Cobramatic H665-RZ

Hello fellow enthusiasts, I am new to the forum. I was hoping that I might tap your vast pool of knowlege for assistance with a few minor, but troublesome issues. Recently, I acquired a 1951 Zenith H665-RZ Radio/Phonograph. I swapped a couple of non-working radios for it. The Zenith appears to have been restored. Cosmetically, it is near perfect. The radio portion functions great. Tuning is sensitive and the sound is crisp and clear. My problems are with the Cobramatic turntable:

A.) The turntable does not shut itself off after the last record. I am not familiar with Cobramatics. With other turntables I have owned, the automatic shutoff is actuated by the positioning of the record stack over-arm. That does not seem to be the case with the Cobramatic.
B.) There is a humming/buzzing through the speaker after warm-up on the phonograph setting. When switched to radio, the humming/buzzing does not occur. The humming buzzing varies with the volume.
C.) The tone-arm is touchy. At times it works fine. Sometimes it becomes overly sensitive and acts as a microphone. If I tap it gently, the tapping is audible through the speaker.
D.) Isn't the turntable supposed to be mounted on springs? This one bolted-down tight to the cabinet. I get a rumble feed-back sometimes with the lid closed while a record plays. I think that might go away if there were springs to absorb motor vibration. Is there a source for Cobramatic parts, like springs?

Do any of you have any suggestions as to how I can get rid of these issues? I am not a radio repair person. I am mechanically inclined, but I tend to avoid tinkering with electrical things that I don't understand. If the solutions are simple, I am good with small tools and may be able to fix it myself. There are no full-time vintage electronic repairmen in my corner of the world. Any advice would be greatly appreciated.

Clark wrote:Hello fellow enthusiasts, I am new to the forum. I was hoping that I might tap your vast pool of knowlege for assistance with a few minor, but troublesome issues. Recently, I acquired a 1951 Zenith H665-RZ Radio/Phonograph. I swapped a couple of non-working radios for it. The Zenith appears to have been restored. Cosmetically, it is near perfect. The radio portion functions great. Tuning is sensitive and the sound is crisp and clear. My problems are with the Cobramatic turntable:

A.) The turntable does not shut itself off after the last record. I am not familiar with Cobramatics. With other turntables I have owned, the automatic shutoff is actuated by the positioning of the record stack over-arm. That does not seem to be the case with the Cobramatic.

The cheaper units repeated the last record. You paid more for the "auto-shutoff accessory" until around 1954. And almost all of the little 45 changers repeated the last record into the 1970s.

The turntables Zenith themselves made in the early 1950s which did shut off after the last record just shut off the power, leaving the arm on the leadout groove of the last record. The electric trip triggered a shutoff solenoid instead of the change cycle solenoid when the overarm or record bail (on the shelf changers) was low. The shutoff solenoid released the power switch latch, turning off the motor.

Zenith also used some V-M changers in that period. Some of those have shutoff devices, and some repeat the last record. And if the overarm on the V-M 400 series is bent upward (so the record pusher doesn't contact it), the changer repeats the last record.

The machines made by Zenith all have a chain drive underneath for the change cycle, and a solenoid operated reject. The V-M changers have either a heart-shaped cam, or a slide cam.

B.) There is a humming/buzzing through the speaker after warm-up on the phonograph setting. When switched to radio, the humming/buzzing does not occur. The humming buzzing varies with the volume.

This is probably due to a bad connection in the pickup wiring. Or it could be something loose in the pickup, or a loose pickup mount. Often a shielded pickup cable develops a break in the shield at the arm pivot.

C.) The tone-arm is touchy. At times it works fine. Sometimes it becomes overly sensitive and acts as a microphone. If I tap it gently, the tapping is audible through the speaker.

This is the same thing as the previous problem.

D.) Isn't the turntable supposed to be mounted on springs? This one bolted-down tight to the cabinet. I get a rumble feed-back sometimes with the lid closed while a record plays. I think that might go away if there were springs to absorb motor vibration. Is there a source for Cobramatic parts, like springs?

They didn't really start floating turntables until after the LP record appeared. I used to have a Philco from 1952 without springs. On the other hand, my grandfather had a Stewart-Warner from 1949 with springs.

Floating doesn't prevent feedback. Floating mainly prevents record skipping when people are dancing on a wood floor which is also holding up the table the turntable is on. With 78s, the stylus force was heavy enough to prevent skipping. But LPs need lower tracking force, and so the record skipping problem started with the introduction of the LP.

Putting the speaker and the turntable in the same cabinet causes feedback. The only cure is an external speaker (or turning down the volume).

Do any of you have any suggestions as to how I can get rid of these issues? I am not a radio repair person. I am mechanically inclined, but I tend to avoid tinkering with electrical things that I don't understand. If the solutions are simple, I am good with small tools and may be able to fix it myself. There are no full-time vintage electronic repairmen in my corner of the world. Any advice would be greatly appreciated.

See above.

With the exception of the tone arm connection, it sounds as if my perceived troubles are just the nature of the beast. I will look the tone arm wiring and connections over, closely.

My record changer is cam driven. The over arm is flat and about an inch, or so, wide. It is chrome plated and slotted. The spindle fits through the slot. I guess the arm is moved out of the way for 45's, unless the individual plastic hole inserts are used. The set did not come with an adapter to slip over the spindle. The tone arm is maroon plastic and the base of the turntable is maroon plastic with faux gold plated trim.

Thanks very much for the advice.

The record changer Zenith made is here:

http://geocities.com/midimagic@sbcgloba ... bramat.jpg

The V-M record changer is here:

http://geocities.com/midimagic@sbcglobal.net/3spvm.jpg

Both had nearly identical maroon tonearms, since Zenith supplied their own cobra tonearms for the V-M changer. The V-M changer shown is out of a Stewart-Warner console, so it does not have the Zenith tonearm.

Note particularly the different locations of the overarms.

Also, later versions of the Zenith changer did not have the chain drive. They had a simple change cycle drive gear with an eccentric stud working everything.

Mine is identical in every way to the Zenith made turntable in the top photo. Thanks for posting those.

I have the repair manuals for both changers.

If yours won't shut off after the last record, then one of the following is true:

Changer repeats last record:

- The changer is the cheaper model without the overarm activated spdt switch.
- The overarm is binding, so it doesn't fall enough to trip the switch.
- The switch is broken or has become loose in its mounts.

Changer does not trip the shutoff on the last record. Turntable continues to rotate with the stylus in the runout groove:

- Bad contact on overarm switch.
- Damaged trip shutoff wiring.
- Open solenoid.
- Solenoid linkage not moving to trip power switch off.

Power shuts off with tonearm still on record:

- It's working the way they designed it.

-------

Automatic shutoff was a new thing then. Different record changers accomplished it in different ways:

- Markel Duo-Playmaster also left the arm on the last record.

- The V-M changer in my post shut off the power at the end of the change cycle, but in the process it returned the arm to the beginning of the record. The user then returned the arm to the rest.

- Webster-Chicago multispeed changers returned the arm to rest, but did not stop the turntable from rotating.

- The Chrysler HiWay HiFi system set the arm down beside the empty turntable and kept running. So did most of the RCA Duo changers, and the 2-side Magic Brain.

- Garrard locked the arm over the rest in such a way that you could not move it. Their arms could not be handled manually at all (You could not return it to rest if it was on a record).

- Philco. Motorola, GE, Detrola, and RCA changers still repeated the last record.

Clark wrote:With the exception of the tone arm connection, it sounds as if my perceived troubles are just the nature of the beast. I will look the tone arm wiring and connections over, closely.

My record changer is cam driven. The over arm is flat and about an inch, or so, wide. It is chrome plated and slotted. The spindle fits through the slot. I guess the arm is moved out of the way for 45's, unless the individual plastic hole inserts are used. The set did not come with an adapter to slip over the spindle. The tone arm is maroon plastic and the base of the turntable is maroon plastic with faux gold plated trim.

Thanks very much for the advice.

This was before 45 spindles were generally provided accessories for drop changers. You were expected to put spiders in the record holes. They were metal back then (I have some).

Only GE, Garrard, and Motorola provided 45 replacement spindles for their changers at that time. All of them used removable small-hole spindles (with Garrard, you had to remove it to get the records off the turntable). So the 45 spindle replaced the small hole spindle. On the Motorola, the entire spindle rotated with the turntable.

All of these are pictured on my website.

The GE changer (made by Milwaukee-Erwood) had 3 different spindles. One was a straight spindle for 10'' and 12'' records. Another was a slanted small-hole spindle to make a 7'' record reach the 10'' side shelf. The third was a 45 spindle which also slanted to reach the side shelf.

I just noticed that this new site no longer provides links to user's sites. My changer pages are at:

http://geocities.com/midimagic@sbcgloba ... angers.htm

The last record continues to repeat. The over arm is going down as far as the pin set into its support rod will allow. I looked underneath the set. The bottom end of the over arm support rod is not connected to anything. I see nothing that it could connect to.

I bought an identical, junked, turntable off of ebay just to study it. It is just like mine underneath, as well. Nothing seems to be connected to the tone arm on that one either.

It is just a steel rod that moves up and down. How does the auto shut off switch connect to the tone arm? Do you have a picture, or illustration of it?

The end of the overarm shaft should touch a leaf switch when the overarm is all the way down. It is mounted on a bracket under the overarm shaft, and has a three-bladed exposed switch. The mount for the switch is in the direction of the spindle from the overarm shaft, with the blades pointing away from the spindle.

If the leaf switch isn't there, the changer does not have automatic shutoff. There will be an empty screw hole in the plinth about an inch toward the spindle from the overarm shaft where the switch bracket goes.

There is a nylon cylinder about 3/16'' diameter and 1/4'' long which extends from the switch leaf to touch the overarm shaft end. If this cylinder is missing, the changer will repeat the last record.

NOTE: If the overarm shaft touches the metal leaf, a short circuit will burn out the cycle transformer. The mechanical coupling from the leaf to the overarm shaft must be an insulator.

If the changer has automatic shutoff, there should be two solenoids. The trip solenoid is mounted horizontally on the plinth next to the transformer. The shutoff solenoid is mounted vertically on the power switch assembly between the switch housing (wires go into a hole) and the plinth. The switch assembly is next to the motor. The changer without automatic shutoff has only one solenoid, mounted horizontally.

Other than those little RCA 45 changers, Zenith was the last company to make changers which repeat the last record. They were still making them in 1958.

This was the only record changer with a continuously variable speed drive covering all 4 speeds. It was also the first changer taking 12'' records with the 16 rpm speed.

Well, that solves the mystery. Thank you. I checked, nothing underneath my turntable fits that description. Mine never had an automatic shut-off.

That seems so strange. I wonder how much extra such an option cost? it must have been a significant amount.

What was the purpose of the sliding "variable speed" control? How is that better that just selecting the pre-designated speeds, with no variance? Did some people like to vary the tempo a little?

Actually, three new speeds had just appeared within 5 years. They were afraid that some nutty company would release yet another speed.

Collaro did the same thing with record sizes after Germany started making 8'' records. They came up with their automatic size sensor which works with all sizes from 12'' to 6'' (see page 3 of my changer pages).

Dual and PE followed suit with multiple-size sensors the following year.

The parts for that auto shutoff cost about $2 back then. They charged $5 more for players which had it.

But we have to remember that the average salary back then (before the money got inflated into being worth less) was around $1000 a year. So that difference of $5 is the equivalent of $100 more today.

According to an online inflation calculator that I found, $10.00 in 1951 dollars is equal to $80.92 in 2007 dollars. That is a significant amount of money. I can understand why someone would say "Heck, I can turn it off myself and save ten bucks".

It sounds as if the transition from shellac to vinyl was far more tumultuous than the transition from vinyl to compact disc. I read through your site several days ago, when I bought my Cobramatic. You certainly put a lot of research into record changers. It is impressive.

When I was a kid, I loved watching record changers. I would hit the reject switch again and again. I have to admit, I still think they are cool.

Clark wrote:According to an online inflation calculator that I found, $10.00 in 1951 dollars is equal to $80.92 in 2007 dollars. That is a significant amount of money. I can understand why someone would say "Heck, I can turn it off myself and save ten bucks".

It sounds as if the transition from shellac to vinyl was far more tumultuous than the transition from vinyl to compact disc. I read through your site several days ago, when I bought my Cobramatic. You certainly put a lot of research into record changers. It is impressive.

When I was a kid, I loved watching record changers. I would hit the reject switch again and again. I have to admit, I still think they are cool.

It wasn't just research. I became interested in 1956 at age 5 (see the story on page 2 about playing a 6'' record on that V-M I mentioned earlier).

At age 10, I pointed out the error in a factory engineer's claim that the RCA RP-215 could intermix all three sizes of records. I said that, because a rising feeler is used to detect the difference between 7'' and 10'' records, 7'' records can't be in the same stack with other sizes. I was right.

And from 1969 to 1976, I repaired record changers professionally.

If you like to watch record changers, the following ones are especially interesting:

Collaro Conquest (the arm moves back and forth twice, as the tip of the arm feels the record size)
Dual 1006 (The arm rolls on little wheels to the record edge)
Miracord 90 (the arm swings back and forth repeatedly to sense size)
Markel Duo Playmaster (A drop changer with a solid spindle which plays both sides of the records)
V-M 1585 (Uses an elevator to lower the record, and feels the size with the arm tip on the way down)

This site has the following record changers in video form:
http://www.myvintagetv.com/changer_videos.htm

- Automatic Orthophonic
- Lincoln two-side changer
- Capehart two-side changer
- Thorens TD-224

The Garrard RC-100 was the most interesting to watch, because it actually took the record off the turntable and turned it over - and it's a drop changer. Unfortunately, you can't buy one. Except for a few samples, the entire production run was sunk by a German U-boat in 1940. But you can see it work in the 1948 movie "Unfaithfully Yours".

Oh, yes, I remember reading that, now.

Thanks for the great videos. That Victor Orthophonic is certainly much fancier than my wind-up Orthophonic. I wonder how many of those survive? I have heard older people mention Capeharts, but I have never seen one in person. The Lincoln was nothing short of amazing.

I bought the Cobramatic, because I have a large collection of 78's. I wanted a vintage electric machine to play them. I chose the Cobramatic for its light-weight tone arm, as well as, the record changer. It seems to have the correct needle for 78's. At least, it sounds o.k. to me, when it is not humming.

Since my first post, I have found a knowlegeable hobbyist willing to check the connection of the Cobra tone arm for me. I don't want to risk making the problem worse by tampering with it myself.

Clark wrote:That seems so strange. I wonder how much extra such an option cost? it must have been a significant amount.

Actually, automatic shutoff has a very strange history:

The first changers (the assembly-line type) shut off by default. The arm set down beside an empty turntable. Sometimes the dropping of the arm head shut off the motor.

The Capehart never ran out of records (they were put back on the stack again).

The throwoff changers removed the records from the turntable one by one after they were played. They also stopped playing because there were no records left on the turntable. They also reversed the stack as they went through it.

None of the above changers had an actual device to shut them off. It just happened.

The Lincoln changer's size roller carried the arm in to the center when no record was on the turntable. This started a shutoff sequence.

Then the drop changer appeared, first in the knife-type form (where knives slice between the records). Most of the companies adapted their other mechanisms to drop technology without much change except for substituting the oscillating knife shelves for the throwoff device. Most of these changers repeated the last record.

But Garrard and Collaro never made changers which repeated the last record.

When World War II started in Europe and the far east, records were made of cheaper materials (japan had all the shellac sources). The throwoff and knife changers started breaking these records. So the push type (single shelf) changer became popular because it is much gentler. These also repeated the last record, unless a special device was added to shut off the changer. With rationing leading up to American entry to the war, the auto shutoff was a luxury.

Then the mixer changer appeared. These could take 10'' and 12'' records mixed in a single stack. Without automatic shutoff, the last record would repeat at the 10'' position whether it was a 10'' oir a 12'' record. That was kind of the last straw. Most mixer changers gained automatic shutoff rather quickly.

After the war, most changer companies started working on the auto-shutoff problem. But then the LP was introduced in 1948, and the 45 in 1949. In 1953, 16 rpm appeared. So the changer companies had to develop some new units fast. Some of the wackiest changers appeared in this period:

V-M, Philco, GE, RCA, Zenith, Centrum, Luxor, and Philips came out with dual-arm changers in 1948-49 which changed 78 rpm records and played 33 rpm records manually.

When 45 appeared, conversion devices were available to play 45s manually on 2-speed changers.

Zenith had a little 7" turntable attachment which was driven by rolling on top of the regular turntable. It had its own little arm.

Columbia had a 3-size changer which turned at only 33.

Both Webster-Chicago and Markel had changers which shut off after stacks of 10'' or 12'' records, but repeated the last 7'' record.

Admiral had a strange changer which had to be adjusted for record size twice. The record shelf had to be set to hold up the edge of the stack, and the arm had to be separately set for size. It repeated the last record.

By 1955, most changers had auto shutoff. The cost of the parts became small enough that leaving them out wasn't worth it. But Zenith made changers without shutoff until the stereo record forced them to replace their line.

Some "stupid" changers appeared in the 1970s. They have semiautomatic shutoff. You have to tell them how many records are in the stack.