A Zenith 8G005YT restore - Printable Version
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+--- Thread: A Zenith 8G005YT restore (/showthread.php?tid=14687)
RE: A Zenith 8G005YT restore - klondike98 - 06-05-2016
Thanks for the info and advice!
Here's the schematic for this version of the 8G005YT.
I started to recap the electrolytic can that contains 3 caps (40, 20 and 10 uF). I was pleased to see that the two power resistors were in good shape. The one mounted to the chassis is a pair of 970 ohm (actually reading 1k each) and the brown one on the left is 88 ohms (reading 128 ).
[Image: https://www.dropbox.com/s/hnza7zchc74p4z5/zenith8G005_16.jpg?raw=1]
So I started desoldering the leads on cap and .... grumble grumble grrrr.... rats.....
[Image: https://www.dropbox.com/s/nkty7elskh4jqdi/zenith8G005_17.jpg?raw=1]
...my hand slipped as I was working one of the leads off and I broke the resistor.
I did finally get the cap out and then thought perhaps I should have tried to take the black cardboard cover off and use the saw off the cap while still in the chassis technique.... too late now.
[Image: https://www.dropbox.com/s/8z4gg5s67pvlist/zenith8G005_18.jpg?raw=1]
Does anyone know if the black cardboard around the can comes off with heating or did Zenith glue them on rather than using tar?????
RE: A Zenith 8G005YT restore - Kenneth F. Besso Jr. - 06-06-2016
I just did one of them,,On a Zenith 6C05Z,,,,I peeled the top open,,,Real Easyly,,,little water to make it roll open,,,and then a little heat on the outside ,,and pulled it off the can,,and you know the rest,,Cheers
RE: A Zenith 8G005YT restore - morzh - 06-06-2016
Bob
The resistor looked a bit baked to start with, and 45% off too! So maybe that was a good thing you broke it.
RE: A Zenith 8G005YT restore - klondike98 - 06-06-2016
Mike, good thought. I've got a 5 watt 82 ohm that I could use. The original was a 2 watt rating.
Kenneth, not sure what you mean by "peeled the top open" and " make it roll open". Were you able to reuse the black cardboard cover.
RE: A Zenith 8G005YT restore - sam - 06-06-2016
Bob
If you heat the sides up a little I believe it will pull off
If I remember right tacked on with little tar
In that phorum free box was one
RE: A Zenith 8G005YT restore - morzh - 06-06-2016
The one single portable Z I vixed is 6G001Y companion and it also used the twistlock quad, so as I recall the cardboard just pulled off. So was the case with a similar cap in HP Oscillator.
Have you given a thought to buying a new cap? There are new twistlock ones, keep seeing on eBay, though not sure of the values.
RE: A Zenith 8G005YT restore - Radioroslyn - 06-07-2016
Hi Bob,
Those two resistors are a little critical in terms of there resistance as they control the amount of filament voltage that goes to the filament string. Too low resistance and you could burnout the filaments or too high not enough filament voltage giving poor performance. There usually a high value cap in the filter can like 100 or 200mfd @ 15 or 20vdc. This is where the filament volt exits the p/s and goes onward to the filaments check your voltage there to be sure it's proper.
GL
Terry
RE: A Zenith 8G005YT restore - klondike98 - 06-07-2016
Yep, there is a 200uF cap in there. Thanks Terry, will do that. Would I check that with all the tubes out except the rectifier tube?
RE: A Zenith 8G005YT restore - Kenneth F. Besso Jr. - 06-07-2016
The top has a roll over effect,,from the side----which has a piece of Black paper on the top of the CAN,,(same as the sides) Tarred down,,had to get that off first,,,soo,you can heat the can up,,to slide the Black sleeve Off,,,,,
RE: A Zenith 8G005YT restore - morzh - 06-07-2016
yes there was a 200uF low voltage cap. I bought some when repairing it and still have those. It is the filament cap I think.
Here's one thing: if any of the tubes plugged in parallel to this cap is removed while the radio is on, or burned out and replaced while the radio is hot, or has been unplugged for a short time, the new tube when plugged in will go "poof!".
To combat that a zener needs to be plugged in parallel to the cap.
RE: A Zenith 8G005YT restore - klondike98 - 06-12-2016
OK, some progress here. The recipe on the Zenith electrolytic was to put it into the oven for about 20-25 minutes @ 250F. The tar softened and the cardboard pulled off neatly.
[Image: https://www.dropbox.com/s/5xkq4wx1ojqtujy/zenith8G005_19.jpg?raw=1]
[Image: https://www.dropbox.com/s/4hh5hoe6sm5gmzp/zenith8G005_20.jpg?raw=1][Image: https://www.dropbox.com/s/f2tpzg5c2k8oupr/zenith8G005_21.jpg?raw=1]
and the recapping has begun. I've elected not to try and restuff the paper caps since many are not zenith, the power resistor will be modern, the safety cap is hard to hide (that's one good thing about those Philco bakelite blocks!) and I'll be adding a fuse under there.
[Image: https://www.dropbox.com/s/4zf88cavxgijxj2/zenith8G005_22.jpg?raw=1]
RE: A Zenith 8G005YT restore - sam - 06-12-2016
nice work so far bob
RE: A Zenith 8G005YT restore - klondike98 - 06-16-2016
Need some advice. I've read that the TOs are particularly sensitive to current inrush and benefit from having a thermistor added. I see two ways to approach that, 1) thermistor (I think a CL-90 ) in series with the 1 amp fuse on the hot side of the house voltage ( seen in red below) OR 2) in series with the R18 resistor on the DC side of the rectifier tube (where the green circle is). Any thoughts on this?
Thanks!!
[Image: https://www.dropbox.com/s/tb6sbixwkozm8un/varistor.jpg?raw=1]
RE: A Zenith 8G005YT restore - morzh - 06-16-2016
Bob
There is no such thing as an inrush after the rectifier tube. Inrush occurs when you apply a full voltage (or very fast rising one) to say an electrolytic cap.
But the tube warms up for seconds/tens of seconds. There is no insrush.
If you had the selenium rectifier...then there would be some.
There is some inrush with the filaments IF (and only if) fed directly from the AC line or battery without tube rectifier in between.
RE: A Zenith 8G005YT restore - klondike98 - 06-19-2016
Yes Mike, its the filaments that folks write about and which they say the thermistor provides some protection for. At this point I just added a fuse. I didn't want to drill any new holes in the chassis so opted for the inline style fuse holder. Also replaced that 88 ohm power resistor that I broke with two 2 watt 180 ohm resistors in parallel (yellow circle in photo). The recapping continues (working left to right in the chassis).
[Image: https://www.dropbox.com/s/d58wmtpg8nhkbdj/zenith8G005_23.jpg?raw=1]