2mnyvets

About three years ago, I bought a 1973 454 4 speed car. I am in the final stages of a frame off and need some help. The car came without a radio. I found an OEM stereo radio from a 1973 and would like to install it.
First question: where does the convector (aka heat sink/amplifier/transistor set) mount? I thought this would be easy to find, but cannot find a picture of a car with an original stereo radio. Can anyone help? The AIM manual is not very clear.
Second question: The AIM manual references an “adapter”. One post said that the adapter turns the stereo indicator light on in the main unit. Is this the case or is it mounting hardware? Does anyone have a picture of it? Do I need it?
Third question: When I bought the car, it was partially disassembled and the PO was trying to replace the wiring harness. He bought a lot of new parts which he passed on to me. He included a set of Custom Autosound CAM 462 30 watt 4 OHM speakers that are mounted in the dash pad. I believe I need 8 OHMs for this radio. Your opinions on whether I would be better off keeping these speakers and adding 4 OHM speakers in the kick panels or replacing the two in the dash pad with higher quality 8 OHM. If so, what is the highest wattage you would recommend for the stock stereo?

Blue73Shark

Here is a picture showing the location of the convector (transistor) on my 1973. My radio is a mono version but the mounting location is the same for a stereo one.
For a stock radio, the speakers were 8 ohms. Using speakers with less will overdrive the amplifier. Two 4 ohm speakers wired in series will give you 8 ohms impedance.


Fran

blue by you

Fyi they make 2 different amps for the stock radio one is for the mono and one for the stereo if don't have one just make sure you get the correct one

Scrrem

I am performing this now on my 69. The mono radio just has a heat sink as pictured in above thread. if you have a stereo radio it has an additional multiplexer unit that mounts to the underside of the dash pad support. I found I needed different speaker harnesses to go from mono to stereo and waiting on those now. I was told that with the OEM radio that 8 ohm speakers is what you want to use but is your radio mono or stereo? The wiring coming out the back should tell you. If your speaker wire has three prongs, it' mono and two prongs is stereo.
Rich

2mnyvets

thanks for your reply My radio is a stereo and I do have the 2 transistor convector with the six wires. Are you installing a stereo radio and if so do you have a wiring diagram? Do I need an adapter and how is that wired into the radio? Who are you getting the harness from?

As far as the 8 ohm speakers, I can do that two ways; I can replace the 4 ohm speakers in the dash with 8 ohm speakers, or I can add another set of 4 ohm speakers in the kick panels similar to where they are in your 69, and wire them in series. The advantage is that I have 4 speakers. The disadvantage is I don't think my speakers are "high quality".

I am not sure about the plug. My radio has three plugs. A three pronged flat power/light plug with yellow, black and grey wires, a 6 terminal flat plug that connects to the convector with two sets of yellow, blue and green wires, and a three pronged triangular plug that I assume goes to the speakers. The plug from the radio has blue, green and black wires. The plug is female but the spades inside the plug are male.

An NCRS post indicates the 1973 radio may be unique. My 73 has 2 transistors and a large heat sink. I found a picture of a 69 stereo. That radio had two heat sinks, each with a single transistor. One of the heat sinks had two transformers; one on either side of the transistor. Is this what yours looks like?

Scrrem

Yes it sounds like our radios are similar, the radio my 69 had in it was from a 71or 72. I don't really know because the sticker has come off but it was a mono radio. The radio I am installing is the stereo and is as you descried but splits the speaker connections. The wiring harness I am going to fab up from parts I found at Volunteer Vette Products. Here is a wiring diagram I was able to find on this forum that may help.
Rich

7T1vette

You want to have at least 8 ohms speaker impedance on R and L side of the radio output. If you install 4 ohm speakers (only), you run the risk of frying the radio amp if you turn up the volume. You can install 8 ohm speakers in the dash; or you can install 4 ohm speakers in dash and kick-panel areas and wire them in SERIES to get 8 ohm total impedance. That method works very well and sounds so much better than only the dash speakers.

2mnyvets

Some closure for future readers:

Blue 73 Shark
Thanks for the picture. Unfortunately, the (later?) 73 stereo has a single convector that is three to four times larger than those used in previous years. My convector will not fit in that location. Unless someone else has a 73 or possibly 74 picture, I am just going to install the passenger dash pad and find an open spot behind it. As a side note, the 73 AIM shows the older style radio which created a lot of the confusion on my part. An NCRS forum post alludes to a radio change mid production 1973.

7T1Vette
Thanks. I understand that I have to get 8 OHMs of speaker resistance per channel. The question is "am I better off doing it with 2 each 4 OHM speakers of lower quality or a single 8 OHM speaker". My main concern was having way to large a speaker for the radio in either case. If I hook the speakers in series, I will have 60 watts of speaker capacity running at 16 watts RMS. With "good" 8 OHM speakers the smallest I found was about 80 watts. At this point, I am probably going to add an additional set in the kick panels. I am not that much of an audiophile that the possible decrease in fidelity is going to matter and that is my cheaper alternative.

Scrrem
I really appreciate all your help. I have come to the conclusion that the 73 radio is substantially different than the 69 so the wiring diagram does not work for my vehicle. Based on pictures on E-bay it looks like I have all the parts.

72ragtop

check with turnswitch.com. they make a 10 ohm replacement speaker for 70-82 vettes. Handle up to 40 watts, which isnt a problem with stock system.$90 pr. Installed them with my stock am/fm stereo in my 72 that has been restored/rebuilt.

7T1vette

There is no relationship between the size of the speaker and its impedance. Because of the way the dash speakers are mounted, you need to retain [tweeter] speakers of the 4" x 6" size. Doing anything else will cause you significant problems with installation.

You can install larger 4 ohm speakers (mid-range/bass) in the kick-panel areas. Separating the dash and kick-panel speakers will make a world of difference in the depth and quality of the radio output.

You might go to onlinecarstereo.com and check out the many brands of speakers and their various options. I will tell you that 8 ohm car speakers are relatively difficult to find...which makes the two speaker-8 ohm total approach a very good one.

The Delco head has only 16 watts RMS output power. That's plenty for inside a car; but you don't want to put high-power (low efficiency) speakers in your car, as they are not a good choice for that low-powered radio. Select speakers that are 4 ohm and have power capability in the 30 -50 watt range. Select a good brand name and they should do you good service. Choose single stage tweeters only (500Hz- 5000Hz, for example); do NOT get dual-stage mids/highs tweeters which will reproduce sounds in the 200Hz range.

For the mid/bass speakers, something in the 50 watt (100 watt max) range would be good. Dual range (mid/bass) speakers are what you want with low frequency capability in the area of 50Hz. You will not get great bass response from 6" speakers, but music sounds will still be reproduced reasonably well except for sub-bass sounds.

Wire the two speakers on each side in SERIES so that impedance is additive, yielding 8 ohms.

P.S. You do not have to cut holes in the stock kick-panel covers to mount the speakers (if you do not wish to). You can mount them to the metal structural ribbing behind that panel and just place the panel over the speakers. If you mount the speakers to the kick-panels, you will also have to mount the panels to those structural ribs, or you will get a lot of vibration with 'floppy' speakers.

Richard454

I would not run two different kind speakers in a series-

Only of you are passively crossing them over- like accomplished in a 2 way two speaker. In this case the woofer/midrange and tweeter use a capacitor (1 order x-crossover) and/or coil (2nd order x-over) to separate the highs and lows to each speaker.

Connecting two different speakers in a series- mainly do to different efficiencies but also affected by the different impedance curve - one speaker will play louder than the other- and there is no easy way to balance them out.

Just go w/ 2 of the same size- same speaker.

Richard

7T1vette

If you purchase tweeters that cannot respond to low frequencies, you don't need to bother with putting band-pass filters on it. Hooking the two speakers in series presents absolutely no problem for your Delco radio.

Richard454

I didn't say hooking two speakers to one channel of a OEM radio was a problem- they just should be the same model...

The main reason being one speaker will more than likely play louder than the other one and attenuation of that speaker will be problematic.

Second a speaker is rated at a NOMINAL Impedance- Impedance varies widely over the audio spectrum-And depending on the mechanical damping of the speaker design, impedance will either show a peak at the resonant frequency or twin peaks either side of resonance. It's doubtful you'll be able to match two different speakers impedance curves thus they will not play well with each other.... Speaker manufacturers spend thousands of hours trying to accomplish that perfect match....


And please- before you start calling BS- you probably need to re-read your posts.

Richard

7T1vette

If you pick speakers (regardless of brand) that have the same general capabilities and quality, there will be no problem. Remember, Richard, we are talking about sound quality INSIDE the passenger compartment of a Corvette!! There is nothing 'acoustically correct" about that environment. One should be trying to get DECENT audio....not sound-room perfection.

2mnyvets

7T1 Vette, the tweeters I was able to locate are not 4x6. Do you know of any that will fit in the dash without manufacturing a bracket? If not I will probably go with 4 each 2 way speakers.

Richard454, in a prior post you mentioned distortion issues if the voltage is lowered. If I wire speakers in series, than the voltage to each is about half of what it would normally be. I assume this will affect volume but will it also affect performance? What actually causes the speaker to modulate? Is it modulating current, voltage or both?

BOTH The mixing speaker issue just became moot. I bench tested the radio yesterday and it didn't sound right. One of the new speakers had an anomaly in the high frequency cone, so I will be replacing 4 speakers.

The Autosound speakers were mounted in the dash pad using the OEM bracket with the X brace. The bars of the brace dented the surround on the tweeter cone. (they also dented the surround on the woofer cone, but I assume that is ok) I assume these should not contact. Is that correct? I will make a gasket from mass loaded vinyl to provide clearance.

At this point, I am looking at the POLK DB461 speakers mainly because a previous poster said they fit his 81 "perfectly". They seem to be reasonable quality. As a second choice I am considering Kenwood KFC 4675C. One poster had issues installing these but the issue appears to be the contact with the X brace and i think I can remedy this. ( I suspect the Polks may have the same issue, but it may have gone unnoticed) Your thoughts?

7T1vette

FYI--

When I replaced my dash speakers, I chose some with plastic frames having several mounting holes already formed in them. Once received, I found that NONE of them fit the C3 dash pad mounting bolts.

However, because the frame was plastic, I was able to use a pencil-tip soldering iron to 'burn' new mounting holes in the speaker frames that would fit/install just fine. Worked well...no problems.

For multiple speaker output (on single line), the power output from the radio amp (volts x amps) is distributed proportionally by impedance of the speakers. If you have two 4 ohm speakers in series, 1/2 of the output signal will be sent to each speaker. The power actually used will be 'as required' by that speaker (function of frequencies reproduced). Very little electrical power will be absorbed by the tweeters...but sound power will be appropriate to that produced by your mid/bass speaker's sound level.

Richard454

That's just not true...

In a simple circuit- yes- you'd apply Kirchoff's Voltage Law which dictates the sum of the voltages within a circuit must equate to zero. So the higher impedance would see more voltage- same impedance each would see half.


A loudspeaker isn't a simple resistor (resistance) - it's an electroacoustical-mechanical device. And a speaker presents a complex impedance which varies with frequency and power level. "Complex" here means impedance is a vector quantity which has both phase & magnitude.



2mnyvets-

"If I wire speakers in series, than the voltage to each is about half of what it would normally be. I assume this will affect volume but will it also affect performance? What actually causes the speaker to modulate? Is it modulating current, voltage or both?"

Speakers are 'moved' by AC current- at varying hertz AKA cycles or frequency. Plug a speaker in the wall outlet of your house and you will get a 60HZ bass hum- till it blows up!! If you connect a speaker to a 1.5 volt DC battery the speaker will move all the way forward and stay there till the power is removed.

Polk speakers are great-I was the manufactures rep for them many years ago... Kenwood- good stuff too- but a little biased because I worked for them as well.

Speakers use to come with plastic spacers to keep the speaker cone from interfering-but I don't think anyone does that anymore- all I've seen is a 4 x 6 to 4" or 3˝" adapters. Make sure the cones does not interfere as you'll get a nasty buzzing sound.

Richard

72ragtop

OP stated he's using stock head unit. Thats why i mentioned the 10ohm speaker from turnswitch.com. direct fit and direct replacement.
Also PM sent to Original Poster.

7T1vette

Except that those 'stock' 10 ohm speakers are essentially junk....same as the REAL stock speakers.

C376FL

The more I read this post the more confused I am. There must be a big change between 73 and 76 radios. I bought a radio that is a stereo and I checked to see if the op took out the convector/ amp when he installed an after market unit. Lucky for me he did not remove it. It is for a stereo, with two transistors. The radio has the six wires that go to the amp. For the speakers there is a plug that comes out of the radio that has two black wires and a light green, and a dark green that split and goes to the speakers, using one connector. In the drawings stereo is totally different from a 76 model. I only had one speaker in the dash, the other one has been removed. It is the one that came in the car new, the part number is the same as in the AIM. The problem is I can't read what ohm it is, it looks like an 8 on it's side. The AIM does not say what ohm the speakers are. The part number on the speaker is #7312421. I am looking just to replace the two in the dash like it was from the start. Some of the speakers I have seen has a cone in the middle, I don't see how they would work because they would hit the housing that the speaker bolts to, if they stick above the speaker at all.I am at a loss. I do do not care about all the hype of a big sound system, just looking to have a radio that came in the car. Thanks for any help