- Maybe I need another 'scope? - 19 Updates
- Cell phone signal booster - 1 Update
- ME/MA UK 1970's transistors? - 1 Update
| etpm@whidbey.com: Nov 19 04:01PM -0800 Hey all youse 'scope gurus, I'm gonna be getting a new and a used tube amplifier. The new one is on the way and the used one is in my neighbor's garage. He still needs to dig it out so I don't know anything about it except that has tubes in it. If the new one doesn't come with a schematic then right off the bat I want to draw one so I can learn more about vacuum tube audio amp workings. If I have to draw a schematic then I will put in the actual values of the passives as well as the marked values. And I want to measure the voltages in the circuit as well and put them into the schematic. If the old one needs a schematic as well then if I can't find one online I'll need to give it the same treatment as the new one. If I do have schematics then all I will need to do is the measurements and write them down. So.... I have a TEK 465B oscilloscope and it has served me well until now diagnosing my CNC equipment. All the voltages I have needed to measure have been below 50 volts. But looking at the 'scope it seems like at the 10x setting on the probes the highest voltage I can measure is 200 volts. That's 4 divisions at 50 volts per division. And that's peak to peak, not RMS. I do have one 20x TEK probe, a P5120, that I used for measuring the mains power, but the voltages inside tube equipment go much higher. I have been watching YouTube videos about vacuum tube equipmet and have learned a lot so far. "Uncle Doug" has several videos that have taught me a lot. Maybe it's because he used to be a teacher I am learning so much. Anyway, do I need a different 'scope to to measure accurately what is going on inside vacuum tube equipment? Should I just look for different probes with even more attenuation? I certainly don't need the 100 MHz bandwidth that the 465B has for working with audio equipment. If you all think another 'scope should be in my future I would love some advice. Since this is a hobby I don't wanna spend a lot of money on yet another toy, er tool. So a used 'scope is fine with me. I love my used TEK 465B. Now before everybody starts giving me advice about high voltages and all that I need everybody to know that I am expert and know all there is to know about working with high voltages. Don't waste my time telling me to put down my drink before I start working around high voltages. I always use plastic cups for my drinks when working with high voltages. Oh, and I don't put any salt on the rims of my Bloody Marys either. And no cans of beer either, only glass bottles. Safety first. As an expert I know alcoholic drinks are good. They keep my hands from shaking too much in the morning. And I don't like smoking pot. I figure I'm just as expert as some other self professed experts here who don't need any extraneous advice. I just watched a video about isolation transformers, how to build one in a proper enclosure and how to use it properly. So even though I have the isolated variac I think I'll make a 1:1 isolation xmfr too with a little more ampacity. And if anybody here thinks I could use some more advice about working around high voltages I welcome it and will certainly take heed. Thanks, Eric |
| tabbypurr@gmail.com: Nov 19 04:07PM -0800 > will certainly take heed. > Thanks, > Eric 200v limit sounds most unlikely. Enjoy frying yourself. It sounds like you will at some point. NT |
| Rheilly Phoull <rheilly@bigslong.com>: Nov 20 08:21AM +0800 > will certainly take heed. > Thanks, > Eric An expert who has no knowledge of voltage dividers :-) |
| John Robertson <spam@flippers.com>: Nov 19 04:22PM -0800 > will certainly take heed. > Thanks, > Eric Most tube amps are serviced in our shop with a digital voltmeter...not a scope. Really all that you need to know are correct are the plate and cathode voltages, and if they are off then you check the screen and grids for proper bias - after testing the tubes for proper operation. Most common failures are electrolytic caps, then inter-stage isolation caps followed closely by plate resistors (they overheat with bias goes wrong) and then cathode resistors, bias circuit, grid resistors, and then - perhaps - a damaged output transformer. Virtually all of that can be tested quickly with a voltmeter once you know the average plate voltages. If the plate voltages are good then the amp is fed a known AC signal of a set level and you then follow the AC signal through the amp using your AC setting on the voltmeter. I check first the input level, if good I then check the high side of the volume control and if is on spec I then go to the output of the phase splitter tube(s). Divide the amp in half, then halve the remaining sections to find the problem. If you are doing high end amp work where distortion is a factor then you will break out a slow dual trace scope to find the issues, but for regular tube amps like guitars and jukeboxes we usually don't bother. Not that we don't have scopes (have almost ten in various sizes and speeds), but they rarely help - at least for tubes! John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
| Ralph Mowery <rmowery28146@earthlink.net>: Nov 19 11:02PM -0500 In article <d_WdnYzCwa0jzm7GnZ2dnUU7-QXNnZ2d@giganews.com>, spam@flippers.com says... > scope. Really all that you need to know are correct are the plate and > cathode voltages, and if they are off then you check the screen and > grids for proper bias - after testing the tubes for proper operation. I agree. Forget about the scope if you want to just measure voltages. I have the same scope and would never try to make accurate voltage measurments with it. You can always get a 100 to 1 probe. However, you can get one of the 'free' Harbor Freight meters and do better for what you want. For just DC measurments you can just make your own 100:1 voltage devider. |
| Phil Allison <pallison49@gmail.com>: Nov 19 09:44PM -0800 John Robertson wrote: > Most tube amps are serviced in our shop with a digital voltmeter...not a > scope. ** Wow, that is contrary to how most audio amplifier techs do it. With a scope probe, you can check DC levels and AC waveforms at the same time - so the first step is to connect an audio generator and dummy load and see if there is any clean output. > Really all that you need to know are correct are the plate and > cathode voltages, and if they are off then you check the screen and > grids for proper bias - after testing the tubes for proper operation. ** OK, maybe having a good tube tester changes how you do things. > Most common failures are electrolytic caps, ** I see amplifiers from the 1960s up to a year or so old and faulty electros are not the most common parts to be replaced - faulty tubes are. Electros always get replaced if my ESR meter says they are bad or there are visible problems like leaking electrolyte. > then inter-stage isolation caps followed closely by plate resistors ... ** Only rarely need replacing, IME. > If you are doing high end amp work where distortion is a factor then you > will break out a slow dual trace scope to find the issues, but for > regular tube amps like guitars and jukeboxes we usually don't bother. ** I find I use the scope and DMM in combination until the amp is all working properly. This will usually take longer on an unfamiliar example where no circuit is available. .... Phil |
| Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>: Nov 20 01:18AM -0500 > some advice. Since this is a hobby I don't wanna spend a lot of money > on yet another toy, er tool. So a used 'scope is fine with me. I love > my used TEK 465B. Everybody should have another scope now and again. I have 11 at the moment, which is none too many. ;) (On average I pay about 3 cents on the dollar, which makes new scopes an easier sell.) ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com |
| tabbypurr@gmail.com: Nov 20 02:03AM -0800 On Tuesday, 20 November 2018 06:18:38 UTC, Phil Hobbs wrote: > > Hey all youse 'scope gurus, > > Anyway, do I need a different 'scope to to measure accurately what > > is going on inside vacuum tube equipment? no > easier sell.) ;) > Cheers > Phil Hobbs If you're going to get one you don't need, consider making it a pocket scope. Quite handy, even with modest specs. NT |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Nov 20 04:24AM -0800 Find a mirror. Put it at eye level and stare into it for one (1) full minute. Then repeat ten (10) times: I don't need a scope to service tube amps. Repeat as necessary. Your isovariac will be adequate for the work. That, reasonable caution, common sense, understanding of what tubes are and do (and do not), and patience. None of which are common characteristics. On tube testers: YES, they are handy if you have a good one that tests for shorts and gas. And if you are going "full audiophile", one that allows you to match is also useful. But the brute fact of the matter is that there are few testers out there that actually give information that is both good and useful. That a tube has no shorts and is not gassy is good to know, but not particularly indicative of its function-in-use. I keep two - one a fairly simple Simpson emissions tester, good for about 90% of my needs, and a Hickok 539B, which is allows proper matching with additional equipment (2 x VOM). Sadly, tube testers that have been restored, calibrated and are reliable are getting scarce and expensive. The amount of *stuff* that crosses my bench in a given year justifies the need. I also keep a very good scope - that I have used twice in five years to find that niggling problem, and that was on solid-state devices. If I ever get another scope, it will be a "pocket" device as they take up a LOT of real-estate otherwise. Peter Wieck Melrose Park, PA |
| Tim Schwartz <tim@bristolnj.com>: Nov 20 08:08AM -0500 Eric, I'd suggest using a voltmeter (analog or digital, whatever you prefer)for the DC voltage measurements. I like my old Heathkit VTVM for troubleshooting, as you are unlikely to cause any serious damage to the meter, as could happen with a digital. The scope you have is all you need, as what you need it for is the AC part of the waveform. Set the scope to AC coupling at the input and you'll be looking at the ripple on the supply. If the ripple exceeds 400 volts (8 divisions at 5 volts each is 40Vp-p and with a 10x probe that gets you to 400Vp-p) then something is seriously wrong with your power supply or measurement technique, or you don't have a good ground between the amp and the scope. Regards, Tim |
| Tim Schwartz <tim@bristolnj.com>: Nov 20 08:10AM -0500 Eric, I'd suggest using a voltmeter (analog or digital, whatever you prefer)for the DC voltage measurements. I like my old Heathkit VTVM for troubleshooting, as you are unlikely to cause any serious damage to the meter, as could happen with a digital. The scope you have is all you need, as what you need it for is the AC part of the waveform. Set the scope to AC coupling at the input and you'll be looking at the ripple on the supply. If the ripple exceeds 400 volts (8 divisions at 5 volts each is 40Vp-p and with a 10x probe that gets you to 400Vp-p) then something is seriously wrong with your power supply or measurement technique, or you don't have a good ground between the amp and the scope. Regards, Tim |
| tabbypurr@gmail.com: Nov 20 06:28AM -0800 > I also keep a very good scope - that I have used twice in five years to find that niggling problem, and that was on solid-state devices. If I ever get another scope, it will be a "pocket" device as they take up a LOT of real-estate otherwise. > Peter Wieck > Melrose Park, PA Maybe it's time to make some new tube testers. While we're here, an iso won't help if you connect an earthed scope to the thing. It will bite you if you touch, and that's how HT is. NT |
| Ralph Mowery <rmowery28146@earthlink.net>: Nov 20 10:02AM -0500 In article <45a5d682-139d-4aaa-9ca2-b4d9243ea05e@googlegroups.com>, tabbypurr@gmail.com says... > Maybe it's time to make some new tube testers. > While we're here, an iso won't help if you connect an earthed scope to the thing. It will bite you if you touch, and that's how HT is. It is usually easier to just pop in a good tube instead of testing unless looking for a matched set. I have bought a $ 300 Hantek scope. It is suppose to be good to 200 MHz and rated for 600 volts peak. Good thing about it, you can set the screen up for waveform and digital volt meter. YOu see the waveform and good resolution of voltage at the same time. Sometimes it may be better or easier to just isolate the test equipment from the ground and not the unit under test. I don't know how much the solid scope draws without going to check, but it could probalby be powered by 2 transformers of 24 volts at 2 amps or so placed back to back. |
| John-Del <ohger1s@gmail.com>: Nov 20 07:09AM -0800 > > Peter Wieck > > Melrose Park, PA > Maybe it's time to make some new tube testers. There's plenty of them out there, and they're very simple circuits. I probably have half a dozen or more, the only one that's kind of a dead end is a very nice one that checks the four pin tubes that has a dead meter. Otherwise, the standard recap and check for off value resistors and maybe replacing a selenium rectifier. But very simple to restore. These testers are very handy and I do use them, but the best way to check any tube is to observe it's behavior and measure it's performance in the circuit itself. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Nov 20 07:54AM -0800 > Maybe it's time to make some new tube testers. > While we're here, an iso won't help if you connect an earthed scope to the thing. It will bite you if you touch, and that's how HT is. > NT http://amplitrex.com/ This is one of several currently available. They are not cheap. If one is into tubes at a level to justify a new tester at this level, I would posit that the need is beyond the hobby level. I tripped over my 539B when an old friend closed his business. The Simpson I found at a garage sale in Tamaqua, PA. "Popping in" a new tube is OK for those of us with a couple of thousand tubes in a closet. Not so much for those working on operating inventory only. I do, also, like to screen tubes prior to installation. Peter Wieck Melrose Park, PA |
| etpm@whidbey.com: Nov 20 08:38AM -0800 On Mon, 19 Nov 2018 16:22:22 -0800, John Robertson <spam@flippers.com> wrote: >Not that we don't have scopes (have almost ten in various sizes and >speeds), but they rarely help - at least for tubes! >John :-#)# Thanks for the reply John. I think my tongue in cheek "expert" comment fell flat but you saw through my poor attempt at humor. Since I will be interested in looking at the AC signal through to the speaker to see how it changes, when clipping starts, a scope will be necessary. From what you say it looks like using a VOM for the DC and a scope for AC would be a good way to see how the amp is working. Thanks, Eric |
| etpm@whidbey.com: Nov 20 08:41AM -0800 On Tue, 20 Nov 2018 08:21:51 +0800, Rheilly Phoull >> Thanks, >> Eric >An expert who has no knowledge of voltage dividers :-) I know what a voltage divider is and have used them for some DC stuff, but I don't know enough about AC signals to know if one would affect the way the signal looks on a scope. TYhjanks, Eric |
| etpm@whidbey.com: Nov 20 08:41AM -0800 On Mon, 19 Nov 2018 23:02:22 -0500, Ralph Mowery >'free' Harbor Freight meters and do better for what you want. >For just DC measurments you can just make your own 100:1 voltage >devider. Thanks Ralph. Eric |
| etpm@whidbey.com: Nov 20 08:48AM -0800 >Maybe it's time to make some new tube testers. >While we're here, an iso won't help if you connect an earthed scope to the thing. It will bite you if you touch, and that's how HT is. >NT See that's exactly the kind of advice that I can't be told often enough. Even though I did already know about this. My isolated variac does not have an isolted ground so I bought one of those plug/socket adapters that doesn't pass the ground through but instead provides a tab to connect to ground. Thanks, Eric |
| "Albert Hodge" <albert_h@isp.org>: Nov 20 09:27AM -0600 Has anyone used a cell phone signal booster, and would like to share their experience? The one i'm considering can be seen at https://www.ebay.com/itm/850-1900MHz-Cell-Phone-Signal-Booster-GSM-3G-4G-Amplifier-Kit-for-AT-T-Verizon/181961955840?epid=712424363&hash=item2a5dc71a00:rk:1:pf:0 |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Nov 19 10:58AM -0800 Got a bunch in my vintage (70s) AR tuner, receiver & integrated amp (Made by Fairchild per the service manual). I have had to do some pretty substantial rebuilding over the years, but never to those transistors. Also a few of this type: http://www.gpecsrl.net/img_componenti19/19727.jpg made by Motorola. Peter Wieck Melrose Park, PA |
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