I have a LK 500NTC (no tune) amp that ran well for several years. Now one
of the 3-500Z's (both Eimac)
filament pins came unsoldered.

K4DLI helped me resolder the pin with a torch and silver solder. Just for a
test I swaped the tubes and within a week the other tube had unsoldered.

I had this problem in a Henry 2K with the tube not fully sitting in the
socket but the 3-500Z's are firmly in the socket. I have a new tube socket
to install but is this the only problem? I really see nothing wrong with
the old socket. Filament voltage is 5V as it should be
on all pins.

Ideas?

Thanks in advance.

73 Dave K4JRB

Hi David from Ken in the UK,

This is a common fault with these valves ( tubes ).
It's due to heat built-up over time.
The only solution that I know of is to blow cold air up around the valve
pins.
One final point, to extend the life of the '500Z' is to lower the heater
voltage to around 4.75v. This will save the valve from premature filament
failure.

Hope this helps, cheers, Ken, G4KIR.

"David Thompson" wrote in message
nk.net...
I have a LK 500NTC (no tune) amp that ran well for several years. Now one
of the 3-500Z's (both Eimac)
filament pins came unsoldered.

"David Thompson" wrote in message
nk.net...
I have a LK 500NTC (no tune) amp that ran well for several years. Now one
of the 3-500Z's (both Eimac)
filament pins came unsoldered.

K4DLI helped me resolder the pin with a torch and silver solder. Just for
a
test I swaped the tubes and within a week the other tube had unsoldered.

I had this problem in a Henry 2K with the tube not fully sitting in the
socket but the 3-500Z's are firmly in the socket. I have a new tube
socket
to install but is this the only problem? I really see nothing wrong with
the old socket. Filament voltage is 5V as it should be
on all pins.

Ideas?

Thanks in advance.

73 Dave K4JRB


Seems like you already know if the contact in the socket is "leaking" the
filament pin will get hot. It's not hard to check.

Al WB7NXB

David Thompson wrote:
I have a LK 500NTC (no tune) amp that ran well for several years. Now one
of the 3-500Z's (both Eimac)
filament pins came unsoldered.

K4DLI helped me resolder the pin with a torch and silver solder. Just for a
test I swaped the tubes and within a week the other tube had unsoldered.

I had this problem in a Henry 2K with the tube not fully sitting in the
socket but the 3-500Z's are firmly in the socket. I have a new tube socket
to install but is this the only problem? I really see nothing wrong with
the old socket. Filament voltage is 5V as it should be
on all pins.

Ideas?

Thanks in advance.

73 Dave K4JRB


Regarding your filament problem. Look for the November and December
1990 QST, "Circuit improvements for the Heath SB-220 Amplifier Part 1
and Part 2." Your answer is there. For example: One weakness in the
SB-220's cooling system is that the infared radiation (heat) reflected
back into the tubes from the bright aluminum surfaces adjacent and
parallel to the anodes shortens tube life. This deficiency is easily
corrected: After removing the tubes, apply black liquid shoe polish to
the vertical aluminum surfaces near the tubes. In the design of your
Amplifier, are the filament pins facing each other so the air from your
blower is creating the maximum cooling? Does the blower direct the
flow of air above and below the chassis at the same time? These
criteria are important. The fans have to be lubricated at least once a
year with thin non gumming oil such as Hoppe's no. 1003. A drop or two
will do, more oil is not better, just messier. 73, Bob, VE6RI.