As I mentioned before, a big clue is given in the grid to cathode short
description.

It takes a heck of a lot of energy to make these tube elements repeatedly
short. A parasitic bang is just such an animal.

Rich not only sells the kits cheap, but he provides the information to
"roll your own" on his web site.

cheers
skipp
http://sonic.ucdavis.edu

: Dale J. wrote:
: 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 adds a little more wrote:

As I mentioned before, a big clue is given in the grid to cathode short
description.

It takes a heck of a lot of energy to make these tube elements repeatedly
short. A parasitic bang is just such an animal.

Rich not only sells the kits cheap, but he provides the information to
"roll your own" on his web site.

cheers
skipp
http://sonic.ucdavis.edu

: Dale J. wrote:
: 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

Hows come mine (AL-80A) doent parasite? I don't want to make a big
argument of this, but this has frustrated me with this talk of parasites
curing all the problems.

--
Dale J.
Bloomington, Minnesota

E-mail:

"Dale J. " wrote in message ...
In article ,
Skipp adds a little more wrote:

As I mentioned before, a big clue is given in the grid to cathode short
description.

It takes a heck of a lot of energy to make these tube elements repeatedly
short. A parasitic bang is just such an animal.

Rich not only sells the kits cheap, but he provides the information to
"roll your own" on his web site.

cheers
skipp
http://sonic.ucdavis.edu

: Dale J. wrote:
: 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

Hows come mine (AL-80A) doent parasite? I don't want to make a big
argument of this, but this has frustrated me with this talk of parasites
curing all the problems.


Its been pointed out to me that I have been an unhelpful old grump -
and, re-readinfg the Amateurs Code, I can see its true. My aplogies
all round - should have engaged brain before opening mouth.

Its an interesting fault - have downloaded the MFJ manual and will
study it when I have some spare time. However, a few comments in the
meantime...

1. If there was a faulty batch of tubes, they would have been cleared
out by now - MFJ would have had words with Amperex, so they can be
eliminated as future fault causes.

2. is it a design error - possibly, but then again MFJ would be aware
of it by now and offered a correction - this company would not stay in
business in the Amateur Radio marketplace if it didnt.

3. The filaments high at 5.7 volts - it can be safely assumed that MFJ
would have set them up properly at the factory - this suggests that
the AC line voltage is high - variations are not unknown (here its
plus/minus 10% on 240VAC - fine, except when it causes marginally
rated 220V European equipment to die - took me a while to figure
that one out....). Check the AC line voltage with a KNOWN ACCURATE
voltmeter (I like Fluke, because they come out of the factory set up
properly) and adjust transformer taps if necessary.

4. is it a parasitic oscillation - the traditional check is to swing
the plate tune capacitor acrtoss its range and check for multiple
small dips - if so, there is one. A more scientific way is to use a
spectrum analyser if available, a cheap way out there is to sit a
scanner near it and tune across every band etc and look for birdies
etc.

5. the dynamic bias (good way for QSK switching) and ALC circuit in
this thing looks interesting - possibly a fault there (which would
explain why the AL80A doesnt have problems - its fixed bias) - but
this is speculation, as I said I havent had time to check/compare both
circuits or analyse how the AL80B circuit is suppossed to work.

Anyway, again my aplogies to the group for being a Grump - will try
not to do it again.

73 de VK3BFA Andrew

"Dale J. " wrote in message ...
In article ,
Skipp adds a little more wrote:

As I mentioned before, a big clue is given in the grid to cathode short
description.

It takes a heck of a lot of energy to make these tube elements repeatedly
short. A parasitic bang is just such an animal.

Rich not only sells the kits cheap, but he provides the information to
"roll your own" on his web site.

cheers
skipp
http://sonic.ucdavis.edu

: Dale J. wrote:
: 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

Hows come mine (AL-80A) doent parasite? I don't want to make a big
argument of this, but this has frustrated me with this talk of parasites
curing all the problems.


Its been pointed out to me that I have been an unhelpful old grump -
and, re-readinfg the Amateurs Code, I can see its true. My aplogies
all round - should have engaged brain before opening mouth.

Its an interesting fault - have downloaded the MFJ manual and will
study it when I have some spare time. However, a few comments in the
meantime...

1. If there was a faulty batch of tubes, they would have been cleared
out by now - MFJ would have had words with Amperex, so they can be
eliminated as future fault causes.

2. is it a design error - possibly, but then again MFJ would be aware
of it by now and offered a correction - this company would not stay in
business in the Amateur Radio marketplace if it didnt.

3. The filaments high at 5.7 volts - it can be safely assumed that MFJ
would have set them up properly at the factory - this suggests that
the AC line voltage is high - variations are not unknown (here its
plus/minus 10% on 240VAC - fine, except when it causes marginally
rated 220V European equipment to die - took me a while to figure
that one out....). Check the AC line voltage with a KNOWN ACCURATE
voltmeter (I like Fluke, because they come out of the factory set up
properly) and adjust transformer taps if necessary.

4. is it a parasitic oscillation - the traditional check is to swing
the plate tune capacitor acrtoss its range and check for multiple
small dips - if so, there is one. A more scientific way is to use a
spectrum analyser if available, a cheap way out there is to sit a
scanner near it and tune across every band etc and look for birdies
etc.

5. the dynamic bias (good way for QSK switching) and ALC circuit in
this thing looks interesting - possibly a fault there (which would
explain why the AL80A doesnt have problems - its fixed bias) - but
this is speculation, as I said I havent had time to check/compare both
circuits or analyse how the AL80B circuit is suppossed to work.

Anyway, again my aplogies to the group for being a Grump - will try
not to do it again.

73 de VK3BFA Andrew

In article ,
Skipp adds a little more wrote:

As I mentioned before, a big clue is given in the grid to cathode short
description.

It takes a heck of a lot of energy to make these tube elements repeatedly
short. A parasitic bang is just such an animal.

Rich not only sells the kits cheap, but he provides the information to
"roll your own" on his web site.

cheers
skipp
http://sonic.ucdavis.edu

: Dale J. wrote:
: 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

Hows come mine (AL-80A) doent parasite? I don't want to make a big
argument of this, but this has frustrated me with this talk of parasites
curing all the problems.

--
Dale J.
Bloomington, Minnesota

E-mail:

As I mentioned before, a big clue is given in the grid to cathode short
description.

It takes a heck of a lot of energy to make these tube elements repeatedly
short. A parasitic bang is just such an animal.

Rich not only sells the kits cheap, but he provides the information to
"roll your own" on his web site.

cheers
skipp
http://sonic.ucdavis.edu

: Dale J. wrote:
: 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

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:

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