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Re: [Amps] Item # 170692212503

To: Sam Carpenter <>
Subject: Re: [Amps] Item # 170692212503
From: "Roger (sub1)" <>
Date: Fri, 09 Sep 2011 21:54:51 -0400
List-post: <">>
On 9/8/2011 10:01 AM, Sam Carpenter wrote:
> These are two totally different amps. The one with the 4cx1500b is new and
> is basically the Eimac type 4cx1000 with more dissipation. The older 4cx1600
> is a Svetlana type (Russian) tube. No interchange except that Svetlana
> renamed the tube to sound like an American type (EimacType). I understand
> that the tube in russian nomenclature has a 2500-3000w dissipation but if
> they said that, they might have had fcc acceptance problems and downrated it
> for the American market.

Although a good many tubes get over rated when I look at the 4CX-1600B 
the anode doesn't look anywhere near capable of the dissipation of the 
GU-84B (4CX2500).  How much emission it had, I don't know.  For example 
the 4CX1500B doesn't have a lot of excess emission, yet it has a 1500 
watt anode. I don't think, but don't know for sure Carl probably does) 
that running a 4CX1500B in AB1 or 2  you couldn't even reach the tubes 
rated dissipation.   OTOH the Chinese FU728F which has a slightly larger 
anode than the 4CX1500B (1/2" taller but is the electrical equivalent )  
only is rated at 1200 watts dissipation, BUT it will easily run 2KW 
nominal, or 2500 watts PEP output. 2 KW nominal at 60% would use the 
1200 watts nominal  and it has the emission to run 2.5KW PE

I have heard the renumbered 4CX800s only have a 600 watt anode, but 
that's still plenty for running the legal limit.  OTOH if you want to 
run the legal limit class A you are going to need some serious tubes 
with at least 3 KW anode dissipation.

Tubes that will work in legal limit amps are fast becoming expensive.


Roger (K8RI)
> -----Original Message-----
> From: [] On
> Behalf Of Roger (sub1)
> Sent: Thursday, September 08, 2011 2:11 AM
> To:
> Subject: Re: [Amps] Item # 170692212503
> On 9/6/2011 3:02 PM, Roger (sub1) wrote:
>> I was reading the description of this Alpha 6-meter amp that claims
>> "Robust 4CX1600B (Svetlana GU-91B) which is very affordable and readily
>> available."
>> ** Has the 4CX1600B gone back into production? It's listed as a GU-91B
>> from the company that took over Svetlana but I've not found any source
>> for them.
> The last 6-meter Alpha I saw advertised (on their site) uses a
> 4CX1500B.  I'd think a good replacement might be the Chinese FU728F.  As
> the FU728F has a slightly larger centering pin (bout 0.003") it should
> fit the socket nicely.  The only change needed would be a different
> filament voltage and adjust the bias. It should add a good 30% of
> available overhead.  Only downside I can see is what appears to be a
> rather high infant mortality rate for the FU728F
> 73
> Roger (K8RI)
>> 73
>> Roger (K8RI)
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