545 HV won't oscillate 100% of the time.
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Daniel Koller
Howdy, The recent discussions on HV repairs has me thinking I should look into the issues in my 545 (not A or B, old style square case). It works
very very well, but about half of the time, increasingly more, the HV circuit will not oscillate. If I pull the plug-in out and drop it back in, it will work. I know this is not a recommended option! Alternatively, if I shut it off and wait for
it to cool, it will work when I turn it on with about the same probability, or a little less. Once the scope is on it's up to spec. The 6AU5 is not brand new, but is good. It was replaced recently with no improvement. So, suggestions as to where to start on this intermittant problem are welcome. Is there anything I should look for or measure that might indicate what is getting tired? Dan
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Daniel Koller
--- Re-sent in plain text, just in case the first one did not go right. ---
Howdy, The recent discussions on HV repairs has me thinking I should look into the issues in my 545 (not A or B, old style square case). It works very very well, but about half of the time, increasingly more, the HV circuit will not oscillate. If I pull the plug-in out and drop it back in, it will work. I know this is not a recommended option! Alternatively, if I shut it off and wait for it to cool, it will work when I turn it on with about the same probability, or a little less. Once the scope is on it's up to spec. The 6AU5 is not brand new, but is good. It was replaced recently with no improvement. So, suggestions as to where to start on this intermittant problem are welcome. Is there anything I should look for or measure that might indicate what is getting tired? Dan
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Albert Otten
Hi Dan,
Again I suggest to add a protection diode from screen grid to the +100V supply. This prevents excessive anode current. Just some wild thoughts: I guess such excessive DC current might more or less saturate the transformer core and also reduce the tube's transductance (at zero control grid voltage). Such might create a stable state even before the power supply lines come up fully (specifically the center tap voltage?). The clamp might even guarantee start-up. If, when running, the regulated screen voltage is below 100 V, you can make the clamp permanent. I don't see why the plugin-trick works. Maybe it generates spikes at the supply lines that introduce enough resonance to start oscillation. I also don't see the true reason for the failures. Albert
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Morris Odell
If it's an older non A non B it's very unlikely to be to be the HV transformer problem but could be a faulty capacitor. I'd start by de-black beauty-ing it, especially all those in the low andhigh voltage power supplies. Leaky caps across the voltage dividers in the LVPS can cause the power supply voltages to be out of range so check them first. Morris
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Chuck Harris <cfharris@...>
Most of the time with the 545, the problem is the black beauty oil/paper
toggle quoted messageShow quoted text
tubular capacitors used for the HV filters. They always go bad, and if they haven't been replaced, you must replace them. Ceramic is fine. There is also a BB cap that is in series with the grid feedback winding, and another in parallel with the plate winding. Both must go. -Chuck Harris Daniel Koller wrote:
Howdy,
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Daniel Koller
I'll check and see what's in there. And when I take them out, I'll sell them on e-bay to an audiophool!!
toggle quoted messageShow quoted text
http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26 (No affiliation with the seller!) Dan
On Friday, December 6, 2013 11:27 PM, Chuck Harris <cfharris@...> wrote:
Most of the time with the 545, the problem is the black beauty oil/paper
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Don Black <donald_black@...>
I'm not so sure. Yours may be faulty,
these are tested good so they must be a rare animal.
Don Black. On 08-Dec-13 2:31 AM, Daniel Koller wrote:
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Daniel Koller
Hi all,
My caps probably are bad. When I first got the scope around 1980, I learned about "black beauties" and had to replace them in the power supply, but I think I recall being told that the bumble-bee types were fine, so those stayed in. Now it looks like I have leakage from them in the HV power supply. See the attached photo here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781 The two shiny black 0.001 uF caps stand out because they are coated in oil. You can't see it on the photo, but there is a film of liquid oil between the middle cap and the 56K resistor below it. Those two are coming out but being a big fan of "don't mess with it if it ain't broke" I might leave the other caps in unless there is an obvious failure. Mind you, my scope works well when it does turn on. But I've had some other modifications it seems. What's that square cap on the left and the 2.2K resistor doing there? I'll have to trace the circuit to see where they were put in and why. Maybe that was a long ago patch for the oscillator failure? Or the cause of it now? I see now why I had originally thought my scope was much younger than it is - before I learned from the group here that the "brown" Teks were pre-1954. There is this circuit board in my scope: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052 Someone seems to have made factory improvements circa 1967. What was in its place before this? Is it possible my additional HV circuit components were placed in the same upgrades/refurbishment? Back to the shop. I've got an hour before guests arrive! Dan On Saturday, December 7, 2013 10:58 AM, Don Black <donald_black@...> wrote: I'm not so sure. Yours may be faulty, these are tested good so they must be a rare animal.black beauty oil/paper always go bad, and iftubular capacitors used for the HV filters. They them. Ceramic is fine.they haven't been replaced, you must replace feedback winding, must go.and another in parallel with the plate winding. Both thinking I should look into the issues It works very very well, butin my 545 (not A or B, old style square case). circuit will not oscillate. Ifabout half of the time, increasingly more, the HV will work. I know this is not aI pull the plug-in out and drop it back in, it off and wait for it to cool, itrecommended option! Alternatively, if I shut it probability, or a little less.will work when I turn it on with about the same replaced recently with noOnce the scope is on it's up to spec. intermittant problem are welcome. Isimprovement. might indicate what is gettingthere anything I should look for or measure that tired?
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Don Black <donald_black@...>
I hope you get it sorted out Dan but I
was being facetious about the eBay tubes advertised as tested
good. I wonder what tests were done? I noticed another ad for
similar caps saying they were tested OK on a bridge. No mention of
leakage or if the bridge had to be adjusted for losses. Maybe I'm
just getting cynical in my old age.
Don Black, On 08-Dec-13 10:33 AM, Daniel Koller wrote:
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Don Black <donald_black@...>
Oops. I meant eBay bumblebee and black
beauty caps, not tubes. Freudian slip??
Don Black. On 08-Dec-13 8:09 PM, Don Black wrote:
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bonddaleena@...
I have replaced literally BUCKETS full of BBOD, Bumblebees, wax caps, etc. I have NEVER seen a single one that would pass a leakage test at rated voltage.
toggle quoted messageShow quoted text
They might 'test' fine for VALUE on my NIST traceable bridge, but they all leak at HV. As the Prez would say: "PERIOD!" ha ha ron N4UE
-----Original Message----- From: Don Black To: TekScopes Sent: Sun, Dec 8, 2013 4:17 am Subject: Re: [TekScopes] 545 HV won't oscillate 100% of the time. Oops. I meant eBay bumblebee and black
beauty caps, not tubes. Freudian slip??
Don Black. On 08-Dec-13 8:09 PM, Don Black wrote:
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Daniel Koller
Yup - I agree! I Ended up replacing C800, C803, C805 and C806 - basically all the remaining bumblebees in the primary circuit of my HV power supply. The two 0.001 uF caps were clearly leaking oil on the photo I posted earlier. What was less evident, and I didn't notice until I got some better lighting, was the crack lengthwise across the 0.01uF cap, second from the top in: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781
...and the 0.047 uF cap was similarly cracked on the bottom. Yet ALL tested just fine at low voltage on my new Chinese tester. But apply any voltage to them whatsoever (~>10V) and they all leaked to different degrees. They all had effective resistances of ~~10's of Megohms, so at 100V, ~~10 micro amps leakage. I'm glad I did not get rid of my old Eico 950 tester! So, now my HV works, but with a catch. It turns on by itself about 1 minute after the tubes turn on. That's about 1 minute after the B+ relay clicks on. I can occasionally accelerate the turn-on by jostling the intensity knob. So, it's not 100% fixed, but I am fine with this. I don't have the patience to troubleshoot further since it is working well when warmed up. I'm thinking a weak 6AU5 is the culprit here, no? In addition I replaced the vertical output capacitor because I measured ~20V DC at the vertical signal out terminal with no vertical deflection on the screen - leakage. There are a couple oil filled caps left in the power supply that don't appear to be cracked or leaking, and I am just going to have to leave them there for now. I'll stock up on replacement parts in the meantime. All voltages are dead on - I'm not touching the power supply. Finally, I now understand those extra components in my photo. The 33K (not 2.2K - it's hard to tell the orange from the red) and the 470 pF cap seem to have been added in some sort of factory refurb. These are present in the 545A schematic, so it seems my 545 was partly upgraded to a 545A. That probably also explains the Silicon diodes on that board in the power supply. Dan On Sunday, December 8, 2013 9:35 AM, "bonddaleena@..." <bonddaleena@...> wrote: I have replaced literally BUCKETS full of BBOD, Bumblebees, wax caps, etc. I have NEVER seen a single one that would pass a leakage test at rated voltage.scope around 1980, I learned about "black beauties" and had to replace them in the power supply, but I think I recall being told that the bumble-bee types were fine, so those stayed in. Now it looks like I have leakage from them in the HV power supply. See the attached photo here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781 they are coated in oil. You can't see it on theThe two shiny black 0.001 uF caps stand out because photo, but there is a film of liquid oil between the middle cap and the 56K resistor below it. Those two are coming out but being a big fan of "don't mess with it if it ain't broke" I might leave the other caps in unless there is an obvious failure. Mind you, my scope works well when it does turn on. What's that square cap on the left and the 2.2K resistor doing there? I'll have to trace the circuit to see where they were put in and why. Maybe that was a long ago patch for the oscillator failure? Or the cause of it now? much younger than it is - before I learned from the group here that the "brown" Teks were pre-1954. There is this circuit board in my scope: 1967. What was in its place before this? Is ithttp://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052 possible my additional HV circuit components were placed in the same upgrades/refurbishment? arrive! tested good so they must be a rare animal. I take them out, I'll sell them on e-bay to an audiophool!! Harris <cfharris@...> wrote:http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26 is theMost of the time with the 545, the problem filters. Theyblack beauty oil/papertubular capacitors used for the HV replacealways go bad, and ifthey haven't been replaced, you must with the gridthem. Ceramic is fine. winding. Bothfeedback winding,and another in parallel with the plate has memust go. square case).thinking I should look into the issuesin my 545 (not A or B, old style more, the HVIt works very very well, butabout half of the time, increasingly back in, itcircuit will not oscillate. IfI pull the plug-in out and drop it if I shut itwill work. I know this is not arecommended option! Alternatively, about the sameoff and wait for it to cool, itwill work when I turn it on with good. It wasprobability, or a little less.Once the scope is on it's up to spec. on thisreplaced recently with noimprovement. measure thatintermittant problem are welcome. Isthere anything I should look for or because avast! Antivirus protection is active.might indicate what is gettingtired? This email is free from viruses and malware because avast! Antivirus protection is active.________________________________________________________________This email is free from viruses and malware because avast! Antivirus protection is active.
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bonddaleena@...
Hi Dan. One thing I collect is test equipment. I have a LOT of cap testers. The battery powered ones work OK for value but not leakage, as you mentioned.....
toggle quoted messageShow quoted text
Even though I have some high $ commercial leakage testers, my go-to cap tester (on my main bench) is an OLD VTVM and a HVPS that increments in 50V steps up to 600VDC. It was explained to me years ago by Dr. Jerry, the Technical Consultant for the Collins Radio Collector Assn. Simple, fast and dependable. ron N4UE.
-----Original Message----- From: Daniel Koller To: TekScopes Sent: Sun, Dec 8, 2013 5:48 pm Subject: Re: [TekScopes] 545 HV won't oscillate 100% of the time. Yup - I agree! I Ended up replacing C800, C803, C805 and C806 - basically all the remaining bumblebees in the primary circuit of my HV power supply. The two 0.001 uF caps were clearly leaking oil on the photo I posted earlier. What was less evident, and I didn't notice until I got some better lighting, was the crack lengthwise across the 0.01uF cap, second from the top in: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781
...and the 0.047 uF cap was similarly cracked on the bottom. Yet ALL tested just fine at low voltage on my new Chinese tester. But apply any voltage to them whatsoever (~>10V) and they all leaked to different degrees. They all had effective resistances of ~~10's of Megohms, so at 100V, ~~10 micro amps leakage. I'm glad I did not get rid of my old Eico 950 tester! So, now my HV works, but with a catch. It turns on by itself about 1 minute after the tubes turn on. That's about 1 minute after the B+ relay clicks on. I can occasionally accelerate the turn-on by jostling the intensity knob. So, it's not 100% fixed, but I am fine with this. I don't have the patience to troubleshoot further since it is working well when warmed up. I'm thinking a weak 6AU5 is the culprit here, no? In addition I replaced the vertical output capacitor because I measured ~20V DC at the vertical signal out terminal with no vertical deflection on the screen - leakage. There are a couple oil filled caps left in the power supply that don't appear to be cracked or leaking, and I am just going to have to leave them there for now. I'll stock up on replacement parts in the meantime. All voltages are dead on - I'm not touching the power supply. Finally, I now understand those extra components in my photo. The 33K (not 2.2K - it's hard to tell the orange from the red) and the 470 pF cap seem to have been added in some sort of factory refurb. These are present in the 545A schematic, so it seems my 545 was partly upgraded to a 545A. That probably also explains the Silicon diodes on that board in the power supply. Dan On Sunday, December 8, 2013 9:35 AM, "bonddaleena@..." <bonddaleena@...> wrote: >I have replaced literally BUCKETS full of BBOD, Bumblebees, wax caps, etc. I have NEVER seen a single one that would pass a leakage test at rated voltage. >They might 'test' fine for VALUE on my NIST traceable bridge, but they all leak at HV. > >As the Prez would say: > >"PERIOD!" > >ha ha > >ron >N4UE > > > > > > > >-----Original Message----- >From: Don Black <donald_black@...> >To: TekScopes <TekScopes@...> >Sent: Sun, Dec 8, 2013 4:17 am >Subject: Re: [TekScopes] 545 HV won't oscillate 100% of the time. > > > >Oops. I meant eBay bumblebee and black beauty caps, not tubes. Freudian slip?? > >Don Black. > >On 08-Dec-13 8:09 PM, Don Black wrote: > > >>I hope you get it sorted out Dan but I was being facetious about the eBay tubes advertised as tested good. I wonder what tests were done? I noticed another ad for similar caps saying they were tested OK on a bridge. No mention of leakage or if the bridge had to be adjusted for losses. Maybe I'm just getting cynical in my old age. >> >>Don Black, >> >>On 08-Dec-13 10:33 AM, Daniel Koller wrote: >> >> >>>Hi all, >>> My caps probably are bad. When I first got the scope around 1980, I learned about "black beauties" and had to replace them in the power supply, but I think I recall being told that the bumble-bee types were fine, so those stayed in. Now it looks like I have leakage from them in the HV power supply. See the attached photo here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781 >>>The two shiny black 0.001 uF caps stand out because they are coated in oil. You can't see it on the photo, but there is a film of liquid oil between the middle cap and the 56K resistor below it. Those two are coming out but being a big fan of "don't mess with it if it ain't broke" I might leave the other caps in unless there is an obvious failure. Mind you, my scope works well when it does turn on. >>> >>>But I've had some other modifications it seems. What's that square cap on the left and the 2.2K resistor doing there? I'll have to trace the circuit to see where they were put in and why. Maybe that was a long ago patch for the oscillator failure? Or the cause of it now? >>> >>>I see now why I had originally thought my scope was much younger than it is - before I learned from the group here that the "brown" Teks were pre-1954. There is this circuit board in my scope: >>>http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052 >>>Someone seems to have made factory improvements circa 1967. What was in its place before this? Is it possible my additional HV circuit components were placed in the same upgrades/refurbishment? >>> >>>Back to the shop. I've got an hour before guests arrive! >>> >>>Dan >>> >>>On Saturday, December 7, 2013 10:58 AM, Don Black <donald_black@...> wrote: >>> >>>>I'm not so sure. Yours may be faulty, these are tested good so they must be a rare animal. >>>> >>>>Don Black. >>>> >>>>On 08-Dec-13 2:31 AM, Daniel Koller wrote: >>>> >>>> >>>>>I'll check and see what's in there. And when I take them out, I'll sell them on e-bay to an audiophool!! >>>>>http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26 >>>>> >>>>>(No affiliation with the seller!) >>>>> >>>>>Dan >>>>> >>>>>On Friday, December 6, 2013 11:27 PM, Chuck Harris <cfharris@...> wrote: >>>>> >>>>>>Most of the time with the 545, the problem is the >>> black beauty oil/paper >>>>>>tubular capacitors used for the HV filters. They >>> always go bad, and if >>>>>>they haven't been replaced, you must replace >>> them. Ceramic is fine. >>>>>> >>>>>>There is also a BB cap that is in series with the grid >>> feedback winding, >>>>>>and another in parallel with the plate winding. Both >>> must go. >>>>>> >>>>>>-Chuck Harris >>>>>> >>>>>>Daniel Koller wrote: >>>>>>> Howdy, >>>>>>> >>>>>>> The recent discussions on HV repairs has me >>> thinking I should look into the issues >>>>>>> in my 545 (not A or B, old style square case). >>> It works very very well, but >>>>>>> about half of the time, increasingly more, the HV >>> circuit will not oscillate. If >>>>>>> I pull the plug-in out and drop it back in, it >>> will work. I know this is not a >>>>>>> recommended option! Alternatively, if I shut it >>> off and wait for it to cool, it >>>>>>> will work when I turn it on with about the same >>> probability, or a little less. >>>>>>> Once the scope is on it's up to spec. >>>>>>> >>>>>>> The 6AU5 is not brand new, but is good. It was >>> replaced recently with no >>>>>>> improvement. >>>>>>> >>>>>>> So, suggestions as to where to start on this >>> intermittant problem are welcome. Is >>>>>>> there anything I should look for or measure that >>> might indicate what is getting >>>>>>> tired? >>>>>>> >>>>>>> Dan >>>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>> >>>> >>>> >>>>>________________________________ >>>> >>>> This email is free from viruses and malware because avast! Antivirus protection is active. >>>> >>>> >>>> >>>> >>> >> >> >>>>________________________________ >> >> This email is free from viruses and malware because avast! Antivirus protection is active. >> > > >>________________________________ > > This email is free from viruses and malware because avast! Antivirus protection is active. > > > >
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Don Black <donald_black@...>
Does anyone know if the leaking oil is
PCB?
Don Black. On 09-Dec-13 9:48 AM, Daniel Koller wrote:
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Daniel Koller
Good question. But in any case, I treated it as if it was PCB - wiped it up before handling, and washed my hands frequently. Dan
On Sunday, December 8, 2013 6:44 PM, Don Black wrote:
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Chuck Harris <cfharris@...>
It is not PCB. Once you have smelled PCB, you will never forget
toggle quoted messageShow quoted text
the odor. It is just mineral oil. -Chuck Harris Daniel Koller wrote:
Good question. But in any case, I treated it as if it was PCB - wiped it up
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