Date
1 - 20 of 25
New Member intro and needing help
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druid_noibn
Hi Mike,
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I likely have a VTVM in my collection that needs a little TLC as well...now, getting those mercury batteries.... Thanks! Kind regards,DBN aka John On Saturday, July 2, 2022 at 04:12:32 PM EDT, Mike Dinolfo <mdinolfo@...> wrote:
The method suggested by John Kolb is somewhat similar to a method described at https://www.londonsound.org/Vintage%20valve%20hi-fi.htm And although the "London Sound" method was apparently intended to apply to vacuum tube audio equipment, I suspect it's equally applicable to older vacuum tube Tek scopes. I tried the London Sound method only once; it was successful in the sense that an old vacuum tube radio transmitter powered up without any component failure. But as they say- "caveat emptor." Mike Dinolfo On 7/2/22 13:01, John Kolb wrote: In my younger days, I've turned on a long unused scope, and after a |
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druid_noibn
Hi John,
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Ah...theory vs. practice - sometimes it works well.... Thanks! Kind regards,DBN aka John On Saturday, July 2, 2022 at 01:01:41 PM EDT, John Kolb <jlkolb@...> wrote:
In my younger days, I've turned on a long unused scope, and after a couple of minutes, heard a loud bang as a cap exploded. The electrolytic cap anode is a metal with a thin insulating oxide layer. After long idle periods, the oxide layer disappears. When voltage is applied without the insulating oxide layer, large current flows, causing heat, pressure, and eventually BANG. I power up unknown equipment by turning power on for 10 sconds, then off again, Wait awhile so that if heating occurred, the cap can cool off again. Another power on, 15 seconds, this time; another cooldown. The process continues with increasing on time periods until I run out of patience. The applied voltage causes the oxide layer to form again I don't know if this theory is correct or not, but I haven had any explosions while using it. John On 7/2/2022 8:17 AM, David C. Partridge wrote: Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltageJust don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes). |
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druid_noibn
Hi David,
Indeed, there are a few circuits that don't do well with ramping currents - thanks for the comments. Kind regards,John aka DBN On Saturday, July 2, 2022 at 11:17:21 AM EDT, David C. Partridge <david.partridge@...> wrote: > Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage Just don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes). Just plug in an turn on (after checking the voltage selector is set correctly). Dim bulb approach is fine. D. -----Original Message----- From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jim Adney Sent: 02 July 2022 12:48 To: TekScopes@groups.io Subject: Re: [TekScopes] New Member intro and needing help On Fri, Jul 1, 2022 at 09:50 AM, druid_noibn wrote: What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?There are two good approaches: Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage or Build a fixture that puts an incandescent bulb in series with the old device. I built mine using a 2x4 box and a cover that had an outlet and a socket for a screw-in (Edison base) lamp. Choose a bulb that will almost, but not quite, blow the fuse. As long as the lamp doesn't glow brightly, you're okay. If the lamp suddenly goes bright, you know that something in your old device has shorted. You could also do both, using the Variac to bring the voltage up slowly, while watching the lamp to monitor the current. |
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druid_noibn
Hi Jim,
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Thanks for the comments. Kind regards,DBN, aka John On Saturday, July 2, 2022 at 07:48:22 AM EDT, Jim Adney <jadney@...> wrote:
On Fri, Jul 1, 2022 at 09:50 AM, druid_noibn wrote: What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?There are two good approaches: Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage or Build a fixture that puts an incandescent bulb in series with the old device. I built mine using a 2x4 box and a cover that had an outlet and a socket for a screw-in (Edison base) lamp. Choose a bulb that will almost, but not quite, blow the fuse. As long as the lamp doesn't glow brightly, you're okay. If the lamp suddenly goes bright, you know that something in your old device has shorted. You could also do both, using the Variac to bring the voltage up slowly, while watching the lamp to monitor the current. |
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The method suggested by John Kolb is somewhat similar to a method
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described at https://www.londonsound.org/Vintage%20valve%20hi-fi.htm And although the "London Sound" method was apparently intended to apply to vacuum tube audio equipment, I suspect it's equally applicable to older vacuum tube Tek scopes. I tried the London Sound method only once; it was successful in the sense that an old vacuum tube radio transmitter powered up without any component failure. But as they say- "caveat emptor." Mike Dinolfo On 7/2/22 13:01, John Kolb wrote:
In my younger days, I've turned on a long unused scope, and after a |
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John Kolb
In my younger days, I've turned on a long unused scope, and after a couple of minutes, heard a loud bang as a cap exploded.
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The electrolytic cap anode is a metal with a thin insulating oxide layer. After long idle periods, the oxide layer disappears. When voltage is applied without the insulating oxide layer, large current flows, causing heat, pressure, and eventually BANG. I power up unknown equipment by turning power on for 10 sconds, then off again, Wait awhile so that if heating occurred, the cap can cool off again. Another power on, 15 seconds, this time; another cooldown. The process continues with increasing on time periods until I run out of patience. The applied voltage causes the oxide layer to form again I don't know if this theory is correct or not, but I haven had any explosions while using it. John On 7/2/2022 8:17 AM, David C. Partridge wrote:
Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltageJust don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes). |
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Zentronics42@...
I agree with this as well Variac turn on for linier power supplies is the way to go. However using a variac on a switches can cause damage to the switching components as they try and force regulate without enough power. They make up for it in current. And can easily over current the switching transistors. A good rule of thumb in the 7xxx frames is 3 bay units are usually linier power supplies 4 bay units are always switchers. There are a few 3 bay units with switching supplies if I remember correctly.
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Zen -----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of David C. Partridge Sent: Saturday, July 2, 2022 11:17 AM To: TekScopes@groups.io Subject: Re: [TekScopes] New Member intro and needing help Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltageJust don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes). Just plug in an turn on (after checking the voltage selector is set correctly). Dim bulb approach is fine. D. -----Original Message----- From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jim Adney Sent: 02 July 2022 12:48 To: TekScopes@groups.io Subject: Re: [TekScopes] New Member intro and needing help On Fri, Jul 1, 2022 at 09:50 AM, druid_noibn wrote: What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?There are two good approaches: Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage or Build a fixture that puts an incandescent bulb in series with the old device. I built mine using a 2x4 box and a cover that had an outlet and a socket for a screw-in (Edison base) lamp. Choose a bulb that will almost, but not quite, blow the fuse. As long as the lamp doesn't glow brightly, you're okay. If the lamp suddenly goes bright, you know that something in your old device has shorted. You could also do both, using the Variac to bring the voltage up slowly, while watching the lamp to monitor the current. |
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Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltageJust don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes). Just plug in an turn on (after checking the voltage selector is set correctly). Dim bulb approach is fine. D. -----Original Message----- From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jim Adney Sent: 02 July 2022 12:48 To: TekScopes@groups.io Subject: Re: [TekScopes] New Member intro and needing help On Fri, Jul 1, 2022 at 09:50 AM, druid_noibn wrote: What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?There are two good approaches: Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage or Build a fixture that puts an incandescent bulb in series with the old device. I built mine using a 2x4 box and a cover that had an outlet and a socket for a screw-in (Edison base) lamp. Choose a bulb that will almost, but not quite, blow the fuse. As long as the lamp doesn't glow brightly, you're okay. If the lamp suddenly goes bright, you know that something in your old device has shorted. You could also do both, using the Variac to bring the voltage up slowly, while watching the lamp to monitor the current. |
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Jim Adney
On Fri, Jul 1, 2022 at 09:50 AM, druid_noibn wrote:
What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?There are two good approaches: Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage or Build a fixture that puts an incandescent bulb in series with the old device. I built mine using a 2x4 box and a cover that had an outlet and a socket for a screw-in (Edison base) lamp. Choose a bulb that will almost, but not quite, blow the fuse. As long as the lamp doesn't glow brightly, you're okay. If the lamp suddenly goes bright, you know that something in your old device has shorted. You could also do both, using the Variac to bring the voltage up slowly, while watching the lamp to monitor the current. |
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druid_noibn
Hi Roy,
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What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years? Kind regards,John aka DBN On Thursday, June 30, 2022 at 03:28:01 PM EDT, Roy Thistle <roy.thistle@...> wrote:
On Thu, Jun 30, 2022 at 09:29 AM, KStrauss wrote: With old gear... out of service for a long time (and perhaps, stored inappropriately) ... IMO...it's asking for it to just plug it in, turn it on, and hope for the best. IMO, one should never do that. (We've all learned the hard way!) One can potentially avoid cascading failures, and destroying hard to get (and expensive!) parts by taking the time to go through an appropriate "power up" procedure. -- Roy Thistle |
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j.stumreiter@...
No, I got it to do mostly other projects. Antique radios is just my primary hobby. I work with lots of other analog circuits as well.
So I managed to score another blue filter and an Intensity pot. Now it looks like I just need the power supply board spacers, A4 board plastic mounting socket, handle, and front bezel. |
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John Kolb
If it is the 4 Amp Line fuse (F3001) instead the 2 Amp Inverter fuse (F3003) (page 6-17 of service manual), that's good news. There's not much circuitry between the two fuses. A short after that should blow the 2 A FUSE FIRST. In my case, it was the bridge rectifier with a shorted diode. Replaced with a BR610, 1 KV 6A bridge I had handy.Broke my arm and haven't been able to reassemble :)
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John On 6/30/2022 8:57 AM, KStrauss wrote:
Greetings everyone- |
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Roy Thistle
On Thu, Jun 30, 2022 at 09:29 AM, KStrauss wrote:
As these smps were designed in the most byzantine fashion (necessitated by the semiconductors, and magnetics of the time... as well as circuitry's multi-voltage power requirements)... an off-the-shelf, or "functional replacement" smps turns out to be a 7704A mule. -- Roy Thistle |
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Roy Thistle
On Thu, Jun 30, 2022 at 09:29 AM, KStrauss wrote:
With old gear... out of service for a long time (and perhaps, stored inappropriately) ... IMO...it's asking for it to just plug it in, turn it on, and hope for the best. IMO, one should never do that. (We've all learned the hard way!) One can potentially avoid cascading failures, and destroying hard to get (and expensive!) parts by taking the time to go through an appropriate "power up" procedure. -- Roy Thistle |
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Roy Thistle
On Thu, Jun 30, 2022 at 10:42 AM, stevenhorii wrote:
Hi All: IMO, it's worth mentioning that one is more likely to damage a Phillips screw, with a Pozidriv bit, than the other way around. I'm not saying to use a Phillips bit, in a Pozidriv screw... just saying... I do it all the time; but, 'feel' for cam out, and watch for damage. I have seen, more than a few, damaged screw heads on older HP test gear. Besides the damage possibly occurring through using the incorrect bit to try to extract the screw... HP seems to have had a fashion of using steel screws in cast aluminum parts... that sometimes gall. -- Roy Thistle |
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stevenhorii
Barry mentions that the screws are Pozidriv for a reason. They look like
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Phillips but are not. Using Phillips screwdrivers for them can damage the heads especially if they are tight. That can make future removal or tightening difficult. I bought a used H-P counter and had to drill out one of the Pozidriv screws because it was so damaged. It is worth buying a set of Pozidriv drivers or bits if you work on Tek or H-P equipment. On Thu, Jun 30, 2022, 13:23 n4buq <n4buq@...> wrote:
Hi Karl, |
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SCMenasian
Getting the power supply out is a cinch. It is held in by 4 screws on the back and you can slide it out with the cables still connected.
The manual has a procedure for finding faults. IIRC, you measure various resistances and see how they change as you disconnect cables on the interface board. The power supply, itself, has only 2 cables - one for power and one for load point sensing. Mine did not blow fuses. Yours might have a switcher problem, or a shorted rectifier or capacitor. In my case, the fault Itick mode) was a capacitor on the interface board. Removal of this board involves careful disassembly with lots of notes (which cable goes where, etc.) . |
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n4buq
Hi Karl,
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The power supply is held in with four (Pozidriv) screws from the back side. Removing those allows the entire LVPS to be slid out the back. There are two coaxial wires (pay attention to which color goes where but it's outlined in the manual) and two multi-connector plugs where the output and sense wires connect. It is a switch-mode power supply (SMPS) and will need a sufficient load to work properly or it will go into "tick mode". One of our members, Dennis Tillerman(sp?), created a document showing how to build one of those. It's pretty simple and I built a similar one when I was troubleshooting my 7704A's power supply. Hopefully you have a manual. It's invaluable for this sort of thing. Thanks, Barry - N4BUQ ----- Original Message -----
From: "KStrauss" <capnslo@...> Greetings everyone- |
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KStrauss <capnslo@...>
Greetings everyone-
I have a 7704A that I acquired years and years ago and (sadly) stored in the garage. And for at least 10 years never used or powered on. I have now established a repair shop in my office. The Main AC fuse (4A) blows immediately upon application of power. I suspect a power supply problem, but could use assistance on: a - how to get the PS out of the chassis and b- look for obvious signs of trauma - e.g. leaky capacitor, discolored resistor, etc etc Or - rather thnt dig in the issue, would there be a functional replacement on the market? Thank you Karl Strauss Santa Clarita CA |
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Yup. Me too Joel.
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On Wed, Jun 29, 2022, 10:15 PM Joel B Walker <joelandjoyce@...> wrote:
There seems to be quite a few ARF members here. Welcome! |
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