Zenith Cobramatic Stroboscope - Muffled Audio?
 

The audio sounds like it's coming through an AM radio. I bought this thing restored a few years ago, and the amplifier has previously been recapped and was working fine. Here's what I do know:

1: About a year ago, I damaged the needle while dusting it. Literally broke the thing off of the cartridge. I was able to source a new needle and install it, but for awhile I didn't use it because there was an issue with the drive mechanism that I fixed a few weeks ago.

2: Around the same time that I replaced the needle, I discovered that I had accidentally turned the turntable off but left the amplifier running. It may have been on and cooking the tubes for over a month at the time - is it possible that I wore out one or more of the tubes doing that? I just replaced the 12AU6 today but had no change.

3: I pulled a different, restored player out of the closet and tried this same record on it. The audio was much clearer, so this is definitely something up with the player.

Example video here: https://photos.google.com/share/AF1Q...d6SlJhQkJYVEZB

If you changed the TT with another & it sounds good on
the Zenith amp its probably the cartridge. IIRC these had EV carts.
Look at the needle & be sure the needle is resting on a rubber thing
that goes to the cart. They break & fall off often.
This shows a magnetic but the layout is basically the same.

https://www.google.com/search?q=need...id:h5t4t5lzzA4
s
The part to look at is the "suspension".

73 Zeno:smoke:
LFOD !

Oh, I should have been clearer - it was the other turntable with its built-in amp. Just confirming the record shouldn't be this muffled.

Just checked the rubber bit. It looks right, but maybe I installed the needle wrong? Tried to grab a photo to see if anything jumps out as an issue: https://photos.google.com/share/AF1Q...l1dVhpTkRJZ1B3

Looks OK. The other test you can try is unplug the audio from the TT
and hook it to a low level audio source like a cassette deck.

Let me see if I can figure out how to do that. Sounds like it would require actually building an adapter or something. I need to see if this turntable is soldered or just plugged into the amp.

Almost always the TT audio plugs in with an RCA jack. Yours is mono
so just one. If stereo two plugs. Some do use other type jack.

Zeno:smoke:

Okay so I was able to work out the plugs on the bottom - it's a three prong plug similar to the one on my restored RCA suitcase player. Is that a standardized design? If so and if I knew what it was called I might could wire up something that could plug into the aux jack of a cassette player and run the audio through the amp to see if that's where my issue is.

Only 2 wires go to the cart. Dont know what they called the plug.
Unplug it and tack on a jack. BE SURE its not the AC power cord !

Zeno

No I can definitely see the wires from the tonearm connected to the plug on the turntable side. I think what I'll do is identify the live pins to the amplifier and then find a way to run some alligator clips or something from a radio to that. Then I can hear how the amp sounds with a different source.

Haven't seen a photo to know if this was one of the capacitive REAL cobra pickups, but if it is a normal audio signal from a normal audio source won't work.

The early cobras used a variable capacitance cartridge that NOBODY else made (and only wurlitzer bought from Zenith to use). The capacitance carts needed a tube RF osc that was modulated by the cartridge to make sound out of the variable capacitance. Zenith used this from 1948 until the late 50s when instead of making a stereo version they just used the stylized cobra tone arm with a conventional ceramic or magnetic cart.

I'm not sure what mine started off with, but I know that the cartridge was replaced with a modern, stereo compatible equivalent. It's not the radionic cartridge so I presume mine started its life with the ceramic cartridge.

Unless I'm mistaken and the radionic could have been replaced with a modern cart without significantly redesigning the electronics.

Just for sake of an update, I think I have a plan worked out. It's a bit convoluted so bear with me.

I've been wrapping up a restoration project on a Norelco EL3542. Thing's basically done, I'm just seeing if I can quiet down the takeup reel clutch before I haul it back up to my office.

A few days ago, I picked up a Wollensak T-1500. Unrestored, but it came with an adapter cable that allows a 1/4" audio jack to connect to an external source using alligator clips.

So - knowing that the Norelco is tested and sounds great, and with that cable in hand, I should be able to comfortable check the speaker on the Zenith and then work my way back to the amplifier to see if I can narrow down the source to a speaker or amp issue. Worst case, if it's the amp I can crack that open and see about sorting out the issue.