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Entries by Chris (34)

Tuesday
Feb112014

A new bench multi-meter for the lab

Even though my work on vintage Marantz audio equipment has slowed down a lot in the past year, my over time spent in the lab and on the bench has increased.  

With so many projects to complete each week, I am always looking for ways to improve my work bench and become more efficient.  So what does this mean in real world terms. . . new bench equipment.

This past week I receive my new Agilent bench multi-meter, a 34461A.  The 34461A will replace my old Fluke 8050A.

The capabilities of the 34461A are so advanced compared the the 8050A that it's like going from a Model T Ford to a Tesla Model S.  

I'm not going to try to review the 34461A, there are so many really good reviews already on line that anything I could says would just be redundant.  

My decision to buy the 34461A was based on my need for better and more accurate measurements.  Many of the projects I work on each week are much more advanced than my Vintage Audio projects.

After just 1 week of having the 34461A. I can already see an improvement in my productivity. 

 

Wednesday
Jan082014

New Lighting for the Workbench

I have been looking for a better lighting solution for my workbench.  When I built up my workbench I thought that have three overhead lights would be more than enough, I was wrong.

I switched over from incandescent PAR20 halogen lamps to some Philips PAR20 LED lamps, and there was some improvement but it still wasn't good enough.  The PAR20 LED lamps are rated at 520 Lumens which isn't bad, but the biggest problem is that they are recessed up in the fixture quite a lot and the light gets lost inside the baffle.

The parameters for choosing better lamps were, they had to fit into the existing fixtures (with the trims attached) and they had to be long enough to place the face of the lamp very near the flat surface of the ceiling.

I found the perfect PAR30 LED Lamp made by Leapfrog Lighting.  Right off I was impressed with the technical information that Leapfrog had posted about their products.  Each lamp had a proper data sheet with specifications, Polar Intensity Diagrams, Spectral Power Distribution and Beam Angles.  

I choose the model 1001-P30LC-5001 which has a 5000K color temperature and a 38 degree beam angle.  It is rated at 1000 lumens.

I was very impressed with the manufacturing quality of the lamp itself, even the packaging was very well done.  The lamp fit into the fixture just as I had planed after measuring everything very carefully before ordering it.

As you can see, the difference is amazing.  The 5000K color temperature produces a very bright white light.  I was very careful to consider the height of the fixture above the workbench when choosing the beam angle.  I didn't want to have the light washing off the work surface, this is where the beam angle charts come in handy.  

The Leapfrog LED lamp worked out so well that I ordered 2 more for the other fixtures. 

Here's some links to Leapfrog:

Specifications Link 

LED lighting Brochure

 

 

Wednesday
Mar132013

Chassis mounted capacitors for a marantz 1060

I've been working on another Marantz Model 1060 rebuild and I was getting ready to install the three chassis mounted capacitors when I had a revelation.  Two of the original capacitors measure 35mm diameter and one is 51mm diameter, all three of the capacitors measure 35mm diameter.

In the previous 1060's I have rebuilt, I added some speaker gasket tape to the inside of the 51mm clamp and around the capacitor to make it stay in place securely.  While this worked well enough it never really looked very good.

As I was getting ready to yet again wrap the 51mm clamp with foam tape, I remember that I had a smaller clamp leftover from another project I finished recently.  Not only was it a 35mm clamp but the mounting clips matched up with some unused screw holes in the 1060's chassis.  (The blue squares are where the original clamp was attached to the chassis).

This was such an easy fix, the new capacitor fits into the smaller clamp perfectly and the clamp mounts to the chassis perfectly.  It all really looks like its always been done that way.

Capacitor clamps are commonly available from on-line seller who sell vacuum tubes and other parts for tube radios and amplifiers.  I have used Tube Depot and Antique Electronic Supply and I'm sure there are many others.

Now I wish I could go back and redo all of my previous 1060's so they would look as good as this one.

 

 

Friday
Mar082013

Which lamp works well for Marantz Models 1200 and 1200B

When it comes time to replace the pilot lamp in a Marantz model 1200 or 1200B which is the right bulb to use?

The service manual does not specify any lamp number and the parts list just shows a Marantz part number.  Unlike many other models, there isn't a lamp number printed on the rear panel of the amplifier.

I have seen many suggestions for different miniature lamps, most of which are probably worng.

In a 1200 or 1200B the pilot lamp is powered through resistor R711, which is a 220 ohm 2 watt resistor.  When inspecting this resistor on these models, I ususally find that the resistor show signs of heat stress from way to much current flowing through them.

The heat stress is of course bad for the resistor and also for the board where it is mounted.  When replacing this resistor, it should be mounted up off the circuit board about 3/8" to allow for better air flow around the resistor.

The lamp circuit supplies 51 volts DC to the empty lamp socket.  The goal when choosing a lamp is to find the correct style of lamp with the correct voltage and current rating for the application.

After researching miniature lamps I decided to use a Chicago Miniature Lamp #1835.  The 1835 is rated for 55 volts at .05 amps.  This means that the filiment resistance is 1100 ohms.  This lamp should use only 0.23 watts of current through R711, which is nothing for a 2 watt resistor.

After installing the 1835 into my completed model 1200B I found my choice in using the 1835 seems right.  R711 now runs cool as it should.

 

Tuesday
Jan152013

Restuffing a Multi-Section Can Capacitor

Saturday I was in the lab working on an radio from 1962. This little AM FM radio is a vacuum tube design and certainly was showing it age. When it came into the lab it had not worked for years and the owner wanted it repaired.

The most difficult component to replace turned out to be the original Sprague multi-section power supply can capacitor. This is a 4 section can capacitor with values of 100mfd @ 250 volts, 2) sections were 40 mfd @ 250 volts and the fourth section was 50mfd @ 25 volts.

These types of multi-section can capacitors use different symbols to identify which solder lug belongs to which section. In this case the symbols were:

Δ = 100mfd @ 250 volts

p = 40mfd @ 250 volts

m= 40 mfd @250 volts

- = 50mfd @ 25 volts

     

While there are several different companies that manufacture new multi-section can capacitors, none of them had the correct values for this tube radio.

I decided that the best method would be to “restuff” the original can with new modern capacitors. Sometimes it's practical to install individual capacitors in place of the original can, however this often looks messy and securing the components can be tricky. It's also important to remember that the original can capacitor has a common negative ground, this means that the negative lead from each section (capacitor) would need to be tied together and then jumpered across all 4 ground terminals on the circuit board, this can become quite messy.

The first step was to search for new capacitors that fit into the 1.5” diameter can properly. I found Nichicon CS Series which are pencil shaped capacitors. This series is a long and thin radial capacitor which only took up a small amount of the available space. I choose two 47mfd capacitors from the same series to take the place of the 40mfd sections. The original 50mfd section was replaced with a 47mfd from a different series, mostly for its small size.

 After removing the can capacitor from the circuit board, I took it over to the band saw and carefully cut the aluminum can right where it begins to flair into the larger diameter at its base. The aluminum is very thin and cutting it open was very easy. I think it would also be very easy to cut with a small hand held hack saw.

When you pull the cover off, inside you will find the capacitance roll. This is made up of a long thin sheet of insulating paper which has a thin layer of aluminum foil attached to it.

As you unroll the capacitor you will find points within the roll that have aluminum strips fastened to the aluminum foil by some type of crimping method.. These strips are connected to the solder lugs on the bottom of the can.

The more you unroll the capacitor the more aluminum strips your will find. Since this is a 4 section capacitor, there are 4 aluminum strips, plus 1 more which is the common negative and is attached to the can itself.

After the entire roll is removed you are left with the cans base and all of the aluminum strips.

One think to keep in mind is that you can not solder the leads of the new capacitors to the aluminum, it won't stick. If you look at the bottom of the original can capacitor, you will find 8 solder lugs. The 4 around the perimeter are the common ground lugs and each of the other 4 lugs are the 4 sections within the can.

Of course all of the 8 lugs were soldered to the circuit board. If you look carefully at the lugs, you will see when the aluminum strips have been crimped to the metal lugs. The aluminum strip for the common ground is crimped in between the aluminum can and the metal ring which holds the non-conductive base, this ring has the 4 ground solder lugs.

It will be necessary to install the 4 replacement capacitors onto the base of the original can. I carefully drilled (8) 1.25mm holes in the original base, 1 along side of every positive solder lug on the original base and 1 along side each of the common ground lugs around the perimeter ring for the negative terminal.

Drilling the holes in these locations will allow the leads of the new capacitors to align with the metal lugs on the base, where they will be soldered. All you have to do is push the leads through the holes, the positive lead can be tightly wrapped around the top of the lug and soldered. I bent the negative lead to match the curve of the cans base and solder it to the metal ring.

After all 4 of the new capacitors where in place, I used my LCR meter to verify that the each of the new capacitors where in the proper location, referenced by the symbols on the cans cover. I then used a multi-meter to make sure that the common ground was intact on all 4 ground lugs.

To close up the can, I simply placed the cover back on the base, matching up the cut marks and sealed it first with electrical tape followed up with a section or large diameter heat shrink tubing.

Once the can was remounted on the board, you really couldn't tell that it had been modified at all.