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 Post subject: 40/2.6 audio transformer?
PostPosted: Jan Tue 05, 2016 3:53 am 
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Hello, guys.

This is my first post on your fine forum. I am trying to bring a 1963 Motorola Vibrasonic R200 back to life.
It is a reverberater attaches to a car radio rear speaker to create "concert hall" effect.

I have the unit but not the switch that went with it.
The switch had an input transformer that accepted input from the radio.
The parts list calls the transformer a "primary 40 ohm, secondary 2.6 ohm" and the schematic calls it a "primary 22 ohm, secondary 1.6 ohm".

Can you offer a suggestion as to:
(a) where I could find either one of these?
(b) is there a readily available part that could substitute for either of the specified parts?
(c) which should be more believed, the parts list or schematic?
(d) why would the parts list and schematic list different values?

Thnaks, Dennis in Tampa.


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Tue 05, 2016 5:25 am 
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They both have a similar impedance ratio, which is typically what matters. I've never seen anything that low

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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Tue 05, 2016 5:34 am 
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Is that the dc resistance or the impedance?

If it is the impedance that is listed, maybe you could contact Edcor and see if they can make you one that will work.

The only other way I can think of would be to find the correct switch.


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Wed 06, 2016 2:13 am 
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pixellany wrote:
They both have a similar impedance ratio, which is typically what matters. I've never seen anything that low


Hello, Pixellany and Tube Radio.

Thanks for your quick replies. I want to post some pictures (worth 1,000 words), but am evidently "too new". The danged whippersnappers. Maybe after this post or maybe by tomorrow I can better show you what I have.

Thanks, Dennis.

"Your post looks too spamy for a new user, please remove off-site URLs. Click for help."
"New User Restrictions:
These restrictions only apply to new users. They are removed automatically after your account meets the following critera:
• You have made one post.
• Your account has been active for more than 24 hours."


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Wed 06, 2016 6:56 am 
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Posts: 11420
Location: Powell River BC Canada
Why not round of the Z ratio to 10:1.. 30:3 ohm winding

Make it work for 2 watts.

2 Watts at 3 ohms Z = ~ about 2.5 volt. what now ?

Find a old wall wart. 6 Volt at .5 amps Break it !

Pull off the winding. Wind as follows : 3 ohm winding 15 turns ;
30 ohm winding 45 turns;

(Based on 6t/v for wallwart)

The other thing is, could it be an auto transformer? Common in 60's
car radio with solid state output.

I looked up GMC reverbs and switches for various GM cars 66-68 , and
the only transformers were the auto transformers on the output of the spring
amplifier.

Has someone got better numbers ?

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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Wed 06, 2016 7:36 am 
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Location: Saskatoon
As pixellany points out, either 40:2.6 or 22:1.6 is pretty much the same impedance ratio, and it works out to a turns ratio of about 4:1. So, if you find a small power transformer with an input of 120 volts and an output close to 30 volts that should do the trick. I'd suggest a Tamura 3FD-336, available from Digi-Key for about $5.
http://www.digikey.com/product-detail/e ... 2-ND/53442


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Wed 06, 2016 11:56 am 
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BobWeaver wrote:
As pixellany points out, either 40:2.6 or 22:1.6 is pretty much the same impedance ratio, and it works out to a turns ratio of about 4:1. So, if you find a small power transformer with an input of 120 volts and an output close to 30 volts that should do the trick. I'd suggest a Tamura 3FD-336, available from Digi-Key for about $5.
http://www.digikey.com/product-detail/e ... 2-ND/53442


Hello, RadioTech & Bob.

Thanks for the replies. My background: I took basic electricity and electronics in the Navy in 1980. That was 36 years ago and I am a bit rusty on this stuff. You guys have just given me a lot of information that will take me a bit to understand.

Whoa! It seems that I just figured out how to post a photo. (Sorry. The posted photos turned out to be small to see. I will post enlarge details this evening when I get home from work.)

What I am missing is the switch that is to the left of the four-pin connector as show in the following schematic. The more that I look at the switch circuit, the more confused that I become.
(a) What is the purpose of the input audio transformer (T1)? I read that they were used to match the high impedance of vacuum tube radios to low impedance speakers. But, .... my car has a vacuum tube radio and the output goes straight to the dashboard speaker without a transformer coupling.
(b) T1 appears to be a step down transformer. That would drop voltage and boost current. But, ... a lead to the front speaker feeds off the backside of T1. What is the reason for that?
(c) Is the "Reverb" R1 a potentiometer? A potentiometer has three inputs. R1 has an input on the left and three outputs on the right. One of the outputs on the right looks like it is a center tap off the resistor. What is a component like that called?

Thanks, Dennis.
Image

Image

[imghttps://im1.shutterfly.com/media/47a6df24b3127cceeb5f69da3d8400000030O00AaOHDhi3bt3IPbz4S/cC/f%3D0/ls%3D00907771888420160106010112990.JPG/ps%3D50/r%3D0/rx%3D720/ry%3D480/][/img]

Image


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Wed 06, 2016 9:31 pm 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Could be a varistor, to prevent a fire, if the bottom + wire in your drawing
crossed to vehicle battery by accident.

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Amateur Radio Literacy Club. May we help you read better.
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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Wed 06, 2016 10:32 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2324
Location: Lakewood, California
Hi Dennis,
Welcome to the forum! It’s been quite a while since I serviced one of these units, but I’ll try to answer some of your questions.

(a) T1 isolates the output of the existing car radio from the Vibra-Sonic, allowing the choice of using the existing speaker with or without the reverberation. Some models used resistors instead of the transformer (American Motors RV4R). If you are using information from Sams AR-19, note that the pictorial on page 108 has mistakes. The transformer marked “T1” is actually T2, and the one marked “T2” is actually T3. T1 is the transformer mounted on the reverb control that you are sadly missing. I didn’t make any notations on the schematic, so it is probably correct.

(b) If you look close at the schematic, the front speaker is actually fed from the primary of T1, not the secondary.

(c) R1 is a 200Ω potentiometer with a tap at an unknown point of its rotation, not necessarily the center. Typically, full rotation in one direction provides full reverb with the rear speaker with a hint of audio from the front speaker. Full rotation the other direction is audio from the front speaker with either no audio or slight audio from the rear speaker. Settings in between full CW and full CCW are-------something in between.
It has an integral on-off switch for Reverb power. Some models provide some audio from the rear speaker with the reverb power off.

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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Wed 06, 2016 10:32 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2284
Location: Saskatoon
ew1usnr wrote:
What I am missing is the switch that is to the left of the four-pin connector as show in the following schematic. The more that I look at the switch circuit, the more confused that I become.
(a) What is the purpose of the input audio transformer (T1)? I read that they were used to match the high impedance of vacuum tube radios to low impedance speakers. But, .... my car has a vacuum tube radio and the output goes straight to the dashboard speaker without a transformer coupling.
(b) T1 appears to be a step down transformer. That would drop voltage and boost current. But, ... a lead to the front speaker feeds off the backside of T1. What is the reason for that?
(c) Is the "Reverb" R1 a potentiometer? A potentiometer has three inputs. R1 has an input on the left and three outputs on the right. One of the outputs on the right looks like it is a center tap off the resistor. What is a component like that called?


The switch isn't missing. It's part of the potentiometer. It's the black plastic part mounted on the back.

a) There's no doubt that it's an odd connection, and it would have to be analyzed in detail, or simulated, to find out exactly its behavior.
b) It looks to me that it simply is there to maintain a proper balance between the audio going to front speaker and the reverb unit.
c) Yes, it's a potentiometer. There are four terminal versions of these where one of the connections is to a fixed tap on the resistance stator.

Without analyzing in detail, I think it's safe to say that the manufacturer used this odd connection to get a particular volume contour or balance between the front speaker and the reverb speaker.


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Thu 07, 2016 3:30 am 
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Posts: 10
BobWeaver wrote:
The switch isn't missing. It's part of the potentiometer. It's the black plastic part mounted on the back.


Hello, Bob.

My apologies. I was in a hurry this morning to leave for work and did not properly explain the pictures. I do not have a switch. The picture of the switch was copied from e-bay and shows what I am missing.

Here is a close up of the switch/potentiometer schematic to the left of the four-pin connector so that it can be better seen:
Image

Here is a parts description of the T1 transformer. As one of you had earlier asked, it is indeed listed as ohms impedance and not resistance. I had seen the ohm sign and thought resistance.
Image

Questions:
If I were to assemble a substitute for the switch out of individual components, how would you recommend to do it?
Is the transformer something that is nice but not necessary?
Is finding an exact 22/1.6 (on schematic) or 40/2.6 (on parts list) transformer not necessary, or do I also have flexibility to use any low impedance transformer of roughly the same ratio?
Could the radio output just be wired directly to the potentiometer instead?
Is the four post potentiometer necessary or would a three post also work?
What is a four-post potentiometer called? Four-post, center-tap, what?
The fuse power-input note says "0.4 A @ 12.6V". Does that indicate that I need a 5-watt potentiometer?

Thanks for your help, Guys.

The 1963 Vibrasonic reverberator will be hooked to a vacuum tube AM radio in my 1963 Ford Falcon to provide a genuine 1963 sound experience.
Image


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Thu 07, 2016 6:45 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11420
Location: Powell River BC Canada
Just get the turns ratio correct, with a transformer with low DC resistance windings
and you will be OK. The other point is the phasing may make a difference,
so when its ready to, be able to swap the leads around.

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Amateur Radio Literacy Club. May we help you read better.
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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Thu 07, 2016 7:49 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Saskatoon
ew1usnr wrote:
The picture of the switch was copied from e-bay and shows what I am missing.

Okay, thanks for clearing that up. Does that mean that you're also missing the potentiometer, or just the switch section on the back?
You can always substitute a regular toggle switch if necessary. If you are missing the potentiometer as well, then it could be quite difficult to find one with that resistance rating and with the fixed tap. But, it should be possible to get it up and running reasonably well with commonly available parts.


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Thu 07, 2016 9:53 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11420
Location: Powell River BC Canada
Here is an output stage of a Motorola 1963 car radio that has a 4 pin connector
as in one of your drawings. It may help to explain the circuitry on the reverb
back to a radio that you have. Those radios did not reference any speaker leads
to ground, hence the need for an isolating input transformer.

Attachment:
Motorolla 1963 car radio snippet.JPG
Motorolla 1963 car radio snippet.JPG [ 149.04 KiB | Viewed 4780 times ]

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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Thu 07, 2016 11:57 am 
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BobWeaver wrote:
Does that mean that you're also missing the potentiometer, or just the switch section on the back? You can always substitute a regular toggle switch if necessary. If you are missing the potentiometer as well, then it could be quite difficult to find one with that resistance rating and with the fixed tap. But, it should be possible to get it up and running reasonably well with commonly available parts.


Good morning guys.

Hello, Bob.

I have been calling it a switch, but I am referring to the whole integrated assembly that contains the audio transformer, switch, potentiometer, and a resistor.

Image

My plan is to build a little switch panel with individual components to substitute/replace the original integrated switch/potentiometer. I had already ordered a switch and a three-tab 220 ohm / 5 watt potentiometer off e-bay. It looks like I may have jumped the gun though on the potentiometer. I will look around on the internet tonight for 12V DC center-tap potentiometers and low-impedence transformers and see if you guys think that they might work before ordering them.

Image

Image

Note to RadioTechnician: You are correct. In 1963 Ford introduced transistor radios in the Falcons. You are also right in that the speaker is not grounded. The radio has two output leads that go to the speaker. The Bendix transistor radio in my car was not working so I replaced it with a 1962 Ford Falcon vacuum tube radio that I bought off e-bay. The vacuum tube radio works just fine. I had a 1963 Falcon station wagon when I was in high school (1977-1979) and it had a vacuum tube radio. If you requested the optional radio in 1963, the car dealers were probably installing their leftover vacuum tube radios until they were used up. So, the vacuum tube radio in the 1963 Ford is not a big deviation from keeping it original. Installing a stereo would be. I have just left it alone with the AM radio and dashboard speaker. A rear speaker and reverberator were an available option in 1963. Ford called it StudioSonic and it was made by Motorola. Motorola also sold the same item at the same time (with a different switch) and called it a VibraSonic R200.

Image


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Thu 07, 2016 5:55 pm 
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Location: Powell River BC Canada
With an exact schematic of your existing radio, you may find that
isolating input transformer is not needed. From my 1966 Delco manual,
in the reverberation section, the wiring shows a front-rear fader pot
and, an a 3 way switch, but no transformer. The reverb spring assembly
is, in itself, isolated. The other aspect of the input transformer is
for level matching.

The spring assemblies from auto reverbs, as well from the much larger
ones from Hammond organs, were used by audio experimenters and
musicians in 1960 to build effects boxes.

Attachment:
Delco  GM 1965 reverb.jpg
Delco GM 1965 reverb.jpg [ 135.84 KiB | Viewed 4735 times ]

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Amateur Radio Literacy Club. May we help you read better.
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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Fri 08, 2016 4:18 am 
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radiotechnician wrote:
With an exact schematic of your existing radio, you may find that
isolating input transformer is not needed. From my 1966 Delco manual,
in the reverberation section, the wiring shows a front-rear fader pot
and, an a 3 way switch, but no transformer. The reverb spring assembly
is, in itself, isolated. The other aspect of the input transformer is
for level matching.


Hello, Radio Technician.

I am studying your GM schematic and thinking "Hmmmmm".
The GM diagram shows the speakers as grounded. My Vibrasonic schematic shows the rear speaker as similarly grounded, so it looks like it would work.
It is interesting that your schematic for the Buick and Oldsmobile shows that they have a potentiometer but the schematic for the Pontiac does not have a potentiometer.
Question: Why does the input to the Oldsmobile potentiometer have a two-arrow resistor contact (wiper) and not a single arrow (see picture)?

Image


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Fri 08, 2016 6:44 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
There are potentiometers in audio with multiple moveable elements:

A L pad has 2. An L pad keeps the amplifier load constant.
A T pad has 3. So does the T pad, and also provides constant speaker damping.

The thinking is, there are two speakers, connected to one amplifier. If one,
front or rear, is playing, the impedance reflected back to the amplifier is the
speaker's impedance if both are playing, it is desirable that both speakers play
at the same volume, and reflect back to the amplifier, the same impedance as one.

1. Car radios are something special. In that small closed space,
it has got sound good.

2. If the car designer got saddled with a radio that developed a reputation for
sounding crappy, the whole car, in that model year would suffer.

3. Because a car is such a small space, the car radio has an ample power budget,
so some resistance losses can be tolerated.


1,2,3 my opinion.

Below is the 1965 Delco. There they name it a Fader Control.

Attachment:
FADER CONTROL.jpg
FADER CONTROL.jpg [ 140.19 KiB | Viewed 4675 times ]

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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Fri 08, 2016 6:45 pm 
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radiotechnician wrote:
Car radios are something special.


This is true. I was marveling yesterday at how clear the sound is from my un-restored 1962 vacuum tube radio.

There appears to be multiple ways to skin this cat.

The following schematic is from a 1963 Ford StudioSonic. The control/switch on this one does not use the transformer or the twin-wiper potententiometer. It uses a three-wire lead rather than a four-wire lead because it does not use a a center-tap potentiometer.

I think that I will go with this method. It appears to be the simplest arrangement and just uses a switch and a standard potentiometer.

Image

I like this antique radio forum. It is amazing that I can find people with so much information on such an obscure item as a 1963 Motorola Vibrasonic sound system. Thanks for helping me understand what I was looking at in these schematics.

Dennis.


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 Post subject: Re: 40/2.6 audio transformer?
PostPosted: Jan Tue 12, 2016 12:53 pm 
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In response to the original question, here is a transformer for sale:
viewtopic.php?f=15&t=291943

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"Measure voltage, but THINK current." --anon.


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