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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