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 Post subject: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 08, 2020 12:49 am 
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My first post! I searched the entire forum and found nothing for this radio. It's a Standard SR-G901 MW SW 7 transistor radio. I got it from my uncle many years ago and I believe he bought it in Japan, in the 60's. It will work, sort of, but the volume is very low. For some reason (no clue why), I removed the earphone jack and just wrapped the two black and red wires together. I swear I put that jack somewhere... but it's been nearly 50 years now!
I have some electronics troubleshooting experience but it's in 80's 90's slot machines. I'm hoping someone might know about this, and direct me to a schematic or just let me know where to start. It appears to have electrolytic caps inside and I'm wondering if those (or some) need to be replaced. I added some shots of the radio. And yes, it's not symmetrical, as if it was just "cut" wrong.
Hope this all makes sense.


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 08, 2020 1:21 pm 
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Location: Mountains of Mourne. Ireland.
SOP (standard operating procedure) is to replace the electrolytic capacitors as a first step.
Don't go looking for Electrolytic capacitors that are rated at 6V and 10V

The Voltage rating of a capacitor is how much Juice that it can handle - this can be increased.

Modern day electrolytic capacitors have become so much smaller since the 1960s
viewtopic.php?p=3029559#p3029559

------------

MW medium wave is how the AM broadcast band is known in many countries outside of the US

The two little triangles on the dial are CD (CONELRAD) marks aka duck and cover and Officially used from 1953 to 1963

Image
https://en.wikipedia.org/wiki/CONELRAD


Welcome aboard Skater-dood... :)
Greg.


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 08, 2020 5:05 pm 
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Location: Mountains of Mourne. Ireland.
Standard model SR-G900L (Tiny Pal) LW long-wave & MW

Image

Image
https://www.radiomuseum.org/r/standard_ ... g900l.html


If your set employs the same chassis, the schematic pages can be download for free.

Downloading from radiomuseum.org (non members).
Click a schematic page from the right-hand scrolling window, then again in the main center window.
A download link page will be emailed to you immediately.
You can only download three pages a day + up to a maximum of ten every 30 days.

If you experience any downloading difficulties... see this→ viewtopic.php?p=2571007#p2570117


:) Greg.
oh... if the tuning is scratchy/crackly, do not spray any liquid (magic spray) anywhere near the clear plastic Polyvaricon tuning capacitor... never ever. lol


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 08, 2020 6:37 pm 
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Thanks for that information Greg. As for my username - I used to compete in short track speed skating, on ice. Now I'm on long in-line skates, for fun and fitness. Sadly our short track club folded about 6 years ago. One good thing: it's free to skate on wheels since I don't need a rink!

I never know about those arrows for the emergency stations. I remember drop drills!
I attached a shot of the inside. It appears identical, although for some reason I have one yellow wire protruding just to the left of the transformer. It's just one clean wire - looks like its always been that way.
I actually have a stock of multiple value "through hole" electrolytic caps that I just bought, and you're right... they're tiny. When I started dabbling again in electronics, I was amazed at SMT parts! I replaced a SMT diode in my multimeter a year ago. That was challenging; I almost couldn't handle it, but I'm good at feeling my way with tiny parts, and it worked.
I'll post back on my progress with the radio.
Thanks again!
~Mark


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 08, 2020 7:35 pm 
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The lead spacing of today's Electrolytics rated at 50V 35V or 25V will be okay to use.
Short unconnected wires found at times in sets may be a left-over from final factory testing.

If it's working don't fix it.

Eat Sleep Skate
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Tony Hawk, back in the day.


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 08, 2020 7:50 pm 
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Sounds good, thanks.
Funny I never skate boarded. I'd probably be ok at it, but I always loved the ice. Here's me, back in the day... well 6 years ago now. But the inline roller skating still keeps me fit. Have to keep my youthful look for those pretty women on the bike trails. Ha!


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Last edited by shortrackskater on Dec Wed 09, 2020 7:04 pm, edited 2 times in total.
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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 08, 2020 8:00 pm 
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yup... one of my ex-girlfriends had a thing about men in Spandex... :)

We should probably not pursue the reasons. lol
Greg.


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 08, 2020 11:15 pm 
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egg wrote:
yup... one of my ex-girlfriends had a thing about men in Spandex... :)

We should probably not pursue the reasons. lol
Greg.


Haha! Yes I'd definitely NOT wear that suit when I'm out on the river trails!!!
Only on ice, where everyone else wore the same stuff. If I'm inline skating, it's cycling shorts and a regular jersey or T shirt. :)


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Thu 17, 2020 1:32 am 
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Ok I'm just now starting this. Newbie question: can I replace a 30uf 3volt cap with a 33uf 16v? I know that voltage is ok, but not sure how much it will make a difference. I'm sure this comes up frequently. Many of my new replacement caps are off just a few micro-farads.

UPDATE: I did just find a post stating some of the values are no longer available and to "round up or down" so I'm going to stick this one in!


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Thu 17, 2020 4:43 am 
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You could replace a 30uF with a 10, 22, 33, or 47 and it most likely wouldn't make a difference as to which one was used in most portable Transistor receivers. the only somewhat critical value is the Electrolytic going to the VC wiper. Usually a small value and should be replaced with similar.

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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Thu 17, 2020 5:46 am 
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Good to know. Thank you. :)


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Sat 19, 2020 10:14 pm 
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This is my first posting on this forum. I hope I'm doing this correctly.
My experience with old transistor radios is in agreement with the previous post about replacing the electrolytic caps. In
regards to your SR-D901 there are two things I would check. First- you mentioned that you removed the jack and wrapped the wires together. Most earphone jacks have both the audio output signal and ground wires attached. You need to be sure that you do not have the audio out signal shorted to ground. Second- I have seen many small electrolytic coupling caps (10 mfd down to .47) open between the wiper of the volume control and the base of the first audio amp. This will certainly case low or no audio out.


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Sun 20, 2020 2:02 am 
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Thanks Transistor Fan!
I barely know what I'm doing here.
Here's a shot of the connections to where the earphone plug was. I still have no clue where it went or why it's out! This radio was basically sitting nearly 50 years now.
I think I see, to the left where the third wire went. So I'm not sure what should be where here. And after what you said about changing the coupling cap (s) first, I feel like I shouldn't just be shotgunning all the electrolytic caps. There's no space here to work and it took some time to get the first one out and the new one in.


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Sun 20, 2020 3:45 am 
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TransistorFan welcome to the board! The Electrolytic cap going to the VC wiper is usually the prime culprit in a "dead" receiver, but it's good to also replace the (normally) other three as well, so the circuit will work as well as it should.

shortrackskater, you stated in the OP that the radio was working even with those two earphone jack wires D/C. If you don't plan on putting another earphone jack in, I would suggest unsoldering those wires.

How has your progress been on further recapping?

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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Sun 20, 2020 5:14 am 
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Shortrackskater- your picture shows that there has been some work done on this board (probably yours). A schematic would be great to have but I doubt that one is available. So it may come down to a bit of luck and patience on your part. Fifties is correct in that a full re-cap would be a good thing to start with. You state "barely know what I'm doing here". Do you have the equipment necessary to do a re-cap? It's really not that hard if you have a small soldering iron and some solder wick. Without a schematic you need to take your time and remove one cap at a time. Be sure to note the polarity of each cap before you remove it. Your radio has just one audio output transformer. The secondary (or output) of that transformer will probably have two connections. One is typically connected to ground (which on most transistor radios is a positive ground). The other connection usually goes to the earphone jack and from there out to the speaker. You should be able to hook the speaker directly to the two transformer terminals. I would try that before doing any re-capping to see if you hear anything when you turn on the power. if you hear a click or a rushing sound your speaker is probably connected correctly. If the audio is still weak- you can start the re-cap.


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Sun 20, 2020 5:50 pm 
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Fifties - With those two wires twisted together, I got very low audio and could receive the more powerful stations in the LA area, but just barely enough to hear.
That's why I stopped at one cap, well... plus I'm still recovering from major surgery.

(I had a c3 - c7 discectomy/fusion [neck] and the recovery has been 6 weeks so far. I can finally drive. This has been a little rough!)

I did want to put an earphone jack back in but dammed if I can find it. I think I stated earlier I put it somewhere "safe" 49 years ago! I just hate that empty square in the side, but for now I will just unsolder the wires. It just bothered me that, with the red and navy wires twisted together, I got something. Without them, there was no output whatsoever. Comments on this for troubleshooting?

Transistor Fan - Sorry I didn't meant to sound completely inexperienced. I do have a decent soldering station, heat gun, solder wick, etc... I've primarily worked on slot machines from the 80's and 90's and recapped a few old CRT monitors. I do have the schematic for the G9001 which appears to be an identical radio, circuitry that is. I've never worked on this other than messing with the earphone jack when I was maybe 10 years old. My uncle bought this in Japan so there's a slight chance he may opened it up, but I doubt it. The circuit board is "clean" but it looks like they just left flux in there after soldering all the parts on at the factory. Maybe someone else with another similar radio can confirm this?

Let me get my act together and try the steps listed. I do have a capacitor tester but I don't know if it's wise to put a tested "good" one back in. Do electrolytic cap values slowly go out of tolerance or can they just "die" all of a sudden? In the past, I've identified some caps on CRT's that were visually bad: bulging, etc.
Again I apologize for sounding confused! I moderate on a slot machine forum with 7000 members, so I deal with people like me! haha
~mark


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Sun 20, 2020 7:33 pm 
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shortrackskater wrote:
Fifties - With those two wires twisted together, I got very low audio and could receive the more powerful stations in the LA area, but just barely enough to hear.
That's why I stopped at one cap, well... plus I'm still recovering from major surgery.

I did want to put an earphone jack back in but dammed if I can find it. I think I stated earlier I put it somewhere "safe" 49 years ago! I just hate that empty square in the side, but for now I will just unsolder the wires. It just bothered me that, with the red and navy wires twisted together, I got something. Without them, there was no output whatsoever. Comments on this for troubleshooting?

With the wires twisted together, you get a capacitive coupling. Leave them be until you can complete the recap, then advise. Have you tried connecting them together?

You can get a replacement mono earphone jack from a junked Transistor radio. IDK if anyone sells them just by themselves anymore. Or you could install a large head short body machine screw (or small head + washer) into the jack hole.

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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Mon 21, 2020 1:07 am 
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fifties wrote:

With the wires twisted together, you get a capacitive coupling. Leave them be until you can complete the recap, then advise. Have you tried connecting them together?
[/quote]

Do you mean leave them connected or apart? When they're connected I get that low volume reception of higher-watt stations.
Thank you, again!


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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Mon 21, 2020 5:00 am 
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shortrackskater wrote:
fifties wrote:

With the wires twisted together, you get a capacitive coupling. Leave them be until you can complete the recap, then advise. Have you tried connecting them together?


Do you mean leave them connected or apart? When they're connected I get that low volume reception of higher-watt stations.
Thank you, again!

I misunderstood, and thought you meant that the two wires were twisted around each other, but not electrically connected together, which now appears to be the case. Yes, connect them together and tape the bare wiring. Then when you are able, finish doing the recap and post your results.

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 Post subject: Re: Standard SR-G901 7 transistor radio - low volume
PostPosted: Dec Tue 22, 2020 5:27 am 
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Ok this took some time. I had soldered a jumper between the points where the earphone wires were twisted together, but managed to create a short by accident. The radio was still getting power, even with the power off! There's so little space to work on the circuit board.
I removed my jumper and just soldered in a very small piece of wire between the two spots. So far I've only replaced that 30 uf 3v cap. When powered on I now get loud volume on stations at the very high end. As you tune down in frequency, the signal/amplitude drops.
Should I just keep replacing the electrolytic caps?


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