Newcomb EDT-15C record player

[radiotvnut]

Here's a Newcomb EDT-15C solid state classroom record player from 1970 that I just obtained. I've cleaned and lubricated the drive mechanism and I'll soon address the cartridge and amplifier problems. The 89T cartridge is shot and the holder is damaged; so, I'd be looking at around $30 to get a sapphire tipped LP/78 cartridge and a holder. Lately, I've noticed 89T's are getting expensive and Gary no longer has the diamond LP/sapphire 78 version. So, I'm thinking of replacing the whole thing with a Pfanstiehl P228 cartridge and I'll probably have to modify the input circuit, since the P228 is not as hot as the 89T. It's now being said that the current P132, P226, and P228 are all the same cartridge and put out .5V Vs. the 1.3V of an 89T. I'll do some experimenting to see what works best. In another thread, someone mentioned removing the .001 uf input capacitor are adding a resistor in series with the capacitor. I like the idea of using a P228 cartridge because it is a true stereo cartridge and I won't be forced into replacing the whole cartridge when the needle becomes worn.

There is also a fairly loud waterfall sound coming from the speaker that is especially noticeable when no record is playing or during soft passages. I suspect this is due to a noisy transistor (probably germanium, I haven't checked yet). I'm sure my friend the oscilloscope will come in handy for this one.

[bob91343]

Those are silicon transistors. The hiss may well be due to a noisy first amplifier transistor but don't rule out a bad resistor.

Biasing for both transistors determines the required beta of a replacement. Generally, any common NPN will do, such as 2N2222A or 2N3904 or whatever you have in the junk box.

If the hiss is present with volume set at zero, suspect also the 2.7 Megohm resistor in the base.

The electrolytic coupling capacitor may be leaky.

[radiotvnut]

The hiss varies with volume; but, the only place I could find it on the oscilloscope was at the collector was at the driver transistor (at the transformer). I replaced the transistor and the 330K resistor; but, the hiss is still there. It's not noticeable when a record is playing; so, the hiss may be an artifact of the design of the amp.

I replaced the 89T cartridge with a Pfanstiehl P228; but, as I expected, the output was weaker and tinny sounding because the P228 only kicks out .5V Vs. 1.3V for the 89T. I was able to make things better by jumping out the 680K resistor in the input circuit. It's still not as bold as the 89T; but, it's a lot better than it was. Later, I may experiment more with the input circuit to see if I can make it even better.

I think the P228 will be better for records than an 89T.

[bob91343]

Noise is usually from the input stage. Replace that and you may be okay.

[tvtimeisfun]

That tonearm reminds me of the same style as the 70s model of talking book record players tonearm...

[Celt]

My Jr. High School had a stereo Newcomb similar to that. Had separate bass, treble and two 6x9" speakers. Had a nice sound as I recall.

[radiotvnut]

Originally Posted by tvtimeisfun

That tonearm reminds me of the same style as the 70s model of talking book record players tonearm...

It is the same Astatic tonearm, just a different color. That same tonearm can be found on some Audiotronics players and other institutional-grade record players.

[KentTeffeteller]

Will this accept a 1/2" mount? If so, why not an internal preamp and a magnetic cartridge like a Shure SC35C. A la transcription player. It would sound better and be easier on records. A good hot rod project.

[Sandy G]

REALLLY like that Tooob Newcomb AM/FM "Portable" radio I lucked into about a month ago..