Amps
[Top] [All Lists]

Re: [Amps] Advice

To: "'Paul Decker'" <kg7hf@comcast.net>, <garyschafer@comcast.net>
Subject: Re: [Amps] Advice
From: "Joe Subich, W4TV" <lists@subich.com>
Reply-to: lists@subich.com
Date: Sun, 6 Dec 2009 00:40:46 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>

The current Eimac data sheet gives the cooling requirements 
at sea level as:  

   Anode    CFM      Pressure 
   Diss              In. Water 
---------------------------------
   400        6        0.09 
   600       11        0.20 
   800       19        0.50 


However, the original (1983) Eimac data sheet for the 3CX800 
gave the following: 

   Anode    CFM      Pressure 
   Diss              In. Water 
--------------------------------- 
   800       19        0.35 


> The cooling requirements are the same per watt of dissipation 
> for the 8877 as they are for the 3CX800. 

Not according to the Eimac data sheet (1971) for the 8877 

   Anode    CFM      Pressure 
   Diss              In. Water 
--------------------------------- 
    500     7.7        0.10 
   1000    20.3        0.23 


Each of the points has a different cfm/W value: 
     6/400 <> 19/800 <> 7.7/500 <> 20.3/1000 

73, 

   ... Joe, W4TV 
 

> -----Original Message-----
> From: amps-bounces@contesting.com 
> [mailto:amps-bounces@contesting.com] On Behalf Of Paul Decker
> Sent: Sunday, December 06, 2009 12:11 AM
> To: garyschafer@comcast.net
> Cc: amps@contesting.com
> Subject: Re: [Amps] Advice
> 
> 
> 
> 
> Hi Gary, 
> 
> 
> 
> I don't know if it's a linear relation.   Perhaps a typo, but 
> on page 13.19 of the 1995 handbook, it says 12 CFM at 0.09" 
> back pressure for two 3cx800's operating at 400 Watts 
> dissipation each. 
> 
> 
> 
> Paul (KG7HF) 
> 
> 
> ----- Original Message ----- 
> From: "Gary Schafer" <garyschafer@comcast.net> 
> To: "Paul Decker" <kg7hf@comcast.net> 
> Cc: amps@contesting.com 
> Sent: Saturday, December 5, 2009 11:57:34 PM GMT -05:00 
> US/Canada Eastern 
> Subject: RE: [Amps] Advice 
> 
> 
> 
> 
> Hi Paul, 
> 
> I didn’t mean that I didn’t understand the 2 nd paragraph but 
> that I didn’t read it. I just overlooked it when I read your 
> first post with it. 
> 
> 
> 
> I do think that you have the cooling requirements wrong for 
> the 3CX800 though. I got the info from the 2000 ARRL handbook 
> section on amplifiers. There is a table there that list the 
> cooling requirements. 
> 
> The cooling requirements are the same per watt of dissipation 
> for the 8877 as they are for the 3CX800. 
> 
> 
> 
> By the way I see that I made a type in one place where I show 
> .03333 cu ft/watt. It should be .02333 cu ft/watt. 
> 
> 
> 
> At 400 watts dissipation each they should require around 
> (.02333 x 400) 9.3 cu ft of air each or 18.6 for a pair for 
> 800 watts dissipation. 
> 
> 
> 
> A single 3CX800 operated at 800 watts dissipation would 
> require 19 cu ft of air per the chart at .5 back pressure. 
> 
> 
> 
> 73 
> 
> Gary  K4FMX 
> 
> 
> 
> 
> 
> 
> 
> From: Paul Decker [mailto:kg7hf@comcast.net] 
> Sent: Saturday, December 05, 2009 6:26 PM 
> To: garyschafer@comcast.net 
> Cc: amps@contesting.com 
> Subject: Re: [Amps] Advice 
> 
> 
> 
> 
> Hi Gary, 
> 
> The point of the second paragraph was that with a pair tubes 
> operating under their specificed dissipation rating require 
> less cooling then a single tube operating at or above its 
> dissipation range. 
> 
> 
> 
> Two 3cx800's operating at legal limit only require 12 CFM at 
> about 0.09 - 0.1" of back pressure, this is because the tubes 
> are only operating at 400W dissipation each.   
> 
> 
> 
> 
> 
> Paul Decker (KG7HF) 
> 
> 
> ----- Original Message ----- 
> From: "Gary Schafer" <garyschafer@comcast.net> 
> To: garyschafer@comcast.net, "Paul Decker" 
> <kg7hf@comcast.net>, amps@contesting.com 
> Sent: Saturday, December 5, 2009 5:11:10 PM GMT -05:00 
> US/Canada Eastern 
> Subject: RE: [Amps] Advice 
> 
> Paul, sorry I missed your second paragraph. 
> Air flow needed depends on how much power is being 
> dissipated. If you divide 
> the airflow by the dissipation rating of the 8877 as an 
> example 35/1500 = 
> .02333 cu ft/watt. multiply that by 1600 (for a pair of 
> 3CX800s) and you get 
> 37.3 cu ft of air flow. The cooling efficiency of both are 
> about the same 
> .02333 cu ft/watt. 
> 
> So if you ran the pair of 3CX800s at the same power level as 
> the 3CX1500 it 
> would require just about the same amount of air flow. .03333 
> x 1500 on the 
> pair of 3CX800s = 35 cu ft. 
> 
> I don't know what the back pressure would look like on the 
> pair of 3CX800s 
> at reduced air flow but it would probably be pretty close to 
> the 3CX1500. 
> 
> 73 
> Gary K4FMX 
> 
> > -----Original Message-----
> > From: amps-bounces@contesting.com 
> [mailto:amps-bounces@contesting.com] 
> > On Behalf Of Gary Schafer 
> > Sent: Saturday, December 05, 2009 4:40 PM 
> > To: 'Paul Decker'; amps@contesting.com 
> > Subject: Re: [Amps] Advice 
> > 
> > The chart that I am looking at says: 8877 requires 35 cu ft at .41 
> > back
> > pressure. 
> > 
> > A 3CX800A7 requires 19 cu ft at .5 back pressure. Two of those would
> > require 
> > 38 cu ft at .5 back pressure. 
> > 
> > 73
> > Gary  K4FMX 
> > 
> > 
> > > -----Original Message-----
> > > From: amps-bounces@contesting.com 
> [mailto:amps-bounces@contesting.com] 
> > > On Behalf Of Paul Decker 
> > > Sent: Saturday, December 05, 2009 4:26 PM 
> > > To: amps@contesting.com 
> > > Subject: Re: [Amps] Advice 
> > > 
> > > 
> > > 
> > > When I was writing the original reply I was thinking more 
> along the
> > > lines of different tubes for example a single 8877 requires more 
> > airflow
> > > and has more back pressure than two 3cx800's.
> > > 
> > > 
> > > 
> > > Agreed, two tubes of the same type would require more 
> airflow than a
> > > single tube.  However, I think we could assume that two 
> tubes of the 
> > > same type would produce 2x the power of the single tube 
> amp.   If the 
> > > twin tube amp were run at the same output as the single holer, it 
> > would
> > > also follow to reason the airflow requirements could for the two 
> > > holer
> > > could be reduced because each tube is only being driven 
> to a reduced 
> > > output. 
> > > 
> > > 
> > > 
> > > Paul
> > > 
> > > 
> > > 
> > > 
> > > ----- Original Message -----
> > > From: "Gary Schafer" < garyschafer@comcast.net > 
> > > To: < dezrat1242@yahoo.com >; < amps@contesting.com > 
> > > Sent: Saturday, December 05, 2009 11:04 AM 
> > > Subject: Re: [Amps] Advice 
> > > 
> > > 
> > > There is no free lunch. While it may seem like you could 
> get by with
> > > less 
> > > air flow it doesn't follow. 
> > > A pair of tubes will require twice the air flow at the same back 
> > > pressure as 
> > > a single tube. Tubes being the same of course. 
> > > 
> > > 73
> > > Gary  K4FMX 
> > > 
> > > 
> > > 
> > > _______________________________________________
> > > Amps mailing list 
> > > Amps@contesting.com 
> > > http://lists.contesting.com/mailman/listinfo/amps 
> > 
> > _______________________________________________
> > Amps mailing list 
> > Amps@contesting.com 
> > http://lists.contesting.com/mailman/listinfo/amps
> _______________________________________________
> Amps mailing list
> Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps
> 

_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
<Prev in Thread] Current Thread [Next in Thread>