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Re: [Amps] How to read the 3-500Z spec sheet?

Subject: Re: [Amps] How to read the 3-500Z spec sheet?
Date: Sun, 23 May 2010 09:30:48 EDT
List-post: <">>
Bill, considering you can run up to 3500 volts on the 3-500, the 1950v you  
have is low.  When you raise the plate voltage you lower the amount of  
plate current and grid current you need for a given output which is a good  
thing,  However the bottom line still comes down to plate  dissipation.  I 
would say that 520 mills at CCS for the 3-500 is high,  however not for SSB.  
I'd like to see you up the plate voltage in that  amp.  It might be difficult 
to read the seal temperature of a tube in the  socket.  I wonder if there is 
a envelope temperature you can read  which would be easier, although I 
suppose that could be good and the seal temp  could be bad depending on how the 
air distributes around the tube.  My  guess would be that seal temperature  
would be best managed by a  pressurized plenum using chimneys for CCS 
operation.  Seems like some other  types of amps with fan cooling do not keep 
seals cool enough during CCS  operation.  Some 3-500 tube pins melt the 
solder on the pins they get so  hot when run in CCS operation.  
In a message dated 5/23/2010 9:13:07 A.M. Eastern Daylight Time, writes:

Thanks, Lou.  There is little info available about  this homebrew amp so 
I'm just trying to be safe.  Have not yet  tried it in WSJT mode but tube 
appears normal in color during my testing  so far.  The amp has 2 fans so 
hopefully cooling will be  adequate.  The spec sheet says max 200C at the base 
seals and 225C  at the plate seal.  The infrared thermometer is a good  idea.

What this amp really needs, I think, is higher plate  voltage.  This 
transformer was intended for the tubes in an SB-200,  not for a 3-500Z.  It 
to me that 400w key down is about the  best I can hope for with just 1950v 
on the plate.  The .52a key  down current is higher than the .4a "singletone" 
on the spec sheet and  was not sure if that was a concern.

73, Bill 

--- On  Sun, 5/23/10, <>  wrote:

From: <>
Subject: Re: [Amps] How  to read the 3-500Z spec sheet?
Date: Sunday, May 23, 2010, 8:37 AM

Bill, Any tube run within its specified limits is OK, however  with ham 
radio the limiting factor is cooling.  You have to take  into account that tube 
specs are listed for CCS operation.  This  assumes that the tube is 
receiving the specified amount of cooling  which is ALSO a spec on the tube 
chart.  So the question to  your question is this.  Does your amp provide a 
CCS rated amount  of cooling?  This is not an answer to your question but 
rather  the information you really want to know.  If you could find the  
operating temperature of the glass envelope of the 3-500, you can buy  a rather 
inexpensive infra red thermometer and shoot the temperature  of the envelope 
when you are running WSJT at the end of the  transmission and see what the 
temperature is and if it is in the  ballpark.  On the other hand perhaps 
someone knows for sure what  the level of cooling is in your amp and if it is 
up to the CCS  rating of the tube.  If you are savvy about the anode color 
of a  3-500 under normal CCS operation you can probably tell if the tube is  
within limits.  I don't know if this helped you, but I think this  is the 
information you are after.  Lou
In a message dated 5/23/2010 8:25:43 A.M. Eastern Daylight Time, writes:

Does anyone have any further thoughts or comments on  this?  Is it OK to 
put the amp into WSJT service at 400  watts?

73, Bill NZ5N

--- On Sat, 5/22/10, Bill  Dzurilla <> wrote:

> From: Bill  Dzurilla <>
> Subject: Re: How to  read the 3-500Z spec sheet?
> To:
>  Date: Saturday, May 22, 2010, 5:54 PM
> Thanks for the reply,  but I don't
> think I follow.
> Guess I had  interpreted the spec sheet as meaning that, if
> you configure  the tube in class B grounded grid and apply HV
> of 2000v, you  should expect to see 400ma of plate current
> and 500 watts of  peak "useful" output.
> I am just trying to figure  out if this homebrew amp, which
> does not have any manual or  detailed info, is working as it
> should.  If the spec  sheet means what I think it means,
> it seems the amp is in  the ballpark.
> 73, Bill NZ5N
> >Spec sheets  don't know anything about load or no load.
> If it says  for
> >example, 3000 volts at 500 mA, that's what it means.  
> >73, Bill W6WRT
> ---  On Sat, 5/22/10, Bill Dzurilla <>
>  wrote:
> > From: Bill Dzurilla  <>
> > Subject: How to read the  3-500Z spec sheet?
> > To:
> >  Date: Saturday, May 22, 2010, 10:39 AM
> > Hi,
> >  
> > I'm looking at the spec sheet for the 3-500Z  at
> >
> >  
> > At the top of the second pages, it gives numbers  for
> > various parameters at different levels of  high
> voltage
> > (3000, 2500, 2000, and  1500).  Are these voltages at
> > load or  no-load?  And how do Single-Tone DC Plate
> > Current  and Peak Envelope Useful Output Power
> correlate with
>  > key down plate current and output?
> > 
> >  The reason I ask is because I picked up a homebrew 6m
>  amp
> > with a single 3-500Z, which uses a power  transformer
> from an
> > SB-200.  Key down  power output is 400w.  Assuming
> > the amp's meters  are accurate, no-load plate voltage
> is
> > 2300v,  and plate voltage under full load is 1950v. 
> > Plate  current with no drive is 100ma and plate current
>  with
> > full drive is .52a.  About 40 watts of  drive
> produces
> > the full 400w out.  Further  increases in drive, up
> to
> > 100w, do not increase  output.
> > 
> > Judging from the spec sheet's  2000v table, my guess is
> that
> > the amp is  performing as well as it can with this
> power
> >  supply.  I know that a converted AL-80B with a
>  single
> > 3-500Z can produce 900w or so on 6m, but it has  a
> 3000v
> > p/s.
> > 
> > Do you  think it would be OK to run this amp at the
> full
>  > 400w in WSJT (continuous carrier) modes?
> > 
>  > 73, Bill NZ5N 
> > 
> > 
> >    
> > 

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