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Radiomobile 501t vintage radio

Trevor Baillie

Jun 9, 2017
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IMG_7714.PNG hello all, I am new to the forum and any help would be greatly appreciated.
I have a 1961 HMV radiomobile 501T valve radio with an S98200A amp.
The amp is completely shot and beyond repair so I would like help as to how I can introduce a new amp and I am unsure of the methods of connection.
The circuit diagrams are as follows, if anyone could tell me how I would be very grateful.
This is to bring an original car back to factory spec for a charity.
 

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73's de Edd

Aug 21, 2015
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Sir Trevor Baillie . . . . .


If you have none of the original power output amplifier.
Would you be up to putting in a load resistor for completing the collector circuitry of that TR1 driver transistor that originally fed a driver transformer within that now missing power amp ciruitry.

That would then create an audio signal to then feed via a shielded line into only one channel of this amplifier that would then only feed one speaker.

Then the volume control on this unit is set one time for max volume needed, with the main radio, then being the principal vol control.

The original old unit only had one power transistor amp for 2.5 watts or the old dual transistor model had only 5 watts output.

What is the 1961 car ?

What say ye . . . . .

REPLACEMENT AMPLIFIER:

https://www.aliexpress.com/item/Min...2761158091.html?spm=2114.40010408.3.11.z2JHcr

http://www.ebay.com/itm/Mini-Digita...198119?hash=item212061c127:g:km0AAOSwux5YQBT1


73's de Edd
 
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Trevor Baillie

Jun 9, 2017
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Hi 73's de Edd, i assume you men a 150 ohm load resistor across 4 and 1 then fed onto the amp. If that is correct is there any impact on leaving the return on 3 open circuit as I dont understand what its purpose is.
Thanks and regards
Trevor
 

73's de Edd

Aug 21, 2015
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No, might just as well eliminate that prior driver circuitry and pull that transistor and take out audio from its base connection circuits pair of resistors thru an isolating cap..
 

Trevor Baillie

Jun 9, 2017
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Jun 9, 2017
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Forgot to mention its a 61 Rolls Royce that has been modified to be a convertible with wheelchair access on the passenger side.
I am a bit confused now, sorry for my lack of understanding but is there any chance you could sketch what you mean?
I already have a seperate audio amp and just need to be able to drag the audio from the radio to the audio input of the amp.
Best regards
Trevor
 

73's de Edd

Aug 21, 2015
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Sir Trevor Baillie . . . . .

Well how ‘bout that . . . in my mind’s eye I was fully expecting a JAG-WAR . . . . . BENTLEY . . . .’59 Gull wing Mercy-Days or a Rolling Royster, so you didn’t come up below my expectations. . . . if this was to be an auction item.

It’s worthy of a Radiomobile “His Masters Voice“ radio, with its use of low plate potential tubes. . . . but ratty old gerani-mum-mum transistors . . . now to be dumped..

This mark-up gives the original power amp and the GREEN area is the no longer needed items. I only left the 1 and 5 connections to relate to the fact that there was a needed capacitor on the power unit, as is shown as C1, you might find space for it across the pilot light connection just below the power input..

Also it seems logical for the the 12V power input was into the power amp with the C2 and C3 caps and their intermediate hash coil .

The audio take off point to your audio amp is at YELLOW circled BLUE A connection with a shielded audio line. If your amp does not include an isolation capacitor for DC isolation in its input circuitry . . . use one.

Also that amp of yours will be getting its power from the switched power line at the old terminal 1 line.

Is this enough info for you . . .?

TECHNO-REFERENCING:

Radiomobile_Series_500_Schematic_Conversion.jpg

https://s12.postimg.org/8at0ph6cd/Radiomobile_Series_500_Schematic_Conversion.jpg


73’s de Edd

.
 
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Trevor Baillie

Jun 9, 2017
5
Joined
Jun 9, 2017
Messages
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Fantastic, thanks, will install the new valves and hook it all up a week on Monday (waiting delivery of valves) will let you know how it goes.
You are right it just looks the part on the dash and the new amp which is hidden has aux and bluetooth on it, coupled with a different speaker array it should be pretty good.
Your help is much appreciated and will send you pictures of it when its done.
Regards
Trevor
 

Trevor Baillie

Jun 9, 2017
5
Joined
Jun 9, 2017
Messages
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Sorry But just for clarification, the yellow A provides the audio input to the amp rca centre connector, what about audio common, is that 12v?
 

73's de Edd

Aug 21, 2015
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No the ground is the other shell / shield connection . . .NOT 12V.
 
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