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Re: Slightly OT: How can I dissolve Potting Compound?
MEK is really nasty stuff and a precursor to methamphetamine, from what I understand.? A funny but horrifying story about MEK came from a coworker.? Seems a coworker of his years ago wanted some of the used MEK to clean engine parts.? His boss signed off on a 55 gallon drum of the stuff, which he put in the back of his pickup truck.? On down the road, it started leaking onto the highway, which caught the attention of a state trooper!? Not only was he dripping MEK, but he had crossed the state line and had some serious explaining to do!? He and his boss got fired in short order.? ?Moral of the story is be very careful if you're going to use MEK.? IIRC, MEK is flammable and carcinogenic.? ? ?Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone
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-------- Original message --------From: Glenn Little <glennmaillist@...> Date: 1/2/21 6:26 PM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting Compound? You can try MEK, methyl ethyl keytone.It will dissolve a lot of epoxies.Be careful to not dissolve other things.73GlennWB4UIVOn 1/2/2021 9:18 PM, Dennis Tillman W7pF wrote:> I need to dissolve the black HV potting compound of a 12VDC powered> Helium-Neon laser inverter power supply I have that stopped working. I would> appreciate any suggestions on what works to do this. I¡¯m guessing it may be> epoxy. I stuck the tip of a hot soldering iron in it for a few seconds> without much effect.>> When it was working it turned out to be perfect for powering gas filled> Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled> with a variety of gasses are an excellent source of spectral lines for the> 7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.>> Spectrum tubes require an initial high voltage (1,000V to 1,500V for> example) to break down the gas and start it conducting. Once the gas in the> spectrum tube conducts the voltage across the gas drops (250V to 450V for> example) and unless you limit the current (to a few mA) it will destroy the> tube. Can anyone can point me to a source of information on how to determine> the proper voltage and current I need to power these spectrum tubes? Is> there a web site or group devoted to Spectrum Tubes?>> Something happened to the inverter and it stopped working. The input is now> open. The inverter is a black potted brick 3¡± x 1?¡± x 1¡±. The ballast> resistor has continuity so that is not the problem. The original label on> the inverter is partially destroyed so I can¡¯t tell what its initial high> voltage output was or what it current limits at. All I do know is that it> was made by> Laser Drive Inc.> 5465 Wm. Flynn Hwy. Gibsonia, PA 15044> Model: 1150-6330, S/N: 610574> The input was +12VDC at 0.35A.>> I wrote to the company that took over the company that took over Laser Drive> Inc. asking if they could tell me the output voltage and limiting current> but I didn¡¯t receive a reply.>> At this point I am hoping if I can remove the potting compound I can figure> out what went wrong with it.>> I have a different, bigger Laser Drive Inc. potted inverter which is powered> by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to> flicker. They do not run continuously. I am guessing that this because 6.5mA> is more current than the tube can conduct. The amount of current the tube> draws increases in proportion to the inside diameter of the tube but I don¡¯t> know much about this matching the power supply to the tube. All I do know is> the one that went bad seems to be an ideal match for the spectrum tubes I> have.>> Battery operated (DC input) inverters are much more desirable than AC input> inverters for this application because the AC rectification and poor> filtering shows up on the output DC as significant ripple causing the> amplitude of each spectral line to be blurred.>> Dennis Tillman W7pF>>> >>-- -----------------------------------------------------------------------Glenn Little??????????????? ARRL Technical Specialist?? QCWA? LM 28417Amateur Callsign:? WB4UIV??????????? wb4uiv@...??? AMSAT LM 2178QTH:? Goose Creek, SC USA (EM92xx)? USSVI, FRA, NRA-LM??? ARRL TAPR"It is not the class of license that the Amateur holds but the classof the Amateur that holds the license"
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
On Sat, Jan 2, 2021 at 07:05 PM, Larry McDavid wrote:
Please include me in the list as "JF" since I meet the above qualification as, not identified by full name and some limitation. I'll send you and email now so you know who I am. Thank you sir. |
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Re: Slightly OT: How can I dissolve Potting Compound?
If the heat gun can melt epoxy resins, it may be hot enough to melt other
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plastics - like the insulation on wires (unless it's Teflon or silicone - which it may be in an HV supply). There are quite a few spectral lamp power supplies on eBay (some show up under "arc lamp power supply", but most I would call questionable. One shown operating with a lamp is the most expensive. Likely not worth taking a chance on the others but you could take a look. Steve H. On Sat, Jan 2, 2021 at 10:08 PM EJP <esmond.pitt@...> wrote:
On Sun, Jan 3, 2021 at 01:24 PM, Vince Vielhaber wrote:A heat gun is often the method for removing the potting, but care mustIt is also extremely smelly. Work outdoors or with fume exraction, or at |
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Re: Slightly OT: How can I dissolve Potting Compound?
Breaking down epoxies at room temperature has often come up here and in the hpagilent group. My standard answer is Dimethylformamide, but other solvents can do it too. It's a messy process and some internal parts may get damaged or lose their identity. I think it would be cheaper and cleaner to just get a fresh HeNe driver in the same size class as the original (probably for standard 1 mW HeNe). These used to be commodity items, and I would think used or NOS ones ought to be available cheap since HeNe lasers aren't used so much anymore.
As I recall, the ones I have are labeled something around 2-2.5 kV at 6-15 ma running, depending on tube size, with ignition voltage up to around 10-12 kV. I can't recall the ballast resistor size, but think around 75 kohms, 5W is typical. If your other driver is too big for the discharge tubes you have, you can up the ballast resistance. Also, the driver boxes usually have auto-ignition, so if it doesn't see approximately the normal HeNe load, it will re-strike maybe up to ten times a second, thinking the tube isn't lit. This could be the apparent stability problem you see. All these things can be fixed externally, but it's simplest to get the small kind that you had working already. Ed |
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Re: Slightly OT: How can I dissolve Potting Compound?
On Sun, Jan 3, 2021 at 01:24 PM, Vince Vielhaber wrote:
A heat gun is often the method for removing the potting, but care mustIt is also extremely smelly. Work outdoors or with fume exraction, or at least seriously good ventilation. EJP |
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Folks, a surprising number of you have asked to be included in a group purchase of the sets of four boards for this tester that Jared Cabot developed. I'm keeping a list of those who committed to the purchase and I have these in my list:
ML PA SM DC HB GL MH JR WR JT EW RD AW SG DS MU PE SC LM Those 19 above have identified themselves and not indicated any question or qualification to participating. But, there are others who either did not identify by full name or expressed some qualification or limitation. I recognize these: AA PD S? MP A? B? BO And, two additional with fully cryptic email addresses to whom I sent an email asking for full identity, but with no response. So, there are nine more who may, or may not, commit to the purchase. Please, each of these nine contact me with clarification. If you reply, please be sure your email includes your full name. Later I will need full postal shipping address. Jared has asked for a price quote for sets of three boards from a supplier of his choosing; we'll know that quote next week. For USA buyers, I can determine a packaging and shipping cost. With so many sets to be ordered, I must have payment in advance of ordering the boards. PayPal Friends and Family is an easy way to do this; if you object to that, we can talk about it. Jared is located in Japan and cannot practically offer these board sets himself. I, with Jared's help, can place the order and redistribute the board sets. I will not provide any other parts, including the rotary switch, which I now note is available from DigiKey. Jared below suggests an approximate board set cost but packaging and postage must be added to that. My preference is to ship by USPS Priority Mail; with packaging in an appropriate box, that might add $10 as an estimate. I'm a bit surprised at the number who want to build this TM500 tester. I'll reply again when I know more. Larry On 1/1/2021 10:31 PM, Jared Cabot via groups.io wrote: On Sat, Jan 2, 2021 at 06:29 AM, Larry McDavid wrote:...One small addendum to this, the PCB's will likely not be black as that is a premium option that adds significant cost. They will most likely come in the usual green (more period accurate! :) ) to save as much on cost as possible. -- Best wishes, Larry McDavid W6FUB Anaheim, California (SE of Los Angeles, near Disneyland) |
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Re: Grid Bias Adjustment on 475A
So I've measured everything EXCEPT the high voltage levels (waiting on an HV probe).
R1396 and R1399 feed the second grid on pin #8, the schematic says they should see +50 V, and I measured +50 V R1398 feeds the astigmatism grid, schematic says the range should be -8 V to +110 V, I see that range, the original setting was +40.82 V R1330, R1329, VR1329, C1329, and CR1329 feed the mesh and all meet at a node on one of the ceramic terminals, according to the schematic that node is supposed to be -150 V, but I measure -110 V. The -150V level is supposed to have (if I am reading the schematic correctly) a sine wave superimposed with a range of 300 mV peak to peak, but what I see when I hook the scope up to the common node on the ceramic terminal (rather than the opposite side of CR1329, which I think is high voltage) is only 150 mV peak to peak, and not very sinusoidal. So the mesh voltage is low (high?) and its AC signal looks wrong. Maybe one or more of the passive components is failed (which I can check pretty easily, with the power off, by lifting the legs attached to the ceramic terminal), but it might also be a problem with T1320, which I guess is on the opposite side of the board? I have an HV multimeter probe coming on Tuesday, so I'll feel better about checking the high voltage stuff then. I don't really understand what the mesh is doing in this CRT. Is the mesh bias really a good candidate for the symptom I'm seeing? -- Jeff Dutky |
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Re: Slightly OT: How can I dissolve Potting Compound?
You can try MEK, methyl ethyl keytone.
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It will dissolve a lot of epoxies. Be careful to not dissolve other things. 73 Glenn WB4UIV On 1/2/2021 9:18 PM, Dennis Tillman W7pF wrote:
I need to dissolve the black HV potting compound of a 12VDC powered --
----------------------------------------------------------------------- Glenn Little ARRL Technical Specialist QCWA LM 28417 Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178 QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR "It is not the class of license that the Amateur holds but the class of the Amateur that holds the license" |
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Re: Slightly OT: How can I dissolve Potting Compound?
A heat gun is often the method for removing the potting, but care must be taken since some of the potting compounds get very toxic with heat.
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Is there a model number on the dead supply? Vince. On 01/02/2021 09:18 PM, Dennis Tillman W7pF wrote:
I need to dissolve the black HV potting compound of a 12VDC powered --
K8ZW |
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Slightly OT: How can I dissolve Potting Compound?
I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would appreciate any suggestions on what works to do this. I¡¯m guessing it may be epoxy. I stuck the tip of a hot soldering iron in it for a few seconds without much effect. When it was working it turned out to be perfect for powering gas filled Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled with a variety of gasses are an excellent source of spectral lines for the 7J20 / J20 Rapid Scan (Optical) Spectrometer to measure. Spectrum tubes require an initial high voltage (1,000V to 1,500V for example) to break down the gas and start it conducting. Once the gas in the spectrum tube conducts the voltage across the gas drops (250V to 450V for example) and unless you limit the current (to a few mA) it will destroy the tube. Can anyone can point me to a source of information on how to determine the proper voltage and current I need to power these spectrum tubes? Is there a web site or group devoted to Spectrum Tubes? Something happened to the inverter and it stopped working. The input is now open. The inverter is a black potted brick 3¡± x 1?¡± x 1¡±. The ballast resistor has continuity so that is not the problem. The original label on the inverter is partially destroyed so I can¡¯t tell what its initial high voltage output was or what it current limits at. All I do know is that it was made by Laser Drive Inc. 5465 Wm. Flynn Hwy. Gibsonia, PA 15044 Model: 1150-6330, S/N: 610574 The input was +12VDC at 0.35A. I wrote to the company that took over the company that took over Laser Drive Inc. asking if they could tell me the output voltage and limiting current but I didn¡¯t receive a reply. At this point I am hoping if I can remove the potting compound I can figure out what went wrong with it. I have a different, bigger Laser Drive Inc. potted inverter which is powered by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to flicker. They do not run continuously. I am guessing that this because 6.5mA is more current than the tube can conduct. The amount of current the tube draws increases in proportion to the inside diameter of the tube but I don¡¯t know much about this matching the power supply to the tube. All I do know is the one that went bad seems to be an ideal match for the spectrum tubes I have. Battery operated (DC input) inverters are much more desirable than AC input inverters for this application because the AC rectification and poor filtering shows up on the output DC as significant ripple causing the amplitude of each spectral line to be blurred. Dennis Tillman W7pF |
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Re: Peter Keller's Book Mailing Status
If he does that with the same account the money was sent, paypal will likely turn around and charge him fees for each F&F transaction. It's happened to me.
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Vince. On 01/02/2021 09:08 PM, John Griessen wrote:
On 1/2/21 2:19 PM, Dennis Tillman W7pF wrote:It takes time to verify theSo, you're not using paypal/shipnow interfaced to pitney bowes? --
K8ZW |
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Re: A question from the unwashed relative to: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Out of about 30 TM 500 power frames I have had 7 that had misphased AC windings in at least one slot, no sign of any post-factory work in them.
Failed pass transistors are pretty common. I have not seen any misphased AC windings in TM5000 series frames. -Mac |
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Tek 475 scopes.
Hi,
I have two 475 scopes. One is almost working as of a few years ago, but the trace brightness knob broke off some years ago. I haven't been using it. A friend of mine bought a 475 for parts, its a newer model I think but more trashed. I'm interested in selling them. Anyone interested in buying? Comes with an original 475 service manual. I hope to get some photos by next week. |
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
On Sat, Jan 2, 2021 at 03:44 PM, Michael W. Lynch wrote:
Is there a way to easily bring the EBC of each pass transistor to the frontIt isn't necessary. Several of the existing tests exercise the pass transistors in various ways. EJP |
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Re: Grid Bias Adjustment on 475A
On Sun, Jan 3, 2021 at 02:13 AM, Roy Thistle wrote:
Nice. It completely matches (except for the limitation to transistors or (other) active networks) the grid bias term as used in a 'scope: the most negative level of the (first) grid, causing blanking of the beam. The actual grid voltage continually changes (to and from less negative) during operation,. Raymond |
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Re: A question from the unwashed relative to: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
If you might indulge a few inquiries...No. It just caused a large hum at low output levels. Is that something you did to the TM504?... or was it miswired at theI fixed it. I'm sure it was done at the factory. Hard to believe it could have been done during a repair: why? The FG504 manual mentions all this as a known problem with some early TM504s. It didn't matter a damn about consistent phasing until someone designed the FG504. Do you know... was the TM504... and early manufacture... or a later one?I am assuming it was an earlier one. Serial number is inaccessibl without heavy lifting, as there is a fully populated TM506 on top of it. I have a later TM504 that never exhibited the problem. Would have swapped them but I had wired the back panel of that one for three PS503As in series and a DM502. I mis-spoke earlier when describing the FG504 PSU. It uses the 17.5VAC and two 25VAC windings connected in series after the bridge rectifiers. The +11.5VDC rail also comes into this somehow. I'm not clear why the phasing error causes this problem but it does. EJP |
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Re: Grid Bias Adjustment on 475A
On Sat, Jan 2, 2021 at 09:07 PM, Michael W. Lynch wrote:
Although English is not my mother tongue (Dutch is), I fail to see why using the term "Grid Bias Adjustment" for 'scope CRT's is wrong. If I'm correct, two reasons are given to disparage the term: 1. Grid bias is not specified as a voltage with respect to "zero", "gnd" or the like (but against the cathode, which usually is at negative voltages exceeding - 2 kV) 2. Grid bias is not a steady state (DC) voltage Ad 1. This to me seems an unnecessary bias towards a particular voltage point (namely, zero volts) in a circuit. Pun intended. Ad 2. When adjusting "Grid Bias", that part (in time) of the voltage waveform necessary to achieve blanking of the beam (a negative-enough voltage with reference to the cathode) is adjusted. Class B (as an example) audio amplifiers contain a "bias current" setting to minimize cross-over distortion. The actual current through the circuits carrying the bias current at rest, when producing an audio signal, is an AC current many times larger at any sensible volume than that zero-signal DC-current. In a 'scope, the Intensity adjustment pot sets the relatively positive amplitude excursions, where the grid is less negative in relation to the cathode, making the beam visible. So, Grid Bias is the most negative voltage of the grid, often 50 V to 80 V more negative than the cathode. Raymond |
Raymond Domp Frank
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