The Work Bench



Fuses for your Equipment

About a month ago I finished up a rebuild of a Marantz model 30 integrated amplifier. I had it set up in the workshop for daily use so I could give it a good listen for a month or so. Everything turned out well and I was pleased with the sound and power the model 30 produced. It sounded especially good with my Pioneer HPM100's

One afternoon I turned it on and there was that unmistakeable sound of a fuse blowing, damn. It had been about two weeks at that point since I had finished the rebuild and of course all sorts of things flash through your mind about what I may have done wrong or missed during the rebuild.

The next day I opened the 30 up and started to troubleshoot the issue. That was until I discovered that I didn't have any more fuses. So, I did what any would do, I robbed a fuse from another unit. What I found was a shorted bridge rectifier. No big deal to fix and the 30 was playing again in a few days.

The real lesson here was about the lack of fuses. I spent some time doing an inventory of all the different models I have and complied a list of the different fuses I should have on hand.



Having extra fuses on hand may be an overlooked part of owning vintage equipment, but I think it's essential.


Variac & Watt Meter Make a Great Combination

Two of my most useful pieces of workbench equipment are my Variac and my Simpson 390-2 watt meter. Separately they both are useful but together they make an important tool for determining the initial condition of a piece of equipment.

The variac allows the voltage powering any unit to be brought up slowly and be set at the specified voltage required. If your testing or adjusting an amplifier and the service manual states the voltage should be set at 110 volts, the variac will allow you to set that voltage accurately. This makes adjustments and test results more accurate than just using what ever your line voltage is.

The Simpson 390-2 watt meter will show you the amount of current the device is using at any given moment. With an amplifier plugged into the 390-2 the meter will show 0 watts. Turn the amplifier on and the meter will show the current at idle.Click on Image to View Operator's Manual

Together the variac and watt meter will allow you to bring up the voltage of a unit while monitoring the current at the same time. If you have a normally operating amplifier you will see the current (watts) rise slowly as you increase the voltage with the variac. With a damaged amplifier you will see the current (watts) rise quickly and over the idling specification as the voltage is raised. Seeing this in real time allows you to identify that the unit has a problem and shut it off before you do some real damage.

This type of testing is necessary and helpful when performing initial testing after repairing any unit.



The Work Bench Library

While a lot of attention is given to the test equipment on an audio work bench, there's an equally important part of any work bench which remains mostly hidden, its technical library. I started building my library while I was working one of my first projects, rebuilding a Marantz model 32 amplifier.

The Marantz 32 dates from 1971. It uses components which were common in its day, but are difficult to find today. As I was studying the amplifiers design, I realized that there were components that I wanted specific technical information for. So I did what just about everyone would do today, I Googled part numbers and surprisingly almost nothing useful came up. I tried different search ideas and the results were equally poor.

The problem seems to be that while there is a great amount of technical information available for parts made in the past 20 years, before that not much has been added to the web. It was then that I realized that vintage books, catalogs and manuals were going to be needed for the information I wanted.

I started by looking for vintage transistor manuals and books because transistors seems to be the most difficult parts to find or interchange today. Many of the original transistors from the 1960's through the 1980's are no longer manufactured and their part numbers are obsolete. A vintage transistor specification manual along with an interchange book are a great way to find substitutes. Sometimes one manual will provide a small clue, like a similar transistor number that can be looked up in another book that will add a clue that can be found in yet another source which will have the answer.

Of course this means that I needed lots of books and not just for transistors, diodes were next and now I'm adding capacitors. Along the way I have found text books that easily apply to vintage audio. Text books that explain the theory behind how a component works or the reason why a circuit is designed the way it is and how it works helps to add depth to our knowledge based. While I don't understand everything I read, I do have those moments that everything comes together and I do really get it.

I'm still searching for library items. There are gaps in the component time line that need to be filled.

Perhaps one day I will find the Rosetta Stone of vintage audio components.

The search continues. Take a look my library.



My Vintage Audio Work Bench

When I decided to become more serious about vintage audio equipment, I decided that I needed a proper work bench that is dedicated to just audio equipment. The work bench needed to include all of the necessary tools and test equipment while also being functional and of course cool looking.

I began by doing a remodel of my garage and carving out enough space for the work bench. I built some cabinets for storage and made sure that there are plenty of electrical outlets and good lighting.

Now it was time to start adding equipment to the bench, but what to buy? I noticed that in each Marantz service manual there is a list of necessary test equipment to work on that particular model. This seemed like the perfect shopping list and the search was on. Ebay can be a wonderful resource for just about anything including good quality used test equipment. The following is a partial list of what I bought over a four month period.

Powerstat model 116B variac 10 Amp $82.00

Simpson model 390-2 watt meter $18.00

Simpson model 312 VTVM $113.00

Fluke model 8050A DMM $85.00

Fluke model 1900A frequency counter $10.00

Hitachi model V-152 Oscilloscope $82.00

Cenco Audio Oscillator $56.00

Hewlett Packard 333A Distortion Analyzer. $100.00

Weller model WES51 Soldering Station $48.00

Jackson model 810 Transistor Tester $12.00

Sound Technology 1000A $120.00

Total $726.00


Everything piece of equipment I bought is really necessary to work on vintage audio equipment. I looked every single morning for each item, I waited until I found a unit in good condition, preferably having come for a recent working environment. I bought units that included power cords, test leads and manuals if possible. When manuals were not included I found free downloads or purchased copies.

I will be reviewing each piece of equipment and point out things to be aware of when buying a matching unit. There is a lot of information available on how to use this type of equipment however I will included what I have found out about each unit as I have used them.  

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