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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Sun 12, 2017 8:09 pm 
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When you take the pin wheel off be careful not to lose the 2 pins that set in there , as I remember also there are springs also these provide the detent action for each position. I remember one falling out and was glad I saw it.


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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Sun 12, 2017 9:17 pm 
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Norman - thanks for that info. Here are the measurements off of my receiver for comparison:
BCB: 44.1 ohms
SW1: 1.4 ohms
SW2: 1.5 ohms
SW3: 0.4 ohms

Lou - timely advice thank you. I was just about to remove the wave change turret.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 5:05 pm 
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So one of the problems with the AW23 is a bit of brittle rubber covered wire in the front end. There are 3 exposed wires on the top of the chassis that I replace when rebuilding. The following photos will give you a feel for the process. It looks scarier than it is.


Attachments:
#11-Brittle Wires Top.jpg
#11-Brittle Wires Top.jpg [ 119.58 KiB | Viewed 387 times ]

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 5:06 pm 
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Lou deGonzague wrote:
When you take the pin wheel off be careful not to lose the 2 pins that set in there , as I remember also there are springs also these provide the detent action for each position. I remember one falling out and was glad I saw it.


Right so visual representation of what Lou is talking about here.
Image with the wave change turret still in place
Attachment:
Wave change turret small.jpg
Wave change turret small.jpg [ 102.25 KiB | Viewed 387 times ]


Here is the same view after removal of the turret and one of the pins.
Attachment:
Wave change contact switch small.jpg
Wave change contact switch small.jpg [ 109.32 KiB | Viewed 387 times ]


You can get a pretty good look at what the contacts look like on the wave band switch. High quality stuff. All of the contacts look clean and the springs are all still functioning normally.

Photos of the top and bottom side of the chassis after stripping down.
Attachment:
RF chassis bottom small.jpg
RF chassis bottom small.jpg [ 107.81 KiB | Viewed 387 times ]

Attachment:
RF chassis top small.jpg
RF chassis top small.jpg [ 107.79 KiB | Viewed 387 times ]

This is definitely not for the feint of heart. There is a lot going on in this chassis.

I also have a photo of a "bankers box" full of tube shields and coil covers but thought I would spare you.

Cheers.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 5:07 pm 
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First, remove the antenna coil by unsoldering the two highlighted connections, then remove the two screws underneath the chassis. (You will have to remove the coil wheel to access these screws).


Attachments:
#17- Cleaning.jpg
#17- Cleaning.jpg [ 126.74 KiB | Viewed 387 times ]

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Kent King
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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 5:10 pm 
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kent3256 wrote:
So one of the problems with the AW23 is a bit of brittle rubber covered wire in the front end. There are 3 exposed wires on the top of the chassis that I replace when rebuilding. The following photos will give you a feel for the process. It looks scarier than it is.


Hi Kent. Thanks for chiming in. Yes I inspected this wire on my set yesterday and just moving it ruins the insulator. All of it will be replaced. Dave P had mentioned using test lead wire for this process.

Do you have a good image of the following area on an aw23? Whoever was in here before disconnected this piece of wire.
Attachment:
what is this.jpg
what is this.jpg [ 119.34 KiB | Viewed 387 times ]

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 5:10 pm 
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The I remove the switch contacts, put new wires in place and replace it onto the chassis, being very careful to align the rotating switch contacts.


Attachments:
#18- Ant Sec wires 1.jpg
#18- Ant Sec wires 1.jpg [ 133.87 KiB | Viewed 387 times ]
#19- Ant Sec wires 2.jpg
#19- Ant Sec wires 2.jpg [ 132.74 KiB | Viewed 387 times ]
#20-Ant Sec wires 3.jpg
#20-Ant Sec wires 3.jpg [ 137.71 KiB | Viewed 387 times ]

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Kent King
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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 5:11 pm 
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And finally, with cover replaced...


Attachments:
#22-Ant Sec wires 4.jpg
#22-Ant Sec wires 4.jpg [ 171.73 KiB | Viewed 387 times ]

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Kent King
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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 5:18 pm 
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Wow. I hadnt even noticed that little detail yet. I will probably be surveying all of the components and schematic over the coming week.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 6:05 pm 
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You are getting great info here Bosch and very interesting to me.

Really like the way the little rotary switch is inside the can keeping it out of the dirt. This probably cuts wear considerably.

Don't know if you use it but Solder Wick is great for removing excess from tags. Do one and remove some and then move on to the next. Then come back and go around again and ... This way no tag gets over heated.

Gary


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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 6:11 pm 
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Radio Fixer wrote:
You are getting great info here Bosch and very interesting to me.

Really like the way the little rotary switch is inside the can keeping it out of the dirt. This probably cuts wear considerably.

Don't know if you use it but Solder Wick is great for removing excess from tags. Do one and remove some and then move on to the next. Then come back and go around again and ... This way no tag gets over heated.

Gary


Yep great stuff. I use solder wick often. Probably going to go quiet here for a bit until I can complete an initial survey.

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Last edited by Bosch's Fault on Nov Mon 13, 2017 9:11 pm, edited 2 times in total.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 7:13 pm 
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I have restored both the early 5 knob and the later 7 knob Scott AW-23's.
A lot of work but well worth it, especially with as nice an example as you have with your upscale Scott cabinet. And what an education!
The early version AW-23 has more of that rubber covered wire in the tuner sections.
*
Again I liked the black test lead wire to replace the deteriorated rubber covered wire. The right size and very flexible making it easy to thread everywhere. Especially to those silver plated contacts which are flexed every time the band switch is operated. Replace just one piece at a time. Use it for all the tube grid cap wiring as well for correct appearance.
- Dave Poland

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 7:18 pm 
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Here is a pic of roughly the same area on an AW23 I'm currently working on. If you can't see the wire you need, highlight and PM me, I'll see if I can get a better pic or just describe it.


Attachments:
20171108_185445.jpg
20171108_185445.jpg [ 242.99 KiB | Viewed 379 times ]

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Kent King
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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 7:25 pm 
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Great thank you. I will be getting a hold of some test lead wire for all of the rubber covered stuff.

Kent thanks for the photo. That shows exactly what I need.

Cheers.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Mon 13, 2017 11:24 pm 
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Fascinating look into restoration of one of these wonderful sets.
I didn't know the bandwidth was adjusted with capacitors rather than physically move the IF coils.

Great work and will be great reference! :D

Thank you!

-Steve

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Tue 14, 2017 10:03 am 
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I see what you mean Steve?

They certainly on a blow up look like variable capacitors in the cans and not all the same. Not seen that done before.

From P70 of Marvin Hobbs book "One might have thought that the benefits of variable selectivity, which could be varied continuously to provide an audio bandwidth of from 2 kHz to 16 kHz, would be useful ...

Pretty surprising that such a range could be achieved whilst keeping a good shape.

Gary


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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Tue 14, 2017 5:08 pm 
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The IF amplifier has nine tuned circuits. When adjusting from a sharp bandpass to a broad (hi-fi) bandpass, three tuned circuits remain centered, three add capacitance moving down in frequency, and three subtract capacitance moving up in frequency. Near the broad bandpass position the top of the bandpass characteristic is more or less flat with mild dips between the sets of tuned circuits. When opening up the bandpass characteristic (adjusting from selective to high fidelity), the energy conveyed by the IF amplifier is increased. If I understand correctly, the energy conveyed is proportional to the area under the bandpass characteristic. For a bandpass that is variable from 2-khz to 32-khz (audio bandwidth is half the IF bandpass), there is a tremendous range of energy reaching the detector, far more than the AVC circuits can address. Hence, EH Scott Radio Laboratories included a variable resistor on the selectivity-fidelity control to adjust bias in a manner that compensates for the variation in energy reaching the detector while adjusting the IF bandpass characteristic. As such, the volume of a tuned station remains nearly constant when adjusting the bandpass characteristic. What one should hear is a pure change in tone rather than a change in volume and tone. That is elegant circuit design!

Incidentally, the audio bandwidth varies between 1-kc and 16-kc. Marvin confused the low IF bandwidth with the high audio bandwidth.

Fun with the variable selectivity... Some night, with the AW-23 bandpass control set to the selective position, tune to a distant station located 10-kc off a strong local. Then slowly turn the bandpass control toward high fidelity and hear what happens.

Norman

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Tue 14, 2017 6:40 pm 
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Getting that IF strip right must have taken a lot of development time: thanks for the explanation of how it works. Your energy under the curve to me is spot on.

Is alignment something that needs to be done and is it difficult?

Having a gain levelling potentiometer harks back to TRFs like the Majestic 90's, and Philips used it as well, to keep the gain approximately constant as the tuning goes from the high to the low end of the waveband by applying more cathode bias to the RF stages. This was back in about 1930. I thought it was elegant circuit design then and it is as you say on this Scott.

As to what happens with the local versus the weak signal 10 kHz away I guess as the IF bandwidth is increased then the local takes over, AVC increases and the distant station goes down in the noise. Really cant see how the distant is still listenable to.

Gary


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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Tue 14, 2017 11:29 pm 
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It does amaze me the engineering talent and skill that went into the design!

Most other manufacturers went the way of variable mechanical coupling.
Some others used switching arrangements.
The Philco 200X and 201X use a different method with tertiary IF windings and variable resistance to increase or reduce the Q of the transformer.

All is fascinating!

Thanks for the description Norman!

-Steve

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Nov Tue 21, 2017 9:00 pm 
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Hi all,

Still gathering parts. Exciting getting pretty close to actually working on this instead of re-stuffing caps.

Please see below photo. There is a 400K resistor (circled red) attached on one end to ground and the other end is some of the rubber low loss wire that has been disconnected entirely (termination is circled in yellow). Any ideas what is going on here? I didn't find any listing of a 400K on the parts list. The shielded cable looks to be connected to the volume control on the photo Kent provided.
Attachment:
400K resistor.jpg
400K resistor.jpg [ 93.19 KiB | Viewed 116 times ]

Thanks in advance.

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