These should be easy answers, but believe it or not, tons of electronics pages on the Web doesn't seem to provide them (or at least, provide them readily enough).
Question one:
From this early part of the Tube Faq:
"When you open up an amp, you need to find a way to drain off any residual high voltage. A handy way to do this is to connect a shorting jumper between the plate of a preamp tube and ground."
"Ground" in this case meaning what?
What's the ground - the chassis itself? Some specific part of the amp? "How-to" articles often neglect to explain exactly what they mean by "attaching to ground".
Question two:
From an Instructables article on discharging caps, written for absolute beginners:
"THEN,
--Take a screwdriver or a jumper and short the capacitors leads.
--OR jumper the power amp tube plate pin to GND for a minute or so (Class A, single power tube only.)
--OR jumper the positive (+) lead of each large cap to GND for several seconds. A jumper with a built-in resistor (10K or so) will help prevent sparks here..."
Wait! Rewind. HOW does one "short" something using a screwdriver? What touches what? What doesn't touch what? How do you know the short was successful?
Question three:
Pictures of some equipment I've recently picked up. What are the rectangular components? (I've actually watched a whole bunch of Youtube vids of people displaying their tube amps, pointing out the tubes, caps, and large transformers, but then completely neglect to explain or even acknowledge the very rectangular things below I was hoping they'd explain!)
Thanks in advance from a frustrated novice
Question one:
From this early part of the Tube Faq:
"When you open up an amp, you need to find a way to drain off any residual high voltage. A handy way to do this is to connect a shorting jumper between the plate of a preamp tube and ground."
"Ground" in this case meaning what?
What's the ground - the chassis itself? Some specific part of the amp? "How-to" articles often neglect to explain exactly what they mean by "attaching to ground".Question two:
From an Instructables article on discharging caps, written for absolute beginners:
"THEN,
--Take a screwdriver or a jumper and short the capacitors leads.
--OR jumper the power amp tube plate pin to GND for a minute or so (Class A, single power tube only.)
--OR jumper the positive (+) lead of each large cap to GND for several seconds. A jumper with a built-in resistor (10K or so) will help prevent sparks here..."
Wait! Rewind. HOW does one "short" something using a screwdriver? What touches what? What doesn't touch what? How do you know the short was successful?
Question three:
Pictures of some equipment I've recently picked up. What are the rectangular components? (I've actually watched a whole bunch of Youtube vids of people displaying their tube amps, pointing out the tubes, caps, and large transformers, but then completely neglect to explain or even acknowledge the very rectangular things below I was hoping they'd explain!)
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Thanks in advance from a frustrated novice
Hi,
Question one, chassis is often called earth and is connected to the mains earth for safety should the casing raise in potential.
Ground is 0V reference for signals in the equipment and is often but not always connected to earth.
To discharge equipment:
You are best taking a resistor of say 1Kohms @ 2 watt or so and holding it using a pair of insulated pliers short ( short = connect the two terminals togeather) of a power supply reservoir capacitor using the two legs of the resistor.
The capacitor will discharge through the resistor and the resistor will get hot.
Use a Voltmeter to carefully check that the capacitors are discharged before playing about.
I dont think shorting capacitors with a screwdriver is a good idea at all really, so dont do it.
The metal boxes i believe are variable capacitors, looks like radio chassis or somthing.
Hope ive been fairly clear here, but probably there is some ambiguity somewhere.
P.S. I dont think you should fiddle around with valves unless you have a good idea of safety and basic power supply knowledge, they can be dangerous.
Question one, chassis is often called earth and is connected to the mains earth for safety should the casing raise in potential.
Ground is 0V reference for signals in the equipment and is often but not always connected to earth.
To discharge equipment:
You are best taking a resistor of say 1Kohms @ 2 watt or so and holding it using a pair of insulated pliers short ( short = connect the two terminals togeather) of a power supply reservoir capacitor using the two legs of the resistor.
The capacitor will discharge through the resistor and the resistor will get hot.
Use a Voltmeter to carefully check that the capacitors are discharged before playing about.
I dont think shorting capacitors with a screwdriver is a good idea at all really, so dont do it.
The metal boxes i believe are variable capacitors, looks like radio chassis or somthing.
Hope ive been fairly clear here, but probably there is some ambiguity somewhere.
P.S. I dont think you should fiddle around with valves unless you have a good idea of safety and basic power supply knowledge, they can be dangerous.
Those rectangular cans are IF (Intermediate Frequency) transformers. What you have there is a superheterodyne receiver that beats a local oscillator against the incoming signal to produce sum and difference frequencies. Because the local oscillator is adjustable by the tuning control, we can arrange for any selected radio frequency to produce a required (and constant) difference frequency, which is known as the intermediate frequency. Because the IF is constant, we can make a special amplifier that amplifies that frequency with very high gain and rejects all other frequencies. Doing that makes our receiver able to pick out the radio station we choose and reject all others. To make the IF amplifier so selective, we need lots of tuned transformers, and those are what you see. The larger cans that aren't in a row with the valves might be the stereo decoder, whereas the ones in a row are the IF amplifier - often called an IF strip because of the mechanical arrangement.
It's probably historical. (Always a good answer when you're not certain.)
I vaguely remember that it's to do with images and broadcast spacing. Remember that the mixer is deliberately nonlinear, so the trick is to make it produce sum and difference frequencies, but not all the other possible intermodulation products. You don't want any of the unwanted images to coincide with a broadcast frequency, so you choose your IF carefully w.r.t. broadcast spacing. So, did WARC** that changed spacings to multiples of 9kHz suddenly make all old receivers duff? Probably not, probably receivers were good enough by then.
I expect a radio ham would be able to give a better answer.
I vaguely remember that it's to do with images and broadcast spacing. Remember that the mixer is deliberately nonlinear, so the trick is to make it produce sum and difference frequencies, but not all the other possible intermodulation products. You don't want any of the unwanted images to coincide with a broadcast frequency, so you choose your IF carefully w.r.t. broadcast spacing. So, did WARC** that changed spacings to multiples of 9kHz suddenly make all old receivers duff? Probably not, probably receivers were good enough by then.
I expect a radio ham would be able to give a better answer.
Its an old radio receiver, not an amp EC8010 knows more than I do
I think everyones got to start somewhere, as long as he reads up on safety it will be a good learning experience to do somthing with this thing.
Looks like a nice chassis with good parts to me
Have a look at the HV safety thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=30172
I think everyones got to start somewhere, as long as he reads up on safety it will be a good learning experience to do somthing with this thing.
Looks like a nice chassis with good parts to me
Have a look at the HV safety thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=30172
Craig405 said:
Thanks for the response.
So then, re. the Tube Faq: " connect a shorting jumper between the plate of a preamp tube and ground.", the ground would simply be any part of the chassis, and if so, is that always the case? (Actually, I'm also confused by what the Faq means by "the plate of a preamp tube" -- isn't a preamp tube's plate one of the components inside the tube itself?
shnaggletooth said:
If I were you I would buy a book on basic electronics and learn about components and circuits.
Play about with some low voltage solid state first before getting involved with dangerous valve amps.
I use +/-60 volts on my solid state amps and that can give a shock/tingle if I get across both rails.
How about a tube head who is a radio ham and has worked as a radio design engineer for the past 36 years?
The answer to this question is really pretty complex, but EC8010 has most of the main points covered. Why not 450KHz. In the US AM broadcast band the channel spacing is 10 Khz. The band is over 1 MHz wide, so it is possible for two strong broadcast signals to combine to produce an IF frequency of 450 KHZ regardless of the local oscillator frequency. Imagine a strong signal on 1000 KHz and another on 1450 KHZ (both legal channels), they could combine in the mixer (purposely non linear) to make 450 KHz. Hence the IF should be an odd multiple of 5KHz. FM has 200 HKz channel spacing, so we need an odd multiple of 100KHz here.
A mixer will produce a signal at the sum and the difference of the two applied frequencies. This can create images (like aliasing in a DAC). No local oscillator is pure, they all have harmonics. Even if the LO was pure, the non linear mixer will create the harmonics, so harmonic responses for both the LO and the applied RF frequencies must be considered. No amplifier is perfect either and (just like our tube amps) they create harmonics (THD) and intermodulation products (IMD). Since the radio spectrum (like music) does not consist of a single signal (and music isn't a pure sine wave) , we must consider the wanted signal (or band of signals) the harmonics of the RF and LO frequencies, all of the possible IMD products, the images, and their possible IMD products and........
When is is all said and done today we input all of this into a custom "spur search" program or an Excel spreadsheet to find a suitable IF frequency. There is always some reason NOT to use any given IF frequency and we try to minimize those. The biggest are to make sure that there will never be any strong signals ON your IF frequency, and strong signals on the 1st image frequency should also be avoided. All of the possible spurious response frequencies are checked to make sure that they won't be occupied by a megawatt level transmitter (UHF TV broadcast stations run up to 5MW of ERP) anywhere you plan to sell the product.
The choices for a given application in a given location are really pretty limited, and even with the modern advances in technology like SAW filters we still use the same IF frequency that we have used for 20 years in our radio products.
shnaggletooth said:
If yuo have a year, then buy and read a couple books
This book has been a standard for 50 years... It covers mainly radio electronic but as good chapters on basic electronicsm and talks about how resistors, transformers, tubes and so on work. It is written for for a motivated reader that has little electronics education and only high school math. but covers some advanced topics.
New ed. of this book comes out every year and there is only a little change. So buy a copy that is acouple years ould for 1/3rd the price. The link below is to the 2002 ed. It is a bargin at double the price.
http://www.amazon.com/Arrl-Handbook...91/ref=sr_1_10?ie=UTF8&qid=1250113314&sr=8-10
After that if you want to learn about tube technology the "Radiotron" book is an absolute must read. The copyright expired so now it is free and legal to download. this book is very well written. Evey subject s covered with a intro that is easy to follow then he makes a second pass with more details and finally a third pass with some more math and theory. This book is aimed at the series hobbyst. It is not quite at the level of an enginerring text book but comes close.
Radiotron Designer's Handbook, Fourth Edition, P. Langford Smith, 1953, 1,498 pages!
http://www.pmillett.com/technical_books_online.htm
BTW the above site also has some VERY old copies of the "ARRL Radio Amateur's Handbook" from ther 30's and 40' but you are best off spending $15 at amazon for a modern version. Even if you only read the chapter on basic electronics and construction techniques it is worth it. It has plans for ome projects too.
Snaggletooth: As already mentioned, it's not a good idea to short charged caps directly to ground with a screwdriver, etc. It makes big sparks, arc welds your screwdrivers, and isn't very healthy for the caps, not to mention the user!. Make up a large value 2W resistor (100K-200K ohms) with some short wires and insulated clip leads to drain the residual voltage from the reservoir caps. You can either clip the R across the cap or clip the positive side to chassis ground through the R. Connect the clip leads using one hand and keep your other hand in your pocket or behind your back. I grab a belt loop with one hand on my backside when connecting/testing live tube stuff. You don't want to complete the circuit with both hands, as this could put lethal voltage/current across your heart 
The larger the R value, the longer it will take for the caps to discharge. I would give them 30 seconds to a minute or so and then check the voltage across the cap with a multimeter. It's a good idea to get some clip leads for your multimeter also, so you can connect them with one hand. They also come in handy when firing up a circuit, as you can connect them when everything is off before firing it up and be "hands-off" of the live circuit.
Some amps have these drain resistors built-in but many do not, so it's a great habit to check the volts on the power supply caps (with one hand) before diving in to work.
One final note: You didn't mention if the equipment has been powered up or works. If the amp has not been powered up for decades, applying 115VAC instantaneously may also pop the electrolytic caps, as they may need time to "reform" an oxide layer on their foils. You want to apply voltage gradually using a variac or the lightbulb trick (do a search here for the lightbulb trick, as I have never done it) over the course of 30 minutes to an hour or so.
The larger the R value, the longer it will take for the caps to discharge. I would give them 30 seconds to a minute or so and then check the voltage across the cap with a multimeter. It's a good idea to get some clip leads for your multimeter also, so you can connect them with one hand. They also come in handy when firing up a circuit, as you can connect them when everything is off before firing it up and be "hands-off" of the live circuit.
Some amps have these drain resistors built-in but many do not, so it's a great habit to check the volts on the power supply caps (with one hand) before diving in to work.
One final note: You didn't mention if the equipment has been powered up or works. If the amp has not been powered up for decades, applying 115VAC instantaneously may also pop the electrolytic caps, as they may need time to "reform" an oxide layer on their foils. You want to apply voltage gradually using a variac or the lightbulb trick (do a search here for the lightbulb trick, as I have never done it) over the course of 30 minutes to an hour or so.
Back to school
Yikes! Sounding like my ol' teachers a talkin'......Thought those were IF cans..hadn't peered upon those dang things in YEARS. See how they are all lined up, guess that would be your "strip".
Shnaggletooth: Yeah, you really should read up on stuff.We will all still be here when your done. "Short across with a screwdriver"??? Ye Gods! I thought that kind of thing was long gone! No, using a screwdriver to "short" out capacitances is/was a patently stupid, crude way to do things. Its kinda like taking a pair of pliers to a hex nut.....will chew up the nut and it might not come off, a wrench would be the proper way to do it.
Hook-up a multimeter to it to measure the voltage with some alligator clips...sit back & watch the voltage slowly go down. The meter itself "draws" power itself to give you the voltage reading.
________________________________________________________Rick.........
Yikes! Sounding like my ol' teachers a talkin'......Thought those were IF cans..hadn't peered upon those dang things in YEARS. See how they are all lined up, guess that would be your "strip".
Shnaggletooth: Yeah, you really should read up on stuff.We will all still be here when your done. "Short across with a screwdriver"??? Ye Gods! I thought that kind of thing was long gone! No, using a screwdriver to "short" out capacitances is/was a patently stupid, crude way to do things. Its kinda like taking a pair of pliers to a hex nut.....will chew up the nut and it might not come off, a wrench would be the proper way to do it.
Hook-up a multimeter to it to measure the voltage with some alligator clips...sit back & watch the voltage slowly go down. The meter itself "draws" power itself to give you the voltage reading.
________________________________________________________Rick.........
I use a light bulb too, but I've never seen it light up. Except for that one time I forgot to unplug the amp
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.