point does not make a trend. But it's easy to make the
> calculation and then a guy can KNOW rather than just guess.
>
> And if we were perhaps talking about an SB220, that transformer is pretty
> light weight to begin with, and a guy would definitely want to check the
> efficiency there.
>
> Hope to see you in the SARTG.
>
> 73/jeff/ac0c
> www.ac0c.com
>
>
> --------------------------------------------------
> From: "Rob Atkinson"<ranchorobbo at gmail.com>
> Sent: Friday, August 20, 2010 10:09 AM
> To: "Patrick Barthelow"<apolloeme at live.com>
> Cc:<amps at contesting.com>
> Subject: Re: [Amps] Can I cool too much the tubes?
>
>>> Pat,
>>>
>>> I have the amp, manual with schematic. There is nothing in there
>>> about any sensor that throws the amp in standby if it gets too hot.
>>> That's why I asked.
>>>
>>> It must be an aftermarket mod in your amp Rudy.
>>>
>>> But, I am always willing to be surprised and eat crow. Why not give
>>> Ten Tec a call and ask them? There might be something in there
>>> having to do with current draw I don't know about, thay may have been
>>> taken out in later models. Anyway, my comment about specifiying mode
>>> was not directed at you.
>>>
>>> It's up to you whether or not 400 w. is enough, but in my opinion a
>>> new Alpha is not the answer if you want a really robust amp. If you
>>> can afford a new Alpha you can afford an old one back before they
>>> tried to jam everything into a teeny desk-top cabinet, or an old
>>> Henry, or two, or homebrewing one in a rack....maybe an old TMC or
>>> Collins commercial communications amp...
>>>
>>> On Thu, Aug 19, 2010 at 11:40 PM, Patrick Barthelow<apolloeme at live.com>
>>> wrote:
>>>> Does anyone have a schematic for the amp under discussion, or perhaps
>>>> looked
>>>> to see the sensor device that senses excessive heat to
>>>> trigger a shutdown? I am curious what they sample for the heat trip
>>>> function. And, if it is an internal sensor for the transformer core,
>>>> it
>>>> might not help, but perhaps some extra muffin fans, mounted external or
>>>> internal to the amp could add enough cooling to extend its duty cycle on
>>>> RTTY.
>>>>
>>>> Back in the olden days, as a kid, I used to sit a muffin fan right on top
>>>> of my Drake TR-4 Finals Cage, drawing upward, and the whole radio became
>>>> and
>>>> ran dramatically cooler.
>>>>
>>>> Best Regards,
>>>> 73, de Pat Barthelow AA6EG
>>>>
>>>>
>>>>
>>>>
>>>>> Date: Thu, 19 Aug 2010 20:16:13 -0700
>>>>> From: r_bakalov at yahoo.com
>>>>> To: amps at contesting.com; ranchorobbo at gmail.com
>>>>> Subject: Re: [Amps] Can I cool too much the tubes?
>>>>>
>>>>> Rob,
>>>>> I am the second owner of this amp and don't know its age. It is the grey
>>>>> model. I can certainly look up the serial number when I am back to VE3
>>>>> where
>>>>> my contesting QTH is.
>>>>> As far as mode goes, my very first post noted that this is with respect
>>>>> to
>>>>> RTTY where I can't really run it longer than 30 min at full power. I
>> am
>>>>> not
>>>>> a SSB guy; CW runs all day long at full power. Standby or not, some
>> sort
>>>>> of
>>>>> protection kicks in when the amps gets too hot and the orange STBY LED
>>>>> is
>>>>> on.
>>>>> So now my dilemma is if I should run low power, without the amp, or high
>>>>> power at only 400 W during the upcoming CQWW RTTY contest :-) Or time
>>>>> for an
>>>>> Alpha :-)
>>>>> Rudy N2WQ
>>>>> --- On Thu, 8/19/10, Rob Atkinson<ranchorobbo at gmail.com>  wrote:
>>>>>
>>>>> From: Rob Atkinson<ranchorobbo at gmail.com>
>>>>> Subject: Re: [Amps] Can I cool too much the tubes?
>>>>> To: amps at contesting.com
>>>>> Date: Thursday, August 19, 2010, 4:28 PM
>>>>>
>>>>> Rudy,
>>>>>
>>>>> Is this automatic standby mode protection a new thing with the
>>>>> Centurion? Mine is around 10 years old and it has nothing like this.
>>>>>
>>>>> When did you get yours?
>>>>>
>>>>> N.B. When you guys write about transmittion time at some power level,
>>>>> it is very important that you specify the mode.
>>>>>
>>>>> There is a huge difference between "1.5 KW no time limit (operating
>>>>> SSB) and 1.5 KW no time limit carrier.
>>>>>
>>>>> SSB is the "Coors Light" of transmission modes.
>>>>>
>>>>> 73
>>>>>
>>>>> Rob
>>>>> K5UJ
>>>>>
>>>>>
>>>>> On Wed, 18 Aug 2010 10:34:58 -0700 (PDT), Rudy Bakalov
>>>>> <r_bakalov at yahoo.com>  wrote:
>>>>>
>>>>>> Experience trumps specs. The amp goes into standby mode after about 30
>>>>>> minutes
>>>>>> running at full power, i.e. about 1200 W. If I run it at around
>>>>>> 400-500
>>>>>> W it
>>>>>> is fine.
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