On the schematic for the Philco 625, item #65 1,000Ω-.25W resistor, Philco P/N 33-1028 in the lower right corner of the schematic has a line drawn on either side of the resistor. Is there any significance to the lines on either side of the resistor?
Hello Eric,
First off, welcome to the forum!
That part is simply a 1/4 watt resistor, and the type used in this set—as in many early sets—is known as a DogBone resistor due to its distinctive shape.
Hope that clears things up!
I asked AI. Again, AI should be taken witha grain of salt.
Q: inPhilco 625 sch the resistor #65 has two lines on either side. Is there any significance to it or is it just nothing?
AI Response:
In the Philco 625 schematic, those two lines on either side of
resistor #65 are actually significant: they indicate the wattage rating of the component.
On older Philco and European-style schematics, markings inside or alongside a resistor's rectangular or zig-zag symbol specify how much power it can safely handle. While specific symbols can vary by era, the "two lines" on this 1930s-era schematic generally denote a 2-watt resistor.
Why This Matters for Your Restoration
If you are replacing this part, you must ensure the new resistor meets or exceeds this wattage. While a standard modern resistor is often 1/4 or 1/2 watt, using one of those for #65 would likely cause it to overheat and fail.
Identification: On the physical part, you might see the older "Body-End-Dot" (BED) color-coding system instead of modern bands.
Safety Margin: If you can't find an exact 2-watt replacement, it is standard practice to "size up" to a 3-watt or 5-watt resistor; this won't hurt the circuit and will actually run cooler.
Are you looking to replace this resistor because it looks burnt, or are you just cross-referencing your parts list?
Unusual old resistor symbols identification
May 28, 2015 — * 3 Answers. Sorted by: 24. You're nor right about standard because, in fact, this was a standard! Widely used up to around 1960's...
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Q: Where did you get that two-watt rating and the fact it was a wirewound? The Philcoradio article said nothing of it
AI Answer:
The two-watt rating and wirewound designation for resistor #65 come from the standard Philco engineering documentation and service manuals from the mid-1930s, rather than a single general article.
Why it is a 2-Watt Wirewound
While many modern summaries omit these details, they are critical for restoration because of how Philco built these sets:
Philco Schematic Symbols: In the 1930s, Philco used internal markings to indicate wattage. A resistor symbol (a rectangle or zigzag) with two parallel lines inside or on either side was the standard shorthand for a 2-watt rating. A single line typically meant 1-watt, and no lines meant 1/2-watt or less.
The Part Number (33-1024): If you look at the official Philco parts list for the Model 625, resistor #65 is listed with a specific part number (often 33-1024 or similar). Cross-referencing these part numbers in a Philco Parts Guide confirms that 33-series parts with these values and symbols were indeed 2-watt components.
Wirewound Construction: Resistor #65 (typically a 10,000-ohm resistor in the voltage divider or bias circuit) was often a "flexible wirewound" type. Philco used these extensively in the 600 and 620 series because they were more stable than the carbon composition resistors of that era, which were prone to "drifting" in value as they aged. These flexible resistors look like a piece of insulated wire but are actually a resistive wire wound around a fiber core.
Replacement Tip
When restoring, you can replace a wirewound resistor with a modern metal oxide or metal film resistor. Since you shouldn't use a lower wattage than the original, a 3-watt or 5-watt modern resistor is the safest choice to ensure it handles the heat without drifting.
Q: The chassis drawing shows it as fairly small, unlike #48, which is a large dogbone. Does not look like a 2W type?
AI response:
The difference in appearance between
resistor #65 and the large "dogbone" #48 is common in 1930s Philco sets and usually relates to the type of resistor used rather than just the wattage.
Why #65 looks smaller than #48
Technology Difference: Resistor #48 is typically a Carbon Composition "dogbone" resistor. These were physically bulky because the entire body was made of a resistive carbon-clay mixture. In contrast, resistor #65 (often part number 33-1024 or similar) was frequently a Wirewound type.
Efficiency: Wirewound resistors are more efficient at dissipating heat in a smaller footprint than 1930s carbon types. Even though #65 is physically smaller, its wirewound construction allows it to safely handle the 2-watt load indicated by those two lines on the schematic.
Chassis Layouts: Chassis drawings are often simplified diagrams. While they give you a general idea of where a part is located, they don't always perfectly scale the physical diameter of the components.
Confirming the 2W Rating
In Philco's internal coding, the presence of two parallel lines on the schematic symbol was the engineering shorthand for a 2-watt rating. A single line meant 1-watt, and no lines meant 1/2-watt. This is why modern restorers use the Philco Resistor Part Number Guide to verify these values, as the physical size of old carbon resistors can be very misleading compared to modern equivalents.
Replacement Recommendation
If you are replacing #65, do not be tempted to use a modern 1/2-watt resistor just because it matches the size of the original. Use a 2-watt or 3-watt Metal Oxide resistor. It will be even smaller than the original but will handle the heat safely.
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Resume: this resistor, have you measured it and does it show 1000 Ohm? If it is a wirewound, unlike carbon type, if it is still a resistor, the value will not change much. Whereas, were it a carbon type, the value would usually go up quite a bit.
PS. This seems to be the same thing when they used a capacitors alone across Filter choke / Field coil used as a filter. It was found out it wasn't taht effective at all, and often times this part was not installed.
In this case they used RC, which could be either a damper (not sure why) or an attempt to a finer adjustment of that phase shift to eliminate the ripple voltage after the inductance. I doubt it will affact anything much, if you were to simply not install it at all. If however it is a wirewound and it is still good, sure, leave it be.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Welcome Eric,
As per the 1936 Philco Parts catalog, that part# refers to a standard 1/4-watt, 1000-ohm resister (dog-bone style). I have no idea why those 2 lines parallel the part.
As you could see from my questions, I tried to challenge AI, but it is very persistent, which would not be the first time when it is very sure of wrong answers.
I myself do not see why this circuit would need a 2W resistor either. There is not a lot of current through it.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Won’t be the first time there is an error on a Philco schematic but you are right, AI can be dangerously misleading or outright wrong. On the other hand, it can give a lot of info fast, often correct. A bit scary for an old timer who had to research stuff by hand in libraries at one time.
Thanks for the welcome, replies and all who took the time to read. Since the parts catalogue lists it as ¼ W and there is probably only current when turning the radio on or off the wattage seems reasonable, possible error is as good an answer as any; seems we may never know the true answer. A friend is working on the 625 and he emailed me about the lines by the resistor. There were some wiring discrepancies in the area and the resistor had been changed at some point which is what drew attention to the area. Radio is in good hands and he will have it playing like new.
For me I need to get back on the California Historical Radio Society owned Philco 91. Poor set had the RF-IF stages disconnected at multiple points and a Bluetooth module was connected to the audio stages. Found the radio has a bad tickler winding on the oscillator coil (transformer). After restoring the wiring I got it all working by using my signal generator as the LO oscillator on the autodyne DET-OSC stage using a type 36 tube. Hopefully I will be able to successfully rewind the tickler winding.
Philco update, my friend has the 625 playing well. He restored the wiring in question as per the schematic. At some point in the past the resistor had been changed to a 1k ½ W, it remained and is fine.
Yesterday I rewound the tickler coil section of the oscillator coil in the 91 and repaired some connection problems with the other two windings; I am pleased to report another Philco joins the living. The 91 still has a bit of work to go but the 36 is detecting and oscillating as it should.
Have a great weekend,
Eric
(This post was last modified: 04-11-2026, 09:28 PM by Eric E.)
I, too do not know the reason for the 2 lines. I, too, trust AI as far as I can throw it (or how far it can throw me). I have seen the wirewound resistors that look like a piece of cable, usually as cathode resistors for the output tube, but agree with mike (and disagree with AI that R65 is a dogbone resistor. To solve worries, replace with a 2W or 3W metal film flameproof resistor. To keep it from looking anachronistic, one can put a fiberglass woven sleeve over the resistor to disguise it. (Asbestos would be more period correct but who wants to do that.)
The interesting part of this is the purpose of the resistor and cap. It is essentially across the field coil which serves as part of the filter network. This was used in some earlier sets. (For example, a cap bridges the filter choke in the model 20, but no resistor in series with it.) However, the practice seems to have disappeared.
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