a real challange?

[Yamamaya42]

Originally Posted by Kevin Kuehn

That is a shield because the signal level is so low at the detection point. You really should not need to disturb much under there.

I took these hand held photos of what Riders has on the model 895. You can compare the audio section to your Sams. I did not study it in depth, but it appears basically the same minus your set is not using the 1st audio or output tubes. It's curious that your chassis actually has the 6AT6 1st audio tube installed, but it's not being used.

If you want to keep these Riders pages you'd better save them because I can't promise how long they will be posted on my Flickr page.

https://www.flickr.com/photos/152661...57713086856613

THANKS!

That does help quite a bit!
I was pulling my hair out and screaming trying to figure it out...
SAMS left some things out :O
like the green wire that runs back to the tuner, not sure what it does, or why it was left out, but IT CAN BE SEEN on all SAMS versions, ( photos ) , just not on the schematic, it is however on what you uploaded !

and yes I did remove that plate, I have to get under it to remove the wire and add the normal sound circuits, will put it back after.

thanks again that makes this easier!

[Yamamaya42]

Originally Posted by Kevin Kuehn

but it appears basically the same minus your set is not using the 1st audio or output tubes. It's curious that your chassis actually has the 6AT6 1st audio tube installed, but it's not being used.


https://www.flickr.com/photos/152661...57713086856613

Looking closer at the data for the 6AT6, it seems that it IS being used for something in the set.

The tube is... a “Duplex-Diode High-Mu Triode”
The diode part is being used for something, but not sure what, or how, it goes down to the contrast control, and to the tuner ( not shown on sams schematic, but I can see the wire in photo page 6 0074-3 )

not really sure what this does however

[Kevin Kuehn]

Originally Posted by Yamamaya42

Looking closer at the data for the 6AT6, it seems that it IS being used for something in the set.

The tube is... a “Duplex-Diode High-Mu Triode”
The diode part is being used for something, but not sure what, or how, it goes down to the contrast control, and to the tuner ( not shown on sams schematic, but I can see the wire in photo page 6 0074-3 )

not really sure what this does however

Good eye, I missed that. Those two diode plates share a common cathode with the triode section. It appears to me they are using the forward bias of those diodes as a voltage reference for the Picture(Contrast)control. That variable voltage is feed to the grids of rf and if tubes, which in turn varies the gain of those stages. Unless I'm missing something I don't believe the set has any automatic gain control, only that manual picture adjustment.

[Kevin Kuehn]

They do show the same thing in Sams 74-3. It's just a little harder to follow because Sams doesn't label the b+ and b- supplies very well.

[Yamamaya42]

Originally Posted by Kevin Kuehn

They do show the same thing in Sams 74-3. It's just a little harder to follow because Sams doesn't label the b+ and b- supplies very well.

Main difference I see, ( prob does not matter, but is confusing :/ )
on SAMS 0074-3 tuner section, rf amp area v1, r11,r10, c9, point where the 3 meet goes to r12
(1k) then gnd.

on other schematic (895 ) same area,
r13 r3 ( r11,r10 above ) , c5 ( c9 above ) this is hooked up the same as shown in the SAMS,
however after that it's different, r12 (same as above ) the 1k resistor does NOT tie to gnd, but to a green shielded wire, back to that contrast / picture control circuit.


Which is what is weird, cause before you sent your scans, I was looking and looking, wondering WTH that green wire was, cause I could see it on my set, I could also see it in the underside photos in 0074-3, but could not work out what it was doing going to the tuner, till now.

But who ever said SAMS were 100% accurate? :p

[Electronic M]

Sam's can have mistakes. Early Sam's had yet to adopt some practices and notations that in the 50s were their calling card.

Also factories make production changes... different publishers might have different revs in front of them. Some makers gave the publishers production change notice, other makers (I'm looking at you Magnavox) outright didn't want others publishing their service data and tried to thwart that...

I always say if it looks original it probably is despite what the paper indicates...

[Kevin Kuehn]

After looking at that circuit a while longer, those two diodes may be nothing more than a rf gain clamper. In other words they limit how far the if grids can swing positive. Apparently that contrast method didn't work very well because most manufactures soon abandoned it in favor of moving the contrast control to the video amp stage. Then AGC was used to control the if gain. Interestingly the same thing happened in the early days of radio when AVC came on the scene.

[Yamamaya42]

hmmm...

when I start to try to put audio back into this, one thing I have always heard, always use film caps where there was paper, and it looks like there was paper caps ment to be in C64/C67, but I do not have any film ones in the .0025 that is shown on the schematic, but I DO HAVE 2200pF film caps, and I really don't think anything will explode or catch fire if I use them there. :P

[Electronic M]

Originally Posted by Yamamaya42

hmmm...

when I start to try to put audio back into this, one thing I have always heard, always use film caps where there was paper, and it looks like there was paper caps ment to be in C64/C67, but I do not have any film ones in the .0025 that is shown on the schematic, but I DO HAVE 2200pF film caps, and I really don't think anything will explode or catch fire if I use them there. :P

2500 vs 2200 at audio frequency nobody will notice the difference.

[Yamamaya42]

To start with, as far as replacing the capacitors, I will go down the list on the SAMS and replace all the ones that have a voltage rating listed, this SHOULD take care of most of the problematic caps in there and allow slow power up, I hope.

[Kevin Kuehn]

I'm not sure about doing only those with voltage ratings listed, but electrolytic and anything paper dialectic are going to be your primary concern. Occasionally mica types if the cap has a large DC voltage across it. But I tend to leave those unless an issue proves them defective.

[Yamamaya42]

Originally Posted by Kevin Kuehn

I'm not sure about doing only those with voltage ratings listed, but electrolytic and anything paper dialectic are going to be your primary concern. Occasionally mica types if the cap has a large DC voltage across it. But I tend to leave those unless an issue proves them defective.

I did a bit of looking and basically, the ones on the list with voltage ratings ARE the paper ones and the electrolytics, I can't say this with 100% accuracy, but it does seem to be the greater bulk of them, so I'm thinking to start with that, while doing a visual along the way for any missed.

[Electronic M]

Originally Posted by Yamamaya42

I did a bit of looking and basically, the ones on the list with voltage ratings ARE the paper ones and the electrolytics, I can't say this with 100% accuracy, but it does seem to be the greater bulk of them, so I'm thinking to start with that, while doing a visual along the way for any missed.

Some of the RCA sets of that time (don't know about clones) had something like 1000-2000pF micas in the IF strip that are fairly prone to failure (which is unusual in an IF). If it won't pass video after recap it would be worth changing those.

[Yamamaya42]

Originally Posted by Electronic M

Some of the RCA sets of that time (don't know about clones) had something like 1000-2000pF micas in the IF strip that are fairly prone to failure (which is unusual in an IF). If it won't pass video after recap it would be worth changing those.

going to have trouble with IF no matter what, due to the broken 3rd IF coil (L11) , I managed to put it back together, and it can be adjusted, but any setting on it was long lost.

It might work.

[Yamamaya42]

https://imgur.com/KPAR24N
empty hole filled.