[TenTec] Centurion & Tubes

[Stan Gammons]

Hi Bob,

The 3-500 is subject to going gassy.  IF and that's a big if, I put the 
old Eimac 3-500 in the amp (best I can read the date code on it, it was 
made in 1979); I'll bring the amp up with a variac.  The variac I have 
is 110/120 volts, so I'd have to re-wire the amp since it's wired for 
220 volts.  Yes, when a tube flashes over; it's fireworks for sure!


73

Stan
KM4HQE

On 08/03/2018 09:08 PM, Bob McGraw K4TAX wrote:
> A comment on 3-500 type tubes.  These types of tubes have an extremely 
> high vacuum.   NOS units are subject to air leakage into the envelope 
> around the pin seals.  The coated anode in the 3-500Z and 3-500ZG 
> serves as the getter to burn the extraneous air out of the envelope.   
> It is a very incorrect belief of many hams that having the filament on 
> for a few hours will burn the air out. This is not true with this type 
> of tube thus having only the filament on serves no useful purpose.  
> The only correct way to burn the air out is to have the tube 
> operational and with enough voltage and current to cause the anode to 
> show color.   It is this heat and chemical action of the anode coating 
> that removes the extraneous air from the envelope.
>
> Other smaller tubes may have a getter that is ignited by external 
> microwave energy.  Once the getter is ignited, it is consumed, and any 
> leakage from that point forward will only deteriorate the tube.  
> Again, having the filament on for some hours does no good in this regard.
>
> External anode tubes, such as the 3CXxxx and 4CXxxx types, are 
> different designs and thus running the heater will remove any remnants 
> of air leakage as the getter is part of the cathode coating.
>
> If you intend to prepare a 3-500ZG or such, a filament supply, an 
> adjustable bias supply, and an adjustable HV supply, with proper 
> metering for each supply is the correct way to static burn in this 
> type tube.  The values are adjusted such that anode does show color. 
>    Just putting the tube in an amplifier and hitting the switch will 
> most likely produce a flash, bang, pop and the smoke may then exit the 
> box.
>
> 73
>
> Bob, K4TAX
>
>
> On 8/3/2018 8:30 PM, Stan Gammons wrote:
>> I think most/all of the 3-500's are made in China now.  One can still 
>> find some Eimac's that may still be good after all these years.  The 
>> near 40 year old one I have may still be good.  Need to put it in my 
>> L-4B some times and see. This is what we get for outsourcing so much 
>> of our manufacturing to China.  I've said for many years that that 
>> was a bad idea. At one time Amperex tubes were made in France.  Don't 
>> know if that's still the case.  I'm thinking no.  Maybe we can talk 
>> CPI/Eimac into making 3-500's here again? Probably not, but might be 
>> worth a try.
>>
>> 73
>>
>> Stan
>> KM4HQE
>>
>>
>> On 08/03/2018 08:12 PM, Bob McGraw K4TAX wrote:
>>> Yes, thanks to the new tariffs we can expect tube prices to go 
>>> through the roof.   Most tubes are made in China and branded under a 
>>> US company.   a.k.a. RF Parts.
>>>
>>> Bob, K4TAX
>>>
>>>
>>> Sent from my iPhone
>>>
>>>> On Aug 3, 2018, at 5:03 PM, Carter <k8vt at ameritech.net> wrote:
>>>>
>>>>> On 8/3/2018 4:45 PM, Greg S via TenTec wrote:
>>>>> There will be a price increase SOON. RF Parts apparently will no 
>>>>> longer be importing Chinese tubes.
>>>> Hmmm...bad news, as I thought China was the *only* one making 
>>>> 3-500s. If not China, who else?
>>>>
>>>> Carter
>>>> K8VT
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