[Amps] 4CX1600B options

Carl km1h at jeremy.mv.com
Sun Apr 6 00:10:36 EDT 2014


Pop in a big GG triode and be done with it. Sell the tetrodes and sockets to 
someone really needing them.

Carl
KM1H


----- Original Message ----- 
From: "Alek Petkovic" <vk6apk at bigpond.com>
To: "AMPS" <amps at contesting.com>
Sent: Saturday, April 05, 2014 8:48 PM
Subject: Re: [Amps] 4CX1600B options


> Hi John.
>
> I don't know if this is the same fault but a few years ago, in my local 
> club's amp, which runs a similar but larger tube, the Russian GU84B, we 
> had a runaway situation. We found that the ZSAC was not staying constant. 
> it was rising and rising and we could not stop it. It became worse very 
> quickly and it did it even when the amp was not keyed. As the tube warmed 
> up after turn on, the plate current started rising and it didn't stop 
> until we turned it off.
>
> We changed out the tube for a new one and the problem went away.
>
> We did not have a hi pot tester. All we had was a 1000V megger and with 
> the tube cold, we could not find any evidence of any solid or partial 
> short. The fault only appeared when the tube was hot.
>
> I still have the dead tube here and I have a socket and filament 
> transformer as well. I was going to warm it up and see what I could see 
> with the megger. I guess lack of interest has kept me from doing it. I 
> will have to do it one day, as I have 3 tubes here and I can't remember 
> which one is the dud. I/we never marked it. Yeah. Pretty dumb!
>
> Maybe your GU91B (4CX1600B) is showing a similar fault. I have a spare one 
> of those here but I also have an amp that uses it and so it is not for 
> sale. There is a guy in ZL who has or had one or more for sale. He may be 
> a subscriber on this list.
>
> Your idea of a tube transplant sounds like the cheapest option though.
>
> Cheers, Alek
> VK6APK
>
> On 6/04/2014 7:24 AM, John Lyles wrote:
>> I have a Ten Tec Titan II model 416 with a supposedly bad tube, according 
>> to the factory. I haven't high potted it yet, and with an ohmmeter I 
>> measured clear between elements except there is 1.2 Meg ohm between 
>> heater and cathode ring. The 1600 has crossover geometry where the 
>> control grid contacts are completely below and inside of the cathode 
>> ring. For a 4CX1500B or 1000A with breechlock terminals G1 is between 
>> cathode and G2.
>>
>> It was said (by factory) that this tube blows up the amp. I assume they 
>> meant the screen regulator board or bias circuits. This may indicate a 
>> hot fault where anode is breaking down to the grid(s). Anyone else 
>> experienced this sort of failure with this tube/amp combo? The Titan II 
>> used bipolar series regulator, and the later Titan III (4CX800A) used a 
>> mosfet, both had shunt resistor of 15K only across G2 to K, for reverse 
>> screen current handling. The regulators were only capable of working 
>> positive current, with a series diode between them and the shunt R.
>>
>> Are there any more Svetlana 4CX1600B's available?
>>
>> I have both a 4CX1000A and 4CX1500B plus SK-800 socket and filament 
>> transformer. Cin, Cout and Cgp are the same for all three tubes. 
>> Transconductance of the 1600B is highest, followed by 1000A and 1500B.
>>
>> For cooling, taking an example of 1 kW anode dissipation at > 5000 feet 
>> above sea level, estimated air from datasheets:
>> Eimac 4CX1000A   ~32 cfm, ~0.3" water bp
>> Eimac 4CX1500B   ~21 cfm, 0.3"
>> Svet. 4CX1600B    27 cfm, 0.3"
>>
>> From the constant current curves, the biggest differences are noted. This 
>> is indicated by the different cutoff characteristics, where the 4CX1500B 
>> requires considerably less negative bias on G1 to cutoff the electron 
>> beam. The older Eimac and Svetlana are similar, ~-56 volts for 200-250 mA 
>> of Ib with Eb at 3 kV. Eimac 4CX1500B is plotted only with 225 volts of 
>> G2, whereas the other tubes are defined for 325 volts.
>>
>> From the collective wisdome here, I welcome experience/knowledge in 
>> converting from a Svetlana to Eimac tetrode in this amp. Or a reasonable 
>> source for 4CX1600B. I think conversion to a better screen regulator is 
>> needed too. I am not interested in a pair of 4CX800A/GU74b as I already 
>> have the bigger tubes and 800s are pricy and become rare as well.
>>
>> 73
>> John
>> K5PRO
>> _______________________________________________
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>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
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