Audio Generator or Function Generator? Which to get?

On Tuesday, 14 March 2017 13:46:23 UTC, dca...@krl.org  wrote:
> On Monday, March 13, 2017 at 8:43:24 PM UTC-4, tabby wrote:
> 
> > > Solid state equipment is a lot more reliable than vacuum tube equipment.
> > 
> > It _can_ be more reliable, but making it so is a challenge most equipment fails. If 50 year old valve kit is working it has proven itself, and any new electronics has a very low chance of lasting that well. So in practice old valve kit is on average more likely to last better.

> I do not agree with you.   A fifty year old  valve kit that is working does not prove that it is a reliable gear. 

It proves the design is capable of great longevity

> There may have been 50 thousand of those produced and all have failed except for one.

There's always a 1 in 50k chance of that. Statistical conclusions are only a reflection of the data fed into them.

> Way back in the 1960's the mean time to failure for some transistors was 1500 years.  

And the mean time to failure for soldered connections, electrolytics, bits of plastic, switch contacts and all other parts?


NT

On Tuesday, March 14, 2017 at 10:02:05 AM UTC-4, tabb...@gmail.com wrote:

 
> > Way back in the 1960's the mean time to failure for some transistors was 1500 years.  
> 
> And the mean time to failure for soldered connections, electrolytics, bits of plastic, switch contacts and all other parts?
> 
> 
> NT

On the stuff I was  designing  there were no bits of plastic, switches , or soldered connections.  The electrolytics were the biggest problem and we used mostly dry slug tantalum caps  ( as I remember it,  It was a while back )

It was somewhat after someone at MIT or Harvard built a difference analyser with something like 50,000 tubes.  The tubes had a 50,000 hour average life .  Se it would fail about every hour.  To find the bad tube took something like two hours  It was not a success.

                                          Dan

On 3/14/2017 10:51 AM, dcaster@krl.org wrote:
> On Tuesday, March 14, 2017 at 10:02:05 AM UTC-4, tabb...@gmail.com wrote:
>
>
>>> Way back in the 1960's the mean time to failure for some transistors was 1500 years.
>>
>> And the mean time to failure for soldered connections, electrolytics, bits of plastic, switch contacts and all other parts?
>>
>>
>> NT
>
> On the stuff I was  designing  there were no bits of plastic, switches , or soldered connections.  The electrolytics were the biggest problem and we used mostly dry slug tantalum caps  ( as I remember it,  It was a while back )
>
> It was somewhat after someone at MIT or Harvard built a difference analyser with something like 50,000 tubes.  The tubes had a 50,000 hour average life .  Se it would fail about every hour.  To find the bad tube took something like two hours  It was not a success.
>
>                                           Dan
>
     Still in use by the DMV.



---
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On 3/13/2017 4:26 AM, oldschool@tubes.com wrote:
> I've been looking into buying an Audio Generator (Sine and Square Wave).
> I mainly want this to run thru an amplifier to listen to the frequency
> repsonse of the amp and speakers. Nothing very scientific, just to see
> what these amps and speakers can do.... And on occasion to inject an
> audio signal into amp sections to dee if the audio is passing that
> stage.
>
> Originally I was looking at some of the old tube gear, such as the Eico
> model 377. I also looked at the Heathkit IG-18 a transistorized version
> from the 70s. Because I like that old test gear, I'd be happy to get
> either of these, or another similar. Both of these are Sine and Suqare
> Wave. But what I am finding is the prices combined with high S+H fees,
> make these things very costly, and I have not found any of them which
> claim to work. Sold as-is, for parts or repair. So, I may end up paying
> $60 or more and getting something that dont work, likely needs new caps,
> and so on..... If they were $25 or less, I'd take a chance, but not for
> that kind of money.
>
> My search on ebay lead me to something called a "Function Generator".
> What the heck is that??? And also called a DDS device. (I have no clue
> what DDS means). But I carefully looked at this NEW device, sold without
> a box (case), but only needs a power module and test leads. They sell
> for around $14 from China, but since I dont care to order from China,
> I'll probably have to hunt one down from the US, and pay around $5 or
> $10 more. But that's ok. These have both the Sine and Square wave, as
> well as Triangle wave (what does that sound like?).
>
> While I prefer the older stuff, for around $20 a cheap wal-wart, and a
> little work putting it into a box, I'd probably buy one of these, *IF*
> it will do what I need..... I have read all the info on the ebay pages,
> but I am not 100% sure that this is a modern replacement for the old
> audio generators. One nice thing, is that they will show the exact
> frequency on the digital readout.
>
> IS THIS WHAT I AM LOOKING FOR?
> Is something like this made to really be used, or is it just another toy
> that does little and fails in a few months?
>
> And can something like this work to test tube amps, without blowing up
> from the high voltages in tube gear?
>
> One last thing that has me puzzled. There are two BNC connectors. One is
> labeled DDS, tho other is HS.
>
> I found this in the description.
> DDS frequency range: 1Hz-65534Hz, high-speed frequency (HS) output up to
> 8MHz.
>
> I dont understand how or what the high speed feature does. Why would an
> audio frequency be or need "high speed"? And what is the point for this
> device to go above 20,000 cps, since we cant hear that anyhow? Going up
> to 8MHZ seens senseless, unless this also serves as a RF signal
> generator.
>
> Here is the ebay URL.
>
> http://tinyurl.com/h5celuc

I haven't read all of the posts in this thread, but I see a lot of 
confusion of the terms "function generator" and "audio generator". 
Audio simply refers to the frequency range of the signal generated 
without saying anything about the manner in which it is generated.  But 
most signal generators output a sine wave and perhaps a square and 
triangle wave.  As others have said, they were often analog circuits 
that shaped one waveform into another.  This is different from an 
"arbitrary waveform" generator which some seem to be calling a function 
generator.

An arbitrary waveform generator has a pattern in memory which is played 
through a DAC to produce any function you wish which must repeat only 
when the memory capacity is reached.

A DDS is another type of repeating waveform signal generator that also 
uses digital logic and a DAC.  It uses an incrementer to model the phase 
of a signal cycle which then is translated into a waveform and played 
through a DAC.  If you want a sawtooth wave, you just play the phase 
value through the DAC.  A sine wave may be generated using a lookup 
table or some simple sine generation functions.  Other waveforms can be 
generated using the lookup table or other mathematical functions.  But 
all these signals must repeat at some period as defined by the amount 
the phase register is incremented at each clock.  In fact, that is the 
strength of the DDS over an analog signal generator, the frequency of 
the output signal is very accurately defined.

I'm not sure why you think these devices would not be reliable or are 
inherently inferior.  The Ham community have been using DDS for some 
time now.  Even if they aren't used to directly generate the frequency 
needed, they can be used as a tunable reference frequency with a PLL to 
generate a very accurate frequency of nearly any rational value.

-- 

Rick C

On Tuesday, 14 March 2017 15:51:30 UTC, dca...@krl.org  wrote:
> On Tuesday, March 14, 2017 at 10:02:05 AM UTC-4, tabb wrote:

> > > Way back in the 1960's the mean time to failure for some transistors was 1500 years.  
> > 
> > And the mean time to failure for soldered connections, electrolytics, bits of plastic, switch contacts and all other parts?

> On the stuff I was  designing  there were no bits of plastic, switches , or soldered connections.  The electrolytics were the biggest problem and we used mostly dry slug tantalum caps  ( as I remember it,  It was a while back )

Most testgear of course is built to nothing like those standards.

> It was somewhat after someone at MIT or Harvard built a difference analyser with something like 50,000 tubes.  The tubes had a 50,000 hour average life .  Se it would fail about every hour.  To find the bad tube took something like two hours  It was not a success.

A killer problem with valve computers. At least they were better than relays. A sig gen with a few valves is a very different proposition. Basic maintenance every 16k hours of use, typically several decades, is quite acceptable.


NT

On 3/13/2017 2:59 PM, Jasen Betts wrote:
> On 2017-03-13, dcaster@krl.org <dcaster@krl.org> wrote:
>> On Monday, March 13, 2017 at 4:28:39 AM UTC-4, olds...@tubes.com wrote:
>>> I've been looking into buying an Audio Generator (Sine and Square Wave).
>>
>> In addition to looking at Ebay , look at AliExpress.  Sometimes identical items are much less expensive at Ally or Ebay.  Try including diy to find kits.
>
> Also search "suite", which seems to be a common miss-traslaion of "kitset"
>
>> Solid state equipment is a lot more reliable than vacuum tube equipment. So you are better off buying something new.  Getting a replacement vacuum tube may be nearly impossible.
>
> Electrically, tubes are harder to bust...

No they aren't.   Just leave one on for a few weeks and the filament 
will go out, if it hasn't busted your wallet on the electric bill.

-- 

Rick C

On 3/13/2017 3:23 PM, oldschool@tubes.com wrote:
> On Mon, 13 Mar 2017 09:27:50 -0700, Jeff Liebermann <jeffl@cruzio.com>
> wrote:
>
>> That DDS generator only goes up to 65KHz, does not have a built in
>> frequency sweep feature, and does not have a sawtooth output or built
>> in detector suitable for displaying a frequency sweep on an
>> oscilloscope.  To sweep an audio amplifier with a DDS, you will need a
>> sine wave generator feature, and an up/down counter or frequency
>> modulator to sweep the frequency range.
>>
>> First look at a real function generator.  Next, build a checklist of
>> the features you need.  Then, go shopping using the feature list.
>> You're doing this backwards.
>>
>> Note:  You can use a PC sound card as a swept audio source and
>> function generator:
>
>
> Thanks to all who replied. I read that WIkipedia article, which
> explained what these things are, (even though that article was like
> reading a legal manual).

Wikipedia often is written by those with a certain level of elitism 
rather than an interest in explaining topics to all who wish to learn. 
It is not uncommon for a technical article to be written at such a high 
level that a reader needs much more than just a casual understanding of 
the topic.

In my opinion, this is one of the ways Wikipedia has failed.


> When I descibed this thing, I actually had looked at several of them
> from China, which all looked identical. One of them said it goes to
> 8mhz, using the BNC connector labeled HS. Either way, that dont much
> matter, since I have my old Eico tube signal generator, for RF use.
>
> I probably am doing this backward, but I really was not looking for
> something like this. I was looking for an old tube based audio
> generator, such as the Eico 377. But you know how ebay tends to show a
> hundred other things that are similar, and these function generators
> came up. I had to spend a good amount of time reading about them, since
> I was not familiar with them at all.
>
> I am somewhat aware about using a computer with software to act as a
> signal generator, oscilloscope, etc. I'll have to read up more on all of
> that, but in all honesty, I would not even consider connecting my laptop
> computer to anything other than and audio input connector on a tube amp.
> I said I also want something for testing interstage circuits, and that
> means applying a test probe to a spot inside a device that may have 400
> or more volts on it. Even with a capacitor and other protection, there
> is no way in hell that I am gonna risk destroying an expensive and
> fragile laptop computer. And while I have several spare deshtop
> machines, I do not keep them in my shop. I dont have the space and I
> dont want to be distracted by computers when I'm soldering. If I do take
> any computers in my shop, it's my laptop, and I only do so to view a
> schematic on the screen.

How exactly would a computer distract you while you are soldering??? 
That is very unclear.

If you want to deal with tube circuits you need a buffer between any low 
voltage equipment and the tube equipment.


> In all honesty, what I really want to buy is still an old tube type
> audio generator. That is what was made for the gear that I mostly work
> on, and that old tube stuff is built to hold up, as well as being easy
> to repair if it breaks. The problem is that this old tube stuff is
> selling for way too much money on ebay. Heck, some of those old Eico
> 377's are asking as much just for shipping as I am willing to pay for
> the whole thing, and one of them looks like it went thru a war, and is
> being sold For PARTS.....

Maybe there's a reason why tube equipment isn't made much anymore?


> Which reminds me, does anyone know of other sources for buying that old
> tube test gear, besides ebay? There must be other sources....
> It's NOT Amazon, I checked, even though I have never cared much for
> Amazon. They just dont sell old stuff like this.

Try connecting with a Ham club.  They often use old equipment.


> I might still buy one of these DDS devices, just for the heck of it. For
> $15, I'm sure I'll have some fun with it..... I actually found some of
> them (identical( located in the U.S. for $17. (I dont buy from China
> because it takes too long to get the stuff). I also found another one in
> the US that comes with the matching wall wart for $23. (Which I'd
> probably buy, or I will just end up having to spend another $5 or more
> to order that wart separately.

The problem with buying wall warts is getting one that does what it says 
it does.  If  you type in 5v, 1A for a wall wart on ebay, the first 
hundred or so units have the same picture, are priced within a nickle of 
each other and contain a single transistor for the entire active circuit!


> So, the bottom line is that I may buy one of these DDS devices, but I
> will still continue to look for the tube type audio generator which is
> what I really want in my shop for testing my old tube gear.


You could just insert a tube amp between the DDS and the gear you are 
testing...

-- 

Rick C

On 3/13/2017 3:33 PM, oldschool@tubes.com wrote:
> On Mon, 13 Mar 2017 13:43:04 -0500, amdx <nojunk@knology.net> wrote:
>
>> On 3/13/2017 3:26 AM, oldschool@tubes.com wrote:
>>> I've been looking into buying an Audio Generator (Sine and Square Wave).
>>
>>   If you have any interest in building one, look up the XR2206. It is
>> an old but a pretty cool chip. It will do many functions up to 1 Mhz.
>>  Lots of info available, I even see one Arduino controlled unit.
>>
>>                                             Mikek
>
> I suppose I could look this up, but I have other things to do at the
> moment, so I am just gonna ask.... What is Arduino?
> I'm Old School, so I dont know much about all this new technology.

It's just a single board computer with plug in modules for a wide range 
of I/O functions.  It also has one of the easiest to learn development 
systems for writing code.  If your DDS has a serial port for control the 
Arduino could be used to make it do more complex functions by changing 
it from this waveform to that waveform in real time.

-- 

Rick C

On Tuesday, March 14, 2017 at 11:31:50 AM UTC-7, rickman wrote:
> On 3/13/2017 4:26 AM, oldschool@tubes.com wrote:
> > I've been looking into buying an Audio Generator (Sine and Square Wave).
> > I mainly want this to run thru an amplifier to listen to...

> I haven't read all of the posts in this thread, but I see a lot of 
> confusion of the terms "function generator" and "audio generator". 
> Audio simply refers to the frequency range of the signal generated 
> without saying anything about the manner in which it is generated.  But 
> most signal generators output a sine wave and perhaps a square and 
> triangle wave. 

That's incorrect; most inexpensive signal generators output a square and
triangle (hey, it only takes two op amps); adding a sinewave is complicated.
To do a GOOD sinewave, the old HP20x units had matched pairs of adjustable
capacitors, which are VERY pricey items.

So, the iCL8038 and XR2206 and some other IC generators (which dominate
the market at the low-cost end) distort and/or filter the triangle wave to make
a "sinewave".    The sinewave outputs are dreadfull.

For audio test purposes, a CD with test tracks is a pretty good sinewave source.   Digital
sythesizers are good, too.   Neither is convenient for a test bench, though.

dca...@krl.org wrote:

> 
> 
> I do not agree with you.  A fifty year old  valve kit that is 
> working does not prove that it is a reliable gear.  

** It proves that someone has been keeping it running. 


> 
> Way back in the 1960's the mean time to failure for some transistors
> was 1500 years.  
> 

** Which only means that the unforced failure rate is one in 1500 per year. 
                  
  Says nothing about the typical lifespan and it sure as HELL ain't 1500 years. 



.....  Phil