[Amps] SB-220 and Graphite tubes in high duty cycles

Sun Jul 5 07:03:53 PDT 2009

Never had one blow here Jeff, I get them after the smoke is gone!

Sometimes the damage is extensive. Both transformers, filter caps, diodes, 
meter, and a tube or two. Customers dont like hearing that! And I often wind 
up with another junker for a few remaining parts.

Carl
KM1H

----- Original Message ----- 
From: "Jeff Blaine AC0C" <keepwalking188 at yahoo.com>
To: "Carl" <km1h at jeremy.mv.com>; "Bill W5WVO" <w5wvo at cybermesa.net>; 
<AMPS at contesting.com>
Sent: Saturday, July 04, 2009 11:31 PM
Subject: Re: [Amps] SB-220 and Graphite tubes in high duty cycles

> Carl,
>
> That SB220 stock transformer is really a marginal design.  The SB200 is a 
> far sturdy bird albeit at a lower voltage - even when compared under the 
> same current draw.
>
> And wow, when the winding shorts on that transformer, now that's an 
> exciting time.  :)  I am sure you have had that same pleasure many times 
> in your long history of playing with amps.
>
> 73/jeff/ac0c
>
>
> --------------------------------------------------
> From: "Carl" <km1h at jeremy.mv.com>
> Sent: Sunday, July 05, 2009 10:26 AM
> To: "Bill W5WVO" <w5wvo at cybermesa.net>; <AMPS at contesting.com>
> Subject: [Amps] SB-220 and Graphite tubes in high duty cycles
>
>> Id be concerned about the plate transformer temperature rise as its only
>> rated at .6 kva in CCS service. Also filter cap temperatures.
>>
>> In the RF deck the problem could be RF heating in the input or output
>> circuitry from undersized components or inadequate attachment of high
>> current points.
>>
>> Graphite tubes like a higher airflow which is why Harbach offers the high
>> speed fan.
>>
>> Carl
>> KM1H
>>
>>
>>
>>
>> ----- Original Message ----- 
>> From: "Bill W5WVO" <w5wvo at cybermesa.net>
>> To: <AMPS at contesting.com>
>> Sent: Saturday, July 04, 2009 7:14 PM
>> Subject: Re: [Amps] AL1200, RTTY contesting, temps, duty cycles (not 
>> 100%)
>>
>>
>>>I suppose right up there with RTTY is WSJT with its mode-defined 50%
>>>transmit
>>> cycles (30 seconds "on" for FSK441/JT6M, 60 seconds "on" for JT65). I'm
>>> running
>>> a 6-meter-converted SB-220 with new matched 3-500ZGs in the "throttled
>>> back"
>>> mode (lower anode voltage "CW/Tune" position). Here are the approximate
>>> operating parameters:
>>>
>>> Power In: 85 watts
>>> Anode voltage: 2,000V under full load
>>> Anode current: 700 mA
>>> Grid current: 250 mA
>>> Power Out: 800 watts
>>>
>>> Since I don't have access to accurate temperature-measuring
>>> instrumentation, I'm
>>> going by how stable it "feels" in long-term 50% (30-sec) WSJT duty. 
>>> Power
>>> output
>>> starts at around 875W when the amp is cool and stabilizes at around 800W
>>> over
>>> perhaps 20-30 minutes of continuous 50% operation (30 seconds on, 30
>>> seconds
>>> off).
>>>
>>> Soliciting opinions from those with familiarity with the newer graphite
>>> 3-500ZGs -- am I overstressing it in WSJT mode with these parameters?
>>> About
>>> right? Unnecessarily conservative?
>>>
>>> Bill W5WVO
>>>
>>>
>>> Jeff Blaine AC0C wrote:
>>>> Kevin,
>>>>
>>>> You are right.  RTTY is the big boy challenge for amps.  But it tends
>>>> to make things fall apart in amps in the strangest ways...
>>>>
>>>> You had asked some questions about determining temps.  I had not seen
>>>> any replies specific to that and wanted to mention the tube
>>>> consideration here. The other things that break or melt :) are
>>>> fixable.  But tube damage, well that's a pain that does not go away
>>>> without some $$...
>>>>
>>>> I believe the critical temps for the tube will be listed on the data
>>>> sheet. The issue for the tube, in an RTTY environment, is if the tube
>>>> temp stabilizes, or if it keeps creeping up.  If it stabilizes, and
>>>> the temps are under the limits indicated in the data sheet, then the
>>>> tube should serve you well.  A tube can be run hard - as long as
>>>> "hard" is within the limits of operation.  And with 1200W of plate
>>>> dissipation and maybe 1500w output, you are not going to be pushing
>>>> the plate dissipation limits.  It's the body, anode, pin temps that
>>>> are the question.  I would guess these are probably fine as well as
>>>> the tube is axially cooled.  Put a thermo on the exhaust and look at
>>>> it vs. time at key down.  the temp should rise up to a point and then
>>>> level off.  If it keeps climbing, then that's trouble brewing.
>>>>
>>>> As for the rest of the guts, Bill and Carl have books of stories.  I
>>>> will add my own.  A buddy of mine has a QRO 2500 he plays with on
>>>> RTTY.  Supposed to be rated at 1500w NTL.  Melted the 80 & 160m tank
>>>> toroids.  Quite a few iterations later, he had a dedicated toroids
>>>> for each band to lower down the flux density (a problem with 2-band
>>>> toroid configurations) and the thing hums along fine at legal limit
>>>> RTTY all day long now.  K1TTT had the similar problem so it's not
>>>> specific to the guy.  But other guys with the same amp seem to never
>>>> have problems.
>>>>
>>>> With RTTY, there is only 1 rule.  Your mileage will vary.  And that's
>>>> why RTTY IS the big boy's mode.
>>>>
>>>> 73/jeff/ac0c
>>>>
>>>> --------------------------------------------------
>>>> From: "Kevin Normoyle" <knormoyle at surfnetusa.com>
>>>> Sent: Thursday, July 02, 2009 2:06 PM
>>>> To: <AMPS at contesting.com>
>>>> Subject: Re: [Amps] AL1200, RTTY contesting, temps, duty cycles (not
>>>> 100%)
>>>>
>>>>> Bill, W6WRT wrote:
>>>>> "But here's the Achilles heel of the AL-1200. The low band tank
>>>>> coils used undersized wire and overheated."
>>>>>
>>>>> Thanks Bill. I've read some of your comments in the forum on the
>>>>> AL-1200 before. I think one of the good things we can do as users is
>>>>> to just document what happens in as much detail as we can. There is
>>>>> definitely a place for the price/performance the AL-1200 provides,
>>>>> and I like it a lot.
>>>>>
>>>>> Sometimes the "complaints" about various amps lacks the detail to
>>>>> really assess what happened and why. It can be hard to sort out
>>>>> one-off issues, or generic operating environment issues.
>>>>>
>>>>> I'm just interested in making sure I operate within the AL-1200
>>>>> performance envelope. I was surprised to see all this talk about
>>>>> RTTY duty cycles, as if it was well defined/understood. When it
>>>>> seems not to be. i.e. if if was just RTTY duty cycle, do things melt
>>>>> on a 1 minute RTTY ragchew? I don't know, but as I described, don't
>>>>> care. I'm perfectly happen to limit my RTTY macros.
>>>>>
>>>>> So part of my post is this: There is no such thing as RTTY duty
>>>>> cycles when you talk about RTTY contesting. There is a desirable
>>>>> duty cycle, but people should define it better. It's not key down
>>>>> forever.
>>>>>
>>>>> And how do you characterize the difference between RTTY 50% duty
>>>>> cycle for two hours, versus CW duty cycle for two hours?
>>>>> Does two hours matter? Why isn't a 30 minute test enough?
>>>>>
>>>>> Now the stuff about the low band coils is important. What that says
>>>>> to me is that there's an airflow issue in the box. The wires are
>>>>> undersized for the airflow they see.
>>>>>
>>>>> What I don't understand, is how long it took your solder to come
>>>>> undone in a contest? What was the ambient temp in the shack?
>>>>> Is it possible that there's a constant slow rise of temp at the coil
>>>>> during a contest, such that the failure needs a combination of high
>>>>> ambient temps, and maybe an hour or two of contesting? That doesn't
>>>>> seem to match what I saw, unless it's a behavior that happens at
>>>>> 1500W.
>>>>>
>>>>> Hmm..I'm wondering if what I thought was temperature stability in
>>>>> the box after 15 minutes, isn't stable. I didn't measure the coil
>>>>> area. Maybe I need to? I have a hard time believing that the coil
>>>>> area didn't temp stabilize in my 30 minute test. No coil melted in
>>>>> my 30 minute CQ test at 1200W (80M) into dummy load.
>>>>>
>>>>> Any idea what kind of antenna and SWR you had on 80M? I've not used
>>>>> the amp on 160m yet.
>>>>>
>>>>> I appreciated Tom, W8JI's responses. They made sense to me. He
>>>>> described his use of the amp at 4000v with assisted air (outside
>>>>> fan) but stock blower. Although he apparently doesn't do RTTY.
>>>>>
>>>>> I don't care about the ads. The reality in the ham world is that the
>>>>> users sort out what works and what doesn't and in what environment.
>>>>> That's the nature of the beast. Stuff that really sucks: people
>>>>> eventually stop buying.
>>>>>
>>>>> Hey BTW: in looking at other amps that people seem to like, a bunch
>>>>> seem to have significantly higher CFM blowers (I don't know about
>>>>> noise). I always wonder if a fairer comparison to the AL-1200 would
>>>>> be with an AL-1200 with equal CFM blower/dBA.
>>>>>
>>>>> If you're right that it's a coil wire size issue (maybe other
>>>>> issues), then yeah, maybe it's not that simple. I'm musing on the
>>>>> higher CFM blower, maybe dialed back a bit from full speed.
>>>>>
>>>>> thanks,
>>>>> -kevin
>>>>> ke6rad
>>>>>
>>>>>
>>>>>
>>>>>
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