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Philco 90 pp 47 Restoration Questions - Printable Version

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Philco 90 pp 47 Restoration Questions - buster757 - 12-04-2022

Are 10 watt resistors adequate to rep0lace the candohm in a dual 47 Philco 90 chassis?

RE: Philco 90 pp 47 - Radioroslyn - 12-04-2022

I can't think of a candohm resistor in the 90 chassis. Can you reference it with a pictorial number or part number? There is a large wire wound resistor.

RE: Philco 90 pp 47 - buster757 - 12-04-2022

Thats it.  My bad not exactly a candohm, but a multi section wirewound

RE: Philco 90 pp 47 - buster757 - 12-04-2022

Its a multi section wirewound, not a candohm, my bad

RE: Philco 90 pp 47 - buster757 - 12-04-2022

Part number 6071 -205, 95, 2400, 1200

RE: Philco 90 pp 47 - morzh - 12-04-2022

What do you get when a a safety capacitoris crossed with a power resistor? - A Candohm!

RE: Philco 90 pp 47 - radiorich - 12-05-2022

Hello morzh,
nice one !
Buster that is good news a wire wound .

Sincerely Richard

RE: Philco 90 pp 47 - Radioroslyn - 12-05-2022

I did a ROUGH calculation and came up with about 6 1/2 wts. Rule of thumb is to double or triple that amount. At 6 1/2 wts it will be getting hotter than the hinges of haties. That's why you'll want to increase the the size.

RE: Philco 90 pp 47 - morzh - 12-05-2022

Hades, Terry Icon_smile
Even though I am sure, hinges in Haities (however many of them there are) are also pretty hot.....

RE: Philco 90 pp 47 - MrFixr55 - 12-06-2022

My $0.02:
From the RCA Receiving Tube Manual, Cathode Current (Plate I + Screen I) for one tube is 37 mA or 0.037A. For 2 tubes, 0.074A. Grid Bias is -16.5V (Funny, these are similar specs to 2A5, 42, 6F6, etc.) So if P (Watts)=VI, then 16.5 (the voltage drop across the resistor) X 0.037A (the current for 2 tubes, and it may be less) = 1.23W. Total amplifier power is not the criteria, the voltage drop across the resistor X the current in the circuit determines the power dissipated across the resistor, and therefore the wattage required.

Current in a circuit is constant. The Amp likely delivers between 5 and 10 watts total. The total dissipation of the 2 tubes (250V X 0.074A) is 18W. Usable power is less than that.

In these calculations, I assumed both tubes are conducting. The current varies and should be 180 degrees out of phase. However, at these more severe conditions, the calculations should hold. Therefore a 10 Watt or even a 5 Watt resistor should handle it. I have a Magnavox amp that has 2 6V6s and plate voltage is about 300V. the common cathode resistor is a 2 watt carbon job.

Hope this helps.

Philco 90 pp 47 - buster757 - 02-08-2023

Hi All. I just powered up this Philco 90 chassis with all new capacitors and new resistors. 10 mfd 450 v electrolytics are installed, and everything seems to be correct. However I get a fairly loud 60 cycle hum that doesn't change with the volume control. Any ideas?

Dan Waldschmidt
Fort Wayne Indiana
(469) 785-8105
dwaldschmidt757@gmail.com        

RE: Philco 90 pp 47 Restoration Questions - Radioroslyn - 02-09-2023

Let's take a dive in and see what we can find. Here's the service info:  https://philcoradio.com/library/download/service%20info/service%20bulletins/Philco%20Service%20Bulletin%2085A.pdf  so we can be on the same page.

Starting at the p/s check #'s 48 and 51 the + side goes the filter choke & #50. The - side to the hv center tap. Did you replace or remove #50? If it's original it's probably shorted. This does no damage but will make the filter choke of no effect in the circuit. This will cause hum as will a grounding - side of the filter caps.

Never power the chassis up without the speaker plugged in. You can easily damage the filter caps. If you have to remove the 80 tube this prevents any hv dc voltage. With the spkr plugged in measure the dc voltage from B- (- side of one of the filter caps) to one of the filament pins of the 80 tube. Should see about 275v or so. Then check the voltage over on pin 2 of each the 47 tubes.

RE: Philco 90 pp 47 Restoration Questions - buster757 - 02-09-2023

Hi, yes I replaced #50

RE: Philco 90 pp 47 Restoration Questions - buster757 - 02-09-2023

According to the Bintliff bakelite block book, the 6287-B block should have 1 .15 capacitor in there. I think i found my mistake, I put 2 .1s in it and should only have put 1.

RE: Philco 90 pp 47 Restoration Questions - Steve Davis - 02-09-2023

My recommendation would be to omit cap 50 and increase the value of 51 a bit.

Steve