Wurlitzer P-10 Jukebox (1934)

Symptom: Effects of time travel
Location: Denver, CO

The P10 was Wurlitzer’s first jukebox.  The repeal of prohibition in December 1933 led to the opening of many public drinking places and live musicians and jukeboxes were the primary forms of entertainment.  Wurlitzer and other jukebox manufacturers were quick to capitalize on the repeal.

Advertisement for the Wurlitzer P10 (click for larger).

This jukebox was found in the old Denver Hardware building that was slated for demolition. The owner was able to purchase it for approximately $100. The owner contacted me to determine what was needed to get it working.

Although the cabinet was a little rough, the amplifier and mechanism seemed to be largely untouched. It looked like once it stopped working, no one had tried to fix it and it just sat for decades. The internal counter says it played 40,000 records in its life.

Once I got the mechanism unfrozen and lubricated, I discovered the motor was burned-out. Many electric motors of the 1930s and 1940s didn’t have protection circuits to shut the motor down if stalled or stuck. I later discovered a 15 amp fuse in the 6 amp fuse holder.

Motor with rear casing removed. Note the inner layer of windings which are charred.

Close-up view

Quotes to rewind the motor were in the neighborhood of $700.00. I was able to find a motor on E-bay which came out of a Wurlitzer 412 for $80, so we decided to give that one a try first.

Motor purchased on E-bay was poorly packaged and arrived with broken wires and styrofoam pieces inside of the motor.

I had to take apart the motor I purchased on E-bay to repair it.  I installed a fuse on the motor along with new wiring.  Hopefully the fuse will protect the motor in case the jukebox mechanism jams.

Motor ready to be placed back into jukebox.

The next item was to check the amplifier.  It was missing two 2A3 tubes, but fortunately they are still being made in Russia and China, and I was able to order a pair.  The capacitors in the amplifier needed to be replaced.

Dry electrolytic capacitors in a cardboard box.

Once the amp and the motor were reinstalled (and the correct fuses installed), the jukebox fired up and played a record.

Jukebox playing one of the records that was found in it. Note the original needle.

The needle and sound system was kept original and it sounded good.  Now the only thing it needs is a cabinet restoration, which I no longer do. But I know some cabinetry people who can do this.

Wurlitzer P10

 

 

Seeburg, LPC1 Jukebox

Symptoms: Scans back and forth without picking up record.
Location: Englewood, CO

There are a whole slew of reasons a Seeburg jukebox mechanism from the 1960’s and 1970’s will scan back and forth without picking up a record after pushing the selection buttons. It’s a common symptom without common fixes.

Seeburg was the only jukebox manufacturer from that era to use an electronic means to save selections that a customer selected. All other manufacturers used mechanical pins or levers. There are about a dozen items in a chain that have to work properly for the jukebox to make a selection, find the record and play it.

It’s best to start troubleshooting in the middle of the chain, which is the Tormat memory unit, then determine if the problem is a “write in” or “read out” problem. (Seeburg manuals refer to a third section called “trip”, but I include that as “read out”.)  Tony Miller, a former Seeburg engineer who has written books about working on Seeburg jukeboxes, has written a general guide for determining which part of the chain the problem is located. It simply uses a 1.5 volt battery to test which end of the chain is at fault.

In the LPC jukeboxes, there are two pulse amplifiers, one for each side of the record.  So there are in effect two “read out” and “trip” circuits.  Other models of Seeburgs use a single “read out” combined with the reversing switch to play both sides of the record.  I tested both “read out” circuits and they were fine.

There aren’t as many issues for the “write in” problems compared to “read out” problems. I found two problems with this jukebox, one more critical than the other.

The primary problem was the “write in” voltage was zero. This would normally be around 300 volts.  On TCC1 (Tormat Control Center 1) this can be measured at TS2 pin 2 (TS2 is a test connector facing the front of the jukebox on the TCC1).  Since I was getting zero volts there, I went directly to the OA2 voltage regulator tube (between the 27K and the 270K resistors) and I was getting the full 300 volts there.  So the problem was either the 270K resistor or downstream from it. I unplugged the Album Pricing Unit to isolate the TCC1.  The voltage was still zero. I checked the 270K resistor, and it was okay.  The only thing left was the 0.068uF capacitor.  It was probably leaking current to ground, causing a voltage drop across the 207K resistor.  I replaced it and the voltage came up to 290V which is good enough.

lpcwrite

Simplified schematic (corrected) from the manual showing a portion of the “write-in” circuit.

The secondary problem were the write trigger contacts in the Pricing Unit. I don’t have a photo handy, but they are mounted to a lever that rotates when the cancel solenoid is operated. The contacts are shown in the left yellow shaded area of the schematic above and on the diagram below.

Write trigger switch contacts.

Write trigger switch contacts.

One contact rests on an insulator and the other rests on a copper piece. When the cancel solenoid actuates, the disk rotates moving the copper under both contacts, making a connection. With age, dust and arcing (this switch creates a 300 volt pulse), these contacts often have carbon build-up on them.

I connected an ohm meter across the contacts and measured an “open” when I manually actuated the subtract solenoid armature.  I cleaned the contacts with some 2000 grit polishing paper, followed by some alcohol remove any grimy residue.   I rechecked and I got 0 ohms when I actuated the armature.

I put everything back together and made a selection and the mechanism stopped at the record and played it.  All fixed!

 

Rockola 1488 Jukebox (1960)

Location: Henderson, Colorado
Symptom: Turntable speed too slow

One of the most common problems of Rockola jukeboxes from the mid-1950’s through the 1980’s, is the turntable not turning at the correct speed. This is almost always associated with the old rubber grommets that hold the turntable motor.

Height comparison of new turntable motor grommet with old grommet.

Height comparison of new turntable motor grommet with old grommet.

The turntable motor basically hangs from three of these grommets.  As the grommets age, they get dry and brittle and shrink and the motor gradually sinks.  I assume the weight of the motor is not evenly distributed among the three grommets because it seems like 2 out of the 3 are in worse shape. This causes the motor to tilt and the shaft is no longer aligned properly.

This photo only shows two of the grommets, but you can see that rear grommet is more compressed.  The motor has already been removed.

This photo only shows two of the grommets, but you can see that rear grommet is more compressed. The motor has already been removed.

What’s worse is that many of these jukeboxes are designed to play 33 RPM records. The motor shaft has two milled diameters, the bottom one is for 45 RPM and the top one is for 33 RPM records. As the motor sinks, the idler wheel begins to ride on the 33 RPM portion of the shaft.

Generally these grommets are easy to replace. The motor will be mounted in a variety of ways depending on the jukebox, most using screws or shafts with spring “E” clips. One source for new grommets is here.

West Slope Lubrication Tour

Locations: Basalt, Colorado; Grand Junction, Colorado.

First stop was to work on a Wurlitzer jukebox model 1100 (1948). Like many 1940’s Wurlitzers I’ve worked on, the selector shaft and heart-shaped cam was not rotating due to lack of recent lubrication. This causes it to play one selection regardless of what was selected.  Unfortunately, it’s not an easy thing to get freed up, and takes a lot of exercising and time.

The jukebox needed some other adjustments, such as the turntable height and the clutch. I replaced the line cord because it was in very dangerous condition. The color cylinder plastic sheets were also replaced.  This was an original, un-restored 1100 in good condition.

Next stop was to work on two Williams electro-mechanical (EM) pinball machines, Grand Prix and Aztec (both 1976).  The main problem with these machines were the stepper units were not freely ratcheting up and down. This is the number one problem with EM pinball machines.  A quick disassembly, cleaning and lubrication fixes the problem.  Occasionally the spring tension needs to be adjusted.

The Aztec was missing some electrical parts, which can’t be obtained unless someone is parting one out.  But I got it working as best I could.

Next stop was an AMI jukebox, model A (1946), which is also known as the Mother of Plastic. The selection mechanism was frozen due to lack of recent lubrication.  Like the 1100 above, it took a while to get it unfrozen and moving freely.  The selection buttons needed some contact cleaning and lube (buttons would stick when pressed). The tonearm wire where it plugs into the amp needed to the resoldered.  All in all, a great sounding jukebox.

It was satisfying to breathe some new life into these old machines.

Seeburg Jukebox SHFA1 amplifiers

Location: Littleton, CO
Symptoms: Two amplifiers, both barely working.

Of all of the amplifiers I’ve rebuilt, I’ve never encountered an amplifier with so many bad capacitors as I have on these amplifiers.  Compared to Wurlitzer, Seeburg must have been trying to use the cheapest capacitors they could get their hands on.  I suppose a lot of it has to do with how many hours the jukebox was on and the temperature inside the amp chassis.

I replaced all of the electrolytic capacitors on both amplifiers.  As I pulled each one out, I was hard pressed to find one that was within 20% tolerance of its original value.  And many were not even close, such as a 50 uF reading 0.6 uF.

In addition to the electrolytic capacitors, many of the paper/foil capacitors have been bad as well. These capacitors play a variety of roles, mainly used to block high voltage and couple the audio from each vacuum tube stage to the next. Failures with these capacitors, usually high current leakage, will usually cause a tube to be biased incorrectly. This is especially important in the final power amplifier stage and in the “cathode follower” stage just prior to the volume control.

Also, with the SFHA1 in particular, the Automatic Volume Compensation (AVC) circuit will cease to work.  And when this happens, most people pull the 6BJ6 tubes to disable the AVC circuit, which explains why many amps of this vintage are missing these tubes.

One might be tempted to replace every capacitor, but given there are nearly 80 capacitors in this amp, I prefer to replace all of the electrolytics (21 capacitors), since they have a finite life, and then replace the others (which, in theory, should have a longer life) as needed.

Below I list some of the problem non-electrolytic capacitors. If you read on, you should have a schematic to refer to.

Preamplifier, prior to the volume control

On both of these amplifiers, C108 and C147 (0.22 uF, 400V) were leaky, causing attenuation of the audio signal, even when the AVC tubes (6BJ6) are removed.  This is usually the reason one channel might be louder than the other. These are very large and mounted to the rear side of the larger circuit boards near the sides of the amplifier chassis.

On both of these amplifiers, C121 and C160 (0.005 uF, 400V) were leaky, causing the voltage on V103, V109, pins 7 and 8 to be too low.  This causes clipping and thus distortion of the audio waveform.  The voltage on the schematic for pin 8 (cathode) is listed as 90V.  Before the bad capacitors were replaced, it was reading around 14V.  This circuit is the “cathode follower” I mentioned above.  These capacitors were among the first to be installed and are buried deep under everything else. These capacitors connect between Pin 7 of the tube and the wiper of the treble control.

One amplifier had some distortion in the waveform in one channel that was caused by C110, C150 (0.005 uF, 400V).

Automatic Volume Control

When there is no signal coming into the amplifier, the voltage across C115 (1 uF) should be zero or within a 1 or 2 volts of zero. If it isn’t, then C111, C148  (0.01uF 400V) should be replaced.  One channel on each amplifier had a leaky capacitor.

Likewise, when you have a 4 – 8 mV signal on the amplifier inputs, and pin 3 of muting socket is grounded,  the voltage across C115 should be 30 to 50 volts.  If it isn’t, and everything else is working, then C115 itself is the problem and should be replaced.  One amplifier had this problem and the voltage would never go above about 6 volts, in spite of being nearly 50 volts of signal at the cathode of the selenium rectifiers.

Final Power Amplifier Stage

The 6973 tubes are used in pairs for each channel. They operate in a push-pull configuration.  If the bias of the grid is not correct or if one tube is weaker than the other, the circuit doesn’t work very well.  It’s like a teeter-totter, where the people on it should be nearly the same weight to have a good balance.

On the 6973 tubes (V105, V106, V111, V112) you should see -33 to -35 volts on pins 3 or 6 of each tube (with no input signal on the amp).  A leaky capacitor will cause the voltage to be more positive. The capacitors associated with each tube in the order listed above are C137, C138, C175 and C176 (0.05 uF, 600V).  On one amplifier, all 4 capacitors were bad.  On the other amp, all were good.

Tubes

Usually I don’t see many bad tubes in jukebox amplifiers. Almost all problems are related to bad capacitors. But…

I had a bad 5U4 that was shorting and blowing the fuse.  I had one pair of 6973 that was bad on each amplifier (these should be replaced in pairs).  I had a bad 12AX7 on one amplifier.  And one amplifier had missing 6BJ6 tubes.  With the exception of the 6BJ6 tubes, there are companies still making vacuum these tubes.  Try finding a company still making vintage transistors.

I highly recommend Vacuum Tube Supplies in Denver for anything related to tubes and tube amplifiers.

Seeburg SHFA4 Jukebox Amplifier

Location: Lakewood, CO
Symptom: Loud hum on speaker outputs, amplifier rebuild.

As usual with an amplifier of this vintage, all of the electrolytic capacitors were replaced. This fixed the problem with the loud hum.  Also one of the electrolytic capacitors was causing a bias problem with one of the preamp transistors, causing that channel to be weak.

After the capacitor replacement, I was testing the amp with the oscilloscope, there was still one channel substantially weaker than the other, and both channels had non-linearity distortion. I traced this to the AVC (Automatic Volume Control) circuit.  The AVC circuit is used to level the volume between different records and different sides.

The AVC circuit uses the resistance through diodes to achieve this. The resistance of the diodes changes with the amount of current flowing through it.  The louder the song, the more current flows through the diodes, the lower the resistance, which lowers the volume.

AVC block diagram (click for larger).

AVC block diagram (click for larger).

The problem with this vintage of amplifiers is they used selenium diodes.  These diodes seem to fail with age.  In this case, diodes in both CR103 and CR104 were bad.  One was nearly open, another nearly shorted.  The resistance across the other diodes was high.  My multimeter couldn’t properly read them, so I relied on just measuring voltages across them.

Small selenium diodes are no longer made.Silicon diodes can be used, however, you have to use more than two in series for each selenium diode you replace.  I started with using two 1N914 diodes for each diode in CR103 and CR104.  The resistance was too low and my signal going into V101 was too weak.  So I doubled them, using four 1N914 diodes for each diode in CR103 and CR104.  That was 16 diodes total.

Old selenium diode pairs.

Old selenium diode pairs.

Rework showing the strings of four 1N914 diodes in the AVC circuit.  One string is exposed, the others are in the green shrink tubing.

Rework showing the strings of four 1N914 diodes in the AVC circuit. One string is exposed, the others are in the green shrink tubing.

I also replaced the CR102 diode pair.  For this, a single 1N914 can be used for each diode in CR102. After taking some measurements, I could have used three diodes for each, instead of four.  But with four, I get a little more input into the V101 tube (about 120mV) without causing clipping on the output.

The amp is now working great!

So if you’re rebuilding an amp with selenium diodes in the AVC circuit, replace them with 3 or 4 1N914 diodes in series for each diode in CR103 and CR104 and use single diodes for CR102.  It ends up being a lot of diodes, but they are small and cheap.

 

Seeburg Jukebox Amplifiers, MRA4 and SHFA1

Location: Loveland, CO
Symptoms: SHFA1: one channel not working well; MRA4: generally not sounding good.

Both amplifiers were brought back to my office for bench testing and repair.  It’s really the only way to work on an amplifier.  A known signal, usually a sine wave is injecting into the input.  A dummy 8-16 ohm load is connected to the speaker outputs.  With the oscilloscope, I start at the speaker outputs and observe the signal.  If it looks distorted or weak, I work my way back to the inputs to find the fault.

The SHFA1 had one channel that wasn’t working well.  I found that the output of the first stage 12AX7 wasn’t outputting as well as the other channel at the same point.  The grid of the weak channel had a more positive bias on it of a couple of volts.  I traced it to a leaky 0.22uF capacitor.

Once that was repaired, now the weak channel was much stronger that the other.  I traced that to a bad 12AX7 just before the final output stage.

This amp had some previous work done on it, some capacitors had been replaced throughout, but interestingly, some of the most common ones that would normally be replaced hadn’t been touched, like most of the electrolytics.

The MRA4 hadn’t ever been service.  It still had the original paper and wax capacitors used prior to the 1960’s.

When rebuilding an amplifier, I usually replace every electrolytic capacitor.  If the amplifier is from 1960 or earlier, I usually replace every paper/wax coupling cap that has high voltage across it. I will usually leave tone control and other low signal voltage caps.

Prior to the cap swap, the MRA4 had a weaker output than I normally see.  I traced this to a leaking 0.05uF capacitor in the coupling circuit to the final 6L6 tube.  This caused the tube to be biased so that it wasn’t operating in a push-pull configuration.

This amp still had the original 6L6 tubes installed.  For fun, since I had some brand new 6L6 tubes, I installed those and they didn’t deliver the output that the original tubes did. I put the original tubes back in.  I rarely replace tubes unless there is a good reason to.  And this little experiment proves why.

Both amps are working great!

Wurlitzer 2204 Jukebox, 532 Amp Rebuild

Location: Denver, Colorado.
Symptoms: Amp rebuild.

When I listened to the amp, I didn’t really hear anything in particular that was wrong with it.  But the owner was unhappy with it.  Someone had previously done some work on it, replacing a few capacitors, including the main filter capacitor on the output of the 5U4 rectifier tube.

I brought the amp back and bench tested it.  It failed.

Amplifier working normally at 50% volume.

Amplifier working normally at 50% volume.

 

Amplifier breaking down and oscillating at slightly higher volume.

Amplifier breaking down and oscillating at slightly higher volume.

 

Amplifier in bad shape at full volume.

Amplifier in bad shape at full volume.

The problem was primarily in the power supply as these waveforms were measured at the Aux Amp output, which is essentially the output of the preamp stage.  The final output stage was loading the power supply and breaking into oscillation.  Most often when an amplifier breaks into oscillation, there is a faulty capacitor someplace.

I decided to do my standard “re-cap” where I replace all of the electrolytic capacitors and some of the rolled capacitors of smaller values subjected to high voltages.  I tested some of the old capacitors once they were out of the circuit (except in rare cases, capacitors can’t be tested while they are in the circuit). There are two large can capacitors that contain four capacitors each.  All of the capacitors in one of the cans were dead (reading very low).  All of the capacitors in the other can were better, but all were out of tolerance. Those cans probably were the culprits of the oscillation.

Unmatched 6L6 tubes, not even from the same era. The one on the left is military surplus.  The one on the right might be original.

Unmatched 6L6 tubes, not even from the same era. The one on the left is military surplus. The one on the right might be original.

Both Wurlitzer and Seeburg amplifiers of this era use 6L6 tubes in the final stage of the amplifier. From a theoretical point, the two tubes should be gain-matched because one tube drives the upper half of the waveform, the other tube drives the lower half of the waveform (a.k.a. push-pull amplification).  But these amplifiers seem to be pretty forgiving if the tubes are not matched. I once saw a Seeburg operating with one 6L6 tube missing.

The owner and I decided to go ahead and get new output tubes.  The nice thing about 6L6 tubes is that they are still being made today due to their popularity for use in guitar amps.

After all the work was finished on the amp, it tests perfectly at all volume levels.

 

 

Wurlitzer 850 Jukebox (1942)

Location: Bailey, CO
Symptoms: Needed adjusting and tuning, front door grill repair, broken bubble tube

This jukebox is a beauty, with a wonderful patina that I don’t see very often because it still had its original plastics and the original chrome has worn off most of the metal.  Most jukeboxes of this vintage have had their plastics replaced and their metal re-chromed.  My initial instinct was to replace the plastics and make it look like new.  But the old plastics with their muted transparency really grew on me.  Besides, it doesn’t look like anyone is still making reproduction plastics for this model.

Wurlitzer 850 Jukebox

Wurlitzer 850 Jukebox at night (Click for larger)

And because the German Wurlitzer company recently made reproductions, the patina sets this one apart.

Daytime view

Daytime view

On to the repairs…

There were a lot of small problems with the mechanism because it was gummed up.  It looked like the mech was cleaned sometime in the 1990’s so there wasn’t a ton of old grease.  It just needed some fresh lube.  It also needed some adjustments as the turntable wasn’t lifting high enough and it wasn’t tripping correctly at the end of the records.

The amp didn’t  sound good, but it turned out the needle wasn’t seated into the cartridge correctly.

Some of the wiring in the switch junction box wasn’t looking safe, so I rewired it.  Some of it previously had been bypassed.

The left bubble tube was broken due to a blow to the lower grill castings of the jukebox, probably during moving. Unfortunately it broke the threaded anchor points for the screws in the castings. I removed the grill castings and used some metal epoxy to attach some new standoffs and reinforce one that was remaining.

Front grill casting with new threaded standoff attached.

Rear of front grill casting with new threaded standoff attached.

The speaker bushings were replaced with new ones, as the old rubber bushings were brittle and broken.

Everything was looking, sounding and working pretty well when it was done.  The repairs were performed over the course of a couple of months.

 

 

Seeburg PFEAIU Jukebox

Location: Wallace, Nebraska.
Symptoms: Record would load to turntable and immediately unload, mechanism continuously scanned, only even letters (B, D, F, etc.) would play.

This jukebox had recently been purchased at an auction and the condition of it was unknown to the owner.

I started with getting the mechanism to stop scanning continuously. There were two problems associated with this.  The first was the add/subtract switch in the control center was sticking.  There are two solenoids and a ratchet mechanism that is responsible for starting the mech scan and stopping it after two passes.

After the add/subtract switch was working freely, it was evident that the subtract solenoid was never energizing when the mech reached the right end.  The subtract solenoid is energized by two different switches.  One is a service switch that the operator uses to stop the mech at various locations for loading records.  The other is a leaf switch on the rear of the mech that actuates when the when the mech reaches the right end.

The service switch correctly energized the subtract solenoid.  The problem was with the mech switch.  After removing the back cover of the jukebox, the mech switch was obviously bent. I removed the switch cover and straightened out the switch bracket.  I reassembled and readjusted according to the procedure in the service manual.   The add/subtract circuit then functioned normally.

Next up was finding out why the record would immediately reject after loading onto the turntable.  The first thing I did was to isolate whether the problem was electrical or mechanical.  I held down the trip lever as the record was loaded.  The trip solenoid buzzed loudly indicating that something was tripping it electrically.   I checked the trip switch that senses when the record is finished and found it was stuck on.  I removed the switch and flushed it with contact cleaner to remove the gunk that was causing it to stick.  After several minutes of exercising it, it finally started to work.  I remounted the switch and that problem was solved.

Next up was finding out why all of the letters associated with playing the left side of record.  I had read someplace on the internet that the PFEAIU only reads out in one direction.  This is incorrect.  It reads out in both directions like the majority of other Seeburg jukeboxes.  It took me a bit to find the problem, but it ended up being a broken wire on the Tormat contactor block.  Visually, it looked okay, but electrically it wasn’t making a connection.  I resoldered the wire and all was working.

I lubricated the mechanism.  The amp sounded like it needed to be rebuilt, but I noticed that someone had replaced some of the capacitors in the past.  The sound improved as we played more selections and the owner was happy with it as it was.

P.S. After the original 100 play series, I’ve never understood Seeburg’s model numbering system.