Tubes and Old Tek Scopes
Mark Amundson
scapping an old Tektronix oscilloscope. There are about 50 tubes typically
inside (from experiance) and if the scope was kept in calibration, most of
the tubes would be usable. The last Tek scope I tore apart had several
amperex and mullard 6DJ8's, 12AX7's, and a few video speed tubes like the
6U8 and 6GH8. Many of the 12AX7's had audio designations such as Amperex's
famous "trumpet". Also there are two really beefy industrial grade power
triodes used as B+ voltage regulators that could make good class A audio
power amplifiers.
JEFFREY M. STRANG
: If someone is looking for a lot of good audio tubes, consider purchasing and
: scapping an old Tektronix oscilloscope. There are about 50 tubes typically
: inside (from experiance) and if the scope was kept in calibration, most of
: the tubes would be usable.
Ack! How about... "If you're looking for a very good oscilloscope,
consider purchasing an old Tektronix. If it was kept in calibration, it
is probably a great deal and most likely as useful as a modern product."
There's nothing wrong with old Tek scopes. Many are great pieces and have
carefully matched tubes. If the thing works, why destroy a perfectly good
piece of electronics?
Just my 2 cents worth.
Jeff Strang
jmst...@mtu.edu
Dirk Wright
: If someone is looking for a lot of good audio tubes, consider purchasing and
: scapping an old Tektronix oscilloscope. There are about 50 tubes typically
: inside (from experiance) and if the scope was kept in calibration, most of
: 6U8 and 6GH8. Many of the 12AX7's had audio designations such as Amperex's
: famous "trumpet". Also there are two really beefy industrial grade power
: triodes used as B+ voltage regulators that could make good class A audio
: power amplifiers.
O man, i can't believe this. Another high quality test instrument bites the
dust because some dude is too cheap to go out and buy some tubes. All of
those tube are available new, and are very high quality. It saddens me to
see a audio cannibals on the loose...
Dirk
pdag...@qualcomm.com
<to...@conn.me.queensu.ca> wrote:
> > Mark Amundson (mamu...@atk.com) wrote:
> > : If someone is looking for a lot of good audio tubes, consider
purchasing and
> > : scapping an old Tektronix oscilloscope. There are about 50 tubes
typically
> > : inside (from experiance) and if the scope was kept in calibration,
most of
> > : the tubes would be usable. The last Tek scope I tore apart had several
>
> Glad others agree with me on this - use the scope unless it's
> absolutely junked already. Also, the tubes might not be usable, as some
> may suffer from "cathode interface", which I can't explain but I was warned
> about by an old technician. Go buy some Russian tubes, or pull the tubes
> but save the scope as some are rare and even collected (such as the curve
> tracer scope, the spectrum analyzers and the storage scopes). You could say
> that these scopes are to test equipment what Marantz is to tube amps in
> audio. Also, there is a book out (it's at home so I forgot the author) which
> describes in detail all the Tek tube scopes and their functions. It's
> available from Antique Electronic Supply and is worth while to anyone
> who comes across old scopes alot.
>
> Elton Toma
Got some old tek scopes, Type 661s, several. I need my garage back. any
takers? You pay the freight. And yes, they work.
BILLO88
amps off a cliff, it was neat to hear them hit the rocks...although those
bulky transformers would not come apart....
of course this is fictional....but I did hear that once rf goes
through a tube it is useless for audio....cheers, bill
bil...@aol.com
Dr Distortion
: of course this is fictional....but I did hear that once rf goes
: through a tube it is useless for audio....cheers, bill
Huh? RF goes through tubes in audio amps all the time; then you add a
grid stopper or whatever and it stops. Does that mean you have to replace
the tube? I doubt it...
: bil...@aol.com
^^^^^^^
Ahhhh, that explains it...
BILLO88
bil...@aol.com
Henry van Cleef
Mark Amundson <mamu...@atk.com> wrote:
>If someone is looking for a lot of good audio tubes, consider purchasing and
>scapping an old Tektronix oscilloscope. There are about 50 tubes typically
>inside (from experiance) and if the scope was kept in calibration, most of
>the tubes would be usable.
Usable? Those tubes all suffer from cathode interface. If you want
distortion and phase shift you hadn't counted on, just try using old
scope tubes.
--
***********************************************************
Hank van Cleef vanc...@bga.com vanc...@tmn.com
***********************************************************
Dirk Wright
: BILLO88 (bil...@aol.com) wrote:
: : of course this is fictional....but I did hear that once rf goes
: : through a tube it is useless for audio....cheers, bill
: Huh? RF goes through tubes in audio amps all the time; then you add a
: grid stopper or whatever and it stops. Does that mean you have to replace
: the tube? I doubt it...
Yo man, just relax, Bill is just kidding.
: : bil...@aol.com
: ^^^^^^^
: Ahhhh, that explains it...
Please, let's not partronize somebody just because they have an .aol
account.
Dirk
Henry van Cleef
Eric Barbour <ebar...@netcom.com> wrote:
>Most of you here would not believe how many scopes Tek made for
>the Government! They made a fortune producing 545s etc. at $3500
>each for 20+ years. When I lived in Albuquerque, I went to the
>infamous "Black Hole" in Los Alamos. 3 years ago they had TONS
>of old test equipment like that. Most of it had rat's nests etc.
>inside....yech....unrepairable! Rats will chew on everything, even
>Teflon-insulated wire. So we got old scopes and ended up with a
>vast supply of Bugle Boy 6DJ8s. Sold them to doctors&lawyers with ARC
>SP-12s, heh heh. Good place for old DJ8s with cathode interface, eh?
First of all, the Tek 545 series sold for about $1500-$1600 for most of
its life. Also, 6DJ8's with cathode interface are not "ideal" for
anything much involving "fidelity."
If you want scopes to part out, pick on the Hickock, Lavoie, and
Jetronics 545 wannabes. These were electronic junk when they were
built. I have a Hickock that is feeding various parts into three
genuine Tek scopes.
>
>We'd also go to the Sandia surplus auction, they also were junking
>old equipment. They are probably still selling off old power tubes
>and tube gear to this day. Every ham in central New Mexico must have
>a garage full of old Tek and HP tube test equipment. Your tax dollars
>at work!
>
This is an incredibly sleazy comment, to say "your tax dollars at
work." The genuine Tek 530/540 series scopes were made from 1953/4 to
1972/3, so the newest of them is 22 years old. These sscopes soldiered
on for 15-20 years, which certainly should be enough "return on
investment" for anyone, considering that they accumulated 2000
operating hours a year for most of this period in most places. Most of
them are quite restorable as scopes, and valuable for use as scopes.
The original purchasers of this equipment got plenty of value for the
investment.
Eric Barbour
the Government! They made a fortune producing 545s etc. at $3500
each for 20+ years. When I lived in Albuquerque, I went to the
infamous "Black Hole" in Los Alamos. 3 years ago they had TONS
of old test equipment like that. Most of it had rat's nests etc.
inside....yech....unrepairable! Rats will chew on everything, even
Teflon-insulated wire. So we got old scopes and ended up with a
vast supply of Bugle Boy 6DJ8s. Sold them to doctors&lawyers with ARC
SP-12s, heh heh. Good place for old DJ8s with cathode interface, eh?
We'd also go to the Sandia surplus auction, they also were junking
old equipment. They are probably still selling off old power tubes
and tube gear to this day. Every ham in central New Mexico must have
a garage full of old Tek and HP tube test equipment. Your tax dollars
at work!
eric barbour
Vacuum Tube Valley
Glass Audio
Edward D. Berger
: Teflon-insulated wire. So we got old scopes and ended up with a
: vast supply of Bugle Boy 6DJ8s. Sold them to doctors&lawyers with ARC
: SP-12s, heh heh. Good place for old DJ8s with cathode interface, eh?
I've seen this phrase mentioned before but without clarification.
Please explain what you mean by "cathode interface". What is it?
What caused it? How do you spot such? What measurements can be used
to confirm it? How can the buyer beware?
Thanks in advance. Do you mean the SP-12 is a good place since it
was Audio Research's "cheap" preamp compared to the SP-10/SP-8?
-Ed Berger
ebe...@psc.edu
Eric Barbour
Answer to Hank's comment: You would not believe how much money Los Alamos
and Sandia have wasted over the years. I often saw brand-new, unused
test equipment (and furniture, computers etc) that had been left outside
in the lab's boneyards for several months, BEFORE being sold as surplus.
Their contracts are on a "use it or lose it" basis, so if they have a
cash surplus at the end of the year, they go out and literally blow it
on things that will be directly sold for surplus. This included mountains
of office furniture. Thus the comment about your tax dollars.
They're still doing it today; last year I saw a CDC Cyber 305 supercomputer
that looked like new. It had all the peripherals, software etc---it sold
for $2000 to a junk dealer from Phoenix. I examined it--the CPU had 1984
manufacture date stickers on it. I swear the thing looked like new-
lots of the packing materials were still inside the CPU. It may be obsolete
now, but it was still several million dollars that was basically wasted.
As for the guy who wants to know about cathode interface:
This was caused by impurities in the cathode and coating that
would move to the emitting surface and interfere with the
emission of electrons. Apparently, silicates in the nickel
cathode sleeve were a major cause. This is why Western Electric
tubes used reagent-grade nickel in their cathodes (at much
greater cost). The purer, the better for lifetime.
Interface is exacerbated by long periods of time in cutoff, such as
in computer or O-scope sweep circuits. This is why special
tubes were developed for computers, such as the 5963 and 5965.
They were meant to be operated in cutoff for long periods.
(And they have very high distortion, so don't try them in your hi-fi.)
The only thing you can do is to not buy used 6DJ8s unless you have
a good tube tester to check them out yourself. I should digress:
we sold only the good used Bugle Boys, and many of them were OK
(if sometimes noisy). Some people aren't happy with anything;
we made our $ off them and they often called back, wanting to try
Siemens CCas or somesuch. (Thus my contempt for certain SP-12 owners.)
I hate selling tubes to audiophiles......(anyone got a problem with that?)
Dr Distortion
: Tek scope, same as anyone else, and there are very few people who think
: that they got ripped off by Tek in terms of bang for the buck. Indeed,
: the simple fact that 30-40 year old Tek scopes tend to come right up
: without a lot of sturm und drang says something for the quality.
After trying all kinds of used scopes and having them die on me, I
finally found a real Tek at a hamfest earlier this year at a price I
could afford, a dual-trace storage scope for $75. (I don't recall the
model number and I'm not near the scope right now, but it's an early
solid-state model with plug-ins). I am very, very happy with this scope;
I think I understand now why Tek is considered the king of scopes by many.
At any rate, the idea of scrapping a perfectly good piece of test gear
for its tubes or other components seems shameful. There are many people
(myself included) who need good test gear for their hobbies or small
businesses, and can't afford to buy new. Leave the working scopes for
/them/ and part out the basket cases... Just my two cents.
Henry van Cleef
>and Sandia have wasted over the years. I often saw brand-new, unused
>test equipment (and furniture, computers etc) that had been left outside
>in the lab's boneyards for several months, BEFORE being sold as surplus.
I can't comment on what various outfits do with stuff they get after
they get it. When a gov't agency buys a Tek scope, it gets a genuine
Tek scope, same as anyone else, and there are very few people who think
that they got ripped off by Tek in terms of bang for the buck. Indeed,
the simple fact that 30-40 year old Tek scopes tend to come right up
without a lot of sturm und drang says something for the quality.
The real ripoffs were the Hickock and Lavoie copies of Tek scopes, which
they got away with selling to the gov't for years---though Tek finally
won a lawsuit stopping this. The people who got hung with these Tek
wannabes had junk from day one on their hands.
All of the genuine Tek scopes I have seen in the surplus market,
whether gov't or commercial, have earned their retirement by working
for a living.
>
>As for the guy who wants to know about cathode interface:
>This was caused by impurities in the cathode and coating that
>would move to the emitting surface and interfere with the
>emission of electrons. Apparently, silicates in the nickel
>cathode sleeve were a major cause. This is why Western Electric
>tubes used reagent-grade nickel in their cathodes (at much
>greater cost). The purer, the better for lifetime.
>Interface is exacerbated by long periods of time in cutoff, such as
>in computer or O-scope sweep circuits. This is why special
>tubes were developed for computers, such as the 5963 and 5965.
>They were meant to be operated in cutoff for long periods.
>(And they have very high distortion, so don't try them in your hi-fi.)
>
The Amperex 6DJ8's were prime offenders in the cathode interface dept.
The equivalent circuit of a cathode with cathode interface is a
resistance in series with the cathode sleeve, coupled to a capacitance
formed by the emitting surface of the cathode and the cathode sleeve.
>The only thing you can do is to not buy used 6DJ8s unless you have
>a good tube tester to check them out yourself. I should digress:
>we sold only the good used Bugle Boys, and many of them were OK
>(if sometimes noisy). Some people aren't happy with anything;
>we made our $ off them and they often called back, wanting to try
>Siemens CCas or somesuch. (Thus my contempt for certain SP-12 owners.)
>I hate selling tubes to audiophiles......(anyone got a problem with that?)
>
A tube tester won't show cathode interface.
Steve Goldstein
>
> Snip screed on ridiculous funding practices for federally-supported
> research. It's true! We had the same end-of-fiscal-year spending
> spree in grad school (research funded by Air Force)
>
> As for the guy who wants to know about cathode interface:
> This was caused by impurities in the cathode and coating that
> would move to the emitting surface and interfere with the
> emission of electrons. Apparently, silicates in the nickel
> cathode sleeve were a major cause. This is why Western Electric
> tubes used reagent-grade nickel in their cathodes (at much
> greater cost). The purer, the better for lifetime.
> Interface is exacerbated by long periods of time in cutoff, such as
> in computer or O-scope sweep circuits. This is why special
> tubes were developed for computers, such as the 5963 and 5965.
> They were meant to be operated in cutoff for long periods.
> (And they have very high distortion, so don't try them in your hi-fi.)
>
The above implies that it would be OK to use scope tubes salvaged from
vertical stages, would it not?
sg
Henry van Cleef
Steve Goldstein <sgold@.adsdesign.analog.com> wrote:
>In article 1...@netcom.com, ebar...@netcom.com (Eric Barbour) writes:
>>
>>
>> As for the guy who wants to know about cathode interface:
>> tubes were developed for computers, such as the 5963 and 5965.
>> They were meant to be operated in cutoff for long periods.
>> (And they have very high distortion, so don't try them in your hi-fi.)
>>
>
>The above implies that it would be OK to use scope tubes salvaged from
>vertical stages, would it not?
>
problem.
Dunno about the accuracy of the description I snipped. But I can
assure you that Tek 514 and 524 were cathode interface dogs in their
vertical amps, and 545's aren't far behind.
Don Borowski
: Steve Goldstein <sgold@.adsdesign.analog.com> wrote:
: >In article 1...@netcom.com, ebar...@netcom.com (Eric Barbour) writes:
: >>
: >>
: >> As for the guy who wants to know about cathode interface:
: (long discussion snipped).
: >> tubes were developed for computers, such as the 5963 and 5965.
: >> They were meant to be operated in cutoff for long periods.
: >> (And they have very high distortion, so don't try them in your hi-fi.)
: >>
: >
: >The above implies that it would be OK to use scope tubes salvaged from
: >vertical stages, would it not?
: >
: No, vertical amplifiers are where the cathode interface shows up as a
: problem.
:
: Dunno about the accuracy of the description I snipped. But I can
: assure you that Tek 514 and 524 were cathode interface dogs in their
: vertical amps, and 545's aren't far behind.
interface, but I don't understand how that application would be prone
to developing it in otherwise good tubes. I would think that the
vertical amp tubes would be biased on all the time, just like most
other amplifier applications (audio, music, radios, etc).
Donald Borowski WA6OMI Hewlett-Packard, Spokane Division
"Angels are able to fly because they take themselves so lightly."
-G.K. Chesterton
Chuck Harris
Don Borowski <boro...@spk.hp.com> wrote:
>Henry van Cleef (vanc...@bga.com) wrote:
>: In article <1995Sep6....@analog.com>,
>: Steve Goldstein <sgold@.adsdesign.analog.com> wrote:
>: >In article 1...@netcom.com, ebar...@netcom.com (Eric Barbour) writes:
>: >>
>: >>
>: >> As for the guy who wants to know about cathode interface:
>: >The above implies that it would be OK to use scope tubes salvaged from
>: >vertical stages, would it not?
>: >
>: No, vertical amplifiers are where the cathode interface shows up as a
>: problem.
>:
>: Dunno about the accuracy of the description I snipped. But I can
>: assure you that Tek 514 and 524 were cathode interface dogs in their
>: vertical amps, and 545's aren't far behind.
>
>I can see how the vertical amps would be the most sensitive to cathode
>interface, but I don't understand how that application would be prone
>to developing it in otherwise good tubes. I would think that the
>vertical amp tubes would be biased on all the time, just like most
>other amplifier applications (audio, music, radios, etc).
You are correct, the vertical amps are typically of a class A, or AB form.
The reason that they are sensitive to cathode interface, is they are direct
coupled, and very phase neutral amps. Any amount of cathode interface will
show up as a marked reduction in the low frequency (near DC) response. On an
O'scope this will appear as a sharp spike on the leading edges of a squarewave
being displayed on the screen.
I don't really see why a badly cathode interfaced tube would be a problem
in an audio amp, as these amps never go low enough in frequency to enter
the region of cathode interface. (can you say transformer coupled?)
Well, just one old EE's opinion.
-----
Chuck Harris - WA3UQV
ch...@eng.umd.edu
R. D. Davis
Mark Amundson <mamu...@atk.com> wrote:
>If someone is looking for a lot of good audio tubes, consider purchasing and
>scapping an old Tektronix oscilloscope. There are about 50 tubes typically
[rest or horrid posting deleted]
Please, DON'T do this! These older Tektronix oscilloscopes have the
nicest, sharpest, resolution that I, and many others, have seen on an
oscilliscope. These oscilloscopes are very nice instruments and don't
deserve to be destroyed by parts scavengers.
Remember, audio isn't the only good use for vacuum tubes.
--
R. D. Davis Eccentrics have more fun! :-) http://www.access.digex.net/~rdd
r...@digex.net, r...@mystica.uucp Vintage computer preservationist.
Home telephone: 1-410-744-7964 Unwanted computer systems disassembled
Work (play!) telephone: 1-410-744-4900 and removed for free.