The 10811 that I have has a decal on it that reads "upgraded to series
3010". Do you know what that means?

Lefty-

The 10811-60111 that came in my used HP 5334B counter, had a blown thermal
fuse. Upon considerable investigation, I found that it was a common problem
and had been addressed by HP, using fuse with a higher temperature rating. It
is possible that your 3010 refers to the thermal fuse upgrade.

Incidentally, the going price for a used 10811-60111 was around $100 a couple
of years ago. I trusted a guy and ended up with a second unit that also had a
blown thermal fuse!

73, Fred, K4DII

AFAIK, the 3010 sticker has nothing to do with the thermal
fuse issue. The thermal fuse was a debacle from the get go.
If your fuse fails, just replace it with a piece of wire. Ovens
very rarely run away. It is far more likely the fuse will fail
or its socket will corrode (can't solder it in because the solder
would melt the fuse). If the oven does run away, the heater
transistors will open up and serve as fuses.

Rick N6RK

"Fred McKenzie" wrote in message
...
The 10811 that I have has a decal on it that reads "upgraded to series
3010". Do you know what that means?

Lefty-

The 10811-60111 that came in my used HP 5334B counter, had a blown thermal
fuse. Upon considerable investigation, I found that it was a common
problem
and had been addressed by HP, using fuse with a higher temperature rating.
It
is possible that your 3010 refers to the thermal fuse upgrade.

Incidentally, the going price for a used 10811-60111 was around $100 a
couple
of years ago. I trusted a guy and ended up with a second unit that also
had a
blown thermal fuse!

73, Fred, K4DII

In article 0ZxIc.58659$JR4.11986@attbi_s54,
says...
AFAIK, the 3010 sticker has nothing to do with the thermal
fuse issue. The thermal fuse was a debacle from the get go.
If your fuse fails, just replace it with a piece of wire. Ovens
very rarely run away. It is far more likely the fuse will fail
or its socket will corrode (can't solder it in because the solder
would melt the fuse). If the oven does run away, the heater
transistors will open up and serve as fuses.


I'd always assumed it was there to avoid heat-damage to the expensive
part (the crystal). Unfortunately, it was mounted far outside the
thermal enclosure for the crystal and its oven, so it's unlikely to
detect any failure condition short of a house fire.

-- jm

------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------

The crystal will not be damaged by any temperature the oven
is capable of.

Rick N6RK

"John Miles" wrote in message
...

I'd always assumed it was there to avoid heat-damage to the expensive
part (the crystal). Unfortunately, it was mounted far outside the
thermal enclosure for the crystal and its oven, so it's unlikely to
detect any failure condition short of a house fire.

-- jm

Ovens
very rarely run away. It is far more likely the fuse will fail
or its socket will corrode (can't solder it in because the solder
would melt the fuse). If the oven does run away, the heater
transistors will open up and serve as fuses

Rick-

I've seen photos of these ovens on E-Bay, that had been stained by smoke coming
out of the adjustment hole. I'd rather have some kind of protection.

I believe the oven uses proportional control, so the transistors' maximum
dissipation would occur when the heating element is half on. In a "runaway"
mode, the transistors would be switched on with maximum current but nearly zero
voltage. Also, one transistor failure mode is a short-circuit.

With regard to John Miles' comment about the thermal fuse being to far from the
oven's heating element to be effective, perhaps that is true. However, the
earlier thermal fuse was rated at 108 degrees C, and it occasionally would open
in an oven that was apparently operating correctly in the range of 80 to 84
degrees C. The newer fuse is rated at 115 degrees C. I suspect the problem is
that it is opening due to a combination of time and temperature, not
temperature alone.

I've been running one of the new parts for about two years without a hitch.
The frequency has not been adjusted since about two years ago, and it still
takes 15 or 20 seconds to drift one Hz against a 10 MHz rubidium oscillator.

That HP 5334B is one nice counter!

73, Fred, K4DII

The insulation turns brown with age even in the absence
of smoke.

Rick N6RK

"Fred McKenzie" wrote in message
...
Ovens
very rarely run away. It is far more likely the fuse will fail
or its socket will corrode (can't solder it in because the solder
would melt the fuse). If the oven does run away, the heater
transistors will open up and serve as fuses

Rick-

I've seen photos of these ovens on E-Bay, that had been stained by smoke
coming
out of the adjustment hole. I'd rather have some kind of protection.

I believe the oven uses proportional control, so the transistors' maximum
dissipation would occur when the heating element is half on. In a
"runaway"
mode, the transistors would be switched on with maximum current but nearly
zero
voltage. Also, one transistor failure mode is a short-circuit.

With regard to John Miles' comment about the thermal fuse being to far
from the
oven's heating element to be effective, perhaps that is true. However,
the
earlier thermal fuse was rated at 108 degrees C, and it occasionally would
open
in an oven that was apparently operating correctly in the range of 80 to
84
degrees C. The newer fuse is rated at 115 degrees C. I suspect the
problem is
that it is opening due to a combination of time and temperature, not
temperature alone.

I've been running one of the new parts for about two years without a
hitch.
The frequency has not been adjusted since about two years ago, and it
still
takes 15 or 20 seconds to drift one Hz against a 10 MHz rubidium
oscillator.

That HP 5334B is one nice counter!

73, Fred, K4DII

In article ,
Fred McKenzie wrote:

Rick-

I've seen photos of these ovens on E-Bay, that had been stained by smoke coming
out of the adjustment hole. I'd rather have some kind of protection.

I believe the oven uses proportional control, so the transistors' maximum
dissipation would occur when the heating element is half on. In a "runaway"
mode, the transistors would be switched on with maximum current but nearly zero
voltage. Also, one transistor failure mode is a short-circuit.

Seems like a self-resetting "Polyswitch" overcurrent limiter might be
a workable alternative. You'd probably want to pick one whose "will
pass" current is somewhat above the highest amount of current that the
oven would draw when it's quite cold. If the transistor shorts, and
the oven draws more current than that, the polyswitch would heat up
enough to go high-Z and chop off the current. Cutting power for a
minute or so would reset it.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

The runaway oven problem isn't caused by too much transistor
current, rather it is caused by the transistor staying on too long.
Thus a current based system wouldn't work. Also, in the case
of the 5334A, the power supply is barely able to supply minimum
current for warmup, so the oscillator couldn't draw more than
normal warmup current even if it tried. In the 5334B, I improved
the power supply so that it warms up the oscillator in half the
time or less compared to the 34A.

Rick N6RK


"Dave Platt" wrote in message
...
In article ,
Fred McKenzie wrote:

Rick-

I've seen photos of these ovens on E-Bay, that had been stained by smoke
coming
out of the adjustment hole. I'd rather have some kind of protection.

I believe the oven uses proportional control, so the transistors' maximum
dissipation would occur when the heating element is half on. In a
"runaway"
mode, the transistors would be switched on with maximum current but
nearly zero
voltage. Also, one transistor failure mode is a short-circuit.

Seems like a self-resetting "Polyswitch" overcurrent limiter might be
a workable alternative. You'd probably want to pick one whose "will
pass" current is somewhat above the highest amount of current that the
oven would draw when it's quite cold. If the transistor shorts, and
the oven draws more current than that, the polyswitch would heat up
enough to go high-Z and chop off the current. Cutting power for a
minute or so would reset it.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Hi All,

I had thought the output transistors are the heaters; Q7 and Q8.

There's a couple low wattage resistors in series with transistors for some protection too.

Regards,

Bill Hall
N6TKC