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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Thu 21, 2017 5:06 pm 
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Thanks Gary. Sure not an issue. Lots of documentation so everything can go back together just so.

Here is a typical IF socket from the underside.
Attachment:
IF Diagram small.jpg
IF Diagram small.jpg [ 81.75 KiB | Viewed 1621 times ]

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Fri 22, 2017 3:30 am 
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Wow! I have been working on this receiver for most of the day. Re-working the IF sections is really challenging.

Anyhow, all of the IF sections have been reworked now. I will post more photos tomorrow. Here is a typical IF section from the socket side after re-work.
Attachment:
IF after re-work.jpg
IF after re-work.jpg [ 65.45 KiB | Viewed 1595 times ]


Cool in the nerdiest possible way. :D

Cheers.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Fri 22, 2017 3:48 pm 
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You said it! :D

-Steve

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Fri 22, 2017 6:51 pm 
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Progress shots on the IF chain from the underside (with schematic) and a shot of the 2nd IF from the top.
Attachment:
IF underside progress.jpg
IF underside progress.jpg [ 108.57 KiB | Viewed 1574 times ]

One of the things I noticed while working through the IF chain was how organized this chassis is. The design definitely feels like it was born of an organized mind (or group of minds). Really cool stuff.

This part of the job was a lot of work. I went and highlighted everything and when i zoomed out on my tablet it wasn't very much of the print yet. Guess I better buckle up.

Here is a the 2nd IF from the top.
Attachment:
IF top side progress.jpg
IF top side progress.jpg [ 64.49 KiB | Viewed 1574 times ]

The scribbling in there is a notation from the last person who serviced this in 1995.

Cheers.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Fri 22, 2017 8:22 pm 
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Bosch's Fault wrote:
The design definitely feels like it was born of an organized mind (or group of minds).


Murray Clay, chief engineer at the time of AW-23 production plus prior developments of Ernest Phaff formerly of Silver Marshall.

Norman

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Wed 27, 2017 7:10 pm 
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Hi all,

I will back fill this a bit later on. Here is the next bit of wire that needs to come out.
Attachment:
Antenna coil connections.jpg
Antenna coil connections.jpg [ 124.54 KiB | Viewed 1504 times ]

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Sat 30, 2017 3:47 am 
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Ok I was figuring out where all of the wires route and thought maybe I should do a thorough cleaning while I am at it. Since no one smarter was there to talk me out of it I started to dis-assemble the RF chassis for cleaning and re-wiring. Here is what I took off of the chassis in order to clean the chrome "deck".

Attachment:
Antenna coil with dial scale.jpg
Antenna coil with dial scale.jpg [ 86.58 KiB | Viewed 1464 times ]

I should have removed the dial scale immediately but was busy staring at the chassis. This dial scale has a little bit of damage which I will try to repair (more on this later). In the mean time I have purchased a replacement from RadioDaze.

Attachment:
tube shields.jpg
tube shields.jpg [ 48.71 KiB | Viewed 1464 times ]

The IF shields have an additional tube base shield at the bottom and there are 4 of this assembly.
The 6A7 Converter shield has a piece of phenolic riveted to the side for running a grid cap wire through and there is only 1 of this type.
The rest of the tube shields have no phenolic or base piece and there are 12 of them. During the process I bagged and labeled each shield so it could go back into the same place.
The 4th IF, RF, and Oscillator tube shields are all difficult to get out for one reason or another.
Note that the tube shields also keep all of the tube bases in place so working on any of the underside electronics is likely to move things around in an undesirable way.

Attachment:
Antenna coil close.jpg
Antenna coil close.jpg [ 65.22 KiB | Viewed 1464 times ]

Here is a close up of the antenna coil showing both the primary and secondary.

Once I had the connection map that I posted in the last post it was time to move the red blue green band coil.
Attachment:
red blue green band coil.jpg
red blue green band coil.jpg [ 55 KiB | Viewed 1464 times ]

There was a LOT of solder on these connections and I wanted to de-solder them carefully. It probably isn't strictly necessary to remove this coil but I thought I should. This coil is right up next to a tower of 3 variable 50 pF capacitors so is hard to work on.

Attachment:
band switch top side.jpg
band switch top side.jpg [ 65.94 KiB | Viewed 1464 times ]

Next I removed the band switch contact plate so I could de-solder the connections here as well. This part was pretty warped either from age or from heat applied removing the old crumbled wire. In order to correct it I placed it in a vice with it bent straight and used a heat gun for about 30 seconds back and forth. Once it cooled it was straightened out again.

Looking at the wire installed by the previous restorer I knew I had to take out the ganged tuning capacitor.
Attachment:
tuning meter.jpg
tuning meter.jpg [ 60.55 KiB | Viewed 1464 times ]

Next thing to come out was the tuning meter. This is a really cool assembly, I like how well it is built.

Attachment:
partially disassembled.jpg
partially disassembled.jpg [ 105.63 KiB | Viewed 1464 times ]

So the tuning gang has 3 additional bits of old wire attached to it. One leads to a 5000 pF cap and another leads to a 50 pF cap. Both of these caps tested good so I left them in place. I like the look of the originals better and will leave them if possible. I do have replacements if necessary. So far I have replaced 1 of 3. During the restoration process while checking all of the components sometimes I can electrically isolate the part without damaging the contacts and then test. This works well and hopefully I will not have to replace too many of the dominoes.

Attachment:
chassis top disassembled.jpg
chassis top disassembled.jpg [ 81.24 KiB | Viewed 1464 times ]

Ok so here is the disassembled chassis after cleaning with alcohol and polishing with chrome polish. AAAAHHHH! much better!

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Sat 30, 2017 4:02 am 
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Right so i had more than 10 photos in this series so I broke it up into 2 posts.
Here is the tuning gang removed.
Attachment:
tuning condenser with needle.jpg
tuning condenser with needle.jpg [ 77.65 KiB | Viewed 1462 times ]

Also there is a very small gauge wire tuning needle on here so I removed it while working with the tuning condenser. I definitely would have bent that thing while working on the condenser.

Attachment:
shielded antenna cable.jpg
shielded antenna cable.jpg [ 59.83 KiB | Viewed 1462 times ]

The last of the wire is inside of a shielded cable and is the only original wire of this type I will be leaving in the receiver chassis. I opted to sleeve this stuff instead.

Attachment:
coil switch re-wired.jpg
coil switch re-wired.jpg [ 71.81 KiB | Viewed 1462 times ]

Once I FINALLY cleaned all of the deck and removed the items in the way I re-wired the band switch contact plate. Re-wired all of the coils and any old wire that I found with the exception of 2 more pieces (more on this later also).

I would like to point out that this is a HEAVY chassis and I probably moved it more than 100 times to get from one point to the other. These chassis are not only difficult mentally but also very difficult physically.

Attachment:
chassis top reassembled and clean.jpg
chassis top reassembled and clean.jpg [ 104.06 KiB | Viewed 1462 times ]

So there is the chassis top side with all of the parts installed, wires replaced, and properly cleaned.

Cheers

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Sat 30, 2017 4:23 am 
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Good work! Make sure to loosen and retighten the machine screws holding the solder lugs under the tuning capacitor. This electrical connection becomes compromised when the phenolic through which the machine screw shrinks allowing corrosion between the machine screw and the solder lug.

You are well on your way to being prepared to rechrome a Scott Allwave tuner chassis!

Edit... Your second half of the post appeared before I finished posting. Please replace "make sure to" with "hope you remembered to".

Norman

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Sat 30, 2017 9:38 am 
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Great work and progress. Thanks for keep posting the pics.

Gary


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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Dec Sun 31, 2017 7:18 pm 
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Braithwaite wrote:
Good work! Make sure to loosen and retighten the machine screws holding the solder lugs under the tuning capacitor. This electrical connection becomes compromised when the phenolic through which the machine screw shrinks allowing corrosion between the machine screw and the solder lug.

You are well on your way to being prepared to rechrome a Scott Allwave tuner chassis!

Edit... Your second half of the post appeared before I finished posting. Please replace "make sure to" with "hope you remembered to".

Norman


Hi Norman. Thanks for the tip on loosening and re-tightening. I have not done that yet but will. I can imagine now putting the whole thing back together and having a weird, difficult to troubleshoot intermittent short.

The chrome on the receiver is better than the chrome on the power supply and I don't think that either really needs to be stripped and re-plated (thank goodness). If I were going to strip and re-chrome the amount of storage and cataloging would be significant.

My philosophy on this receiver has changed some since I have dug into it. Sure the capacitors and replacement resistors look period and close to correct, but I am not above also using shrink tubing on the grid caps. So maybe along the lines of keeping whatever is there and augmenting with whatever is needed. A good example is the idea of stripping the old wire sleeve off and applying it to a new capacitor wire. The problem here is that some of the old wire sleeve was removed by the last person to service this receiver.

That brings me to the last person to service this receiver. There was some dodgy work for sure. Think un-soldered contacts, incorrect wire, poor solder joints, and bypassed fuses. Still this person put in some effort and also labeled parts of the receiver. His work was completed in 1995 so 22 years ago. While cleaning the chassis a paper label containing the gentleman's name and ham call tag came loose. I am intending to re-attach it somewhere on one of the inside walls of the receiver chassis.

Originally the idea was to make the receiver look as if it had never been worked on. Unfortunately, the receiver had been worked on in the nineties. I think I would rather keep the record of this person's contribution even though I am actually removing almost all of it, ironic right?

Whew brain dump complete!

Cheers

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Mon 01, 2018 6:02 pm 
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Hi all. Todays mission is working on the 4th IF and IF diode adjustment. Here is a snippet from my notebook on the receiver.
Attachment:
IF Diode adjust map.jpg
IF Diode adjust map.jpg [ 84.66 KiB | Viewed 1372 times ]


Will post photos once repairs are done.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Mon 01, 2018 6:42 pm 
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When you get around to aligning the IF circuits, be aware that the adjustment screws on the diodes are at B+ potential.

Norman

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Tue 02, 2018 3:14 am 
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Done with the 4th If and IF diode adjust.
Attachment:
IF Diode adjust complete.jpg
IF Diode adjust complete.jpg [ 85.76 KiB | Viewed 1352 times ]

Diode adjust with new / tested components.
So far I have replaced 2 of 6 mica caps.

Attachment:
4th IF.jpg
4th IF.jpg [ 140.67 KiB | Viewed 1352 times ]

4th IF and surrounding area.

Cheers.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Tue 02, 2018 10:26 am 
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I agree with keeping some history of it original repair and along with yours of course.

Gary


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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Wed 03, 2018 1:23 am 
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Not sure what is going on here. Explanation and questions follow image.
Attachment:
Whaaaaaat.jpg
Whaaaaaat.jpg [ 90.43 KiB | Viewed 1295 times ]

In this image in the lower left one yellow and one brown wire are 6.3 volt heater wires.
They are attached to the 76 (oscillator) tube at pins 1 and 5.
From pins 1 and 5 there are 2 capacitors with one leg to the heater pins and another leg to a ground terminal also shown in lower left.

This arrangement is not shown on the underside parts diagram. The only place on the schematic that this might be is the connection shown between the push pull output heaters to ground in the upper right. Sometimes the connections are not necessarily where shown on the schematic... check.

Even if that is the case the schematic does not show capacitors in this portion of the circuit. Both of the capacitors in circuit now are .05 MF. Can anyone verify this is the correct arrangement?

Thanks in advance.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Wed 03, 2018 2:02 am 
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Yes. Correct. See later versions of service data. These are RF filters to improve oscillator stability. Unlike DC and audio frequencies, RF in the filament circuit can appear on the cathode. Another example of Scott going above and beyond with their circuit design.

Norman

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Wed 03, 2018 5:59 am 
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Norman - thank you for confirmation and also explaining why the capacitors are there. In this particular case it is difficult to tell whether the last person to service this unit was correct or not. A good for instance is the 2nd detector (76) which had a piece of wire soldered from the cathode to chassis. It looked like it was a mistake maybe but it is hard to say for sure. Thanks again for all of the clarification, this unit is starting to come together nicely.

EDIT: I should also point out the phono input. It looks like someone at some point removed the old posts and installed them backwards. JOY!

Cheers.

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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Wed 03, 2018 9:49 am 
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EMI used a single 2300pF mica cap (the ones with all the plates) across the heaters of the RF, Osc and first IF valves with one side being earthed. This was on the 561 and 650 models that go up to 60 mHz.

Gary


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 Post subject: Re: EH Scott Imperial High Fidelity Receiver (new acquisitio
PostPosted: Jan Wed 03, 2018 5:25 pm 
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Braithwaite wrote:
Yes. Correct. See later versions of service data. These are RF filters to improve oscillator stability. Unlike DC and audio frequencies, RF in the filament circuit can appear on the cathode. Another example of Scott going above and beyond with their circuit design.

Norman


Ok more on this for all of us who were NOT electrical engineers for a living. Hopefully I am understanding correctly.

The 6.3 V heater wires run literally everywhere there is a tube socket with the exception of the voltage regulators.

During this path there is the possibility of migration of RF signal (AC) into the wires as a result of inductance. Sort of the same phenomenon used in the coils in the signal chain to pass signal.

The use of a couple of capacitors connected from the heater wires to chassis allows the RF (AC) current to pass. So with what Norman said in a couple of posts forward of this. the 6.3 V is still 60 Hz AC. at .05uF the impedance is something like 53051 ohm. Brain freeze.

Also note on the previous photo that there is a giant solder glob right beneath the cathode pin of the tube, thanks previous repair guy! Anyhow there is also a grounding tab slightly off to the right. It looks like originally there was a bus bar from the cathode of this tube over to the grounding tab. I will be restoring it shortly.

Cheers

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Last edited by Bosch's Fault on Jan Wed 03, 2018 10:57 pm, edited 1 time in total.

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