Realistic specs

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CeaSaR
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Re: Realistic specs

Post by CeaSaR »

Front face plate from left to right:
1/4" headphone jack
On/Off left volume
Right volume
AM/FM/TAPE/PHONO selector
Tuning
FF/EJECT
Tape slot

Rear;
L/R speaker RCA jacks
Power cord
(And now auxiliary input cord)

Tape could use some new belts and a good cleaning. Since I don't have replacement belts yet, I'll wait to do the cleaning. Really, it's the flywheel/capstan belt that's a bit loose. Take-up belt seems good, but I might as well replace that too.

Turntable is one of those smaller plastic platters with the integrated 45 adapter. I'm 99% sure that it's an idler wheel. Torque seems quite good from the top, it takes decent pressure to slow it down. The cartridge must be ceramic, it doesn't go through any amplification before hitting the selector switch. From the looks of the stylus, I don't think it was used much, if at all..the platter is held on via the spindle, which actually has a nut on the bottom. By the time I spied that, I was ready to put it up for the night.

All in all, it really only needed some cleaning and a few age related bits, but not too bad for a 30+ year old bottom of the line unit.

I'll take some more pics and add to the post over there. It's a lot easier to do it there. When, depends on my/my family schedule.
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Janitor Tzap
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Re: Realistic specs

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CeaSaR wrote: Sun Dec 13, 2020 8:05 pm Tape could use some new belts and a good cleaning. Since I don't have replacement belts yet, I'll wait to do the cleaning. Really, it's the flywheel/capstan belt that's a bit loose. Take-up belt seems good, but I might as well replace that too.
Hmmm......
2 belts....
Normally the Tape Decks designed for car radios would only use one.
Well, just be careful when disassembling the Flywheel-Capstan to gain access to that smaller Belt.
There is a small Plastic Split Washer that holds the Capstan in place.
And it is all too easy to have it go flying off to some where else in the room, never to be seen again!
CeaSaR wrote: Sun Dec 13, 2020 8:05 pmTurntable is one of those smaller plastic platters with the integrated 45 adapter. I'm 99% sure that it's an idler wheel. Torque seems quite good from the top, it takes decent pressure to slow it down. The cartridge must be ceramic, it doesn't go through any amplification before hitting the selector switch. From the looks of the stylus, I don't think it was used much, if at all..the platter is held on via the spindle, which actually has a nut on the bottom. By the time I spied that, I was ready to put it up for the night.
Yeah,
Most of the Plastic Platters are Idler Tire driven.
Plastic Platters that are Belt, or Direct Drive have been weighted down and balanced, to cut down on the "Rumble" caused by the motor.
I've even come across a lot of older turntables that are Idler Tire driven, with steel platters that have been weighted and balanced.
If your going to check phonographs 33 1/3 & 45 RPM Speed.
Get your hands on a "Strobe Disk"
Here's a video of a really good one: https://www.youtube.com/watch?v=10Rc1y2_x70
Not only does it help you Calibrate the turntables speeds, but it also has a protractor on the reverse side to help you with the Tracking of the Stylus.
Note: There are Smart Phone App's to that can be used to check the speed, but most everyone of them is not as accurate as a "Strobe Disk".

Addition:
I found the Data Spec Sheet{PDF} of the LM386.
https://www.ti.com/lit/ds/symlink/lm386 ... e.com%252F
When I looked at the Max Watts for the IC.
Only the LM386N will output 1.25 Watts.
So, 2 Watts of power may even be a stretch for this unit.
That is if there are actually two LM386N's under that heatsink. :lol:

Hmmm........
I still have my old Radio Shack Semiconductor Cross Reference Guide, and a old Radio Shack Project Circuits Book.
I remember seeing a Low Power Stereo IC that had GND/Heatsink Tabs coming out of the center of the DIP IC.
I'll see if I can't dig up a part number.


EDIT:
Found It!
Dual 2-Watt Amplifier.
LM1877 / LM377
14 Pin style DIP, Center pins 10, 11, 12, 3, 4, 5, are GND/Heatsink.
Vcc is 10V - 26V
Image

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CeaSaR
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Re: Realistic specs

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Nah, it's only an 8 pin DIP. package so it has to be a stereo amp in this 8 pins. I came across a few that looked to fit the bill from that time period. I'll have to look them up again tomorrow - I should be in bed well asleep at this point. zzzzzzZZZZZZZZZ
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CeaSaR
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Re: Realistic specs

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Closest thing I've come across is the TDA2822. Earliest version I could get a Datasheet for is the M version, dated 2003. :/

https://www.st.com/resource/en/datasheet/cd00000134.pdf

I'll have to trace out the pins, but this what the datasheet shows:
TDA2822 pinout.jpg
No ratings listed for 12V, but it will handle 15V max., so I'm thinking about 1.2-1.4W /channel.

I really need to invest in some parts and equipment...
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Janitor Tzap
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Re: Realistic specs

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Hmmm.........

I'm just guessing by looking at the heat sink, and the side tab's on the Heat sink.
that the Amplifier Chip(s), isn't a single 8 pin DIP IC.
{From what I can see from the picture you took of the Main PCB}
Need a better picture of the IC's pins, to make a better guess.
:P

Hmmm...........
If this is 2 TDA2822's, It could be this old version.
Image
https://www.jameco.com/webapp/wcs/store ... gJKKvD_BwE
The spec's state that it could be run as a Mono Amp, giving out 2-watts of power.
Thus, why I'm thinking it has to be 2 IC's under that Heat Sink, or something like the LM1877 / LM377. :?


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CeaSaR
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Re: Realistic specs

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I had the PCB out to do the aux input, and even though there are enough pads to put the 1877 on the board, only 8 pads are used. Still, whatever the chip is, I won't know until I absolutely have to remove the heat sink. If you open up the board pic in another tab to zoom in, you can see all the support components are oriented to the left side of the chip/heatsink, where there chip is located.
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Janitor Tzap
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Re: Realistic specs

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CeaSaR wrote: Mon Dec 21, 2020 11:14 amIf you open up the board pic in another tab to zoom in, you can see all the support components are oriented to the left side of the chip/heatsink, where there chip is located.
Yes, I did use the Zoom in function.
But, I still can't see the pins on the IC, under the Heatsink clearly enough. :(

Thou, speaking of support components.......
One of the Cap's by the Pre-amp IC {KA1222} looks bulged out on the top.
{Its the one in front of R21.}



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CeaSaR
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Re: Realistic specs

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Ok, I finally had a chance to get into this one again. Got my Aux cable done, verified left/right -swapped wires on the board, figures I'd get them backwards. Took some more pics and re-cleaned the volume pots.

I checked the one cap in question, it is flat on top, it's just the way the covering comes up around the top that makes it look that way. I still think the output caps should be replaced, 220 uf is just too small, 470 or 1000 would make it sound better. It's on the thin side. I know, it's a tiny, low power chip, but it could use a bit of sonic help.

I'm going to try to attach a link to the gallery where I put the pics. I don't want to spam the other forum unnecessarily. Here goes: https://postimg.cc/gallery/hnT47PT

Yep, it works. Go to the gallery and click on the photo you want and it'll open in crisp clarity. I think these will help clear up any questions you may have had.

You can see the 8 pin chip in the first photo. On the tape photos, you can see the belt to the flywheel and the belt to the capstan. Then you can see the turntable drive motor situate in idler wheel style (note, there's no other mechanics, so the speed is electronically set), and then the single sided board (multiple shots) ending with the cartridge/stylus. If you want anymore photos, let me know and I'll put them here.
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Janitor Tzap
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Re: Realistic specs

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Yes, much better pic's!

Hmmm.........
Now that I can see the pins on that amplifier chip, under the heatsink.
Plus, you got a shot of the underside. :)
I'm wondering if putting in 470uF or 1000uF will make much of a difference in the sound quality.
The TDA2822 is only 1 watt per channel.
So changing out the 220uF won't make much of a difference.

Okay,
The new picture of the capacitor in front of R21 looks good.
{Must of been the angle that the other picture was taken.}

Have you checked the turntable to see if the 33 1/3 & 45 RPM speed is correct?
On some electric motors they have a Electronic Speed Governor built in to them.
I don't see a slot on it for speed adjustment on that one.
The turntable motor is wired to a small pcb.
Does that board have a voltage adjustment pot, to control the speed of the motor?
Or......
Instead of a variable speed adjustment, it could have a simple voltage divider with a zener-diode, to control the motor's speed.
If the Speed(s) are fine, then don't mess with it.
Just clean the Idler tire and spindle, and check the Idler tension spring.

The Phono Cartridge is a older ceramic style.
Finding a stylus that fits it is going to be hard.
Try to find any numbers on it.
Maybe one of the Turntable Sellers, or places like the https://www.audioadvisor.com/ will have a replacement. :roll:


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CeaSaR
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Re: Realistic specs

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I should have pulled the power board for the turntable, but it sounded fine when I put a record on that I am quite familiar with. I think I'll leave it alone for now. I doubt she'll have many records before she upgrades. Of course, I could always look at Crosley if I really needed to. Nah, I don't think so. Hahaha.

Wanna know what's funny? The LM386 has a 470 uF as a recommended (by modders) upgrade for the output, and that is usually only around 1/2 watt. So Maybe??? Depends on what I have when the time comes. For now, it's up and running.

Thanks for the link.
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Re: Realistic specs

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CeaSaR wrote: Sun Jan 24, 2021 8:09 pmWanna know what's funny? The LM386 has a 470 uF as a recommended (by modders) upgrade for the output, and that is usually only around 1/2 watt. So Maybe??? Depends on what I have when the time comes. For now, it's up and running.
Well,
If your looking for the Capacitors.
Electronic Goldmine has some that aren't too expensive.
https://www.goldmine-elec-products.com/ ... ?dept=1025
Only I'd work up an order of other parts too, since your going to have it shipped.

Wait a minute.....
The LM386 isn't a stereo chip!
It only has one input & one output.
Thus, this has to be the TDA2822 stereo chip or something similar.
:roll:


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CeaSaR
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Re: Realistic specs

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Janitor Tzap wrote: Mon Jan 25, 2021 1:15 pm Well, If your looking for the Capacitors.
Electronic Goldmine has some that aren't too expensive.
https://www.goldmine-elec-products.com/ ... ?dept=1025
Only I'd work up an order of other parts too, since your going to have it shipped.

Wait a minute.....
The LM386 isn't a stereo chip!
It only has one input & one output.
Thus, this has to be the TDA2822 stereo chip or something similar.
:roll:


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I have some on hand ATM. Electronics Goldmine has some good stuff. That's where I was buying stomp switches when I was building pedals for my oldest. I think most of the other stuff I needed at the time came from there too.

I only mentioned the LM386 because it is used all over the place in hobbies and has a strong modder base. It is DEFINITELY NOT the chip in use here.
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Lenp
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Re: Realistic specs

Post by Lenp »

Regarding cleaning that plastic tuning cap.
Beware, most of those era variable caps used very thin plastic separators between the plates since it was all packed together so tight. The unit is pretty well sealed so anything you inject will take a long time to evporate. If the plates are wet or the cleaner leaves any residue, they may stick together, bunch up, or tear causing the plates to short.
If you have really bad luck the cleaner will affect the spacers or plactic housing and the control will not turn!
But, with any luck at all, it might lock up on or near a local station :cool:
Years ago those tuning caps were plentiful and cheap, so we would just replace a bad one, but today they are not very common.

Side Note: I repaired a tube guitar amp yesterday, bad screen grid resistors. ...
I grew up with tube sockets, but this was my first 'bulb' repair in many years! I AM NOW EXPERT :shock:
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)
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CeaSaR
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Re: Realistic specs

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She's all done and put back together, minus the new belts, but it's been pretty steady. It's still a cheap unit, but it all works, plus 1.

Screen grid resistors, must've been some old carbon comp cookers!
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Lenp
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Re: Realistic specs

Post by Lenp »

Hi CeaSaR
Nope, not carbon comp. These were small, blue, like .5W metal film 100 ohm. One measured ROA (Resistance Of Air) but both got changed with higher rating resistors. This amp originally came in with one side of the primary winding open in the output transformer. These Trace Elliott Velocette amps were notorious for bad transformers. The bad resistor(s) were found after the transformer swap and the EL84 outputs were not damaged.
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)
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