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 Post subject: Re: MASTERPIECE VI RESTORATION 05/19/19
PostPosted: May Mon 20, 2019 11:11 pm 
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Location: Chicagoland, 60194
Tim Tress wrote:
Can you post a schematic link?

http://www.myvintagetv.com/manuals_and_documents.htm

MPV schematics are harder to find online. RM.org doesn't have a thing
Radio Era Archives says they have MPV schematics. I ordered them last week for $25 and haven't yet received. Since then they raised the price to $30. Maybe they're reading these posts... :lol:
http://www.radioera.com/m-manuals.htm


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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/19/19
PostPosted: May Mon 20, 2019 11:38 pm 
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phlogiston wrote:
Interesting that speaker has the hole in the base for the tweeter switch. MSMVIs do not use the switch.

Better check the field coil resistances to make sure that it is truly a VI since the field coils are not the same for the V.


Jon, great post...keep posting please I'm saving it for later.

Russ, My MPV speaker has the switch. I have not done a thing yet, but can you post field coil resistances of MPV version and MPVI versions so we know how to tell them apart? Jensen's mgr of tech services in a letter to the editor of Audio in 1954 said the McMurdo special speaker was listed in their general catalog available as model HF-18 having dural apex and model V-18 having a hard paper apex. What is a dural apex?


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1954_Mar_Audio_ltr2editor_Jensen.jpg
1954_Mar_Audio_ltr2editor_Jensen.jpg [ 68.59 KiB | Viewed 1702 times ]
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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/19/19
PostPosted: May Tue 21, 2019 3:33 am 
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An incredible restoration worthy of museums.


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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/19/19
PostPosted: May Tue 21, 2019 4:37 am 
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Learned the switch on the MP5 speaker is a filter that limits high frequency to either 9000 or 6000 cps. Does the MP6 do that differently? For MP5 circuit description and schematic see Sept and Dec 1936 All-Wave Radio magazine. Sorry don't mean to hijack the thread, just trying to figure out what's the same and what is different.


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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/19/19
PostPosted: May Tue 21, 2019 6:25 pm 
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+Both the V and the VI have crossovers for a tweeter. The V is more elaborate and includes a switch.

DCR in ohms:

V is 400 ohms and 4K ohms
VI is 700 ohms and 7.5K ohms

These differences are consistent with changes to the power supply and result in similar B+ voltage and screen voltage.

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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/19/19
PostPosted: May Tue 21, 2019 9:46 pm 
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phlogiston wrote:
+Both the V and the VI have crossovers for a tweeter. The V is more elaborate and includes a switch.

DCR in ohms:

V is 400 ohms and 4K ohms
VI is 700 ohms and 7.5K ohms

These differences are consistent with changes to the power supply and result in similar B+ voltage and screen voltage.


Thanks Russ, so all the switch does is bypasses the crossover so that high frequencies are either blocked at 6K or run full open at the speakers' (both main spkr or optional tweeter) limit of 9K hz? The article in the Sept '36 All-Wave Radio mag says that 90% of the time the switch should be set to limit the high freq to 6K hz to reduce modulation distortion. AFAIK only the "Apex" stations would have had a chance of being heard at the higher frequencies. Did the MP6 just eliminate the switch and crossover and consider whatever distortion not an issue?


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mpv_supr_giant_sch.jpg
mpv_supr_giant_sch.jpg [ 47.42 KiB | Viewed 1653 times ]
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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/19/19
PostPosted: May Tue 21, 2019 10:42 pm 
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Somewhere I came across a Masterpiece VI schematic that had that capacitor-inductor labeled as "Whistle Trap." I'm not finding it now with a few minutes of searching.

I figured, without studying it further, that it was a band-stop filter centered at 10 kHz, so that you wouldn't hear adjacent carrier waves on the wideband setting.

-Rodney


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 Post subject: ***
PostPosted: May Mon 27, 2019 2:53 pm 
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Last edited by ketron281989 on Oct Sat 26, 2019 11:08 pm, edited 1 time in total.

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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/27/19
PostPosted: May Mon 27, 2019 3:06 pm 
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Jon

Yes, the Jensen theatre speaker is very similar to your speaker with the Capehart label. The back and stand are black also. Mine has the carrying handle and two sets of screw terminals on the stand - one for the speaker field coil, the other for the speaker voice coil. And, of course, a Jensen label instead of a Capehart label.

The cones of your Capehart speaker and my Jensen theatre speaker appear to be identical.

Thanks for the pictures. Prior to this I was not aware that Capehart also used 18 inch Jensen speakers.

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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/27/19
PostPosted: May Mon 27, 2019 5:50 pm 
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Vintage Jensen catalogs indicate that there were at least four versions of the 18-inch Jensen pedestal speaker offered, Types L, M, V, and HF. The HF was high fidelity, the V was "voice", I believe the L was a woofer and I am unsure what the M was. They all differed only in cone characteristics (style, weight) and voice coil construction. All could be special ordered to meet the voice coil impedance and field coil requirements of the customer.

Norman

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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/27/19
PostPosted: May Mon 27, 2019 6:14 pm 
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Patch or recone? Baseball size hole and number of breaks favors recone. Shopping for a new cone has been frustrating. Difficult to get actual dimensions from most cone sellers. All they know is make & model. Have found a couple suspects that might work, but with a cloth edge. The inner cone and vc is good (I can't say if dirt has found it's way through). I'm aware the HF-18 used an aluminum center cone, but are there different inner cone versions of the Super Giant speaker? Reason I ask is this 1936 picture clearly shows a smaller diameter center cone than what I have.
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My_mpv_spkr.jpg
My_mpv_spkr.jpg [ 87.41 KiB | Viewed 1611 times ]

VCID is an estimate, not to scale, and depth is pretty much irrelevant with modern cones. Maybe it would be easier to make a form and grind some pulp in the blender and make my own?
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loudspeakercomponents_p122.png
loudspeakercomponents_p122.png [ 289.86 KiB | Viewed 1611 times ]


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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/27/19
PostPosted: May Mon 27, 2019 7:09 pm 
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matt's basement wrote:
Patch or recone? Baseball size hole and number of breaks favors recone.


Recone only if you can find a correct cone. In the meantime which may extend to forever I would patch it. Try to find a cone you can get a piece similar to this one for the large hole. And patch the rest of the cone breaks.
John k9uwa

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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/27/19
PostPosted: May Tue 28, 2019 4:26 am 
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Re-coned examples of the McMurdo Silver Jensen Super-Giant are worth considerably less than those with the original cone, most likely because the two-material feature is missing.

Bob

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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/27/19
PostPosted: May Tue 28, 2019 1:23 pm 
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That looks pretty darn repairable. As John said, try to get a piece from another cone that will fit reasonably well. The other damage is straight forward.


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 Post subject: Re: MASTERPIECE VI Restoration - Updated 05/27/19
PostPosted: May Tue 28, 2019 2:02 pm 
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Jon, thanks for sharing all this! Wonderful radio and two amazing speakers!

Matt, that should be an easy repair, I've fixed worse.

Now I just got this wonderful Jensen D-7 to fix up. Poor thing, it looks so sad.

-Steve


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PostPosted: Jun Sun 09, 2019 9:09 pm 
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