Going by memory.....you have a switched bias circuit in that amp. It comes
on and off with voice peakes. Enables a cooler operation. That circuit is
having a problem. Ive heard of this before. But since I don't have an amp
like that I can only go by what I remembered.

Dan/W4NTI

"Chuck (Jack) Hawley" wrote in message
...
A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
or so. It just developed a grid-cath short. Supposedly there was a batch
of
tubes that were prone to go bad, but the latest ones from MFJ are supposed
to be ok. Apparently not or something is wrong with the amp. He's a good
operator and seems to be tuning and operating within safe limits for the
AL80B. The latest tube is an Amperex as was the first ones in the reported
bad batch. He reduced the filament voltage last time from 5.7 (from the
factory) to about 5 before the present tube was installed.
Any ideas?
Chuck, KE9UW

Going by memory.....you have a switched bias circuit in that amp. It comes
on and off with voice peakes. Enables a cooler operation. That circuit is
having a problem. Ive heard of this before. But since I don't have an amp
like that I can only go by what I remembered.

Dan/W4NTI

"Chuck (Jack) Hawley" wrote in message
...
A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
or so. It just developed a grid-cath short. Supposedly there was a batch
of
tubes that were prone to go bad, but the latest ones from MFJ are supposed
to be ok. Apparently not or something is wrong with the amp. He's a good
operator and seems to be tuning and operating within safe limits for the
AL80B. The latest tube is an Amperex as was the first ones in the reported
bad batch. He reduced the filament voltage last time from 5.7 (from the
factory) to about 5 before the present tube was installed.
Any ideas?
Chuck, KE9UW

Hi Chuck
You already fixed it. 5.7V on the

"Chuck (Jack) Hawley" wrote:

A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
or so. It just developed a grid-cath short. Supposedly there was a batch of
tubes that were prone to go bad, but the latest ones from MFJ are supposed
to be ok. Apparently not or something is wrong with the amp. He's a good
operator and seems to be tuning and operating within safe limits for the
AL80B. The latest tube is an Amperex as was the first ones in the reported
bad batch. He reduced the filament voltage last time from 5.7 (from the
factory) to about 5 before the present tube was installed.
Any ideas?
Chuck, KE9UW

Hi Chuck
You already fixed it. 5.7V on the

"Chuck (Jack) Hawley" wrote:

A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
or so. It just developed a grid-cath short. Supposedly there was a batch of
tubes that were prone to go bad, but the latest ones from MFJ are supposed
to be ok. Apparently not or something is wrong with the amp. He's a good
operator and seems to be tuning and operating within safe limits for the
AL80B. The latest tube is an Amperex as was the first ones in the reported
bad batch. He reduced the filament voltage last time from 5.7 (from the
factory) to about 5 before the present tube was installed.
Any ideas?
Chuck, KE9UW

Sorry I press send too early, The 5.7 volts on the filament will eat tubes in
a hurry, also, (In the Dark) look for plate choke shorting out,
I find weak points are the Bias circuit and the Bandswitch. I see many of them
that come in for repair with these being the most common problems.
But the 5.7V is a good start, I just can't see tubes being all bad. 73 Chris
VE3NGW/W4 Florida

"Chuck (Jack) Hawley" wrote:

A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
or so. It just developed a grid-cath short. Supposedly there was a batch of
tubes that were prone to go bad, but the latest ones from MFJ are supposed
to be ok. Apparently not or something is wrong with the amp. He's a good
operator and seems to be tuning and operating within safe limits for the
AL80B. The latest tube is an Amperex as was the first ones in the reported
bad batch. He reduced the filament voltage last time from 5.7 (from the
factory) to about 5 before the present tube was installed.
Any ideas?
Chuck, KE9UW

Sorry I press send too early, The 5.7 volts on the filament will eat tubes in
a hurry, also, (In the Dark) look for plate choke shorting out,
I find weak points are the Bias circuit and the Bandswitch. I see many of them
that come in for repair with these being the most common problems.
But the 5.7V is a good start, I just can't see tubes being all bad. 73 Chris
VE3NGW/W4 Florida

"Chuck (Jack) Hawley" wrote:

A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
or so. It just developed a grid-cath short. Supposedly there was a batch of
tubes that were prone to go bad, but the latest ones from MFJ are supposed
to be ok. Apparently not or something is wrong with the amp. He's a good
operator and seems to be tuning and operating within safe limits for the
AL80B. The latest tube is an Amperex as was the first ones in the reported
bad batch. He reduced the filament voltage last time from 5.7 (from the
factory) to about 5 before the present tube was installed.
Any ideas?
Chuck, KE9UW

The grid to cathode short is a clue... You might want to review the
parasitic issues with this and similar amplifiers. A parasitic "bang"
might be the source of this and or similar problems.

Have a look at Rich Measures (ag6k) web page... used to be at
http://www.vcnet.com/measures but is now moving (or has moved to)
http://www.somis.org

There are protections for grid to cathode shorts in 3-500z amps. I like to
use a proper triple bypassed grid resistor and have never had grid/cath
shorts in any amplifier with said after an upgrade to the parasitic
network(s).

If you have questions, you can contact me through the sonic server Email
icons or review Rich's web page and he will also reply to Emails.

cheers and good luck
skipp
http://sonic.ucdavis.edu

: "Chuck \(Jack\) Hawley" wrote:
: A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
: or so. It just developed a grid-cath short. Supposedly there was a batch of
: tubes that were prone to go bad, but the latest ones from MFJ are supposed
: to be ok. Apparently not or something is wrong with the amp. He's a good
: operator and seems to be tuning and operating within safe limits for the
: AL80B. The latest tube is an Amperex as was the first ones in the reported
: bad batch. He reduced the filament voltage last time from 5.7 (from the
: factory) to about 5 before the present tube was installed.
: Any ideas?
: Chuck, KE9UW

The grid to cathode short is a clue... You might want to review the
parasitic issues with this and similar amplifiers. A parasitic "bang"
might be the source of this and or similar problems.

Have a look at Rich Measures (ag6k) web page... used to be at
http://www.vcnet.com/measures but is now moving (or has moved to)
http://www.somis.org

There are protections for grid to cathode shorts in 3-500z amps. I like to
use a proper triple bypassed grid resistor and have never had grid/cath
shorts in any amplifier with said after an upgrade to the parasitic
network(s).

If you have questions, you can contact me through the sonic server Email
icons or review Rich's web page and he will also reply to Emails.

cheers and good luck
skipp
http://sonic.ucdavis.edu

: "Chuck \(Jack\) Hawley" wrote:
: A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
: or so. It just developed a grid-cath short. Supposedly there was a batch of
: tubes that were prone to go bad, but the latest ones from MFJ are supposed
: to be ok. Apparently not or something is wrong with the amp. He's a good
: operator and seems to be tuning and operating within safe limits for the
: AL80B. The latest tube is an Amperex as was the first ones in the reported
: bad batch. He reduced the filament voltage last time from 5.7 (from the
: factory) to about 5 before the present tube was installed.
: Any ideas?
: Chuck, KE9UW

I doubt it's a parasitic, but if you want to explore that, Measures has
his special parasitic kits for sale on his website.

Cheers as they say
Dale, K9VUJ






In article ,
Skipp can be reached through the sonic server
wrote:

The grid to cathode short is a clue... You might want to review the
parasitic issues with this and similar amplifiers. A parasitic "bang"
might be the source of this and or similar problems.

Have a look at Rich Measures (ag6k) web page... used to be at
http://www.vcnet.com/measures but is now moving (or has moved to)
http://www.somis.org

There are protections for grid to cathode shorts in 3-500z amps. I like to
use a proper triple bypassed grid resistor and have never had grid/cath
shorts in any amplifier with said after an upgrade to the parasitic
network(s).

If you have questions, you can contact me through the sonic server Email
icons or review Rich's web page and he will also reply to Emails.

cheers and good luck
skipp
http://sonic.ucdavis.edu

: "Chuck \(Jack\) Hawley" wrote:
: A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
: or so. It just developed a grid-cath short. Supposedly there was a batch of
: tubes that were prone to go bad, but the latest ones from MFJ are supposed
: to be ok. Apparently not or something is wrong with the amp. He's a good
: operator and seems to be tuning and operating within safe limits for the
: AL80B. The latest tube is an Amperex as was the first ones in the reported
: bad batch. He reduced the filament voltage last time from 5.7 (from the
: factory) to about 5 before the present tube was installed.
: Any ideas?
: Chuck, KE9UW



--
Dale J.
Bloomington, Minnesota

E-mail:

I doubt it's a parasitic, but if you want to explore that, Measures has
his special parasitic kits for sale on his website.

Cheers as they say
Dale, K9VUJ






In article ,
Skipp can be reached through the sonic server
wrote:

The grid to cathode short is a clue... You might want to review the
parasitic issues with this and similar amplifiers. A parasitic "bang"
might be the source of this and or similar problems.

Have a look at Rich Measures (ag6k) web page... used to be at
http://www.vcnet.com/measures but is now moving (or has moved to)
http://www.somis.org

There are protections for grid to cathode shorts in 3-500z amps. I like to
use a proper triple bypassed grid resistor and have never had grid/cath
shorts in any amplifier with said after an upgrade to the parasitic
network(s).

If you have questions, you can contact me through the sonic server Email
icons or review Rich's web page and he will also reply to Emails.

cheers and good luck
skipp
http://sonic.ucdavis.edu

: "Chuck \(Jack\) Hawley" wrote:
: A friend has an AL80B (bought new) and is on his fourth 3-500 in two years
: or so. It just developed a grid-cath short. Supposedly there was a batch of
: tubes that were prone to go bad, but the latest ones from MFJ are supposed
: to be ok. Apparently not or something is wrong with the amp. He's a good
: operator and seems to be tuning and operating within safe limits for the
: AL80B. The latest tube is an Amperex as was the first ones in the reported
: bad batch. He reduced the filament voltage last time from 5.7 (from the
: factory) to about 5 before the present tube was installed.
: Any ideas?
: Chuck, KE9UW



--
Dale J.
Bloomington, Minnesota

E-mail: