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 Post subject: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Thu 09, 2017 12:40 pm 
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Just joining you all thanks to a suggestion by John of RadioBoatAnchor

Some years ago my son and I were given a Graymark 508 classroom project (see attached), and I've been sitting on it until now - that my 11 y.o. son is old enough to be interested.

Unpacking it, we discovered that it didn't include even a simple schematic. No problem, I thought ... surely we'll find something on the web. Testing my over-inflated sense of google-searching prowess, I haven't been able to find one - outside of an eBay'er selling a whole kit with unspecified documentation, and clearly stating in the ad that the literature would not be shared.

Looking at the board in the kit, it's pretty well labeled. Almost feels like we could figure it out - but that again is how my overconfidence and ignorance has treated me to frequent popped caps and smoked resistors.

So my questions to the community are:

"Any chance that idea could hold any water? Could that puzzle be solved without schematics?"

"Might anyone have a schematic that would be willing to share?"

Thanks in advance,

Luke

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File comment: Graymark 508 Transistor Radio Project
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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Thu 09, 2017 3:57 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 12332
Location: S. Dartmouth MA 02748-1225 USA
http://www.graymarkint.com/

Contact for schematic. Inquired 15 ya cost was $10...


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Fri 10, 2017 3:15 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Welcome to ARF, Luke !

Are those component values on PCB or just numbers ?

Have you removed the cardboard backing of kit, yet ? Was wondering if schematic might be enclosed between layers of the thin cardboard...

It may use a common 2-transistor "boy's radio" circuit used in a "production" set---you could gather a few schematics online and compare to PCB trace layout and the supplied components...

Be patient as some members only occasionally "check in"...

And good luck !

John


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Fri 10, 2017 4:14 am 
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Location: Rayleigh, BC, CANADA
Send me your email in a private message and I'll try to scan this for you.
I been working crazy long hours on snow plow equipment so it may take a day or two.

You're going to need 3 new electrolytic capacitors, the ones in the kit are guaranteed dead. This kit is from the mid 60's.
you can use 47uf for all 3 caps, even tho 2 of them are listed as 33uf


Attachments:
Graymark 508 Manual.JPG
Graymark 508 Manual.JPG [ 69.53 KiB | Viewed 1714 times ]

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Rocco


Last edited by Rocco53 on Nov Fri 10, 2017 3:48 pm, edited 1 time in total.
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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Fri 10, 2017 5:22 am 
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That's a nice looking kit, it should be a fun project once you have the instructions for it.


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Fri 10, 2017 1:26 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
WOW---Rocco to the rescue !!!


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Fri 10, 2017 4:29 pm 
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John, the numbers on the circuit board are just reference points for the step by step assembly.

There were several kits offered to us when I was in high school back in the late 60's.

We started with the Graymark 502 Power Supply, then we moved on to the 508 Boy's

Radio, the 512 8-Transistor Radio and the 509-Tube Amp, I still have them all.


Attachments:
Graymark Kits.JPG
Graymark Kits.JPG [ 102.04 KiB | Viewed 1672 times ]
Graymark 502 Kit.JPG
Graymark 502 Kit.JPG [ 85.11 KiB | Viewed 1641 times ]

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Last edited by Rocco53 on Nov Fri 10, 2017 10:35 pm, edited 1 time in total.
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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Fri 10, 2017 4:57 pm 
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Wow! (ノ・ェ・)ノ

Thanks for all the responses, and to John for introducing me.

Thank you so much, Rocco, for the offer!! I will contact you shortly.

We moved to Ireland a few months ago, so the time change thing has gotten in the way of timely correspondence with people in the states.

Hopefully, I'll have those caps in my drawers, if not, I'll have to begin to find where best to order components from over here.

We'll post updates, and look forward to more conversations with this community.

P.S. I'm a big fan of old-time radio and radio drama. When I was a kid, I listened a lot to CBS Radio Mystery Theater on the very radio in my avatar. Good old Archer Road Patrol that I took from my bike handlebars to bed with me at night. I love AM radio, and played around with box loop antennas when I was a kid to bring-in the distant stations.


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Sat 11, 2017 2:56 pm 
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Welcome to ARF; I've had so much help from the knowledgeable people on this forum. You've just experienced that helpfulness.

Let us know how your kit turns out.

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Mike
KN4GGM

"This is the last radio I will ever buy, dear; I promise"


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Sat 11, 2017 3:06 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Yes, please let us know how the project turn out...

John


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Thu 23, 2017 10:29 am 
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We just started breadboarding it. I'll post a pic soon. Fingers crossed!!

Thanks again for all the help!!!


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Thu 23, 2017 3:16 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Good---waiting to hear about that moment when power first applied !

John


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Fri 24, 2017 3:27 pm 
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Quote:
[xrhonda91] Good---waiting to hear about that moment when power first applied !

Not sure about how much power will be applied, John ...

What a piece of junk! ... 50 years later and only 4 volts?!?! :lol:

Attachment:
9volt.jpg
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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Nov Fri 24, 2017 5:39 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Amazing that the original battery had any "charge" left !

But still have four Ray-O-Vac "D" batteries that came in a multi-band radio given me in 1974 that still were perfectly good a couple years ago (need to check 'em again)---the radio was given away long ago, but kept them ! Weren't used much, but held their power...

How long before "switch is thrown" on radio ?

John


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Feb Tue 13, 2018 10:19 am 
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Ok, well ... we finally had a minute to breadboard the kit and are coming back to you all for assistance.

Not sure where to continue troubleshooting. We've gone over the diagram several times to check our connections and directions of components; verified power at the rails; pulled no current readings across either transistor's leads.

Should we start checking and replacing individual components? Start with the transistors?

Apologies for the messy board. The layout has some quirks with lots of jumpers used to get space for connections. (T3's physical layout has diagonal connections)

Any advice would be greatly appreciated.

Thanks.
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bb-2.jpg
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diagram.jpg
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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Feb Tue 13, 2018 6:13 pm 
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Location: S. Dartmouth MA 02748-1225 USA
"We"?

Use a VOM and check transistors for leakage, consider replacement. Replace the electrolytics if they are OEM.

Circuit is a reflex. May have to swap one winding of the RF transformer either to make it work or to stop oscillation. That may be what is happening, locked up oscillating. Or, how is Q2 getting its collector volts?

Best check some of the online schematics...

No excuses for the pin-board rats nest. Even at 10 mhz a pin board will be fine with rails laid our properly. It's common practice to stand the resistors up. A hairpin loop of #22 bus sufficed to make a soldered wire connection rather than depend on a tinned stranded wire into a rail. When complete, blobs of hot melt will hold things solid. I OFTEN had arrange and re-arrange a breadboard circuit to get both a neat, compact workable circuit. I have never had a circuit of which had issues with coupling between the rails.

I did my patent models on pin board, there were shipped to test facilities all over the country and GB. worked fine...

Chas


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Feb Wed 14, 2018 10:01 am 
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Chas wrote:
May have to swap one winding of the RF transformer either to make it work or to stop oscillation. That may be what is happening, locked up oscillating.

That's what I'm thinking, may have to pull T3 and turn it around.

I find it difficult to follow the jumpers on that board but I can see one error so far.

The black wire from the ferrite rod ant should go to common (+) positive rail.

are all those original resistors within spec? I had to replace them on my radio, some had drifted beyond their original value.

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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Feb Thu 15, 2018 5:12 am 
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UPDATE!!!

Looking at the schematic in the book earlier today I noticed an error.

C4 .005uf ceramic cap was missing from the original print so I did a complete overhaul of the diagram. The radio will not work without this cap.

This should solve some of the issues.

Edit:
Thanks Chas for spotting that (senior moment) should be C4

it has been corrected.


Attachments:
508 SCHEMATIC-(Updated) (800).jpg
508 SCHEMATIC-(Updated) (800).jpg [ 38.33 KiB | Viewed 781 times ]

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Last edited by Rocco53 on Feb Fri 16, 2018 8:14 pm, edited 1 time in total.
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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Feb Fri 16, 2018 2:20 pm 
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Wow!

Thank you all for the tips, and esp. to Rocco for the time spent on the diagram update! We had wondered about the extra cap. LOL ... Kinda felt like the handful of extra nuts and bolts left after working on the car :)

We'll get on it asap, and report back with results.


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 Post subject: Re: Graymark 508 - "Boys Radio" ┐(´д`)┌
PostPosted: Feb Fri 16, 2018 4:45 pm 
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Location: S. Dartmouth MA 02748-1225 USA
Interestingly, drawing then re-drawing the schematic, that is as long as the drawing remains correct. It will become obvious what each and every component is doing.

A boys radio is not unlike the 20's era reflex radios, each and every component is vital.

Yet consider when they were designed and made, late 50's I recall bicycling 6 miles to a large department store to buy my first radio a Boys two transistor radio that worked so great withing viewing distance of the radio towers. Back home I could barely hear one station.
Then, the radio was $2.95, other stores had similar radios from $4.95 to $9.95.

Considering the store is marking up 40%, the distributor another 10%, factory profiting another 50 to 90% its easy to see the radio probably cost less than 50 cents to make.

And we wonder about the quality of the parts, no question bottom of the barrel...

Rocco53, exchange the start/finish of one winding on the coupling transformer T3 only. Turning around the transformer will exchange the ratio but not the "polarity" If this is a radio on a circuit board then turning it around is the only option unless the terminals or board are labeled such that the transformer fits but one way. The drawing seems to indicate a step-up from the transistor to the detector diode as well as marker dots for the primary winding.

Umm, the drawing now has two "C5's" :)

Chas


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