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WB5LHV
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Joined: 01 Jan 1970
Posts: 75
Location: Las Cruces, NM
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| Posted: Nov Tue 03, 2009 5:42 pm |
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I have just acquired a Grebe CR-5, perhaps an early model. Rider shows a grid leak resistor, but the radio does not have one.
Does anyone know or have a picture of how this resistor may have been installed in some CR-5s?
Thanks,
Charlie |
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Jack Shirley
Member
Joined: 14 Mar 2008
Posts: 2459
Location: SE USA
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| Posted: Nov Tue 03, 2009 10:27 pm |
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| Is it missing or was it never there? Not speaking specifically to the CR-5 but many older radios relied on circuit leakage and didn't use a discrete grid leak resistor. |
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WB5LHV
Member
Joined: 01 Jan 1970
Posts: 75
Location: Las Cruces, NM
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| Posted: Nov Tue 03, 2009 10:52 pm |
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Never there, no holes. Therer is one on the Rider schematic.
Only the Shadow knows.
Charlie |
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Norm Leal
Moderator
Joined: 01 Jan 1970
Posts: 22373
Location: Livermore, CA
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| Posted: Nov Tue 03, 2009 11:32 pm |
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Charlie
Sometimes the grid leak resistor is part of the coupling cap. Maybe be a couple brackets for a plug in resistor? May be a leakage path on the grid cap? See if the cap has several meg leakage.
_________________
Norm |
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Curt Reed
Moderator
Joined: 01 Jan 1970
Posts: 27616
Location: Sandpoint, IDAHO US of A
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| Posted: Nov Tue 03, 2009 11:46 pm |
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I recall reading in some early 1920's QST Magazines that some grid leaks were offered that combined the resistor along with the capacitor in one unit. I often wondered if they hand selected leaky capacitors for this function?  Wish I could remember who the manufacturer was. Muter seems to come to mind, however, but I could be wrong on that.
Curt
_________________
Curt, N7AH
(Connoisseur of the cold 807) CW forever! |
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WB5LHV
Member
Joined: 01 Jan 1970
Posts: 75
Location: Las Cruces, NM
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| Posted: Nov Tue 03, 2009 11:46 pm |
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I thought of that Norm, but it isnt there. What I was hoping was that later serial numbers had one and I could copy the design.
Charlie |
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Jack Shirley
Member
Joined: 14 Mar 2008
Posts: 2459
Location: SE USA
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| Posted: Nov Tue 03, 2009 11:56 pm |
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I bought some NOS Dubilier caps with the grid-leak mounting clips and they are leakier than any grid leak that you would snap into them. And they also leak equally as well to 'ground' depending on mounting. I'm sure they weren't that way when new but with 80-year old components you never know what you will find.
If it were me I wouldn't 'deface' a CR-5 hoping to make it work better. It could well be that the rest of the circuit negates the effect of adding a new gridleak. You could tack in a resistor (1-2Meg) to see if it makes any difference but I'd bet it won't. |
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WB5LHV
Member
Joined: 01 Jan 1970
Posts: 75
Location: Las Cruces, NM
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| Posted: Nov Wed 04, 2009 4:24 am |
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Thanks Jack, good comment. I think a resistor on clip leads will do.
Charlie |
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Jack Shirley
Member
Joined: 14 Mar 2008
Posts: 2459
Location: SE USA
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| Posted: Nov Wed 04, 2009 4:39 am |
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I have high suspicion that you'll be convinced! Let us know if it turns out otherwise.
A quickie test before doing anything would be a resistance measurement from grid to ground (tube in place). VTVM, DMM, no VOM. May be lower than the 1-2-3 Meg resistor that you want to install. |
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Curt Reed
Moderator
Joined: 01 Jan 1970
Posts: 27616
Location: Sandpoint, IDAHO US of A
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| Posted: Nov Wed 04, 2009 12:14 pm |
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I have had good luck with some of those capacitors after heating them in an oven for a couple of days driving the internal moisture out of them.
They all checked just fine on the Sprague Tele-Ohm-Mike at 500 volts after that. But before cooking them, they were all very leaky.
Curt
_________________
Curt, N7AH
(Connoisseur of the cold 807) CW forever! |
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