Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Jun Wed 19, 2019 3:47 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 29 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Explorer 888 audio distortion
PostPosted: Dec Mon 31, 2018 6:08 pm 
Member

Joined: Nov Wed 14, 2012 11:29 pm
Posts: 310
Location: Florissant, Mo 63033
To my surprise my daughter got me a cool Emerson Explorer 888 for Christmas. I was going to just leave it as is (as a collectable), but my curiosity got the best of me and I started working on it. I've got it working somewhat. It tunes and plays, but audio is distorted. To get this far I've replaced the Electrolytics, Replaced the .02 on the pot. and replaced the mic. jack. The audio clears up at very low volume. I've tried a few other speakers ass well. The radio is draws 200 ma.

Schematics here: http://antiqueradios.com/forums/viewtopic.php?f=4&t=315704&hilit=888+distorted+audio

Can anyone offer troubleshooting suggestions?

Thanks in advance.

_________________
KD0UYH


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Dec Mon 31, 2018 6:35 pm 
Member
User avatar

Joined: Jan Tue 31, 2012 1:55 am
Posts: 8469
Location: Mountains of Mourne. Ireland.
Sounds like a shorted transistor. An eight transistor radio should draw about 10 to 25mA

Check the earphone jack... and, audio via the earphone jack. If the sound is acceptable, then your trouble is either the speaker or the output stage.

Greg.

oh... always ensure that you are using a fresh battery when trouble shooting... :)


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Dec Mon 31, 2018 6:47 pm 
Member

Joined: Nov Wed 14, 2012 11:29 pm
Posts: 310
Location: Florissant, Mo 63033
Can you advise on how to find a bad transistor? Do I need to pull them and test them? I've got a cheap Harbor Freight multi meter that has a transistor check socket...but I've never used it.

_________________
KD0UYH


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Dec Mon 31, 2018 7:08 pm 
Member
User avatar

Joined: Jan Tue 31, 2012 1:55 am
Posts: 8469
Location: Mountains of Mourne. Ireland.
Output transistor voltages are shown here...
download/file.php?id=168783

Greg.


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Dec Mon 31, 2018 7:17 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13806
Likely the only transistor that can be shorted and set still play even distorted, will be one of the audio outputs. Reading collector to base junction or emitter to base junction is much like reading any B+ rectifier. Readings(test lead reversal) will be dependant on whether transistor is NPN or PNP. On occasion the tr can be shorted collector to emitter, can usually measure for that condition with tr still installed.

You should practice by checking a few guinea pig transistors.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Dec Mon 31, 2018 10:26 pm 
Member

Joined: Nov Wed 14, 2012 11:29 pm
Posts: 310
Location: Florissant, Mo 63033
I pulled out the two output transistors and indeed I'm getting .5 ohms on Q7. So what now? Is it even possible to find a replacement? The only PNPs I have on hand are some 2n3906s.

_________________
KD0UYH


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Dec Mon 31, 2018 11:39 pm 
Member

Joined: Nov Wed 14, 2012 11:29 pm
Posts: 310
Location: Florissant, Mo 63033
Thanks so much guys! I went ahead and took a chance with the 2n3906. Works and sounds great now.

My hats off to ya'll...you just rescued another one!

_________________
KD0UYH


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 1:34 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13806
Congrats!!

Germanium Tr are easy to find, always a dozen or two on ebay. Usually not cheap but if one shops around.

I got lucky in that I have probably a half dozen different SK & ECG units from a long closed radio/TV shop. Currently I need to replace the RF amp(intermittent) & audio driver(noisy) in a GE P-783. Probably wait till next year. :wink:

_________________
Tom


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 3:18 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31682
Location: SoCal, 91387
35Z5 wrote:
Currently I need to replace the RF amp(intermittent) & audio driver(noisy) in a GE P-783. Probably wait till next year. :wink:

What Transistors do you need?

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 4:19 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13806
fifties wrote:
35Z5 wrote:
Currently I need to replace the RF amp(intermittent) & audio driver(noisy) in a GE P-783. Probably wait till next year. :wink:

What Transistors do you need?

Thanks but I'm good to go.

The RF is a ECG126A or I believe SK 3005 that I have both. The audio is SK 3010 that I have as well. That one has been installed but it test fine on both the ancient GE and B&K testers.

Funny part about that radio is it works and fairly well. If you were not interested in anything but locals, average person would never know the difference. The RF amp can be "shocked" into operation by pressing the light button two or three times, then it's good till it sets for a day or two. The audio can be best described as ocean rolling in background, actually can can add atmosphere. Of course the wife is pissed cause I scattered 500 lbs of sand over the den floor. :wink:

_________________
Tom


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 4:32 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31682
Location: SoCal, 91387
Shes' probably pissed because you didn't also add any fake palm trees...

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 4:43 am 
Member

Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5895
Location: Indianapolis, IN
Congrats Deadshort---glad you got it working ! Did you replace both outputs with the 2N3906 transistors ???

35Z5---Better not leave it on too long---that salt water is corrosive...

John


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 4:56 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13806
fifties wrote:
Shes' probably pissed because you didn't also add any fake palm trees...

Well I have the palms, it's the hula girls she's upset over. Was sort of OK till she found they worked at the strip club down on the highway.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 7:33 pm 
Member

Joined: Nov Wed 14, 2012 11:29 pm
Posts: 310
Location: Florissant, Mo 63033
I just replaced the shorted transistor since I had already reinstalled the good germanium transistor. I wasn't sure how much more soldering the trace on the pcb could withstand. I didn't know what to expect with the new transistor so I brought it up slow on the power supply.

It really does work perfectly. Strong volume and "crystal" clear tuning. I tested it last night for selectivity / sensitivity and that is excellent as well (actually better than my full size radios believe it or not). Also my current draw went from 200 ma to barely readable on the amperage scale of my power supply. I think I've just become an 888 fan.

I couldn't be happier and thanks again to everyone that helped on my first transistor project.

Attachment:
20190101_120031.jpg
20190101_120031.jpg [ 27.52 KiB | Viewed 493 times ]

_________________
KD0UYH


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 10:35 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31682
Location: SoCal, 91387
Congrats on your electronic prowess!
Actually this set should perform better than a garden variety AA5; a six Transistor Superhet circuit is the equivalent of a four tube + rectifier AA5.
This set has two extra Transistors in the RF/IF stages, and their contribution is obvious in the resulting performance.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Tue 01, 2019 11:17 pm 
Member

Joined: Nov Wed 14, 2012 11:29 pm
Posts: 310
Location: Florissant, Mo 63033
Yes my "prowess" is that I ask you good folks here at ARF! But I'll never tell my buddies that :lol: Heck they practically fixed it for me!

When you put it that way..(about the extra stages) it makes perfect sense. It's really amazing still, to see the performance of the little radio.

_________________
KD0UYH


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Wed 02, 2019 1:03 am 
Member
User avatar

Joined: Jan Tue 31, 2012 1:55 am
Posts: 8469
Location: Mountains of Mourne. Ireland.
Sand, palms, hula girls and a strip club... :shock:

Do you live in Vice city Tom. Lol
Greg.


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Wed 02, 2019 2:25 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13806
egg wrote:
Sand, palms, hula girls and a strip club... :shock:

Do you live in Vice city Tom. Lol
Greg.


I wish. :wink:

_________________
Tom


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sat 05, 2019 12:12 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4845
Location: Gainesville, Florida
the cheat about tubes is that many are dual purpose. cant say that about early transistors at least not until OP amp. transistors have a single purpose so there may be many more of them than tubes :wink:


Top
 Profile  
 
 Post subject: Re: Explorer 888 audio distortion
PostPosted: Jan Sat 05, 2019 1:47 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31682
Location: SoCal, 91387
tubeAMP wrote:
the cheat about tubes is that many are dual purpose. cant say that about early transistors at least not until OP amp. transistors have a single purpose so there may be many more of them than tubes :wink:

That's not really accurate; they may have been designed for a specific purpose, but can also work just as well in other applications. Many small signal Transistors can be used in high speed switching circuits, as one example.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
Post New Topic Post Reply  [ 29 posts ]  Moderator: Dave Doughty Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 4 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB