The Work Bench



I've added a HP8640B Signal Generator to my bench

As I've post to my main journal, my long term goal for 2013 is to learn everything about FM and FM Tuners.

Of course to do this, there's got to be some new equipment for the lab.  My most recent acquisition is a HP8640B Signal Generator.  This signal generator was a top of the line model back in the 1980's and it originally cost somewhere around $24,000.00.  I paid just a little over $200.00 to a audio repair shop that was going out of business.

I really can't list all of the features and functions of the 8640B yet because I really don't know how to use it. The manual is 200 pages long and is very detailed, it will take me a few weeks to just get through it.

I do know that the 8640B is capable for generating both AM and FM signals and I think it can generate both of them at the same time.  This model is very popular with HAM Radio operators and there's a lot of good information about the 8640B on the web.

See all of the 8640B pictures here.



Adding an LCR Meter to your Workbench

A really nice addition to your workbench is a LCR Meter. The L stands for inductance, the C is for Capacitance and the R is for Resistance. The main advantage of a LCR meter is that it has the ability to taking readings of components in circuit.

This past Sunday I was working on a preamp with a difficult to trace problem. I was fairly sure that there was either a bad resistor or film capacitor somewhere on the board. By using the LCR meter I was able to check 90% of the components in circuit. By not having to desolder one leg of each component to test it, I saved a lot of time and there is less risk to the board itself.

The LCR meter is not perfect, there are always a few components that will give the meter false readings while they are in circuit. So, how do you tell a false reading from a bad part? It's really fairly simple. Since the LCR meter is a highly accurate and reliable device, when you find a component that measures way off of its stated value, that's the one you pull a leg out and check again.

The board I was working on this past Sunday is divided into 6 different sections and each section contains both right and left channel circuits, which are mirror images of each other. This gave me an advantage when checking for bad components.

For example, if a 270K resistor measured 4.5K on the LCR meter and the reading was the same on both the right and left channels of the same circuit, there is a high probability that it's a false reading. In these cases I would go back and pull one leg of the resistor to double check the actual reading.

Another useful feature of this LCR meter is the ability to plug components directly into the jacks on the front of the meter. The jacks are wide and spring loaded, so the leads can be slipped right in. I have found this to very a very fast way to verify the values of parts when I'm building or rebuilding a board. I find it much faster than using a DMM.

LCR meters are available from most manufacturers of test equipment and there are many that also include a built-in ESR meter. I choose a BK Precision 878A because I already have an ESR meter.    

If your working on modern board with a lot of surface mounted components you can buy a set of tweezer probes which make checking these tiny parts so much easier.

See all of the LCR Meter pictures here.



Cleaning Audio Jacks on a Marantz Model 33 Preamp

Cleaning is the final step in the process of refurbishing any piece of audio gear in my shop.  Cleaning RCA, headphone and dubbing jacks can be a tedious process but it is truly necessary to insure the next owner will not have any problems using the equipment.

I have tried many different methods and cleaning tools, some were fairly good most were marginal at best.  A few weeks ago I made an order from Caig to restock my DeoxIt supplies and while I was hunting around their web site I ran across a Precision Tool cleaning sample kit Model K-AS10.

The kit includes two types of lint-free cleaning clothes, 3 sizes of cleaning swabs and a nylon cleaing brush.

The nylon cleaning brush fits perfectly inside RCA jacks.  I used the brush with a little DeoxIt D5 sprayed on the brush and followed it up with the medium size swab.  This cleaned the inside of the jack very well, certainly better than using a pipe cleaner.

The medium size swab also works very well for cleaning the contact surfaces on the Model 33's selectors switch.  The small swab, could be used on the smallest contact points, but it was my least favorite of the 3 swabs.  It is really a pointed tooth-pick with a little bit of cotton on the end.  The swab is easily pulled off if it gets caught on anything.  The large and medium swabs are a foam type material, mounted on plastic handles and they are very well attached.

The large swab fits perefectly into 1/4" headphone and dubbing jacks and its scrubbing action cleaned the jacks well.  The medium swab also fits inside the shell of an RCA plug nicely and with some D5 cleaned away plenty of oxidation.

This kit adds another tool to your arsenal which keeps your audio gear in top notch condition.


Vintage ITT DC Millivolt Meter

We have a local auction house in our area and the first and third Wednesday nights each month are auction nights.  Last night as we are wandering around looking at all of the treasures that were to be auctioned, I spied something cool.

In a lot of vintage movie camera equipment was a ITT D.C. Millivolt meter in its original case.  The accessory connectors and the instructions were inside the case.  

I waited patiently for the lot to hit the auction block, hoping that there would be little interest in lot.  Right off the bat there were several dealers bidding on the lot and the price shot past $45.00.

Fortunately the winner is a regular at the auction house, so I kept an eye on him making sure that he didn't slip out before I had a chance to talk with him.

Later when he got up to leave, I followed him up front and asked him about camera equipment and if he would sell the meter.  He said "yeah, sure. . . what would you pay for it?"  I said $5.00, he said how about $20.00, I have how about $8.00 because that's all the cash I had with me, He said sure!

This is a really cool old little meter, the kind that a field technician would use on service calls.  It's really nice that it still has the case, instructions and accessories.  I'll probably make a video when I test it out.  


Cleaning a Marantz 1030 prior to starting a rebuild.

When I thought about doing this video, I thought I would edit and show it in a high speed format.   It turned out that the unedited video is only 5:30 minutes long.  That's the actual time it took to clean this integrated amplifier.

This simple process, using a brush with a vacuum cleans the amplifier well enough to start the rebuild.  More cleaning will take place as I rebuild each section, but for starters it's plenty clean enough.

If you look at the pictures in the photo gallery, make sure to look at the original pictures when this amplifier was so dirty and the pictures of what it's like after the cleaning.

See all of the 1030 #7066 picture here.

See the larger format video here.