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Forums | Rap N Tap Clubhouse - Basic Crystal Radio Fun! | Radio Shack Mini Amplifier/Speaker Post Reply Send Topic To a Friend
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RobertCPosted - 5 November 2011 20:20  Show Profile  Email Poster  Edit Message
Hi K,

Interesting info! These little amps are very useful!

John Bruce McCreathPosted - 10 November 2011 19:55  Show Profile  Email Poster  Edit Message  
Hi Guys,

If you can't find one of the RS mini-amps, an old transistor radio can function as one. Wire a jack across the volume control so that when you plug in an external source it disconnects the detector. I've used one for years that way.

73, J.B., VE3EAR

Into radios since 1959.

golfguruPosted - 11 November 2011 2:4  Show Profile  Email Poster  Edit Message  
This link seems to corroborate my findings re:- "earpiece problems" {posted earlier in this thread}.

http://www.usefulcomponents.com/main_contents/information/crystal_earpieces/crystal_earpiece_problems.html

.................

gzimmerPosted - 11 November 2011 6:20  Show Profile  Email Poster  Edit Message
Golf,

Thanks for that, it's an interesting article and clearly explains the problem.

These "modern" units have a flat diagram. Ceramic earpieces from decades ago had a different construction which used a conical diaphragm. You can see the difference if you peer in the hole. There's a blob of glue right in the center of the cone.


I have one old-style unit here, but unfortunately it is dead. I remember pulling one apart about 50 years ago, and if memory serves, the piezo part was a long thin slab, rather than a disk. It was linked to the center of the cone with a thin piece of wire.

I might pull apart my dead one and take some photo's of the internals.

Perhaps readers could have a hunt through the junk box to see if they have any old style earpieces with conical diaphragms.
It would be interesting to compare their sensitivity with the modern units.

...... Zim


Edited by - gzimmer on 11/11/2011 6:26:07 AM

RobertCPosted - 11 November 2011 8:30  Show Profile  Email Poster  Edit Message
That is an interesting article Golf. I agree that the little cheap crystal ear plugs are often junk. That is my experience with them. I think kits today should come with at least two or three of them figuring that one or two will not work.

The writer of the article is Henry Walmsley who runs a cool UK ebay store. He sells a really neat "Ladybird" kit of parts to make up a transistor radio from a 1970's book series. I built one of these kits and Henry is very responsive if you email him questions.

Good idea JB regarding using a transistor radio as a speaker/amp!

Edited by - RobertC on 11/11/2011 8:35:34 AM

Garry NicholsPosted - 11 November 2011 11:33  Show Profile  Email Poster  Edit Message
Thanks for that interesting article Golf.

I've arrived at the conclusion that more of these than you think you will need should be ordered when buying. Then you can take the "pick of the litter".

I wonder if we should "blitz" the manufacturers with emails in an attempt to get them to improve.

Would anyone be willing to pay a bit more for these if they were better built? That might get the factory's attention.


All;

I checked the 5 that I have and all but 1 are flat diaphragm. That one is conical. I remember the earplug that came with my Gilbert Erectronic set way back in about 1962, and it also was conical.

A pair that I use wired in series periodically goes dead (or at least one does), but tapping the back of it against my big tuning knob brings it back to life. I find these to be quite sensitive and very comfortable to use.

I think they are about as sensitive as my circa 1924 Brandes magnetics, and their "sharp" sound makes voice more easily intelligible at low signal levels (at least to my ears!).

Garry

golfguruPosted - 11 November 2011 16:6  Show Profile  Email Poster  Edit Message  
Seriously guys ...... just wondering.

My previous post
>>>>>>>

RE: earplug problems.
I posted a thread at TRB on this. Some of the modern ones are piezo elements on aluminum discs (not the usual brass).
The centre contact is solderd but the other one is just bent over and glued to the aluminium. May go HR.
http://theradioboard.com/rb/viewtopic.php?p=22127&sid=3befb6e8f5eb0180c39b054eb4088dc2
>>>>>>>>>>

I received zero response to the above post, which included my "2009, TRB post" which *showed images" of both types of earpiece including the *actuator arm" as mentioned in Zim's post. (BTW it only recieved 1 response at TRB as well).

I subsequently post a link to a "credible source", which discusses exactly the same thing, and suddenly, there are meaningful responses.

Leads me to ask: "Do people really bother to read some of these posts and actually digest the contents?".

Not "PO'd" just "perplexed".

.............................

gzimmerPosted - 11 November 2011 18:0  Show Profile  Email Poster  Edit Message
Golf,

> "Do people really bother to read some of these posts and actually digest the contents?"

Some do, most don't. Gets up my nose too..

........ Zim

gzimmerPosted - 11 November 2011 18:2  Show Profile  Email Poster  Edit Message
Gary,

> I checked the 5 that I have and all but 1 are flat diaphragm. That one is conical.

Any difference in Sensitivity?


.......... Zim

Garry NicholsPosted - 11 November 2011 18:12  Show Profile  Email Poster  Edit Message
Thanks for the earplug comments, Zim. I do have a 50k pot across them. Decreasing the resistance lowers strong station distortion somewhat, but not a lot.

Don't know if the excessive distortion on strong stations is simply less apparent on weaker ones or if there is simply less distortion. Can't tell.

I figured the 50k was doing whatever a Benny would do with it being across the earplugs.

Did not compare sensitivity on the two types. Just looked in my parts drawer! Will do that, but if Z differs much it may be a confounded experiment.

Also, if you are still looking for ribbon line you could try:

thewireman.com/products.html

They have various 450 and 300 ohm parallel lines.

Is this for TV or radio use? (Just being nosey. . . . )

Garry

Edited by - Garry Nichols on 11/11/2011 6:16:01 PM

RichardPosted - 11 November 2011 19:57  Show Profile  Email Poster  Edit Message  
Golf, Zim,
Matthew 7:6 comes to mind. :)
SWseniorPosted - 11 November 2011 20:20  Show Profile  Email Poster  Edit Message  
Golf,

("Do people really bother to read some of these posts and actually digest the contents?")

I read almost all, but am not knowledgeable enough to reply to some.

SWsenior

golfguruPosted - 12 November 2011 0:49  Show Profile  Email Poster  Edit Message  
Mmm....
It appears some "pearls" (of wisdom) are more easily digested than others, dependant on the source.

Anyway ... no biggy (I guess). It is just that the subject (non working earplugs) rears it's head with monotonous regularity, specially with "newby" posts and I thought it would have been important info. that would have brought a few "ah-ha" moments to the senior contributors. I bought (20) or so earplugs - 50% of which were/are dead. I also posted elswhere that 3/4" brass piezos slot straight in, if you cut the case open carefully with a coping saw.

Peace be with you all.

Golfguru 14:1.

..........................

Garry NicholsPosted - 12 November 2011 7:14  Show Profile  Email Poster  Edit Message
I like that slow tuning ratio, golf'.

Read the Radioboard link that you provided above. Where did you get the 3/4" piezos?

When you cut open the earplug cases with a coping saw, material is being removed. Do they still fit together OK on reassembly? Seems like there would be less space inside and any alignment/mounting contours on the original faces of two pieces might be destroyed.

Garry

Edited by - Garry Nichols on 11/12/2011 7:25:53 AM

RobertCPosted - 12 November 2011 13:29  Show Profile  Email Poster  Edit Message
Hi all,

I really think that the phone/earplug situation is really a big problem for beginners trying to set up a home built radio. I remember way back when I built my first Xtal Set Society kit that the earplug which was supplied went dead shortly after I got the set working. Very frustrating. For $15 the little Radio Shack Mini Amp/Speaker seems like a good investment for a newby. It does not give the same thrill as a no-battery set but it eliminates a big uncertainty.

There are a few other new alternatives to the aging 2000 Ohm headsets, such as listed in the post on the clubhouse forum regarding "NOS 4400 Ohm military headsets." I think it's almost futile for a newby to build an xtal set and depend upon one set of piezo earplugs.

It might be that this situation does not get a lot of attentions on the radio forums because most of the folks have working headphones and don't rely on these cheap earplugs.

Edited by - RobertC on 11/12/2011 1:32:02 PM

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