Hi All,

I know this topic has been covered a bit on the forum, but can I get a definitive answer from someone?

I am running my original 1970 Delco Mono radio in my vette. I need new speakers (they were missing). The radio case says you myust run 8-10ohm speakers.

The usual big vette parts suppliers sell what they call "oem" type speakers, but they are 4 ohm only.

Can anyone help me with this. Is there a supplier who sells 8-10 ohm 4x6" speakers?.

I want to fit them in the kick panels (not the dash).

Thanks

BB

 

If the radio is mono, tying the speakers together in series, will make 8 ohms.

 

Check out this vendor - http://www.turnswitch.com/

 

The original speakers are indeed 8 ohms (the same as Delco's 10 ohm spec). If you have the mono radio, you have two 8 ohm speakers wired in parallel. That yields an equivalent resistance of 4 ohms at the output transistor of the radio. That is what your radio expects to see normally (4 ohms).

So, you can connect one 4 ohm speaker or add two 8 ohm speakers of any size (one in each kick panel) wired in parallel or you can go to www.turnswitch.com/speakers.htm and install two (8 ohm) 4X6's made for the original installation in the dash or kick panels.

The turnswitch.com speakers are the best solution I've seen in the last 13 years and the only ones I recommend to customers (fwiw).

If you have the stereo model, each channel is expecting to see one 8 ohm speaker and that is what the internal bias control is adjusted to deliver.

Hope that helps...

 

The speaker impedence needs to match the output impedence of the amplifier so that the speaker will draw the correct level of current at full volume. If you put speakers with too little impedence, it will draw too much current at full volume and burn out the amp...it may also distort the sound at levels somewhat less than max output. If you put speakers with too high an impedence [for that amplifier], the volume will be much lower than the amp is capable of producing...but the sound quality will be 'cleaner'.

The early '70s Delco amps had a 10 ohm output impedence. I have hooked 8 ohms to those amps and had no problem with burnout, but did get some distortion near full volume. If you can't find 8 ohm speakers, you can tie two 4-ohm speakers in series and have a set that totals 8 ohm. If you hook 4 ohm speakers to a 10 ohm output, don't turn the volume up very high or the amplifier will become "toast" .

 

Hi Guys,

Thanks for the detailed information. I will check out TURNSWITCH and get some 8 ohm babies for my vette!

On a related note, a friend has the same radio in his '71, but is missing the rectifier, amplifier, multiplier, multiplexer (what ever you like to call it!). They are hard to get hold off. Get sold pretty quickly on ebay.

Does anyone know if they can be built up from components available through a electronics store (ie) a heatsink, correct transistor, wires?

It seems like a pretty straight forward design.

Cheers,

BB

 

What I highlighted in bold is very interesting to me, I am an electronics technologist ( you do a design engineers job for lower pay ) and what you said there is true. I am impressed because especially when it comes to electrical or electronics as no one really has clue but you have definitely impressed me.

I run house sealers, 8 ohm Bose 301's straight off a fairly good amp. The amp is only 4 ohm output and there is no 8 ohm switch. I have been running this setup for ten years and it sounds unbelievable.

To make matters worse for the poor amp I am running 4 ohm speakers from the front channel in the dash and 5 in. 4 ohm speakers in the kick and it still sounds killer and like I said I have been running this for 10 years.

Now forget about the Chinese but designing electronic equipment in North America is kinda funny. You have to say to yourself " What happens if a 1 armed monkey with a screw driver walks across the floor and slips on a banana peel and sticks that screw driver right through this panel and trips the alarm "

Then you make it so this will not be able to happen. A good 1/3 of design is trying to make it idiot proof which is no small job,

So to make a long story short ( again dismiss the Chinese ) a half decent amp is already ready for you to plug in the wrong impedance speakers

 

Thanks for your input Motorhead. But I must say I didn't quite get what you were getting at. Maybe too many bumps to my head while under the vette.

My second question though, still stands.

"On a related note, a friend has the same radio in his '71, but is missing the rectifier, amplifier, multiplier, multiplexer (what ever you like to call it!). They are hard to get hold off. Get sold pretty quickly on ebay.

Does anyone know if they can be built up from components available through a electronics store (ie) a heatsink, correct transistor, wires."

Cheers

BB

 

MotorHead...
Interesting... That's the same setup I have in mine: 4 ohm speakers (not original type, of course) in the dash and 4 ohm mid/bass speakers in the kickpanels, wired in series to obtain [approximately] 8 ohms. This is with a Delco stereo head. The tweets reflecting off the glass give incredible high frequency clarity and the bass/mids from the kickpanels fill the cabin pretty well with the rest of the sound spectrum (for small bass speakers).
I'm happy with the sound from a 40 year-old radio head using that speaker setup. But, I still want to replace the convector unit [final amp stage] with a modern stereo amp. I've got the amp and parts to put it together; it needs DC blocking caps to keep the DC signal out of the input circuit, but it should work OK. If it works like I think, I'll post results on the Forum. I think a lot of folks would be interested in keeping the original head unit but getting more power and a cleaner signal from a modern amp.

 

Just a question about the original radio : Is the final output stage a pure Class-A amplifier or what else ?

 

Hi All,

I assume knowone has ever tried building a rectifier, amplifier, multiplier, multiplexer unit from scratch????



BB

 

Would 'scratch' mean using discrete components or IC's??

 

OUtput stages are damn nearly never Class A operation AB sub1 is more like it....

and yes those old Germanium transistors can not take any abuse on loading, the impedance curves go krazy, and the output transformers were not wired for that....

and different resonance peaks in any series wired speakers lend to terrible sound quality...CASE CLOSED.....way to technical a issue for here....

I have built more damn electronic gear from scratch and scrap than most of you can imagine....both hobby and professionally....

but outta the electronic game for some 25 years now....

theory/practice has not changed .....

 

Thanks for that info Mrvette.

In the meantime, i have located an equivillent (cross-referenced) transistor to the obselete Delco DS-501. I was going to get one of these, mount it in a similar size heatsink, and hook up the three terminals to the wires coming out of the radio!

It's a pretty simple system I thought. Do you think I am at risk of damaging my radio for some reason?

Cheers,

BB

 

There's no reason why you can't use a substitute transistor, if it matches the gain and has necessary power handling capability. I've identified at least one that can be purchased for about $10 each...but it has a different case design. That's no big deal, however. It's a very simple amp setup...not brain surgery (although MrVette would have us believe that it is).

 

It has only been 30 years since I was a TV/Appliance shop/store manager, and so my recollection IS that there is a impedance matching transformer from that old familiar DS501 to the speaker....

so to change designs totally with today's parts, you get a much more complex design....honestly, I would go China on it, and get a small cheep amp from some retailer and call it a day....and yes you need a blocking cap....but a .1 mfd at most any voltage will work fine, the inputs of most modern amps are very high impedance....

 

Don't be so quick to assume the level of intellegence in the C3, a stereo or stereo amplifier equipment is kids stuff. I designed cutting edge telecommunications equipment for a decade. The devices I and the my team designed make stereo equipment look like a record player compared to a blue ray player, as part of the new product design team at this company.

This is a multiplexer and has dual Motorola 36 bit micro-controllers and you can't look up on the internet how they work because no one really knows you gotta figure it out yourself

http://bayly.com/Products/dimux.php

And yes, if the part is a cross referenced part and check the specifications closely you can substitute that part

 

And sorry I didn't look at this thread until now but what I was getting at in real simple terms in my first post, you would be fired where I worked if you didn't design into your equipment and have a solution when someone plugs an 8 ohm speaker into your 4 ohn stereo.

What I was trying to get at is the fact that it is a no brainer that the designer has to make his design not blow up real good if you plug in the wrong impedence speaker, you may not get total power expected
out of the system but it should work and the quality should be good for as long as the speakers are plugged in

Man I feel better now and you can peruse the rest of the equipment at that site and if you don't have a clue what any of it does don't feel bad you are in the majority, but this equipment is how you call on your cell phone and tell your wife your gonna be late for dinner

 

As a hobby, I build home stereo loudspeakers - 3-way stuff with woofers, midranges, & tweeters. I always use 8 ohm speakers for these, while automotive speakers are 4 ohm. I don't even know what an ohm is - I just build em & they sound great!

 

It's a unit of resistance.

cc