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PostPosted: Sep Wed 02, 2015 12:58 am 
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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Wed 02, 2015 1:03 am 
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Use this schematic,I don't think either are ground,more like "common" but I haven't looked at the schematic;

http://philcoradio.com/tech/images/511.jpg

Phil

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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Wed 02, 2015 1:06 am 
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Yes, terminal 5 goes to ground.

However, terminal 6 seems to go to the "LOC" binding post. I suspect that binding post will end up being connected to ground with a jumper to the "GND" binding post, but you might as well use that binding post and not connect terminal 6 directly to ground.

I'm not sure what "LOC" means, but I suspect someone else can fill us in on that (or maybe you already know?).

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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Thu 03, 2015 12:20 am 
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Tom Albrecht wrote:
Yes, terminal 5 goes to ground.

However, terminal 6 seems to go to the "LOC" binding post. I suspect that binding post will end up being connected to ground with a jumper to the "GND" binding post, but you might as well use that binding post and not connect terminal 6 directly to ground.

I'm not sure what "LOC" means, but I suspect someone else can fill us in on that (or maybe you already know?).


The LOC. terminal would be jumped to the ANT. terminal for reception of local stations. This connects the AC wiring through a cap to the antenna making reception of local stations without an external antenna possible. Wouldn't pass safety muster today.

Steve Chambers


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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Thu 03, 2015 7:51 pm 
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There should be three terminals on the bypass cap assemblies. One shared between the resistor and cap, and one each for the unshared ends of the resistor and cap. I presume that is what you see?

I don't know whether it is possible to remove the old caps from your assemblies without destroying the resistors. If these are standard Philco bakelite blocks, the resistor is usually underneath, if I remember correctly? In that case, it might be possible to keep the resistor, although I would not necessarily count on it.

It's OK to use ceramic disk caps for bypassing. A little known fact about ceramic caps is that if they operate with DC across them near their rated working voltage, the capacitance can be much lower than the rated value. So it can be a good idea to double the value (use 0.2 uF ceramic disk to replace 0.1 uF paper cap). However, most people aren't aware of this issue, and it is seldom a problem to simply replace with the same value as the original.

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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Fri 04, 2015 12:09 am 
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If you really want to preserve the original resistors inside the bakelite blocks, simply break the ground connection going to the cap terminal on the bakelite block, and leave it disconnected (this takes the original cap out of circuit). Keep the two resistor connections in place, and then connect a new capacitor outside of the block from the shared terminal to a suitable ground terminal.

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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Fri 04, 2015 1:45 am 
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OK - I see the type now. Sounds like you figured out a good system for reworking these types of resistor-cap combos.

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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Fri 04, 2015 2:53 am 
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Looking good Jon!!

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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Fri 04, 2015 1:37 pm 
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500 volt caps will have a high enough voltage rating. I think it's fine to start with simply replacing 0.1 uF paper with 0.1 uF ceramic, even though the ceramic caps may actually have a lower capacitance than their rating because of the DC voltage across them. The exact value of bypass caps usually isn't super critical. If we see some unexpected behavior of the set, we can keep the bypass capacitors in mind as a possible concern.

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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Fri 04, 2015 11:25 pm 
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Yes -- many types of ceramic caps show reduced capacitance once there is substantial DC voltage on them. Depends on the particular dielectric they use. The really common ones with Z5U rating are fairly bad actors in this respect.

Might not be a problem, but possible solutions include using a cap rated for much higher voltage than you expect to apply (for example, 1 kV caps here) or larger capacitance than nominally called for (like 0.2 uF here).

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 Post subject: Re: Philco 511 Restoration & Questions
PostPosted: Sep Sat 05, 2015 3:45 pm 
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Jon

In addition to to capacitance change with voltage they change greatly with heat. Heating a ceramic cap capacitance starts to increase then hotter is goes down. I had a .1 mf cap get down to .01 mf when heated with a soldering iron. I only did this on one cap but expect others will react similarly.

I would only use ceramic caps where exact capacitance wasn't critical. You can buy ceramic caps with controlled changes, some going up others down with heat.

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