A nice big piece of Pye - Page 3 - Videokarma.org TV - Video

Jon A. · #1 10-23-2017, 05:46 PM

I don't know, wouldn't that cause a drop in available power dissipation? I see they're only 3 watts each, and I just haven't been able to get a grip on series/parallel wiring for resistors.

Electronic M · #2 10-23-2017, 06:05 PM

2 3W resistors of equal resistance in parallel or series = 1 6W resistor for series it will have twice the rated resistance of each unit, for parallel it will be half the rated resistance.

Power = Voltage * Current In series each unit takes half the voltage of the pair, in parallel each unit takes half the current....This assumes the two resistors are of equal value....If different the math for power ratings gets more complicated.

It may be useful to do some practice ohms law math, and network analysis math to gain a better understanding.

In other news that part that was low stock turned out to be NO-Stock...I had to call Mouser and ask about it for them to send me the rest of my order....Which apparently they were not going to ship till I asked...

madlabs · #3 10-23-2017, 06:19 PM

Tom, you got that backwards - Two equal resistors in parallel halves the resistance and doubles the wattage. Two equal resistors in series adds the resistance and the wattage remains the same.

So Jon, no problem with the two resistors in parallel. I would make sure there is a little air gap between them for heat dissipation

old_coot88 · #4 10-23-2017, 07:59 PM

Quote:

Originally Posted by madlabs

Two equal resistors in series adds the resistance and the wattage remains the same.

The wattage rating for the pair would double, wouldn't it? For example, with two equal-value half-watters in series, the wattage rating for the pair would be 1 watt, seems like (since the working voltage across each will be halved).

Whereas a pair of half-watters in parallel also has a 1 watt rating because the current through each is halved.

Jon A. · #5 10-23-2017, 06:27 PM

Got it, thanks.

Any leads on the bulbs, grommets and dial string? Once those are secured I'm all set.

madlabs · #6 10-23-2017, 09:53 PM

Nope. With the resistors in series each resistor still has to handle all the current flowing through it. So the wattage rating remains the same. With two equal resistors in parallel each is taking half the current so the wattage rating doubles.

old_coot88 · #7 10-24-2017, 12:15 AM

Quote:

Originally Posted by madlabs

Nope. With the resistors in series each resistor still has to handle all the current flowing through it.

Yup. All the current.

Quote:

So the wattage rating remains the same.

Since they're in series, each resistor sees only half the voltage. So the wattage rating of the pair hasta double.

Just for example - two 20K half-watters in series makes a 40K @ 1 watt rating.

Just as two 20K half-watters in parallel makes a 10K @ 1 watt rating.

Jon A. · #8 10-24-2017, 03:10 AM

Alrightie, I finally got motivated enough to compare the original parts list, my list of parts to replace and the contents of the Mouser shopping cart, all is good there.

Once I get info on a source for tuner capacitor grommets, dial string and bulbs I'm all set. Nevertheless it's good to have the info on the resistors, that was a tough nut to crack. I clipped out the 1.6k 4 watt resistor and smashed it apart just to see how it was made. It had a white cylindrical ceramic core with stranded leads going all the way through each end, was wrapped with very fine wire and topped off with a thin green coating. I have doubts it was one of the more reliable designs.

Now, can anyone point me in the direction of the last things I need? That would be great, a one-stop shop would be best. I'm finalizing a list and an estimate for the owner.

Electronic M · #9 10-24-2017, 11:46 AM

This guy is a local cap vendor (I buy from him at swap-meets) and stocks dial cord and dial lamps as well as yellow film caps and lytics. http://www.radioantiques.com/

Some hardware stores stock rubber grommets if you look through the drawers (IIRC Ace hardware is one).

Madlabs: I fixed the series parallel resistance value thing, I noticed I got it backwards (sometimes I have to finish typing fast and skip a proof read) before I read your post...However I agree with old coot the effective wattage of the pair doubles in both configs. In college I proved that mathematically a few times and can do it again if you doubt us.

madlabs · #10 10-24-2017, 04:18 PM

Tom, I knew it was a typo. And I sit corrected and thank you and old coot for setting me straight!

Jon A. · #11 10-24-2017, 04:53 PM

Oh cool, that's one site I stumbled on, just needed confirmation of a good source.

Oh okay, so I don't need special tuner grommets, just the right size. I already added one grommet to my cart for the power cord. Got to replace the cord too, the insulation was falling apart.

The owner thought it might explode if powered up as-is; maybe not explode but I'm pretty sure the end result wouldn't have been pretty.

Jon A. · #12 10-26-2017, 01:47 PM

I'm sure there's no short answer to this, but can this radio tune FM stations? I can't make head or tail of this dial.

maxhifi · #13 10-26-2017, 03:09 PM

Quote:

Originally Posted by Jon A.

I'm sure there's no short answer to this, but can this radio tune FM stations? I can't make head or tail of this dial.

No. This radio is broadcast band, and "general coverage" shortwave. It will be amplitude modulation only, no FM.

M c/s = MHz, and K c/s = KHz.

Jon A. · #14 10-26-2017, 07:51 PM

Gotcha, the frequencies in MHz looked unfamiliar to me and I didn't know what influence the markings on the right of the dial mean.

Anyway, I totaled up the cost of all the parts and supplies needed to restore this radio - the parts being a fraction of the cost - and at this point it looks like the owner doesn't want to bother with it so worst case I'll be hanging onto it as a long-term project. He wanted to use it regularly but there are no AM stations around here. No big deal, there must be something to listen to in the decent parts of the country.

maxhifi · #15 10-26-2017, 08:01 PM

Quote:

Originally Posted by Jon A.

Gotcha, the frequencies in MHz looked unfamiliar to me and I didn't know what influence the markings on the right of the dial mean.

Anyway, I totaled up the cost of all the parts and supplies needed to restore this radio - the parts being a fraction of the cost - and at this point it looks like the owner doesn't want to bother with it so worst case I'll be hanging onto it as a long-term project. He wanted to use it regularly but there are no AM stations around here. No big deal, there must be something to listen to in the decent parts of the country.

The markings on the right, at the top is BC, which means broadcast, and under that is the wavelength in meters. Wavelength is inversely related to frequency, and is commonly used in short wave and amateur radio.

As for parts count, there isn't really any reason to change all the resistors, and you can use cheaper capacitors. That's a really cool radio and it would be nice to see it work, but I agree without any use for it it's a tough sell.