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@contesting.com> On Behalf Of Stan Gammons
Sent: 04 August 2018 04:28
To: tentec@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@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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