Preamp - Getting Sounds up

After letting the Preamp cook last night, today I broke out the heavy equipment to see if I could get sounds from the input to the output. Items needed for this leg:

• Small MP3 Player
• "Jack-leg" 3.5 mm plug to Phono jack adapter
• Denon Stereo Receiver with left channel speaker connected
• High Speed Oscilloscope

MP3 Player connection
Previously, I built a Tablet to Stereo Line-in adapter for playing music on a standard (ok, old) Stereo system. The interface I built for testing this came in handy to connect my little MP3 Player to the Phono jack input on the Preamp.

MP3 Player and "Jack-let" adapter

Connections and Heavy equipment
I have had an Oscilloscope for several years and it has come in handy on a number of projects. The Scope is a RIGOL DS-1052E which can see waveforms much faster than anything that is coming out of audio equipment, so the scope will not be taxed much by this project.

Once the MP3 Player was playing music and connected to the "Tape" input of the Preamp, I hooked the Oscilloscope probe to the first stage of the Preamp (bypassing the Phono input pre-stage), raised the Preamp Volume control to 50%, and selected the TAPE input. I was now able to see the music waveforms dancing on the scope!! Checking back on the schematic, I walked through the different amplification stages and could see the levels rise. When the scope was connected to the Preamp "Main" output, the levels looked close to what a standard "Line-in" should look like.

Scoping the Preamp Output

You can see that my Denon Receiver is powered up in the background. It took only a few seconds to cable the Preamp out to the left channel TAPE Line-in of the receiver.

Those cool sounds of summer
Once everything was connected, I slowly brought up the volume on the Receiver to hear the Jazz coming through clear! SUCCESS!! Here is a clip of the left speaker output of the Receiver playing into my computer microphone direct to MP3:

Altec Preamp - Cannonball Adderley - Waltz for Debby 

Obviously, this just shows functionality and while it sounds nice, I need to begin looking at the other inputs and measuring noise levels. Also, as I adjusted the volume control, I heard some crackling which means there is some dirt on that Potentiometer (POT).  All the Pots and switches need cleaning (I have the spray bottle in house now).

Packaging of the preamp is coming up and the possibility of replacing the tubes with new ones is on the list. But, this is a major milestone.

Preamp - On a Power Trip

Where were we?? Oh yeah, preparing for power up.

Since most of the parts replacement in the Preamp has been in the power supply sections, I wanted to make sure that these sections were powered up first while disconnected from the main circuitry to ensure any voltage issues would not burn out the audio sections.

Power Supply
I was expecting the power voltages to be higher than the specs, mainly due to the fact that I replaced the Selenium rectifiers with silicon diodes (M1, M2, and M3)

Preamp Power Supply Circuit

Tube Filaments (12.5V - To FILS)
All tube based equipment I have worked on in the past used AC voltage to supply the Tube Filaments (called "Heaters"), so I was somewhat surprised to see rectifiers in the Heater supplies (M3). After some research, I learned that this was done in some older audio equipment to reduce noise. Of course, almost all tube equipment I have worked on in the past was for Ham Radio and those levels of noise were never an issue. Anyway, noise levels in the Preamp will be a project for later, once I am ready to put sound through it and have broken out the Oscilloscope.

The two Electrolytics in the heater supply (C5A, C5B) were not replaced so I will keep a close eye on these (see the earlier post).

High Voltage Output
All of the Electrolytic capacitors in the High Voltage sections were replaced and I was pretty confident that there would be no issues with this section, short of the higher voltages. The new Electrolytics were rated at 450 VDC as opposed to the originals which were rated at 300 VDC.


And then there was light!
After I was convinced that there would be no fire, I plugged the Preamp in to the AC and got the front lamp to light, always a good sign. I made some cursory voltage measurements with my trusty Micronta Multimeter (I probably bought this sometime in the 1990's) then pulled the power and connected the power supply output to the rest of the unit for the real acid test.
 

  Preamp powered up with Lamp glowing and the Multimeter showing voltage

A close look at the meter, for the sticklers...

Burn Rate
Once I was convinced the voltages were reasonable, I left the preamp powered up for about 3 hours for a good burn-in test. Next will be to introduce some waveforms into the Preamp input and check the output of the different stages on the scope.

If this checks out, I might actually plug the Preamp output into one channel of my Denon DRA-345R Stereo Receiver...the Receiver is only about 30 years old, unlike the Preamp which is closer to 60 years old!

Until then, stay cool!

Preamp - parts replacement and maybe power up!

When we last met, I had replaced a number of the capacitors in the preamp, done some cleaning, and threatened to replace the AC cord before power was applied. Well, more research had me determine that I needed to replace more parts in the power sections.

Rectifiers
To provide some background, a Rectifier converts Alternating Current (AC) to Direct Current (DC). What comes out of the wall in your house is 120 Volts AC. However, most electronics built in the past 75 years or so uses Direct Current (DC) to power the tubes, transistors, and chips in them.

Rectifiers have taken many forms over the years, from Tube Rectifiers (like the one in the Altec A-340 Amp we will get to later), to Solid State rectifiers of various flavors which include current day devices often referred to as "Diodes".

"Selenium Rectifier"
In the Preamp, a number of "Selenium" Rectifiers are used in the power supply sections. These devices were state of the art back in the 50's and they were used as a small alternative to the use of tube type Rectifiers.

  Selenium Rectifiers for the high voltage power supply

 
 

  "Dual" Selenium Rectifier for the tube filaments

 
While these were an improvement over the use of Tubes, they have several disadvantages. They are notorious for having short life spans and their operational specs would vary over time. Worse, they are known to fail, which could be anything from opening up (no voltage through) to shorting out, burning up, etc. Since Selenium is toxic, breathing the fumes from one that is failing is not recommended....

Bottom line: replacing these devices is cheap insurance.

Selenium Rectifier replacements and new wiring
Fortunately, silicon rectifiers that will perform the same function are very inexpensive. I picked up 20 pieces of the 1N4007 rectifier for $1.20 ($0.06 each). Since the normal voltage drop across the old and new Rectifiers differed, I also ordered some 100 Ohm "Wirewound" Resistors but will not install those until I have powered up the supply and checked some of the voltages (more on these Resistors later...).

Since the existing rectifiers were mounted to the chassis with screws and nuts and the new rectifiers are solder pigtails, some terminal blocks were needed. While I ordered the rectifiers online, I figured I could find the Terminal Blocks at the local Radio Shack store...well, that took some work with the "Shack" becoming a scarce commodity. Anyway, in the end, I was able to "travel"  to a Radio Shack that carried the Terminals.

After receiving these, I lit up the soldering iron and got to work on the rewire job. It took a few hours to remove the Selenium's, install the Terminal Blocks, add the new rectifiers and hook everything back up. 

 Old and new Rectifiers

 
After completing and checking the wiring, I disconnected the 3 wires that go from the power system to the main circuitry which is good practice before powering up such equipment. I wanted to check all voltages coming out of the power systems before applying it to the circuits. Further, I might break out the Oscilloscope to look at the power filtering.

Power Up?
Normally, the recommendation is to bring things like this up under a Variac (Variable voltage source) to ensure that if something serious is wrong, the voltage can be cranked down quickly. But I do not have one of those, and what fun is it finding out the easy way...

Since anything can happen with such ancient equipment under first power up (and me being so brave!!!), I ran an extension cord to the Preamp power cord and plugged it in on the other side of the room! 

You will have to wait for the next update to find out what happened... 

A440B Preamp - parts replacement

After being in My Southern Exposure for a few weeks in June, I am back to work on the audio projects.

Over the last few weeks, the complete inventory took place for all audio units to see what capacitors needed to be ordered, what parts were in-house, and which parts would be left “as-is”. Since the most notorious component in vintage electronic equipment is the Electrolytic, paper, and non-ceramic capacitors, most of those were targeted to be replaced and ordered if not in-house.

The 440 has two can type Multi-section electrolytic capacitors. I could only find a suitable replacement for one of them – a 40/40/20/10 UF @ 300VDC can. The closest I could find was 40/40/20/20 UF @ 450VDC. This slightly taller replacement model could also replace cans in the tuner and power amp units so I went ahead and bought five of them for $38 each. Back in the day, I could probably have gotten one of these for $15 each, so this is just the [extra] cost of time past.

Picture of original (left) and new Electrolytic Capacitors

Anyway, three other electrolytic capacitors in the 440 were on the list, one I ordered (40 UF @ 250VDC), and the other two were "in stock" (50 UF @ 3VDC being replaced by 47 UF @ 16-and-20VDC respectively).

After receiving the ordered caps, I sat down with soldering iron in hand to swap them out. This is a skill you probably do not lose, even after some 20 years of not being in the trenches (what we used to call “smelling some rosin!”). It took about two hours to complete the replacements. 

 New Electrolytic Capacitor installed (right)

As can be seen above, the new can was almost too high to fit and I had to remove some screws that held the base in place to get it situated. The new one had twist tabs to hold it in place but they seemed to not have tab edges to lock it in place so it wobbles a little right now. I will probably glue the base to the Bakelite riveted mounting. I also had to bend the tabs over on one of the accessory power outlets so it would not hit the top of the can. It does clear it but I will probably put a piece of electrical tape on top of the can. 

The left hand electrolytic cap has a spec that I have been unable to locate a close match (1000/1000 Uf @ 15VDC) so at the moment, I am going with this one. I did order some small radial 1000 UF at 16VDC caps, which I may figure out how to use instead of the can. Amazing the tech advance!

Cleaning

After completing the retrofit, I could not help looking at the grunge so I decided to clean out the tube compartment and wipe down the tubes. Of course, the printing on the tubes mostly came off as I rubbed them lightly with a Que-tip dipped in water. Assuming the tubes are still good, I may hold onto them for now, and consider replacing later.

Still to work on before power up

Besides more cleaning, the two wire A/C power cable will be replaced with a new 3 wire plug (with ground). Hopefully, I will be ready to power up in a week or so.

VM - Back to the plan

I now have a pair of Windows 10 VM's ("Insider Preview" - Build 10041, aka "Palisades"; and "Technical Preview" - Build 10074, aka - "Englewood") loaded and running along with two identical Linux VM's (Ubunutu 14.x).

 
While the Linux VM's will probably be on the back burner for now, I would like to have one of these act as a utility machine for external IP reporting to be used when I am remote (more on this plan later).

Back on the Windows plan, a set of standard apps will be installed onto Palisades and an attempt will be made to live inside Windows 10 (via RDP) this coming week, including connections to my work VM Desktop. The short list of apps:

• Citrix Receiver
• Firefox
• Thunderbird
• Adobe Reader
• Paint Shop Pro
• Office 2007
• Skype
• Host machine access (USB port replicator; External backup drive)
• HP OfficeJet printer

Before this is usable, I need to add more than the 4GB of memory to my ESX box. I think I can push this to at least 16GB. This server may be underpowered as far as the CPU is concerned (pretty old Dell Optiplex 780) but memory first.


Netscaler Appliance

As an aside, I also loaded  a Netsclaer VPX VM to play with. Just one more thank on my list.....

Vintage Audio - Preamp Recon #1

As with all vintage electronic equipment, the capacitors are most likely bad and require replacement. This equipment will be no different, with a number of paper, plastic, film, and electrolytic caps in each component.

Since I have a factory schematic for the Power Amp, all of those caps have been cataloged and some replacements have even been ordered.


On to the Preamp

From those initial pictures and the live view, some kind of mold had been growing on the front panels. After removing the electronics from its wood enclosure, I figured out how to separate the front panel from the chassis by removing the knobs and the chassis screws.

Similar to the power amp, the internal electronics is in fairly good condition since the housing was sealed tightly. Below is the top view. Notice the dust on the 3 tubes on the left (these are exposed in the rear of the unit).

Bottom view shows more of the wiring.

Next is the front view exposing the control shafts. On the bottom left is one of those capacitors that needs to go. Check out that rectifier (in blue): that is a classic!

Finally, the rear view showing the input/output connectors and the 3 tubes.

Notice the plastic container holding up the preamp...this is where I put the filthy knobs. After a failed attempt at trying to remove the white mold-like "substance" from the knobs with water and a toothbrush, I determined that a good soaking or more industrial cleaning would be needed.

 **

With no wiring diagram to follow, it will take some time to "Reverse engineer" the wiring and put it into a schematic. This is something I did often back in the olden days when I was a Ham Radio guy and was always trying to understand circuits from existing equipment. Don't worry, once complete, I will post it here so you can build your own!!

Windows 10 Preview

After getting VMware ESXi 6.0 installed and configured, I placed the server in my dining room with only the network connection to my router (Headless). With the vSphere client installed on my laptop, I can access the console of ESX easily.

Once Win10 Build 10041 (named "Palisades") ISO was downloaded, the ISO was uploaded to the storage on ESX and two VM's were created and built (seen above). As of today, the first VM has been upgraded to Win10 Build 10074 (now called "Englewood") and the Citrix Receiver is installed to allow access to my VM's at work.


Here is a screenshot of Englewood via RDP:

It took some googling but VMware Tools is now installed on Englewood, which speeds up video, keyboard, and mouse response. Next will be to install some additional apps and attempt to use this as my primary.

Palisades will be updated to the next build once it comes out, but I need to start reading the release notes to understand what is being fixed.