6DJ8 substitute idea - reverse engineering


Keith
 

This thread is just a discussion starter for some of you who have older Tek tube scopes. If you've needed to retube them, you've been dismayed to find that some of them use lots of those relatively scarce and expensive 6DJ8 tubes. On this matter, I was scanning old Tektronix documentation when I came across a brief comment from April 16th of 1961. You can read it here

https://w140.com/tekwiki/images/f/fe/Tek_315D_irb.pdf

look on on page 104, but here is the gist of it, and I quote.

"6DJ8 CONVERSION Type 6DJ8 tubes are mproved versions of Type 6BQ7 A tubes. They offer better performance, greater reliability, and more consistent characteristics from tube to tube and between sections of one tube. We recommend 6DJ8 as direct replacements for 6BQ7A's even in those circuits now employing aged and checked 6BQ7A's."

Remember, this is 1961's best advice for advancing what were then the front line Tek scopes - and it made sense back then. Dump the relatively lower tech 6BQ7 for the newfangled and better performing 6DJ8. Makes sense, right? The document goes on to say (quoting again)

"In most cases you need not make any circuit changes. A few minor adjustments are usually necessary, however. These adjustments are described in your instruction manual and amount to no more than routine calibration for the circuits in which the tubes were replaced."

But a lot has changed since 1961 with regard to tube availability, and this got me to thinking. Since at least some of the circuits in question were obviously originally designed to work with 6BQ7 and the 6DJ8 was clearly a later "drop-in improvement", could one not - at least on non-critical scopes - simply decide to put up with the slightly poorer performance of the 6BQ7 and REVERT some (or all) 6DJ8 applications back to the far cheaper and more available 6BQ7? Now I don't claim to be a Tek guru, but I do know a fair bit about tubes, as these are more my specialty, and I get the mechanical and electronic reasons why the 6DJ8 is superior - frame grid and all, but when this recommendation from Tek came out, the 6DJ8 was an apex product from the golden age of US tube manufacturing. Those days are long gone and the supply of premium 6DJ8 continues to dwindle, especially since they have such demand in the audio world.

So - what if we REVERTED some/all of these Tek scope twin triode positions back to 6BQ7? Apparently the scope will still work fine, with a little re-calibration. If I were rebuilding an old Tek scope for mostly sentimental reasons and needed only reasonable performance, I would sure get excited if I could skip buying a couple hundred dollars' worth of 6DJ8 and instead use a $15-20 worth of 6BQ7.

Speaking as someone who has over 200 NOS 6BQ7A in the box, I can tell you that it would be reasonably possible to find matched-section 6BQ7 and simply burn them in a little and double check them (or have a friend or relative with a curve tracer do it for you :-) Again, we're not building stuff for NASA with our 500 series scopes, right? I would venture to guess that one could buy all the 6BQ7 one needed for the cost of two or even one premium 6DJ8.

Anyway, just an idea to kick around as a cost savings approach to keeping older tube scopes running at reasonable performance levels without dropping two hundred extra dollars on premium and scarce tubes.

Cheers

Keith
CBG


Sergey Kubushyn
 

On Sun, 20 Jun 2021, Keith wrote:

Russian 6N23P is a direct equivalent of 6DJ8. There are many thousands of
those available from eBay (519 hits for 6N23P as of right now with some of
those for lots of a hundred or more).

There are many braindead listings for "audiophiles" with totally insane
prices but there are also normal sellers with tons of NOS tubes selling them
at reasonable price. I wouldn't pay more that something like $2-3 per tube,
they are not all that special. There are justifiable high prices like e.g.
circa $5 for 6ZH32P (EF86 equivalent) that were not very common and quite
expensive but 6N23P was a very common Russian tube, nothing special at all.

Here is a reasonably priced lot of 10 6N23P tubes:

https://www.ebay.com/itm/154357833205

Still quite high but not "Rare! Matched! Same date!" nonsense like e.g.
here:

https://www.ebay.com/itm/294009817679

One must be suffering terminal audiophilia to pay even a tenth of the asking
price for those...

Just FYI, if you didn't know it -- tubes with "-EV" (-ЕВ in cyrillic) are
high reliability version of the same tubes without that. Nothing special,
just have longer GUARANTEED life. They might be "-EV" or simply "-E". Some
of those have different construction (like e.g. 6P3S-E vs 6P3S), some are
visually identical.

This thread is just a discussion starter for some of you who have older Tek tube scopes. If you've needed to retube them, you've been dismayed to find that some of them use lots of those relatively scarce and expensive 6DJ8 tubes. On this matter, I was scanning old Tektronix documentation when I came across a brief comment from April 16th of 1961. You can read it here

https://w140.com/tekwiki/images/f/fe/Tek_315D_irb.pdf

look on on page 104, but here is the gist of it, and I quote.

"6DJ8 CONVERSION Type 6DJ8 tubes are mproved versions of Type 6BQ7 A tubes. They offer better performance, greater reliability, and more consistent characteristics from tube to tube and between sections of one tube. We recommend 6DJ8 as direct replacements for 6BQ7A's even in those circuits now employing aged and checked 6BQ7A's."

Remember, this is 1961's best advice for advancing what were then the front line Tek scopes - and it made sense back then. Dump the relatively lower tech 6BQ7 for the newfangled and better performing 6DJ8. Makes sense, right? The document goes on to say (quoting again)

"In most cases you need not make any circuit changes. A few minor adjustments are usually necessary, however. These adjustments are described in your instruction manual and amount to no more than routine calibration for the circuits in which the tubes were replaced."

But a lot has changed since 1961 with regard to tube availability, and this got me to thinking. Since at least some of the circuits in question were obviously originally designed to work with 6BQ7 and the 6DJ8 was clearly a later "drop-in improvement", could one not - at least on non-critical scopes - simply decide to put up with the slightly poorer performance of the 6BQ7 and REVERT some (or all) 6DJ8 applications back to the far cheaper and more available 6BQ7? Now I don't claim to be a Tek guru, but I do know a fair bit about tubes, as these are more my specialty, and I get the mechanical and electronic reasons why the 6DJ8 is superior - frame grid and all, but when this recommendation from Tek came out, the 6DJ8 was an apex product from the golden age of US tube manufacturing. Those days are long gone and the supply of premium 6DJ8 continues to dwindle, especially since they have such demand in the audio world.

So - what if we REVERTED some/all of these Tek scope twin triode positions back to 6BQ7? Apparently the scope will still work fine, with a little re-calibration. If I were rebuilding an old Tek scope for mostly sentimental reasons and needed only reasonable performance, I would sure get excited if I could skip buying a couple hundred dollars' worth of 6DJ8 and instead use a $15-20 worth of 6BQ7.

Speaking as someone who has over 200 NOS 6BQ7A in the box, I can tell you that it would be reasonably possible to find matched-section 6BQ7 and simply burn them in a little and double check them (or have a friend or relative with a curve tracer do it for you :-) Again, we're not building stuff for NASA with our 500 series scopes, right? I would venture to guess that one could buy all the 6BQ7 one needed for the cost of two or even one premium 6DJ8.

Anyway, just an idea to kick around as a cost savings approach to keeping older tube scopes running at reasonable performance levels without dropping two hundred extra dollars on premium and scarce tubes.

Cheers

Keith
CBG







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Tom Lee
 

Yes, the two types are indeed pretty much interchangeable. The ft values are neary identical, the transconductances differ by only about 10%, and the electrode capacitances are also within about 10% of each other. One thing to note, though, is that the 6DJ8 is rated for a higher plate voltage, so subbing with a 6BQ7 can't be done completely casually in all cases.

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 6/20/2021 20:21, Keith wrote:
This thread is just a discussion starter for some of you who have older Tek tube scopes. If you've needed to retube them, you've been dismayed to find that some of them use lots of those relatively scarce and expensive 6DJ8 tubes. On this matter, I was scanning old Tektronix documentation when I came across a brief comment from April 16th of 1961. You can read it here

https://w140.com/tekwiki/images/f/fe/Tek_315D_irb.pdf

look on on page 104, but here is the gist of it, and I quote.

"6DJ8 CONVERSION Type 6DJ8 tubes are mproved versions of Type 6BQ7 A tubes. They offer better performance, greater reliability, and more consistent characteristics from tube to tube and between sections of one tube. We recommend 6DJ8 as direct replacements for 6BQ7A's even in those circuits now employing aged and checked 6BQ7A's."

Remember, this is 1961's best advice for advancing what were then the front line Tek scopes - and it made sense back then. Dump the relatively lower tech 6BQ7 for the newfangled and better performing 6DJ8. Makes sense, right? The document goes on to say (quoting again)

"In most cases you need not make any circuit changes. A few minor adjustments are usually necessary, however. These adjustments are described in your instruction manual and amount to no more than routine calibration for the circuits in which the tubes were replaced."

But a lot has changed since 1961 with regard to tube availability, and this got me to thinking. Since at least some of the circuits in question were obviously originally designed to work with 6BQ7 and the 6DJ8 was clearly a later "drop-in improvement", could one not - at least on non-critical scopes - simply decide to put up with the slightly poorer performance of the 6BQ7 and REVERT some (or all) 6DJ8 applications back to the far cheaper and more available 6BQ7? Now I don't claim to be a Tek guru, but I do know a fair bit about tubes, as these are more my specialty, and I get the mechanical and electronic reasons why the 6DJ8 is superior - frame grid and all, but when this recommendation from Tek came out, the 6DJ8 was an apex product from the golden age of US tube manufacturing. Those days are long gone and the supply of premium 6DJ8 continues to dwindle, especially since they have such demand in the audio world.

So - what if we REVERTED some/all of these Tek scope twin triode positions back to 6BQ7? Apparently the scope will still work fine, with a little re-calibration. If I were rebuilding an old Tek scope for mostly sentimental reasons and needed only reasonable performance, I would sure get excited if I could skip buying a couple hundred dollars' worth of 6DJ8 and instead use a $15-20 worth of 6BQ7.

Speaking as someone who has over 200 NOS 6BQ7A in the box, I can tell you that it would be reasonably possible to find matched-section 6BQ7 and simply burn them in a little and double check them (or have a friend or relative with a curve tracer do it for you :-) Again, we're not building stuff for NASA with our 500 series scopes, right? I would venture to guess that one could buy all the 6BQ7 one needed for the cost of two or even one premium 6DJ8.

Anyway, just an idea to kick around as a cost savings approach to keeping older tube scopes running at reasonable performance levels without dropping two hundred extra dollars on premium and scarce tubes.

Cheers

Keith
CBG







greenboxmaven
 

The 6BQ7, 6BK7, and 6DJ8 were all used extensively as cascode RF amplifiers in receivers and tuners. If my recollections are right, the 6DJ8 had better intermodulation tolerance than the others and could make the difference in receiving weaker FM stations when a powerful FM or television transmitter was nearby. The higher voltage rating of the 6DJ8 allowed it to be reliably operated with higher plate voltage and grid bias, which reduced the chances of a strong signal driving the grid positive or causing other intermodulation effects. I rarely if ever saw a 6BQ or BK7 used in an audio amplifier, but for some reason some manufacturers and the AudioPhools go ape$#1T for the 6DJ8. They are also very picky about the number and location of getters, the color and shape of the plates, age, and of course manufacturer.

    Bruce Gentry, KA2IVY

On 6/21/21 1:18, Tom Lee wrote:
Yes, the two types are indeed pretty much interchangeable. The ft values are neary identical, the transconductances differ by only about 10%, and the electrode capacitances are also within about 10% of each other. One thing to note, though, is that the 6DJ8 is rated for a higher plate voltage, so subbing with a 6BQ7 can't be done completely casually in all cases.

-- Cheers,
Tom


Keith
 

Hi Tom,

Yes, makes sense - and also begs another question. I wonder when Tek stopped merely swapping in the newfangled 6DJ8 and actually started designing circuits that more fully exploited this tube's capability - thus making the reversion to 6BQ7 no longer an option? The 1961 announcement seemed fairly casual and broad-stroke. "We recommend 6DJ8 as direct replacements for 6BQ7A's"...

So I wonder when Tek started consciously pushing plate voltages out of the 6BQ7 range, thus turning what was essentially a 1961 technical bulletin announcement of "sub for better performance" into a "requires 6DJ8" specification? Maybe never? Dunno. They made a lot of scopes that survived a couple decades of design advances. Ah, the mysteries of Tek history.

Hi Sergey,

Yes, I'm well aware of 6N23P (and other Russian-sourced tubes.) I have some. With respect to Russian "equivalent", and with genuine love to all my Russian brothers, I would not personally put Russian branded parts in my Tektronix equipment. I tried it once, and when I turned the scope on half the on-screen information was in Cyrillic. It took months for me to sort it out. :-)

But all kidding aside - yeah, this is another option and similar in spirit to the idea of "going back" to 6BQ7. FWIW, I bought NOS 6BQ7 a hundred at a time for $1 a tube, which is even cheaper than the 6N23P you point out on Fleabay.

So, yes - if you want to buy more 6N23P than you need and want to sort through them (and if you want to allow Russian parts in your Tek scopes) the 6N23P offers something similar in cost to reverting to 6BQ7, perhaps with more plate voltage capability and maybe similar performance specs to 6DJ8 depending on how good the factory was running the day they were assembled or how honest the importer is, etc.

Remember that Tek burned in and sorted 6BQ7A for section balance before putting them in their scope applications. AFAIK there is no "special quality" mil-spec version of this tube, so 6BQ7 were really "average" quality consumer equipment tubes on which Tek did their usual extra purification/selection process. Of course, in the US circa 1961 "average quality" tubes were still generally very good. Not sure how sharp the 6N23P production line is these days, but you know at least that the tooling must be "vintage" at this point. :-0

My point is this; With any non-Tek prepped NOS 6BQ7 OR current production 6N23P we could do the very same thing. Burn in and section balance measurements are not very difficult to do. You just have to tell yourself the truth when measurements show that you have to to reject six of those seemingly "economical" 6N23P. Allowing for waste, these seemingly less expensive tubes might suddenly "cost" you $5 or more a pop, plus the time wasted burning in and measuring. For me, the duds would be write-offs, as I can't personally resell tubes I've tested and found wanting. I suppose those are just my old fashioned scruples.

In contrast, with just about any vintage NOS US/European sourced 6DJ8, I would be very comfortable plugging them right in my average Tek application after nothing more than a routine pass through the tube tester to check for shorts and gas. But of course, we can't get vintage US/Euro 6DJ8 for $2 a tube these days. Fortunately, I have about a hundred of them too - so I don't personally need to worry about this.

I guess I was thinking about the next generation of guys and gals who catch the bug and want to keep these old tube Tek scopes going. They probably DON'T have a big back stock of tubes they've collected in preparation for the coming electronic apocalypse. :-) By then the Audiophools will probably have driven the price of 6DJ8 to $200 a tube, just like 6550A. :-/

So, here's to hoping some future Tek enthusiast now in middle school might find this post after we are long dead and say "wow! I can use 6BQ7 in my 1960 model 315? No kidding?"

Anyway, just a thought thread. Maybe inconsequential.

Cheers,
Keith
CBG


Jim Adney
 

On Sun, Jun 20, 2021 at 10:21 PM, Keith wrote:

Anyway, just an idea to kick around as a cost savings approach to keeping
older tube scopes running at reasonable performance levels without dropping
two hundred extra dollars on premium and scarce tubes.
Sounds like a reasonable suggestion. I checked my favorite vacuum tube source, Michael Marx at vacuumtubes.com, and he lists 6BQ7As for $4 and lots of variations of 6DJ8/ECC88s for $18 to over $100, depending on exactly what you want. Michael is a very reasonable guy, but a lot of the people he sells to fit in the Goldenears/Audiofool category, so don't be annoyed by some of the descriptions. The plain Jane 6DJ8 is probably what you want, but he also has them with gold pins, maybe even in Tek boxes. Just ask.


Carl Hallberg
 

Hi all,
I have a whole bunch? of EEC88 tubes. They have BRIMAR  and FOREIGN BVA written on them.  I got them from a tech school.  What are these particular 6DJ8's and where made?
Carl Hallberg (W9CJH)

On Monday, June 21, 2021, 09:42:16 AM CDT, Jim Adney <jadney@vwtype3.org> wrote:





On Sun, Jun 20, 2021 at 10:21 PM, Keith wrote:

Anyway, just an idea to kick around as a cost savings approach to keeping
older tube scopes running at reasonable performance levels without dropping
two hundred extra dollars on premium and scarce tubes.
Sounds like a reasonable suggestion. I checked my favorite vacuum tube source, Michael Marx at vacuumtubes.com, and he lists 6BQ7As for $4 and lots of variations of 6DJ8/ECC88s for $18 to over $100, depending on exactly what you want. Michael is a very reasonable guy, but a lot of the people he sells to fit in the Goldenears/Audiofool category, so don't be annoyed by some of the descriptions. The plain Jane 6DJ8 is probably what you want, but he also has them with gold pins, maybe even in Tek boxes. Just ask.


Stephen
 

On Mon, Jun 21, 2021 at 04:13 AM, Carl Hallberg wrote:


Hi all,
I have a whole bunch? of EEC88 tubes. They have BRIMAR  and FOREIGN BVA
written on them.  I got them from a tech school.  What are these particular
6DJ8's and where made?
Carl Hallberg (W9CJH)
Both of these are British made.


Carl Hallberg
 

Thanks, Stephen.
I meant ECC88, not EEC88.  Are they a good type?
Carl

On Monday, June 21, 2021, 10:16:19 AM CDT, Stephen <stephen.nabet@gmail.com> wrote:





On Mon, Jun 21, 2021 at 04:13 AM, Carl Hallberg wrote:


Hi all,
I have a whole bunch? of EEC88 tubes. They have BRIMAR  and FOREIGN BVA
written on them.  I got them from a tech school.  What are these particular
6DJ8's and where made?
Carl Hallberg (W9CJH)
Both of these are British made.


Stephen
 

On Mon, Jun 21, 2021 at 04:24 AM, Carl Hallberg wrote:


Thanks, Stephen.
I meant ECC88, not EEC88.  Are they a good type?
Carl
Are ECC88 Good? It depends on want the application is. Now if you’re asking about British made tubes, they are usually top notch quality, all of them.


 

Keith wrote:

With any non-Tek prepped NOS 6BQ7 OR current production 6N23P we could
do the very same thing. Burn in and section balance measurements are not very
difficult to do. You just have to tell yourself the truth when measurements show
that you have to to reject six of those seemingly "economical" 6N23P. Allowing for
waste, these seemingly less expensive tubes might suddenly "cost" you $5 or
more a pop, plus the time wasted burning in and measuring.
Of course you just turn around and resell the "failed" tubes to the audiophools on eBay for $10 each as "burned in and tested." It wouldn't be a lie, or even an exaggeration.

-- Jeff Dutky


Liam Perkins
 

Or, and if you need them, you could buy current production parts from
Eurotubes https://www.eurotubes.com/store/pc/E88CC-6922-or-6DJ8-c52.htm who
can provide them curve tracer, section-to-section matched and noise graded.
They have the RoeTest curve tracer and an ex-Tek guy, Matt Kamina working
with them. They know what they're doing. Here are a couple links to the
RoeTest site http://roehrentest.de/EnglishInfo.html
http://roehrentest.de/RoeTest2.html.
I wouldn't even consider downgrading to the 6BQ7, such a move is neither
productive nor necessary.
Liam

On Mon, Jun 21, 2021 at 12:10 PM Jeff Dutky <jeff.dutky@gmail.com> wrote:

Keith wrote:

With any non-Tek prepped NOS 6BQ7 OR current production 6N23P we could
do the very same thing. Burn in and section balance measurements are
not very
difficult to do. You just have to tell yourself the truth when
measurements show
that you have to to reject six of those seemingly "economical" 6N23P.
Allowing for
waste, these seemingly less expensive tubes might suddenly "cost" you $5
or
more a pop, plus the time wasted burning in and measuring.
Of course you just turn around and resell the "failed" tubes to the
audiophools on eBay for $10 each as "burned in and tested." It wouldn't be
a lie, or even an exaggeration.

-- Jeff Dutky






cmjones01
 

On Mon, Jun 21, 2021 at 4:40 PM Stephen <stephen.nabet@gmail.com> wrote:

On Mon, Jun 21, 2021 at 04:24 AM, Carl Hallberg wrote:

Thanks, Stephen.
I meant ECC88, not EEC88. Are they a good type?
Carl
Are ECC88 Good? It depends on want the application is. Now if you’re asking about British made tubes, they are usually top notch quality, all of them.
European-built Tek scopes, from Guernsey and Heerenveen, are full of
locally-made ECC88 tubes. As far as I'm concerned they're 100%
interchangeable with 6DJ8, and Tek seemed to think the same. I have a
small replacement supply of E88CC (same as ECC88/6DJ8 but 'special
quality', for whatever that's worth) made by Tesla in communist
Czechoslovakia. They seem to work absolutely fine, and were cheap
because they're not, or at least weren't, a brand desirable to the
golden-ears club.

Chris


Joe
 

Hello,

Quite a while ago I was in need of about 30 pcs 6DJ8 for my 585A. Some more that I could locate in my vaults including Siemens E88CC, RCA 6922 and such. So I decided to buy a 50's pack 6N23P from a mil surplus dealer in the middle of Ukraine. NOS and well packed, they arrived safe and sound. So I let them all burn in for 24 hrs and put them on my French Metrix Pont 661 tube tester. One of my criteria was that both systems of each tube should match in transconductance by 5% or closer. What can I say: The cohort behaved just as Carl Friedrich Gauss would have predicted and I ended up with approval for the quantity just needed. Ok, this is just a snapshot showing the "new" status and we will wait and see how they are ageing. However, I found one gassy tube within that brand new "mil-spec" lot.

Regards, Joe


Shaun M
 

Foks,
I have some experience with the Russian 6N23P tubes from various vendors.

To summarize:
Most vendors I have dealt ship from Ukraine and the shipping time can be quite long (up to 8 weeks) to Canada.
I check all the tubes on a curve tracer (uTracer) and run a set of plate curves to sort them.
The quality of the tubes is variable, but I have had many more fair-weak tubes than very good-excellent ones.
I bought the cheaper lot quantity tubes (say 20 tubes) rather than the ones marketed to the audio crowd (date matched, matched quad, etc., etc.)
I have received refunds for tube lots that were really junk and sold as "tested" or "new".
I have used the 6N23P in vintage gear in place of the 6DJ8; in fact, the initial reason I investigated the 6N23P was the HP 428B which uses two of them.

Shaun Merrigan


Tom Lee
 

My guess is that you are in the minority in declaring such a move "neither productive nor necessary." Given the absurd cost of most 6DJ8s, using 6BQ7s is often the only economically practical route to repair (or restoring to service a found carcass that has been stripped of its tubes). Scopes don't care about the things that matter to audiophiles (e.g., "noise grading"). Spending hundreds of dollars for a set of tubes to restore a scope is likely prohibitive to most. If a 6BQ7 will work in the application, I fail to see why one shouldn't use it.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 6/21/2021 11:31, Liam Perkins wrote:
Or, and if you need them, you could buy current production parts from
Eurotubes https://www.eurotubes.com/store/pc/E88CC-6922-or-6DJ8-c52.htm who
can provide them curve tracer, section-to-section matched and noise graded.
They have the RoeTest curve tracer and an ex-Tek guy, Matt Kamina working
with them. They know what they're doing. Here are a couple links to the
RoeTest site http://roehrentest.de/EnglishInfo.html
http://roehrentest.de/RoeTest2.html.
I wouldn't even consider downgrading to the 6BQ7, such a move is neither
productive nor necessary.
Liam

On Mon, Jun 21, 2021 at 12:10 PM Jeff Dutky <jeff.dutky@gmail.com> wrote:

Keith wrote:
With any non-Tek prepped NOS 6BQ7 OR current production 6N23P we could
do the very same thing. Burn in and section balance measurements are
not very
difficult to do. You just have to tell yourself the truth when
measurements show
that you have to to reject six of those seemingly "economical" 6N23P.
Allowing for
waste, these seemingly less expensive tubes might suddenly "cost" you $5
or
more a pop, plus the time wasted burning in and measuring.
Of course you just turn around and resell the "failed" tubes to the
audiophools on eBay for $10 each as "burned in and tested." It wouldn't be
a lie, or even an exaggeration.

-- Jeff Dutky







Liam Perkins
 

I might be in the minority but knowing the guys at EuroTube and having
dealt with them I know their prices are rational and if section-to-section
curve tracer matching is important, as opposed to single-data-point
"matching", they can meet the need and as much to the point; they know the
difference between the two. While noise grading almost certainly isn't
needed for scope work, the fact that they can do it and get it right is
noteworthy.

On Tue, Jun 22, 2021 at 12:06 AM Tom Lee <tomlee@ee.stanford.edu> wrote:

My guess is that you are in the minority in declaring such a move
"neither productive nor necessary." Given the absurd cost of most 6DJ8s,
using 6BQ7s is often the only economically practical route to repair (or
restoring to service a found carcass that has been stripped of its
tubes). Scopes don't care about the things that matter to audiophiles
(e.g., "noise grading"). Spending hundreds of dollars for a set of tubes
to restore a scope is likely prohibitive to most. If a 6BQ7 will work in
the application, I fail to see why one shouldn't use it.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 6/21/2021 11:31, Liam Perkins wrote:
Or, and if you need them, you could buy current production parts from
Eurotubes https://www.eurotubes.com/store/pc/E88CC-6922-or-6DJ8-c52.htm
who
can provide them curve tracer, section-to-section matched and noise
graded.
They have the RoeTest curve tracer and an ex-Tek guy, Matt Kamina working
with them. They know what they're doing. Here are a couple links to the
RoeTest site http://roehrentest.de/EnglishInfo.html
http://roehrentest.de/RoeTest2.html.
I wouldn't even consider downgrading to the 6BQ7, such a move is neither
productive nor necessary.
Liam

On Mon, Jun 21, 2021 at 12:10 PM Jeff Dutky <jeff.dutky@gmail.com>
wrote:

Keith wrote:
With any non-Tek prepped NOS 6BQ7 OR current production 6N23P we could
do the very same thing. Burn in and section balance measurements are
not very
difficult to do. You just have to tell yourself the truth when
measurements show
that you have to to reject six of those seemingly "economical" 6N23P.
Allowing for
waste, these seemingly less expensive tubes might suddenly "cost" you
$5
or
more a pop, plus the time wasted burning in and measuring.
Of course you just turn around and resell the "failed" tubes to the
audiophools on eBay for $10 each as "burned in and tested." It wouldn't
be
a lie, or even an exaggeration.

-- Jeff Dutky













Keith
 

Well, as the OP, I see that I've opened up quite a discussion.

So, in summary (so far) it looks like we've established for future readers and scope restorers the following;

1.) 6DJ8 are scarce and expensive, but not quite unobtanium, yet... as of June 2021.
2.) Russian 6N23P tubes have some definite applicability, but may suffer from reliability and lead time issues. Compensations are required, and available - for a price
3.) 6BQ7 is a viable option, but only with caution in every case since Tek may have pushed particular applications beyond 6BQ7 safe operating zones (Thanks Prof. Lee!)
4.) Some guys on this forum have lots of ECC88 just wasting away in THAT box, and doggone it they haven't sold them to me yet. :-)
5.) I reckon I need to see the little woman about an advance on my tube purchase budget, re; item #4

Future readers and scope builders of tomorrow, we salute you!


Stephen
 

I bought a brand new 6DJ8/ECC88 from Conrad Electronics to replace the one in my 067-0502-01. There are modern productions of this tube.


Michael W. Lynch
 

It needs to be remembered that TEKTRONIX built their equipment to operate within specifications while using various tubes and transistors which fell into a relatively broad envelope of performance. It is absolutely not necessary to use tubes or transistors on the very bleeding edge of their performance specifications. One needs components that are in spec, but certainly NOT (in most cases) perfection. This is the insanity of those who scavenge tubes from old scopes, these tubes are very likely NOT going to pass ALL of the various and rigorous inspections that "audiophooles" seem to require. Sorting through 50-70 year old USED tubes and hoping to find perfection is one definition of insanity. It would be something akin to sorting through each and every transistor in a circuit, then attempting to get every one of the same type to be matched in every respect; simply impossible. TEK knew that these scopes would run for many thousands of hours and that if any semblance of reasonable accuracy was to be maintained, there have to be considerable latitude in the performance requirements of the individual components. Otherwise the instruments would require calibration before every use as these components will change ever so slightly during each use.

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Michael Lynch
Dardanelle, AR