Re: Type 184 Time Mark Generator Transistor Question
On Sun, 20 Jan 2013 19:51:37 -0700, David DiGiacomo <daviddigiacomo@...> wrote: On Sun, Jan 20, 2013 at 3:53 PM, David <davidwhess@...> wrote:
It is 2N918 and not 2N198. The 2N918 was a very common early VHF
transistor. My 184 has 2N3605 transistors as well.
The 2N918 is:
900 MHz @ 4 mA
30 Vcbo 15 Vceo 50 mA
From the Tektronix parts book the 2N3605 is:
300 MHz @ 10mA
18 Vcbo 14 Vceo 200 mA
The ubiquitous and inexpensive 2N2222, 2N3904, and 2N4401 should all
work as replacements. I think those general purpose parts are a bit too slow to be good
substitutions. I would try something faster like PN918, PN2369A,
PN4275, 2N5770, MPSH17, etc. Everyone should have at least one of
those types in the parts box. Tektronix's choice of the 2N918 to replace the 2N3605 was bothering me so I did some research and then some tests on my 185. I had to dig out my National discrete products data book to find that the 2N3605 is a fast saturated switch with a short storage time. The storage time is what matters in this case. I think what happened is the supply became unreliable unless you were buying production quantities (I remember having this problem when I needed fast saturated switches for prototyping), so Tektronix recommended the 2N918 as a field replacement. This may also explain why the 2N3605s were scavenged. I did some tests using 2N4401s to replace the 2N3605s in various stages and at around 50uS and faster, the middle transistor (Q175, Q195, or Q215 for example) delayed turn off for too long and left a glitch in the leading edge of the output pulse when the faster timing pulses were superimposed which makes sense from the schematic. On slower stages, the added storage delay was not enough to even show up because the pulse width is so long. I verified this by adding a 1N270 germanium diode (a small signal schottky diode would work just as well or better) as a baker clamp between the base and collector and that solved the problem nicely. The other places where the 2N3605 was used for buffing the fast outputs where storage delay should not matter (Q123, Q133, and Q153) worked fine with 2N4401s. The change in the output pulse from the substitution was almost insignificant and certainly would not affect operation. That leaves a couple of spots (Q175, Q195, and maybe Q215) that used the 2N3605 where a low storage delay transistor is needed. A baker clamp worked just as well in my tests though. Of the ones you listed, I think the PN4275 would be the best by far. They are cheap, available, and are characterized for exactly the right application. The RF transistors are not characterized for switching so it is unclear what their delay or off time is. They should still work though.
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Re: Type 184 Time Mark Generator Transistor Question
On Sun, Jan 20, 2013 at 3:53 PM, David <davidwhess@...> wrote: It is 2N918 and not 2N198. The 2N918 was a very common early VHF
transistor. My 184 has 2N3605 transistors as well.
The 2N918 is:
900 MHz @ 4 mA
30 Vcbo 15 Vceo 50 mA
From the Tektronix parts book the 2N3605 is:
300 MHz @ 10mA
18 Vcbo 14 Vceo 200 mA
The ubiquitous and inexpensive 2N2222, 2N3904, and 2N4401 should all
work as replacements. I think those general purpose parts are a bit too slow to be good substitutions. I would try something faster like PN918, PN2369A, PN4275, 2N5770, MPSH17, etc. Everyone should have at least one of those types in the parts box.
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Re: 2465 - impending U800 failure?
Thanks Victor, interesting thread. If it is humidity based then I'm glad I live in Arizona. Seams like leaving them for a long time packed in silica gel might also help. Interesting in any event.
Jeff
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On 1/20/2013 6:37 PM, victor_j_silva wrote:
It may fix some of the U800s that have failed:
Please search this forum:
"U800 baking"
This has been discussed ad nauseam.
--Victor
--- In TekScopes@... <mailto:TekScopes%40yahoogroups.com>, Jeff Machesky wrote:
Removing the heat from the plastic should in turn drop the temperature
of the metal fin some. Now does that produce undesirable thermal
shifts,
no idea. In my case I'm pulling heat from a little of both, but mostly
the plastic.
So what does baking the chip actually fix? I know some IC's are
sensitive to humidity, but this is usually only just before the high
temperature of a reflow oven. The trapped moisture can cause defects
when heated.
Jeff
On 1/20/2013 6:07 PM, Dave C wrote:
Last time 'round on this topic I designed a heatsink that contacts
only the metal tab parts of U800, not the plastic body. This is the
intended (I think) means of getting the heat out of the chip.
The drawing of this heatsink is in the Tekscopes files page on the
Yahoo Groups web site. Look for a folder titled "U800". Its in there.
Dave
-=-=-=-
On 20 January 2013, at 2:05 PM, Jeff Machesky wrote:
Is all of this heat related? One of the first things I did when
getting
my 2465BDM was strap a very large heat sink to the U800 chip
with good
quality thermal compound and very secure mounting. It's larger
then the
chip. It runs just over room temperature with the case on. I measured it
with a type K probe through the vents and touching the middle of the
heat sink with a dab of thermal compound over a half hour or so
time
frame.
I do notice mine drifts a tiny tiny bit on warm up, one or two
mm to
the
left. It later snaps back about 1mm to the right.
Jeff
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Re: Type 184 Time Mark Generator Transistor Question
The ones I purschased are from a 100% feedback US Ebay seller.
Listed as made by Phillips, NOS, Item pictured.
I really do not think they are fake.
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--- In TekScopes@..., David wrote:
Has someone actually counterfeited 2N3904s? How desperate did they
have to be?
On Sun, 20 Jan 2013 17:19:02 -0800 (PST), Jim wrote:
I hope they're not counterfeit ....
You should test a few to see where Ft seems to be.
73
Jim N6ITQ?
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Re: Type 184 Time Mark Generator Transistor Question
Everybody counterfeits everything.
Anything that sells for 3 cents a piece in bags of 100 is fair game for counterfeiting.
The crooks pump this stuff out by
the millions, and make their nut by mis-labeling garbage.*
And -- since they're basically mis-labeling substandard parts that sell for a penny in hundred-lots, they make a 300% price up-sell by calling a 2N_CACA a 2N3904.
For low-speed switching apps, it really doesn't matter. ?But for RF amplification, we're screwed.
73 Jim N6OTQ
* ?For high-value devices they actually make and package garbage dies that will pass minimal tests. ?It's exactly the same as how the Chinese dumped melamine into dog food and baby formula -- it passed the minimal tests for protein content.
From: David
To: TekScopes@...
Sent: Sunday,
January 20, 2013 7:24 PM
Subject: Re: [TekScopes] Re: Type 184 Time Mark Generator Transistor Question
Has someone actually counterfeited 2N3904s?? How desperate did they have to be? On Sun, 20 Jan 2013 17:19:02 -0800 (PST), Jim < n6otq@...> wrote: >I hope they're not counterfeit .... > >You should test a few to see where Ft seems to be. > >73 >Jim N6ITQ? ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: ? ? <*> Your email settings: ? ? Individual Email | Traditional <*> To change settings online go
to: ? ? ? ? (Yahoo! ID required) <*> To change settings via email: ? ? TekScopes-digest@... ? ? TekScopes-fullfeatured@...<*> To unsubscribe from this group, send an email to: ? ? TekScopes-unsubscribe@...<*> Your use of Yahoo! Groups is subject to: ? ?
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Re: 2465 - impending U800 failure?
It may fix some of the U800s that have failed:
Please search this forum:
"U800 baking"
This has been discussed ad nauseam.
--Victor
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Show quoted text
--- In TekScopes@..., Jeff Machesky wrote:
Removing the heat from the plastic should in turn drop the temperature
of the metal fin some. Now does that produce undesirable thermal shifts,
no idea. In my case I'm pulling heat from a little of both, but mostly
the plastic.
So what does baking the chip actually fix? I know some IC's are
sensitive to humidity, but this is usually only just before the high
temperature of a reflow oven. The trapped moisture can cause defects
when heated.
Jeff
On 1/20/2013 6:07 PM, Dave C wrote:
Last time 'round on this topic I designed a heatsink that contacts
only the metal tab parts of U800, not the plastic body. This is the
intended (I think) means of getting the heat out of the chip.
The drawing of this heatsink is in the Tekscopes files page on the
Yahoo Groups web site. Look for a folder titled "U800". Its in there.
Dave
-=-=-=-
On 20 January 2013, at 2:05 PM, Jeff Machesky wrote:
Is all of this heat related? One of the first things I did when getting
my 2465BDM was strap a very large heat sink to the U800 chip with good
quality thermal compound and very secure mounting. It's larger then the
chip. It runs just over room temperature with the case on. I measured it
with a type K probe through the vents and touching the middle of the
heat sink with a dab of thermal compound over a half hour or so time frame.
I do notice mine drifts a tiny tiny bit on warm up, one or two mm to
the
left. It later snaps back about 1mm to the right.
Jeff
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Re: Type 184 Time Mark Generator Transistor Question
Has someone actually counterfeited 2N3904s? How desperate did they
have to be?
toggle quoted message
Show quoted text
On Sun, 20 Jan 2013 17:19:02 -0800 (PST), Jim <n6otq@...> wrote: I hope they're not counterfeit ....
You should test a few to see where Ft seems to be.
73
Jim N6ITQ
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Re: Type 184 Time Mark Generator Transistor Question
I am not sure why Tektronix listed the 2N918 as a replacement for the 2N3605 and I even went back and confirmed the specifications. My guess is that it had something to do with storage time, economics, pinout, or a mistake. The worst case problem I can think of is that the 2N3904 transistors oscillate due to higher current gain in some cases but I would consider that very unlikely if Tektronix was recommending the much faster 2N918 as a replacement. If it does happen, those little ferrite RFI suppression beads would fix it. I had to use them when I replaced relatively slow 2N3565s with 2N3904s in my DC505. The 2N3565s were dying of age. On Mon, 21 Jan 2013 01:04:11 -0000, "andersen_bill@..." <andersen_bill@...> wrote: Well, I just ordered a bag of 100 2N3904's for $4.
Hopefully all goes well
B
--- In TekScopes@..., "andersen_bill@..." wrote:
I am repairing a 184 that has had transistors removed from the countdown board.
I am looking at;
Q104
Q114
Q134
SM says "selected from 2N3251"
I can get 2N3251A's local.
I looked at the data sheets. Specs are close. Looks like the A has higher ratings.
Does anyone know if they will work or do I need the non A part?
TIA
B
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Re: Type 184 Time Mark Generator Transistor Question
I hope they're not counterfeit ....
You should test a few to see where Ft seems to be.
73 Jim N6ITQ?
From: "andersen_bill@..."
To: TekScopes@...
Sent: Sunday, January 20, 2013 7:04 PM
Subject: [TekScopes] Re: Type 184 Time Mark Generator Transistor Question
Well, I just ordered a bag of 100
2N3904's for $4. Hopefully all goes well B --- In TekScopes@..., "andersen_bill@..."? wrote: > > I am repairing a 184 that has had transistors removed from the countdown board. > > I am looking at; > > Q104 > > Q114 > > Q134 > > SM says "selected from 2N3251" > > I can get 2N3251A's local. > > I looked at the data sheets. Specs are close. Looks like the A has higher ratings. > > Does anyone know if they will work or do I need the non A part? > > TIA > > B > ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: ? ? <*> Your email settings: ? ? Individual Email | Traditional <*> To change settings online go to: ? ? ? ? (Yahoo! ID required) <*> To change settings via email: ? ? TekScopes-digest@... ? ? TekScopes-fullfeatured@...<*> To unsubscribe from this group, send an email to: ? ? TekScopes-unsubscribe@...<*> Your use of Yahoo! Groups is subject to: ? ?
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Re: 2465 - impending U800 failure?
Removing the heat from the plastic should in turn drop the temperature of the metal fin some. Now does that produce undesirable thermal shifts, no idea. In my case I'm pulling heat from a little of both, but mostly the plastic.
So what does baking the chip actually fix? I know some IC's are sensitive to humidity, but this is usually only just before the high temperature of a reflow oven. The trapped moisture can cause defects when heated.
Jeff
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Show quoted text
On 1/20/2013 6:07 PM, Dave C wrote:
Last time 'round on this topic I designed a heatsink that contacts only the metal tab parts of U800, not the plastic body. This is the intended (I think) means of getting the heat out of the chip.
The drawing of this heatsink is in the Tekscopes files page on the Yahoo Groups web site. Look for a folder titled "U800". Its in there.
Dave
-=-=-=-
On 20 January 2013, at 2:05 PM, Jeff Machesky wrote:
Is all of this heat related? One of the first things I did when getting
my 2465BDM was strap a very large heat sink to the U800 chip with good
quality thermal compound and very secure mounting. It's larger then the
chip. It runs just over room temperature with the case on. I measured it
with a type K probe through the vents and touching the middle of the
heat sink with a dab of thermal compound over a half hour or so time frame.
I do notice mine drifts a tiny tiny bit on warm up, one or two mm to
the
left. It later snaps back about 1mm to the right.
Jeff
|
Re: 2465 - impending U800 failure?
Last time 'round on this topic I designed a heatsink that contacts only the metal tab parts of U800, not the plastic body. This is the intended (I think) means of getting the heat out of the chip.
The drawing of this heatsink is in the Tekscopes files page on the Yahoo Groups web site. Look for a folder titled "U800". Its in there.
Dave
-=-=-=-
toggle quoted message
Show quoted text
On 20 January 2013, at 2:05 PM, Jeff Machesky wrote: Is all of this heat related? One of the first things I did when getting
my 2465BDM was strap a very large heat sink to the U800 chip with good
quality thermal compound and very secure mounting. It's larger then the
chip. It runs just over room temperature with the case on. I measured it
with a type K probe through the vents and touching the middle of the
heat sink with a dab of thermal compound over a half hour or so time frame.
I do notice mine drifts a tiny tiny bit on warm up, one or two mm to the
left. It later snaps back about 1mm to the right.
Jeff
|
Re: Type 184 Time Mark Generator Transistor Question
Well, I just ordered a bag of 100 2N3904's for $4.
Hopefully all goes well
B
toggle quoted message
Show quoted text
--- In TekScopes@..., "andersen_bill@..." wrote:
I am repairing a 184 that has had transistors removed from the countdown board.
I am looking at;
Q104
Q114
Q134
SM says "selected from 2N3251"
I can get 2N3251A's local.
I looked at the data sheets. Specs are close. Looks like the A has higher ratings.
Does anyone know if they will work or do I need the non A part?
TIA
B
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Re: Type 184 Time Mark Generator Transistor Question
33 PN918's @ 0.33 each would be only 11 bucks, so why again would one substitute if an exact/jelly bean brother (PN918) part is available? Far too many times have I seen someone chase down a problem caused by a replacement "that should've worked"
Again, the OP asked "Is their (sic) a more available replacemnt for this type?
One google search, and one can see the originals are available, and are their plastic, TO-92 jelly bean relative.
Not to say that the 2n3904 wouldn't work....but the MPSH11 is obsolete, so that wouldn't help the OP with availabitlity issues.
No flame intended, just trying to help the OP with availability of the orignial parts.
Cheers,
Taylor
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--- In TekScopes@..., David wrote:
The price would add up fast if he was looking to replace all 33 of the
2N3605/2N918 transistors in his 184. Most of the other small signal
NPN transistors could be replaced as well.
Jelly bean parts are produced by multiple manufacturers in large
quantities and are almost always the most economical. New 2N918
transistors only come from Central Semiconductor and everything or
just about everything they make is for the replacement market at a
high premium although not as high as NTE. The original 2N3605
Tektronix used is not manufactured any more.
The 2N3904 is hardly a questionable substitution for the original
2N3605.
On Sun, 20 Jan 2013 23:55:47 -0000, "taylorvandy"
wrote:
OP was looking for a more available part - not a jelly bean part, whatever that is. If the original is still available, why the subs?
And no, most of us buy our parts in onesie-twosie fashion. What cheaper? 3 bucks for the originals, or $3.50/100 for a questionable sub?
Not trying to flame, just honoring the OP's intentions.
Cheers,
Taylor
--- In TekScopes@..., David wrote:
Under $2 is not cheap for a jelly bean part. 2N3904 transistors are
like 3.4 cents each. Even an MPSH11 which is a closer match to the
2N918 can be had for 8 cents each.
Note that the above prices are for quantities of 100 since I never buy
jelly bean parts like that in smaller quantities.
On Sun, 20 Jan 2013 15:29:44 -0800 (PST), Taylor Vandergrifft
wrote:
Why all the subs?? 2n918's are still very available, and at least tow places have them under $2 each.?? Hard to rationalize subbing an available, cheapo transistor.
?
Cheers,
Taylor
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Re: 475 progress but another road-block
The 112 is ok for the 110 measurement.
?
Resistance measurements depend on several variables including lead
polarity, meter type, and active device junction variables.
?
You need to make a dc voltage measurement on each of the deflection plates
(left and right, top and?bottom)?and report the measurements. Let's
see if the beam is anywhere near the center.
?
Next thing to check is the triggering. Are you getting a sweep?
?
That should keep you busy for a while :).
?
Tom
?
?
?
?
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----- Original Message -----
Sent: Sunday, January 20, 2013 3:45
PM
Subject: [TekScopes] 475 progress but
another road-block
?
So, with the help of the folks here and some troubleshooting, I've gotten
my 475 closer to being usable again.
However, I'm stuck at a new spot
now. I am getting almost perfect voltages at each test point except for the
110V TP which shows roughly 112.4 (which is still within tolerance, just not
ideal).
The odd thing is that when I test resistance to ground, only about
half of the points are within tolerance. 110, -15, U50, and 105 all show much
more resistance than they should. Especially -15 which is showing several K of
resistance (book shows it should be 480 ohms).
At some point, I also
found a trace that was broken and made the repair. I now get a display if I
use the beam finder button. However, I do not get a display without using that
button. When I adjust knobs on the front, that "beam found trace" does move
(mostly as I would expect). It doesn't seem to stay perfectly still in all
cases, but I'm assuming that is because something is still bad and causing
issues (including the resistance variances).
I do not have another
scope in order to test ripple. I've been trying to follow the troubleshooting
flow chart in the manual, but I may be getting confused. If I press the beam
finder and adjust the trace to the center, but then release the beam finder
button and still see no trace, should I be disconnecting the delay line as my
next test?
Or have I gotten ahead of myself?
-Josh
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Re: Type 184 Time Mark Generator Transistor Question
The price would add up fast if he was looking to replace all 33 of the 2N3605/2N918 transistors in his 184. Most of the other small signal NPN transistors could be replaced as well. Jelly bean parts are produced by multiple manufacturers in large quantities and are almost always the most economical. New 2N918 transistors only come from Central Semiconductor and everything or just about everything they make is for the replacement market at a high premium although not as high as NTE. The original 2N3605 Tektronix used is not manufactured any more. The 2N3904 is hardly a questionable substitution for the original 2N3605. On Sun, 20 Jan 2013 23:55:47 -0000, "taylorvandy" <taylorvandy@...> wrote: OP was looking for a more available part - not a jelly bean part, whatever that is. If the original is still available, why the subs?
And no, most of us buy our parts in onesie-twosie fashion. What cheaper? 3 bucks for the originals, or $3.50/100 for a questionable sub?
Not trying to flame, just honoring the OP's intentions.
Cheers,
Taylor
--- In TekScopes@..., David wrote:
Under $2 is not cheap for a jelly bean part. 2N3904 transistors are
like 3.4 cents each. Even an MPSH11 which is a closer match to the
2N918 can be had for 8 cents each.
Note that the above prices are for quantities of 100 since I never buy
jelly bean parts like that in smaller quantities.
On Sun, 20 Jan 2013 15:29:44 -0800 (PST), Taylor Vandergrifft
wrote:
Why all the subs?? 2n918's are still very available, and at least tow places have them under $2 each.?? Hard to rationalize subbing an available, cheapo transistor.
?
Cheers,
Taylor
|
Re: Type 184 Time Mark Generator Transistor Question
OP was looking for a more available part - not a jelly bean part, whatever that is. If the original is still available, why the subs?
And no, most of us buy our parts in onesie-twosie fashion. What cheaper? 3 bucks for the originals, or $3.50/100 for a questionable sub?
Not trying to flame, just honoring the OP's intentions.
Cheers,
Taylor
toggle quoted message
Show quoted text
--- In TekScopes@..., David wrote:
Under $2 is not cheap for a jelly bean part. 2N3904 transistors are
like 3.4 cents each. Even an MPSH11 which is a closer match to the
2N918 can be had for 8 cents each.
Note that the above prices are for quantities of 100 since I never buy
jelly bean parts like that in smaller quantities.
On Sun, 20 Jan 2013 15:29:44 -0800 (PST), Taylor Vandergrifft
wrote:
Why all the subs?? 2n918's are still very available, and at least tow places have them under $2 each.?? Hard to rationalize subbing an available, cheapo transistor.
?
Cheers,
Taylor
|
Re: Type 184 Time Mark Generator Transistor Question
Under $2 is not cheap for a jelly bean part. 2N3904 transistors are like 3.4 cents each. Even an MPSH11 which is a closer match to the 2N918 can be had for 8 cents each. Note that the above prices are for quantities of 100 since I never buy jelly bean parts like that in smaller quantities. On Sun, 20 Jan 2013 15:29:44 -0800 (PST), Taylor Vandergrifft <taylorvandy@...> wrote: Why all the subs?? 2n918's are still very available, and at least tow places have them under $2 each.?? Hard to rationalize subbing an available, cheapo transistor.
?
Cheers,
Taylor
|
2247A Channel a Sweep fixed!
????? For those interested in the fixes I found for my 2247A where channel A sweep would not visibly function and the unit would not work at all?
????? What I found was two pins bent under on two cables that someone had put them back and did not pay attention to the pins being put ent back without being bent.?These pins are extremely delicate and can bend very easy.
???? I did notice we had a newcomer that was experiencing issues. CHECK ALL YOUR CABLES. Pull them all off and check the pins!!!
?
?
?? All The Best, Rich D.
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Re: Type 184 Time Mark Generator Transistor Question
Thanks for the replies.
I picked up two of these at the same time. Both work but both had transistors removed.
I was looking for what were the most available parts for me that would work.
Thanks for the info.
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Show quoted text
--- In TekScopes@..., Taylor Vandergrifft wrote:
Why all the subs?? 2n918's are still very available, and at least tow places have them under $2 each.?? Hard to rationalize subbing an available, cheapo transistor.
?
Cheers,
Taylor
|
Re: Type 184 Time Mark Generator Transistor Question
Er, make that "two" places, and that doesn't include evilbay....
Cheers,
Taylor
Why all the subs? 2n918's are still very available, and at least tow places have them under $2 each. Hard to rationalize subbing an available, cheapo transistor.
Cheers,
Taylor
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Show quoted text
--- In TekScopes@..., David wrote:
No, not really. The 2N2222 has a higher power rating than the others
and the 2N4401 has a higher current rating than the 2N3904 but none of
that will matter in this application.
As far as performance, what could be improved? It is a time mark
generator. I would not replace the transistors unless I was fixing a
problem or some had already gone bad presumably because of age.
The 2N3904 is probably the best choice and the least expensive.
On Sun, 20 Jan 2013 23:02:12 -0000, "andersen_bill@..."
wrote:
That was my typo on the 2N918.
Of the 3 you list is one offer any better performance?
2N2222, 2N3904, and 2N4401
Thanks
--- In TekScopes@..., David wrote:
It is 2N918 and not 2N198. The 2N918 was a very common early VHF
transistor. My 184 has 2N3605 transistors as well.
The 2N918 is:
900 MHz @ 4 mA
30 Vcbo 15 Vceo 50 mA
From the Tektronix parts book the 2N3605 is:
300 MHz @ 10mA
18 Vcbo 14 Vceo 200 mA
The ubiquitous and inexpensive 2N2222, 2N3904, and 2N4401 should all
work as replacements.
On Sun, 20 Jan 2013 21:56:17 -0000, "andersen_bill@"
wrote:
Now that I think about that is the 2N198 missing a digit?
They are all listed in the SM as 2N198, semms like the last digit is missing?
--- In TekScopes@..., "andersen_bill@" wrote:
I have another transistor question on this one.
The unit is up and running as stated and looks to be within specs.
I was checking the rest of the transistors on the countdown board and their are quit a few of the same type listed in the SM. Q193, for example. The service manual states for these, "replaceable by 2N198".
All of the ones in my unit are marked 2N3605. They appear to untouched and original.
Is this correct? Is their a more available replacemnt for this type?
Maybe with better performance?
Thanks
|
David Hess