Zenith Cobramatic Self-contained record Player Information needed

[vortalexfan]

Originally Posted by Electronic M

The 2 cobramatic changers I've owned both worked fine after a recap and getting the mech working...If you haven't recapped it yet that would be my first move. If it has fresh caps check tubes and resistors. If it still sounds bad try injecting audio and seeing if it still sounds bad. If it sounds bad with injected audio the problem is likely in the speaker or output transformer, but if injected audio is good then either the cart or the osc circuit that converts it's output to audio is bad.

it has brand new capacitors in the amplifier, the only capacitors that havent been changed were the power supply filter caps which are still working. The thing I have noticed on it is that it seems that it has a grounding issue betweem the cartridge and the amp because it has a hum to it that goes up and down with the volume control and isn't the same hum as the hum you get with bad filter caps.

Also this Cobra-matic changer uses an Astatic model 99 Powerpoint "cartridge" (which is basically a needle and cartridge in one unit that plugs into the tonearm) so the only thing that could be bad would be the needle/cartridge assembly itself which could always be possible seeing as it was a NOS Needle/Cartridge assembly I had bought for this unit.

I've changed out the tubes several times with other known good 50C5 and 12AU6 and 12BA6 tubes and it doesn't sound any better, and the speaker is still good it doesn't have any damage that I can see of.

I do have a Sonotone 2T Cartridge and needle assembly that I could try and install in this record player in place of the original Powerpoint cartridge assembly but unfortunately the tracking weight would be different as the Sonotone cartridge tracks lighter than the original cartridge does by a couple of grams and I don't know how to adjust the tracking weight on these old cobra tone arms.

[Electronic M]

Originally Posted by vortalexfan

it has brand new capacitors in the amplifier, the only capacitors that havent been changed were the power supply filter caps which are still working. The thing I have noticed on it is that it seems that it has a grounding issue betweem the cartridge and the amp because it has a hum to it that goes up and down with the volume control and isn't the same hum as the hum you get with bad filter caps.

Also this Cobra-matic changer uses an Astatic model 99 Powerpoint "cartridge" (which is basically a needle and cartridge in one unit that plugs into the tonearm) so the only thing that could be bad would be the needle/cartridge assembly itself which could always be possible seeing as it was a NOS Needle/Cartridge assembly I had bought for this unit.

I've changed out the tubes several times with other known good 50C5 and 12AU6 and 12BA6 tubes and it doesn't sound any better, and the speaker is still good it doesn't have any damage that I can see of.

I do have a Sonotone 2T Cartridge and needle assembly that I could try and install in this record player in place of the original Powerpoint cartridge assembly but unfortunately the tracking weight would be different as the Sonotone cartridge tracks lighter than the original cartridge does by a couple of grams and I don't know how to adjust the tracking weight on these old cobra tone arms.

Speakers can look fine and still sound like crap. The cone can rub, the suspension fail, the voice coil can have defects. When a problem is not obvious that is the time to test everything carefully.

If that someone is a conventional magnetic or ceramic type instead of the capacitive type most cobras used originally then you could take the output of another Phono with a cart that puts out similar voltage and see if the amp circuits in your unit sound good with that.... I've used that trick a few times.

[vortalexfan]

Originally Posted by Electronic M

Speakers can look fine and still sound like crap. The cone can rub, the suspension fail, the voice coil can have defects. When a problem is not obvious that is the time to test everything carefully.

If that someone is a conventional magnetic or ceramic type instead of the capacitive type most cobras used originally then you could take the output of another Phono with a cart that puts out similar voltage and see if the amp circuits in your unit sound good with that.... I've used that trick a few times.

Well it seems that I spoke too soon about the power supply caps, as they just failed when I powered it on just now, there was a slight hum that started growing louder and then it started squealing and when it started squealing I quickly turned it off but now when I go to turn it on the tubes wont light up.

So I'm thinking the power supply filter caps must of suddenly failed catastrophically as it was working fine hum free for the most part up until just now.

So I wonder if that might of been part of the reason why it was putting out bad audio, because the filter caps were starting to go out and I didn't realize it.