Required Test Equipment for Tube Radios - Page 1
Forum section: electronics / testgear

author: Anson
author_rank: Regular Contributor
timestamp: August 12, 2013, 04:45:19 am
content: What test equipment is required or suggested for proper tube and transistor radio restoration? I have all the standard test gear for typical electronics DMM, Oscilloscope, Function Generator, Power Supplies, and a Frequency Counter. I still need to get an isolation transformer and a variac. I won't be doing this anytime soon as I am not yet ready but would like to start looking out for good deals on the equipment I will need. I would like to be able to restore these properly not just get them working. I will be putting a lot of effort into the actual case restoration as well. I will be focusing on mostly radios with FM capability.Also I know I will be needing a tube tester. Which ones should I look for and which ones should I avoid?

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: August 12, 2013, 09:03:07 am
content: Quote from: Anson on August 12, 2013, 04:45:19 amAn RF signal generator is vital. It needs to cover the tuning range of your radios as well as intermediate frequencies. 100 kHz - 150 MHz would be fine. Doesn't have to be the most stable.An RF probe is also essential to test local oscillators. Very simple to make - basically a diode/capacitor/resistor on a lead that plugs into a digital or analogue multimeter. If you're poking in valve radios an appropriately high voltage low value coupling capacitor is required for isolation. For a simple test just a diode/capacitor/RF choke on the back of a 500uA meter movement can be useful.Some radios will have shortwave. To test this properly you'll need about 20 or more metres of wire outside and an earth connection (desirable). Also a dedicated FM antenna is worth having.Inductance and capacitance measuring. Also desirable in case you need to restore/replace these parts. Either a stand-alone unit, seperate bridge or plug in to multimeter.

author: PA4TIM
author_rank: Super Contributor
timestamp: August 12, 2013, 01:12:13 pm
content: There are very good tube testers but most are over 50 years old so there can be a huge performance difference between two testers of the same type and brand.There are curvetracers that can test tubes and there are some nice DIY tubetester designs. The germans seem to be very creative in that field.I prefere a high BW scope while working on radios, but this is personal.I find an analog TRMS meter also a handy thing, but a scope can be as usable . When aligning it is more easy to find the peak on an analog meter.For the rest a LCR meter and RF and AF generator. For some radios you need a wobbulator (for instance the 40 MHz filter of a Racal RA17 but that are extremes.Very handy and important for old tube equipment but hard to get commercial, a DC leakage tester , reformer for caps. But very easy to make.I often use a variac and always an isolation transformer. I can switch a lightbulb in series with it for shortcircuit protection and inrush current limmiting

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 12, 2013, 03:06:44 pm
content: *) Sweep generator aka. 'Wobbulator'. I have to disagree with PA4TIM here. A linear 10.7Mhz +/- 1 Mhz sweep generator is almost mandatory for working on FM receivers, preferably with some form of logarithmic detector. The dark secret here is that the original factory service manuals from the fifties and sixties are flat out lying here. They were written with the intent that the service personnel wouldn't have access to a sweep generator, so the simplified technique most frequently given, is meant to at least 'blow a hole though' to make the radio generate some form of sound.However, if you are really looking to maximize the audio quality, then the 10.7MHz IF absolutely needs to be swept and properly aligned. Things like Grundig's reflex IF and the monster 8-12 tube models pretty much requires this. This count double, if you intend to extend the IF bandwidth to today's standard. I also wish anyone good luck, who would attempt to align one of the modern receivers from the 80'ies without a sweep generator.Same sweep generator will also come in handy, if you have to repair or align things like the domestic receivers from the fifties with permeability tuned variable bandwidth 455 KHz IF, intended to maximize performance on SW reception.*) Tube tester: I honestly wouldn't put this high on my shopping list, as long as you are working with domestic receivers. The designers working on these radios knew what they were doing, and as a result these radios were usually designed to work splendidly even when the tubes had lost a fair amount of transconductance.Also, at least for mains transformer equipped receivers, the heater/cathode leakage test doesn't really mean anything. Many tubes in these will have nearly zero volts between the heater and cathode, so a minor leak is completely unimportant.So trusting the tube tester when the tubes test bad is a mistake in the general case, you will discard way too many perfectly serviceable tubes. It should be considered the rule rather than the exception, that all the tubes in an old domestic radio work. It is the passive components around them, which fails.Conversely, even if a tube tests good, then you still have to thoroughly test it in circuit. The triode oscillator in the conversion tube is a famous example, particularly if the receivers has SW bands. Additionally, this particular triode is very, very frequently completely dead, but just this half of the converter tube. This happens, when the receiver was mostly used for FM reception, very common here in Europe, where power is turned off to the oscillator (only used for AM/SW reception). So the triode dies from having heater voltage applied without HT, causing cathode poisoning. Yet if you only want the receiver to receive FM, you can simply ignore this issue, and keep using the tube.Eventually you will know which tubes tend to be trouble makers, either inherently, or due to their position in the schematic. For instance the UL41 audio amp pentode, used in radios with series connected tube heaters, is a notorious candidate for H/K failure.The reason why high quality tube testers were made originally, was that many high end circuits, like those found military, communication or video equipment, actually are quite sensitive to for instance both heater/cathode leaks and low transconductance.Low quality tube testers, like those found in your local repair shop back in the day, are largely useless marketing machines, meant to increase revenue for the tube manufacturers.*) Capacitance/inductance meters: Never had much use for those in connection with restoring domestic receivers. The inductors and high frequency caps rarely fails, except when there is obvious, mechanical damage.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 12, 2013, 03:18:13 pm
content: *) Almost forgot: FM stereo test tone generator, almost mandatory for troubleshooting and aligning FM stereo decoders. Particularly for the high end receivers from the eighties you will very, very much need this, if you want to have any hope of restoring the factory spec audio quality. The simple decoders found in receivers from the sixties can also be finicky to align without one.

author: PA4TIM
author_rank: Super Contributor
timestamp: August 12, 2013, 03:35:04 pm
content: I agree on the wobbulator with you but you need to know how to operate it the right way and it can be done without. They did it for decadesi had several and also build a few myself. Today I rarely use one. Still have a nice army version with CRT (4-400MHz ) Most times I use one of my VNAs or a SA with TG but the advantage of a wobbulator is that the input frequency does not have to be the frequency you measure so you can f.i. measiie behind a mixer (but my SA and VNA in SA/TG mode can do that too) And you do not have a 50 Ohm "problem" . However for cavitys I prefere TDR.I use a tubetester mainly for matching tubes used in instruments lile scopes, sweepers, meters or generators. but it is that i ran in tp one by accident , i was not planning to buy one, and it served me well. a very hard to fond problem in a Tek plugin made it impossible tp measure. The Ohm meter showed no problems but my Weston tester showed a short in a tube. I replaced it and the problem was solved.But I rarely repair domestic stuff and the radios I did where shortwave or midwave, AM , DSB or SSB. Done a few radios, a few Yaesu transceivers, a few Racals and Murphys, a collins, T1154 and some otjer militairy stuff. Most jobs are restoring or repairing instruments, from multimetes to network analysers, also a lot of calibration gear, and you need more gear for that.

author: Anson
author_rank: Regular Contributor
timestamp: August 12, 2013, 05:30:40 pm
content: I do have an LCR meter Just recently acquired that. Forgot to mention that. I wont be working on anything from the 80's I don't think. I plan on only working on the old tube radios in the wooden boxes. My other hobby is woodworking so I am hoping to combine the two hobbies.

author: rstoer
author_rank: Regular Contributor
timestamp: August 13, 2013, 02:16:47 pm
content: A Sencore SG-165 will provide all the RF and IF signals you need for both AM and FM/Stereo. You can pick one up on eBay for about $100. If you're not working on short-ware this will generate all the signals you'll need.Sencore also made a couple of units that combined an isolation transformer with a variac. You can sometimes find a PR-57 for about $100 on ebay but the later PR-570's usually go for $200 or more. RCA (later became VIZ) made something called an ISOTAP. The WP-26A was a good model. It provided isolation and a range of voltages from ~100-130 in five volt steps. Not as versatile as a variac but probably good enough and you can find one for under $50.A good analog meter will also be helpful. Don't bother with a plug-in FET type analog as your DMM will work better in situations where that's needed. Get something like a Simpson 260 (or similar).Hopefully your LCR meter has ESR. If so you should be set in that department.As for a tube tester, if you're working with tubes you will need one, despite what some people say. Just because they require some interpretation doesn't mean they're not necessary. Any decent brand (Sencore, B&K, etc) in good condition should do the job. Be a little wary of brands like Knight, Heathkit, and Eico. There's nothing wrong with the design of those units but many of them were sold as kits, so you wind up at the mercy of the unknown person who built it.

author: Anson
author_rank: Regular Contributor
timestamp: August 13, 2013, 05:36:58 pm
content: I was wondering about the Eico brand. I see a lot of them on Ebay for cheap and they look cheap. I love vintage test equipment. I have been fortunate enough to snag some very nice "for parts only" equipment that really needed very little to get running perfectly again. All of these were very cheap also. I now have 3 power supplies by Power Designs that I absolutely love. The first I got was a poor 6050c with rust on the outer shell and dead as a doornail. It needed The two main filter caps replaced as well as 2 other electrolytics and 2 solid tants. That got it working but the digital meter was still not working. That was remedied by a new 7805 and all three IC's. It works great now and I only have a total of about $43 bucks in it. The next is a 2005 surprisingly it's only issue is it's no longer accurate still working on this one. The last is a TP343B This one was $50 and it's malfunction was a missing fuse and whoever worked on it last put in one of the caps backwards.But yeah I love this old stuff the new stuff today just feels so cheap and easily breakable.

author: rstoer
author_rank: Regular Contributor
timestamp: August 16, 2013, 12:53:13 pm
content: Some Eico stuff is Ok. It's just that a lot of it was sold in kit form so you can't be sure of the build quality. We had a few of their power supplies for repairing car radios (very heavy duty but no regulation) and a 965 Capacitance Bridge (only sold assembled) which was the ONLY capacitor tester I would trust at the time. I bought that in 1969 and was still using it when I sold the business in 1992. We had newer models from B&K and Tenma that would miss things the trusty Eico caught.

author: DavidGoncalv
author_rank: Contributor
timestamp: August 20, 2013, 04:23:20 pm
content: I've been restoring radios (AM, FM, ham) and televisions for about 15 years. These are the things I always use - the list is incremental as you read it downward.*****METCAL SP200 Soldering Iron (or equivalent) MY GOD DOES THIS MAKE THE WORK EASIER******AM Radios need the least equipment: good DMM, dim-bulb tester and/or variac, at least an emission tube tester, signal generator, VTVM is great too.Ham transceivers - small dummy load, demodulator probe, good power meter,RF connector adaptor sets, frequency counterFM Radios are about the same, but since I align them so infrequently, I used to take them to a audiophile shop for the step of alignment. When I got equipment for TVs, I ended up with what i needed anyway. Also, VHF signal generator.TVs: CRT checker most important - I won't bother buying a set if the CRT is low/shot. Marker/sweep generator for TVs. HV probe for VTVM or seperate. TV modulator. Capacitor leakage tester (tests mica/etc at working voltage). NTSC pattern generator.Things I've owned:Measurements Model 80 signal generatorDDS VFO signal generator from eBayAADE frequency counter for HF/UHFHeathkit IT-21 emission tube testerB&K I-177 VTVMSimpson 260 VOM (hardly gets used)Fluke 87 DMM, calibratedPhilco dummy loadBird Thruline wattmeter and slugs from NM3EVarious Heathkit, B&K and other demodulator probesPACO HV probeB&K 465 CRT checkerSencore CR70 CRT 'Beam-Builder' CRT tester/restorerHeathkit IG-57A TV alignment generator with mods for external marker and 21 MHZ IFHeathkit capacitor checkerBlonder-Tounge agile modulatorLeader LGC-396 pattern generator (though I wish it did more useful stuff for monochrome)hope this helped.

author: edavid
author_rank: Super Contributor
timestamp: August 20, 2013, 07:23:34 pm
content: Quote from: Anson on August 13, 2013, 05:36:58 pmI would avoid it, unless you research a specific model and like the design. Most of it really is cheap where it counts - it's underdesigned, like a lot of Heathkit equipment.For example, Eico RF generators drift and have leaky output sections - because they didn't want to pay for regulated power supplies, output buffers, shielded attenuators.

author: Anson
author_rank: Regular Contributor
timestamp: August 21, 2013, 07:15:33 pm
content: How do you guys rate the hickok brand? They seem to have some decent tube testers.