[TenTec] Centurion & Tubes

Sat Aug 4 00:17:06 EDT 2018

Yeah, the fireworks can be an oh crap moment!

I hate to say it, but solid state amps are the future.  There are some 
really nice LDMOS amps offered as kits or complete amps from the big 
companies.

73

Stan
KM4HQE

On 08/03/2018 10:36 PM, Rick at dj0ip.de wrote:
> I put my 25 year old NOS into my AL-80A and let it cook for a while, then slowly applied power.
> I slowly ran the output power up until about 400w out.
> It increasingly was showing a light blue inside.
> Then pop, boom, BANG.  Blew the fuse in the house.
>
> I sold the amp, and sold the tube for 20 bucks.
> Now I run a transistorized amp.
>
> 73,
> Rick, DJ0IP
> (Nr. Frankfurt, Germany)
>
> -----Original Message-----
> From: TenTec <tentec-bounces at contesting.com> On Behalf Of Stan Gammons
> Sent: 04 August 2018 04:28
> To: tentec at contesting.com
> Subject: Re: [TenTec] Centurion & Tubes
>
> 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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