Does Model 89 Require Shield On 75 Tube? - Printable Version
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+--- Thread: Does Model 89 Require Shield On 75 Tube? (/showthread.php?tid=4787)
Does Model 89 Require Shield On 75 Tube? - Pepperoni - 05-23-2012
I performed a complete restoration on an early model 89 recently.
http://www.nostalgiaair.org/PagesByModel/876/M0013876.pdf
In an effort to put it back into it's original configuration I removed the 6Q7 and the associated octal socket that someone had installed to replace the 75 2nd detector. I also incorporated the mods that are described here.
http://www.philcoradio.com/tech/89evol.htm
The radio works great in my shop but when the fella takes it to his house he says it makes humming/buzzing noises while on station and between stations. I can't reproduce this problem except by touching the top cap of the new 75. It's hard to understand what people are saying when they try to describe a problem. Whoosh, clunk click, click etc.
I've got the radio back in my shop and there's nothing wrong with it. I'm wondering if when the original 75 socket was removed the shield holder was also removed. I don't know this for a fact.
So I'm asking if the 75 2nd detector was originally covered with a shield on this radio?
Thanks,
Pepper
RE: Does Model 89 Require Shield On 75 Tube? - tab10672 - 05-23-2012
yes it is/was, Also where is the owner grounded? if he uses earth/neutral from his outlet that will sometimes cause the same problem.
RE: Does Model 89 Require Shield On 75 Tube? - Arran - 05-23-2012
A type 75 tube needs a shield in most of the sets I have encountered, even cheap ones, without one the set howls like a banshee. A 6Q7 is normally a metal tube so it already has the shield built in, unless it was a 6Q7 G then it would need a shield, not sure about a 6Q7 GT.
Regards
Arran
RE: Does Model 89 Require Shield On 75 Tube? - Steve Davis - 05-23-2012
Also, the grid wire must be inside the shield.
Steve
RE: Does Model 89 Require Shield On 75 Tube? - Pepperoni - 05-23-2012
Okay guys, Thanks! I just had a hunch that the 75 had something to do with it. But it was only a hunch. Still don't understand why it works great in my shop and not somewhere else. But I'm in the country, he's in the city, more power lines, electrical substations etc. Could be any of those or none. He thinks he needs more antenna but I live 35 miles from the big city and I pick up all the stations from there with no antenna. Attach the 10' 14awg stranded insulated piece of wire to the "ANT" clip and it really pulls them in. And he's closer to them. Maybe too close. He's picking up the radio today and I told him to try it without any antenna hooked up at all. May have to turn the volume up but I know that I get a soft hum from the local AM station I listen too but I'm right on top of their transmitter. Disconnect the antenna and the hum goes away.
Now it's off to the want ads to find a Philco 89 shield and shield holder that is attached to the chassis. I don't mind working on radios that have been chopped up but why don't folks keep all the original parts with the set and pass them down from owner to owner or family to family.
I wish!Thanks again,
Pepper
RE: Does Model 89 Require Shield On 75 Tube? - Radioroslyn - 05-23-2012
I would suspect that he's picking up some sort of rf interference. There's a lot of it around these days. Shielding the 75 won't help if this is the case. A good ground will help but may not completely get rid of it.
GL
Terry
RE: Does Model 89 Require Shield On 75 Tube? - Pepperoni - 05-23-2012
Well I didn't have an original Philco shield but I did have one that fit over the tube. Grid wire wouldn't fit inside the shield though. But he picked it up today, took it home and he says it works perfect. Just needed that 75 shielded. I do have a want ad in that section for an original shield and shield support if anyone has one.
Thanks much for the answer to my question!
Pepper