Topics

Audio foo foo & 3A6 question


Steve B.
 

--- In TekScopes@y..., "Phil (VA3UX)" <phil@v...> wrote:

Relax Steve. A bit of humor, venting and off-topic chat is
something
fairly foreign to a group of mostly serious stodgy engineer/techies
(sorry
guys) that are interested in oscilloscopes. This sort of thing is
a true
abberation.
I do have quite a sense of humor, but on this topic it has been long
exhausted elsewhere, thanx to the persistently reoccuring pointed
derision therein of those who have gone to the trouble to do the
research by those who have not. Careful observation and verification
by the scientific method works as well here as elsewhere IF the test
conditions are likewise properly seen to. "Black magic" and "Snake
oil" will fail the test, as elsewhere. Opinion won't change the
actual result, either way, tho' granted it can bias the observation
either way. Unsupported misinformation is non-contributory to any
resolution of the facts and only adds to the confusion.

What was your first post about ? Perhaps nobody had an answer and
that's
why you didn't receive any replies. Run it by us again and we'll
get
things back on the rails.
Thanx Phil, here goes;
I am trying to understand the failure mode of an 8233/E55L in a 3A6.
Both cathode tabs were melted and the 47^ screen resistor is smoked.
With great trepidation, I replaced the defective tube after checking
the asssociated 6DJ8s, xistors, and diodes. The replacement held and
the screen resistor stayed cool. I suspected possible filament-
cathode leakage/short in the otherwise fresh looking dead tube. No
way to check for that now. I definitely don't want to risk a
presently good 8233/E55L. Any ideas on the probable failure mode?
BTW, there is now a DC imbalance on both traces that the controls
won't comp. Related?
The P/I came in a group w/a 564. It didn't fail here. I have
entertained the possibility that fil voltage was mistakenly applied
to the cathode pins in a tester, but this doesn't explain the smoking
screen resistor observed with the defective tube in place in the P/I.
Thanx in advance; Steve


Stan or Patricia Griffiths <w7ni@...>
 

Steve B. wrote:

Thanx Phil, here goes;
I am trying to understand the failure mode of an 8233/E55L in a 3A6.
Both cathode tabs were melted and the 47^ screen resistor is smoked.
With great trepidation, I replaced the defective tube after checking
the asssociated 6DJ8s, xistors, and diodes. The replacement held and
the screen resistor stayed cool. I suspected possible filament-
cathode leakage/short in the otherwise fresh looking dead tube. No
way to check for that now. I definitely don't want to risk a
presently good 8233/E55L. Any ideas on the probable failure mode?
BTW, there is now a DC imbalance on both traces that the controls
won't comp. Related?
The P/I came in a group w/a 564. It didn't fail here. I have
entertained the possibility that fil voltage was mistakenly applied
to the cathode pins in a tester, but this doesn't explain the smoking
screen resistor observed with the defective tube in place in the P/I.
Thanx in advance; Steve
The reason I did not respond to this question (I remember it now) is that I
have never seen or heard of this failure before. I didn't think I had
anything useful to contribute, but I guess just letting you know I have never
seen it in many years of observing would tell you something . . . My guess
would be a random internal failure of the 8233 and I would do what you did .
. . replace it and cross your fingers . . .

By the way, I believe the 8233 is subject to the dreaded "cathode interface"
and I would keep 8233's with that symptom around just for running such
tests. If you waste an 8233 with cathode interface, you haven't wasted much,
IMO.

Stan
w7ni@easystreet.com


Steve B.
 

--- Stan or Patricia Griffiths <w7ni@easystreet.com>
wrote:
Steve B. wrote:

Thanx Phil, here goes;
I am trying to understand the failure mode of an
8233/E55L in a 3A6.
Both cathode tabs were melted and the 47^ screen
resistor is smoked.
With great trepidation, I replaced the defective
tube after checking
the asssociated 6DJ8s, xistors, and diodes. The
replacement held and
the screen resistor stayed cool. I suspected
possible filament-
cathode leakage/short in the otherwise fresh
looking dead tube. No
way to check for that now. I definitely don't want
to risk a
presently good 8233/E55L. Any ideas on the
probable failure mode?
BTW, there is now a DC imbalance on both traces
that the controls
won't comp. Related?
The P/I came in a group w/a 564. It didn't fail
here. I have
entertained the possibility that fil voltage was
mistakenly applied
to the cathode pins in a tester, but this doesn't
explain the smoking
screen resistor observed with the defective tube
in place in the P/I.
Thanx in advance; Steve
Stan responds;
The reason I did not respond to this question (I
remember it now) is that I
have never seen or heard of this failure before. I
didn't think I had
anything useful to contribute, but I guess just
letting you know I have never
seen it in many years of observing would tell you
something . . . My guess
would be a random internal failure of the 8233 and I
would do what you did .
. . replace it and cross your fingers . . .

By the way, I believe the 8233 is subject to the
dreaded "cathode interface"
and I would keep 8233's with that symptom around
just for running such
tests. If you waste an 8233 with cathode interface,
you haven't wasted much,
IMO.
Thanx Stan for response;
My only present source for 8233/E55Ls is junker
3A1/3A6 P-Is (no extra charge for cath interface laden
& defective tubes), is there another reasonable priced
source? Last retail price I saw was about the same as
a whole surplus working modern scope, ca $85(?!).

Haven't had enough experience with them yet to
recognize cath interface probs, assume it is
near-basline vert anomaly on display? Not good news
for a scarce and pricey tube.
BTW, the internal structure of the dud looked good
under a loupe and direct sunlight, no burned or warped
grids, no discolored plate or lumpy/perforated cathode
visible thru the envelope, just the melted cath tabs
and clean & shiny getter. Strange indeed.

Thanx again. Best Rgds; Steve

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Steve B.
 

--- Stan or Patricia Griffiths <w7ni@easystreet.com> wrote:
Steve B. wrote:

Thanx Phil, here goes;
I am trying to understand the failure mode of an
8233/E55L in a 3A6.
Both cathode tabs were melted and the 47^ screen
resistor is smoked.
With great trepidation, I replaced the defective
tube after checking
the asssociated 6DJ8s, xistors, and diodes. The
replacement held and
the screen resistor stayed cool. I suspected
possible filament-
cathode leakage/short in the otherwise fresh
looking dead tube. No
way to check for that now. I definitely don't want
to risk a
presently good 8233/E55L. Any ideas on the
probable failure mode?
BTW, there is now a DC imbalance on both traces
that the controls
won't comp. Related?
The P/I came in a group w/a 564. It didn't fail
here. I have
entertained the possibility that fil voltage was
mistakenly applied
to the cathode pins in a tester, but this doesn't
explain the smoking
screen resistor observed with the defective tube
in place in the P/I.
Thanx in advance; Steve
Stan responds;
The reason I did not respond to this question (I
remember it now) is that I
have never seen or heard of this failure before. I
didn't think I had
anything useful to contribute, but I guess just
letting you know I have never
seen it in many years of observing would tell you
something . . . My guess
would be a random internal failure of the 8233 and I
would do what you did .
. . replace it and cross your fingers . . .

By the way, I believe the 8233 is subject to the
dreaded "cathode interface"
and I would keep 8233's with that symptom around
just for running such
tests. If you waste an 8233 with cathode interface,
you haven't wasted much,
IMO.
Thanx Stan for response;
My only present source for 8233/E55Ls is junker 3A1/3A6 P-Is (no
extra charge for cath interface laden & defective tubes), is there
another reasonable priced source? Last retail price I saw was about
the same as a whole surplus working modern scope, ca $85(?!).

Haven't had enough experience with them yet to recognize cath
interface probs, assume it is near-baseline vert anomaly on display?
Not good news for a scarce and pricey tube.
BTW, the internal structure of the dud looked good under a loupe and
direct sunlight, no burned or warped grids, no discolored plate or
lumpy/perforated cathode visible thru the envelope, just the melted
cath tabs and clean & shiny getter. Strange indeed.

Thanx again. Best Rgds; Steve


Stan or Patricia Griffiths <w7ni@...>
 

Steve Bringhurst wrote:

Thanx Stan for response;
My only present source for 8233/E55Ls is junker
3A1/3A6 P-Is (no extra charge for cath interface laden
& defective tubes), is there another reasonable priced
source? Last retail price I saw was about the same as
a whole surplus working modern scope, ca $85(?!).
I think you can find 8233's in the Antique Electronics catalog for around
$50, still not cheap. As you have noticed, you can buy a used 3A6 or 3A1 for
a LOT less than that and it contains TWO 8233's, but who can say how good
they are? I think all of mine have come from 3A1's and 3A6's. What else
uses them? Why are they so bloody expensive . . . are they used in some tube
audio stuff? That is the only thing I can think of that would run the price
up so high . . .

Haven't had enough experience with them yet to
recognize cath interface probs, assume it is
near-basline vert anomaly on display? Not good news
for a scarce and pricey tube.
There is a description of cathode interface and how to determine if you have
it on my web page at:

http://www.reprise.com/host/tektronix/reference/cathode_symptoms.asp
http://www.reprise.com/host/tektronix/reference/cathode.asp
http://www.reprise.com/host/tektronix/reference/cathode_remedy.asp

BTW, the internal structure of the dud looked good
under a loupe and direct sunlight, no burned or warped
grids, no discolored plate or lumpy/perforated cathode
visible thru the envelope, just the melted cath tabs
and clean & shiny getter. Strange indeed.

Thanx again. Best Rgds; Steve
OK, my pleasure.

Stan
w7ni@easystreet.com


europachris@...
 

Yup, bingo. E55L/8233's have had quite a bit of interest in some of the audio circles, particularly the low power/single ended amp crowd.

However, due to the extremely high Gm of this tube (45mA/V), it was likely always very expensive, along the lines of the 7788 and Western Electric 437A. However, it's performance as a pentode and also triode wired makes it very suitable for phono stages as well as one tube "spud" amps, putting out a watt or two driving horn speakers or headphones. It dissipates up to 10W, and it represents pretty much the upper limit of conventional glass tube manufacturing. I would imagine the reject rate at the factory was substantial.

Chris

TekScopes@yahoogroups.com wrote:
<Stan wrote>
I think you can find 8233's in the Antique Electronics catalog for around
$50, still not cheap. �As you have noticed, you can buy a used 3A6 or 3A1 for
a LOT less than that and it contains TWO 8233's, but who can say how good
they are? �I think all of mine have come from 3A1's and 3A6's. �What else
uses them? �Why are they so bloody expensive . . . are they used in some tube
audio stuff? �That is the only thing I can think of that would run the price
up so high . . .
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Get your own FREE, personal Netscape Webmail account today at http://webmail.netscape.com/


Steve B.
 

Greetings, Stan;
--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:
There is a description of cathode interface and how to determine if
you have it on my web page at:

http://www.reprise.com/host/tektronix/reference/cathode_symptoms.asp
http://www.reprise.com/host/tektronix/reference/cathode.asp
http://www.reprise.com/host/tektronix/reference/cathode_remedy.asp
I appreciate your response. The refs were most useful and
informative. Seems this should be easy to identify using the cal
source into the P-I under test.
The latest E55L price from AES are lower than I expected for recent,
but even so still come out somewhat over $80 bux per pair shipped.
Perhaps having just a couple good working 3A1/3A6s out of the bunch
is the most economical solution with the easier-to-outfit 3A3 and
63/2A63 diff amps as the audio frequency work-horses & for X-Y.
Thankful that a rare 3M1 was also in that crate of P-Is, to
eventually standardize response of my M-Fs.

Thanx again. Best Rgds; Steve