stock radio question
Thread Starter
Advanced
Joined: Jul 2015
Posts: 98
Likes: 1
From: Bayville New Jersey
stock radio question
on my 76 radio was working as perfect as a 76 could work but now I have just a very faint sound you can barely hear at full volume. checked antenna it;s ok now what to look for
Instructor
Joined: Jan 2009
Posts: 123
Likes: 2
From: Simpsonville SC
Your description is atypical of failed speakers. There's at least one other post on here like yours and the failed speakers were confirmed.
You are hearing sound when placing the radio at full volume because the transformer laminations in the loading coils inside the radio are vibrating.
To confirm this place any type of speaker across one pair of the green and black speaker leads. If the sound returns, call Greg Thompson at 18777802861 for a correct set of aftermarket replacement speakers made for that radio. They work very well!
Use correct speakers as the internal Delco audio amplifier modules are unique in 76's and rare. You don't want to strain them to failure! No, I'm not referring to the dual DS-501 transistors on the convector for anyone thinking that.
The good news is that your radio is probably still working correctly.
You are hearing sound when placing the radio at full volume because the transformer laminations in the loading coils inside the radio are vibrating.
To confirm this place any type of speaker across one pair of the green and black speaker leads. If the sound returns, call Greg Thompson at 18777802861 for a correct set of aftermarket replacement speakers made for that radio. They work very well!
Use correct speakers as the internal Delco audio amplifier modules are unique in 76's and rare. You don't want to strain them to failure! No, I'm not referring to the dual DS-501 transistors on the convector for anyone thinking that.
The good news is that your radio is probably still working correctly.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Yes it does, but it's not that hard of a job...
Click on the pdf at this link and it'll walk you through how to get the pad out. You need to remove the right visor, right pillar post, right lower dash pad and then the center dash bezel. Once you get to this point, remove the upper. When you go back you might wish to add some length to the lh speaker harness, it makes the re-install a little easier.
Willcox
1968-1977-corvette-dash-pad-remove-and-install-instructions
Click on the pdf at this link and it'll walk you through how to get the pad out. You need to remove the right visor, right pillar post, right lower dash pad and then the center dash bezel. Once you get to this point, remove the upper. When you go back you might wish to add some length to the lh speaker harness, it makes the re-install a little easier.
Willcox
1968-1977-corvette-dash-pad-remove-and-install-instructions
Instructor
Joined: Jan 2009
Posts: 123
Likes: 2
From: Simpsonville SC
Yes it does, but it's not that hard of a job...
Click on the pdf at this link and it'll walk you through how to get the pad out. You need to remove the right visor, right pillar post, right lower dash pad and then the center dash bezel. Once you get to this point, remove the upper. When you go back you might wish to add some length to the lh speaker harness, it makes the re-install a little easier.
Willcox
1968-1977-corvette-dash-pad-remove-and-install-instructions
Click on the pdf at this link and it'll walk you through how to get the pad out. You need to remove the right visor, right pillar post, right lower dash pad and then the center dash bezel. Once you get to this point, remove the upper. When you go back you might wish to add some length to the lh speaker harness, it makes the re-install a little easier.
Willcox
1968-1977-corvette-dash-pad-remove-and-install-instructions
A very nice and thorough and helpful collection of information on your site. Thanks for sharing the bliss and well done!
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
It could be failed speaker[s]. But, if you have a stereo unit, and sound is weak on both sides, speaker problems would be very rare.
You also could have a failed pre-amp section in the radio head or a problem with the 'convector' (the aluminum heat sink with either 1 (mono) or 2 (stereo) transistors on it that lives behind the right-side dash pad). The convector is the final stage of amplification; if it is not boosting the pre-amp signal, the sound will be very weak.
You also could have a failed pre-amp section in the radio head or a problem with the 'convector' (the aluminum heat sink with either 1 (mono) or 2 (stereo) transistors on it that lives behind the right-side dash pad). The convector is the final stage of amplification; if it is not boosting the pre-amp signal, the sound will be very weak.
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
1970's technology wasn't "plug n play", sorry to say. Everything was discrete components on a circuit board and maybe a few more complex solid state components. And, the 'replacement' circuits/parts don't exist anymore.
There are folks who actually repair these things and that's who you would need to get the radio to so that it could be diagnosed and have problem component[s] replaced.
Jerry_the_Radio_guy is one of those folks and he is on this Forum occasionally. I don't have his contact info, but you can do a search on his 'tag' and find it from there. Others may chime in with that info or similar info on other good Delco radio repair folks.
There are folks who actually repair these things and that's who you would need to get the radio to so that it could be diagnosed and have problem component[s] replaced.
Jerry_the_Radio_guy is one of those folks and he is on this Forum occasionally. I don't have his contact info, but you can do a search on his 'tag' and find it from there. Others may chime in with that info or similar info on other good Delco radio repair folks.
Burning Brakes
Joined: Dec 2006
Posts: 973
Likes: 85
From: Hoopeston, Illinois
Your description is atypical of failed speakers. There's at least one other post on here like yours and the failed speakers were confirmed.
You are hearing sound when placing the radio at full volume because the transformer laminations in the loading coils inside the radio are vibrating.
To confirm this place any type of speaker across one pair of the green and black speaker leads. If the sound returns, call Greg Thompson at 18777802861 for a correct set of aftermarket replacement speakers made for that radio. They work very well!
Use correct speakers as the internal Delco audio amplifier modules are unique in 76's and rare. You don't want to strain them to failure! No, I'm not referring to the dual DS-501 transistors on the convector for anyone thinking that.
The good news is that your radio is probably still working correctly.
You are hearing sound when placing the radio at full volume because the transformer laminations in the loading coils inside the radio are vibrating.
To confirm this place any type of speaker across one pair of the green and black speaker leads. If the sound returns, call Greg Thompson at 18777802861 for a correct set of aftermarket replacement speakers made for that radio. They work very well!
Use correct speakers as the internal Delco audio amplifier modules are unique in 76's and rare. You don't want to strain them to failure! No, I'm not referring to the dual DS-501 transistors on the convector for anyone thinking that.
The good news is that your radio is probably still working correctly.
I was one of those guys! I changed both speakers just like Jerry said and it corrected the problem.
George
Thread Starter
Advanced
Joined: Jul 2015
Posts: 98
Likes: 1
From: Bayville New Jersey
Instructor
Joined: Jan 2009
Posts: 123
Likes: 2
From: Simpsonville SC
Test it first. If I'm wrong, you won't have strained yourself pulling the dash.
Here's the easy way to test: unplug both speakers. Take a 1.5 volt DC battery (which is the voltage from the radio that is normally measurable on each speaker anyway for a stereo) and touch the batteries + and - ends to the green and black leads of one of the speakers. You should hear a thump sound if the speaker is good. Do the same with the other speaker. Polarity of the battery is not important.
No thump, no good.
The black liquid tape sealant over the voice coil to flexible terminal wires on the front of the speaker hardens up. Then the volume gets turned up and the extremely thin coil wires shear off. Dead speaker.
Other times the carbon wire under that black goop breaks down due to moisture and turns to green powder. No wire left. Dead speaker. :-)
Rejoining the real world for a little while so will check back to see if you had luck when we get back.
PS: HI George! I remember.
Thanks!
Thread Starter
Advanced
Joined: Jul 2015
Posts: 98
Likes: 1
From: Bayville New Jersey
thanks car show Saturday so looks like Sunday to jump into it. it looks like just taking the dash pad out will e xpose the speakers but guess according to Wilcox (is that like according to Hoyle) there is a little more involved
in the kick panel was that originally for speakers also
in the kick panel was that originally for speakers also
Instructor
Joined: Jan 2009
Posts: 123
Likes: 2
From: Simpsonville SC
thanks car show Saturday so looks like Sunday to jump into it. it looks like just taking the dash pad out will e xpose the speakers but guess according to Wilcox (is that like according to Hoyle) there is a little more involved
in the kick panel was that originally for speakers also
in the kick panel was that originally for speakers also
Both Wilcox and Hoyle will remind you that it's a Corvette and therefore always "a little more involved".
If I'm following your question correctly then yes, 68 and 69's have 4X10" speakers in the kick panels, none in the dash.
They improved the mid-range and bass marginally over the 4X6"'s in your dash. The setup in my pace car had stock 6X9's in the rear and that combination of 4X6 and 6X9 was pretty good. The larger speakers move a lot more air at the lower frequencies. And they were closer to ear level like you have.
Delco kick panel speakers are OK if your ears are at ankle level. GRIN Good bass speakers in the panels help because higher frequencies are more directional and low frequencies will saturate. There are only so many watts available in those old radios and how you distribute them is important.
Hope that is useful and in line with your question. Decades ago I designed speakers for use by the deaf and had access to ElectroVoice engineers and test equipment (and an anechic chamber). The moral was keep it simple and efficient in the environment (and affordable).
And yes, your radio and any of the 68-72 stereos can drive a total of four speakers as long as the DC bias on the speaker lines is re-adjusted downward about 0.25 volts!
Thread Starter
Advanced
Joined: Jul 2015
Posts: 98
Likes: 1
From: Bayville New Jersey
Both Wilcox and Hoyle will remind you that it's a Corvette and therefore always "a little more involved".
If I'm following your question correctly then yes, 68 and 69's have 4X10" speakers in the kick panels, none in the dash.
They improved the mid-range and bass marginally over the 4X6"'s in your dash. The setup in my pace car had stock 6X9's in the rear and that combination of 4X6 and 6X9 was pretty good. The larger speakers move a lot more air at the lower frequencies. And they were closer to ear level like you have.
Delco kick panel speakers are OK if your ears are at ankle level. GRIN Good bass speakers in the panels help because higher frequencies are more directional and low frequencies will saturate. There are only so many watts available in those old radios and how you distribute them is important.
Hope that is useful and in line with your question. Decades ago I designed speakers for use by the deaf and had access to ElectroVoice engineers and test equipment (and an anechic chamber). The moral was keep it simple and efficient in the environment (and affordable).
And yes, your radio and any of the 68-72 stereos can drive a total of four speakers as long as the DC bias on the speaker lines is re-adjusted downward about 0.25 volts!
If I'm following your question correctly then yes, 68 and 69's have 4X10" speakers in the kick panels, none in the dash.
They improved the mid-range and bass marginally over the 4X6"'s in your dash. The setup in my pace car had stock 6X9's in the rear and that combination of 4X6 and 6X9 was pretty good. The larger speakers move a lot more air at the lower frequencies. And they were closer to ear level like you have.
Delco kick panel speakers are OK if your ears are at ankle level. GRIN Good bass speakers in the panels help because higher frequencies are more directional and low frequencies will saturate. There are only so many watts available in those old radios and how you distribute them is important.
Hope that is useful and in line with your question. Decades ago I designed speakers for use by the deaf and had access to ElectroVoice engineers and test equipment (and an anechic chamber). The moral was keep it simple and efficient in the environment (and affordable).
And yes, your radio and any of the 68-72 stereos can drive a total of four speakers as long as the DC bias on the speaker lines is re-adjusted downward about 0.25 volts!
so after I get it fixed what speakers should I put in the kick panels so my feet can hear better