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 Post subject: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Tue 16, 2022 7:41 pm 
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Joined: Feb Wed 12, 2020 3:46 pm
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Location: Ballwin Missouri,
I recently acquired this device, which was intended to allow customers in 1920's radio stores to test/listen to 3 different speakers.

Does anyone have any directions or schematics they would share?

Thank you.


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 Post subject: Re: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Tue 16, 2022 7:51 pm 
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Location: S. Dartmouth MA USA
It is just a box with a switch, jacks and plugs.

Plans are in many 20's era handbooks.

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 Post subject: Re: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Wed 17, 2022 2:59 pm 
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it has a couple of other things also, one being a Dubilier Micadon type 640 (.00025MFD condenser). That is why I am looking for something more specific. While I appreciate your reply, is there a specific handbook you are referring to? thank you.


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 Post subject: Re: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Wed 17, 2022 3:51 pm 
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Location: S. Dartmouth MA USA
StoshV wrote:
it has a couple of other things also, one being a Dubilier Micadon type 640 (.00025MFD condenser). That is why I am looking for something more specific. While I appreciate your reply, is there a specific handbook you are referring to? thank you.
If there is a capacitor in the circuit, (the "Micadon" is a mica sandwich capacitor), its purpose is to bypass any RF that may get fed back to the radio. Many radios of the era used regenerative detectors, if miss-adjusted, the detectors stray RF via the speaker lead wires could create a feed back condition. The value noted would bypass RF but would not bypass AF, a small value so as not to change the response of the system.

The value, .00025mfd, is 250 pf., the is no magic going on. It IS possible that the switch is a two pole type because many early battery set speakers carried plate current through the voice coil windings... Hooking up some speakers the polarity is important. It won't fail but the speaker may be somewhat intensive.

https://worldradiohistory.com/

Use the search tool. Craft the search terms with regard that this is a point of sale device, therefore used by radio accessory sellers as a marketing aid in the retail store environment. Radio retailer magazines maybe better search choice.

Not difficult to make, it would be a matter if the device needs to look authentic to the era or just practical.

Here is a start:

https://worldradiohistory.com/hd2/IDX-S ... er_page=10

YMMV

Chas

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 Post subject: Re: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Wed 17, 2022 4:30 pm 
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Location: Keystone Heights, FL 32656
It sounds like you have this thing open or disassembled. How about some photos?

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 Post subject: Re: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Wed 17, 2022 8:18 pm 
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let's see if I can add some photos of the Comparophon.


Attachments:
Comparophon 0152.JPG
Comparophon 0152.JPG [ 497.63 KiB | Viewed 335 times ]
IMG_0154.JPG
IMG_0154.JPG [ 535.66 KiB | Viewed 335 times ]
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 Post subject: Re: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Wed 17, 2022 8:23 pm 
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Joined: Feb Wed 12, 2020 3:46 pm
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Chas, thanks for the advice on where and how to search. When I have some extended time this evening I will do so, ande let you know what I find tomorrow!


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 Post subject: Re: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Wed 17, 2022 8:32 pm 
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Joined: Jan Thu 01, 1970 12:00 am
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Location: S. Dartmouth MA USA
Seems the device has a matching transformer/choke, that probably takes the DC off of the speakers so they are operated without magnetic bias.

IMHO that can be tricky, as some speakers rely on the extra magnetism of the plate current flow to increases sensitivity.

If I were a salesman I could manipulate the outcome to favor a certain speaker :roll:

Interesting device for a 20's era operating display. There is a dramatic difference from a horn to cone to a voice coil type speaker.

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 Post subject: Re: Bristol Loud Speaker Test Set (aka Comparophon)
PostPosted: Aug Fri 19, 2022 5:43 pm 
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Joined: Feb Wed 12, 2020 3:46 pm
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Location: Ballwin Missouri,
I did find one ad that states the device is intended to be hooked up to a phonograph in order to evaluate speakers. Original cost was $60.00. If I find more information I will post it.

Others are welcome to do the same. I have some local experts i will ask to help me test this thing out.


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