开云体育

7904 - NOS CRT ?

K7XYM All Messages By This Member #191935 So I know its a ludicrous question, but, I want to ask anyway. Are there any NOS CRTs that ever come up for the 7904 ? I am asking because I am in the middle of a _major_ restore to new, complete with tons of mods to go beyond original performance, on my 7904 and I am now aware that these CRT age and have issues with beam spot size not related to electronics. I have 3 7904's and I have swapped electronics, as a whole, between the chassis only one tube ends with with a super sharp spot size. The other 2 are larger spot size and one has kinda odd behavior with brightness adjustments. Again that is with swapping ALL the electronics. Its a tube thing. So no hope of getting a NOS CRT for these right ? I am going to refurb and mod 2 and I might have to just buy 7904's looking for a good tube. Anyone have any full parted 7904 chassis with just the tube ?
Morris Odell All Messages By This Member #191938 I'd like one too but down here in Australia the prospects are even bleaker. I have one perfect 7904 and another that's got a dud CRT that will end up as a teaching exercise and parts mule unless a CRT turns up. I'm not holding my breath! Morris
Tom Lee All Messages By This Member #191940 As you might have guessed, it is rare to find one that is truly NOS, and even rarer to find such a beast at a cost that doesn't have to be expressed in dBdollars to avoid sticker shock. To increase your odds slightly, you might consider also looking for a crt from a 7704A. It's the same jug as that in the 7904. Good luck! -- Cheers, Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 toggle quoted message Show quoted text On 3/20/2022 22:30, K7XYM wrote: So I know its a ludicrous question, but, I want to ask anyway. Are there any NOS CRTs that ever come up for the 7904 ? I am asking because I am in the middle of a _major_ restore to new, complete with tons of mods to go beyond original performance, on my 7904 and I am now aware that these CRT age and have issues with beam spot size not related to electronics. I have 3 7904's and I have swapped electronics, as a whole, between the chassis only one tube ends with with a super sharp spot size. The other 2 are larger spot size and one has kinda odd behavior with brightness adjustments. Again that is with swapping ALL the electronics. Its a tube thing. So no hope of getting a NOS CRT for these right ? I am going to refurb and mod 2 and I might have to just buy 7904's looking for a good tube. Anyone have any full parted 7904 chassis with just the tube ?
JOE All Messages By This Member #191947 The 7704A CRT is the same as the 7904 CRT, but the 7904 requires a custom matched set of terminations. A NOS 7904 CRT comes with them. This all assumes my memory is up to snuff.
Jim Ford All Messages By This Member #191961 LOL, dBdollars!? I'll have to remember that one!Jim Ford?Sent from my T-Mobile 4G LTE Device toggle quoted message Show quoted text -------- Original message --------From: Tom Lee <tomlee@...> Date: 3/21/22 2:29 AM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] 7904 - NOS CRT ? As you might have guessed, it is rare to find one that is truly NOS, and even rarer to find such a beast at a cost that doesn't have to be expressed in dBdollars to avoid sticker shock.To increase your odds slightly, you might consider also looking for a crt from a 7704A. It's the same jug as that in the 7904.Good luck!-- Cheers,Tom-- Prof. Thomas H. LeeAllen Ctr., Rm. 205350 Jane Stanford WayStanford UniversityStanford, CA 94305-4070 3/20/2022 22:30, K7XYM wrote:> So I know its a ludicrous question, but, I want to ask anyway. Are there any NOS CRTs that ever come up for the 7904 ?>> I am asking because I am in the middle of a _major_ restore to new, complete with tons of mods to go beyond original performance, on my 7904 and I am now aware that these CRT age and have issues with beam spot size not related to electronics. I have 3 7904's and I have swapped electronics, as a whole, between the chassis only one tube ends with with a super sharp spot size. The other 2 are larger spot size and one has kinda odd behavior with brightness adjustments. Again that is with swapping ALL the electronics. Its a tube thing.>> So no hope of getting a NOS CRT for these right ?>> I am going to refurb and mod 2 and I might have to just buy 7904's looking for a good tube.>> Anyone have any full parted 7904 chassis with just the tube ?>>> >>
Mark Vincent All Messages By This Member #191962 If you find one that is known good, that should help. I do have known good ones, P31 type, that should be give a sharp enough trace for you. The odd behavior you describe may be the double-peaking. Morris, the shipping to where you are is usually the expensive part due to the size instead of weight, in this type of case. Mark
n4buq All Messages By This Member #191966 Regarding this, I've seen the term "double-peaking" used but am not finding examples of it. If I increase the intensity too much in my 7704A, I start seeing a thickening of area around the trace (halo?) whereas lower intensity traces are sharp and without that effect. Is the fatter trace double-peaking? Thanks, Barry - N4BUQ toggle quoted message Show quoted text ----- Original Message ----- From: "K7XYM" <public2@...> To: "tekscopes" <[email protected]> Sent: Monday, March 21, 2022 12:30:12 AM Subject: [TekScopes] 7904 - NOS CRT ? So I know its a ludicrous question, but, I want to ask anyway. Are there any NOS CRTs that ever come up for the 7904 ? I am asking because I am in the middle of a _major_ restore to new, complete with tons of mods to go beyond original performance, on my 7904 and I am now aware that these CRT age and have issues with beam spot size not related to electronics. I have 3 7904's and I have swapped electronics, as a whole, between the chassis only one tube ends with with a super sharp spot size. The other 2 are larger spot size and one has kinda odd behavior with brightness adjustments. Again that is with swapping ALL the electronics. Its a tube thing. So no hope of getting a NOS CRT for these right ? I am going to refurb and mod 2 and I might have to just buy 7904's looking for a good tube. Anyone have any full parted 7904 chassis with just the tube ?
Mark Vincent All Messages By This Member #191967 Barry, What you seeing is a good tube. At high brightness, the phosphour is being struck with a large amount of electrons exciting the phosphour around the ones being struck causing them to glow. Double-peaking is when the tube is weak and the brightness will be fair, low then fair again as the intensity is from low to max. The focus is usually out not matter the position of the focus control. The tube will also be slow to show a trace when turned on. Mark
Harvey White All Messages By This Member #191970 Nope, it's not. Double peaking, as I've heard it, is increasing the intensity, then while still advancing the control, the intensity diminishes, then starts to increase again. As I've heard, the thickening of a trace with intensity beyond a certain point is normal, and I've seen it on all sorts of scope tubes.? The 7904 (and just heard about the 7704A) have dome mesh CRTS, which have their own effect on beam intensity and focus. The halo seems to be an artifact of the dome mesh, at least, early ones. Note that electrons have the same charge, and tend to repel each other.? More electrons in the same space lets them repel each other better, hence a fatter beam. Harvey toggle quoted message Show quoted text On 3/21/2022 12:36 PM, n4buq wrote: Regarding this, I've seen the term "double-peaking" used but am not finding examples of it. If I increase the intensity too much in my 7704A, I start seeing a thickening of area around the trace (halo?) whereas lower intensity traces are sharp and without that effect. Is the fatter trace double-peaking? Thanks, Barry - N4BUQ ----- Original Message ----- From: "K7XYM" <public2@...> To: "tekscopes" <[email protected]> Sent: Monday, March 21, 2022 12:30:12 AM Subject: [TekScopes] 7904 - NOS CRT ? So I know its a ludicrous question, but, I want to ask anyway. Are there any NOS CRTs that ever come up for the 7904 ? I am asking because I am in the middle of a _major_ restore to new, complete with tons of mods to go beyond original performance, on my 7904 and I am now aware that these CRT age and have issues with beam spot size not related to electronics. I have 3 7904's and I have swapped electronics, as a whole, between the chassis only one tube ends with with a super sharp spot size. The other 2 are larger spot size and one has kinda odd behavior with brightness adjustments. Again that is with swapping ALL the electronics. Its a tube thing. So no hope of getting a NOS CRT for these right ? I am going to refurb and mod 2 and I might have to just buy 7904's looking for a good tube. Anyone have any full parted 7904 chassis with just the tube ?
n4buq All Messages By This Member #191973 Mark, Okay - that makes better sense in that the brightness peaks twice. Thanks, Barry - N4BUQ toggle quoted message Show quoted text ----- Original Message ----- From: "Mark Vincent" <orangeglowaudio@...> To: "tekscopes" <[email protected]> Sent: Monday, March 21, 2022 11:58:27 AM Subject: Re: [TekScopes] 7904 - NOS CRT ? Barry, What you seeing is a good tube. At high brightness, the phosphour is being struck with a large amount of electrons exciting the phosphour around the ones being struck causing them to glow. Double-peaking is when the tube is weak and the brightness will be fair, low then fair again as the intensity is from low to max. The focus is usually out not matter the position of the focus control. The tube will also be slow to show a trace when turned on. Mark
Tom Lee All Messages By This Member #191975 There have been multiple discussions here on the topic, with no definite conclusions. But perhaps the best discussion was a couple of years ago. Search for “mechanism of double peaking” AND’ed with “updated”. Cheers Tom Sent from my iThing; please forgive the typos and brevity toggle quoted message Show quoted text On Mar 21, 2022, at 11:19, David Templeton <vexorg.calibra@...> wrote: ?So what physically inside the tube cause it to dim then go brighter again David On 21 Mar 2022, at 17:55, n4buq <n4buq@...> wrote: ?Mark, Okay - that makes better sense in that the brightness peaks twice. Thanks, Barry - N4BUQ ----- Original Message ----- From: "Mark Vincent" <orangeglowaudio@...> To: "tekscopes" <[email protected]> Sent: Monday, March 21, 2022 11:58:27 AM Subject: Re: [TekScopes] 7904 - NOS CRT ? Barry, What you seeing is a good tube. At high brightness, the phosphour is being struck with a large amount of electrons exciting the phosphour around the ones being struck causing them to glow. Double-peaking is when the tube is weak and the brightness will be fair, low then fair again as the intensity is from low to max. The focus is usually out not matter the position of the focus control. The tube will also be slow to show a trace when turned on. Mark
JOE All Messages By This Member #191978 I happen to have a true NOS 154-0644-00 CRT in my possession. It includes the matched termination. What I don't know is specifics of the -00 version. At one time I had an awesome Tek CRT cross-reference but can't find it. I am willing to part with it, but it would be helpful if someone could supply specifics of the -00. Also, sorry to our off shore friends, but continental USA only. Joe
Mark Vincent All Messages By This Member #191979 Joe, Here is what Hakan said in a previous post about the -00 version.: There were four revisions of 154-0644-0x, -00, -04, -05 and -09. Only -00 (< B040600) and -05 (repl for -00 and used from B040600) were used in 7704A. The other two were used by 7854 and 790x series opt 78 i.e P11 phosphor. For some reason 7704A opt 78 used another CRT. If the CRT was replaced on 7704A below B221300 a Part Replacement kit (050-1732-01) was required. It contained the -05 CRT and two resistors (one for 7704A and one for 7904/R7903) used to reduce the heater voltage to extend CRT life. Kit instructions here: /H?kan Mark

Previous Topic Next Topic