I am working on a Wards Airline 62-288 radio. Of course resistors have colored bands to indicate their tolerances. But I am trying to get a feeling for other radio component values. The schematic for this radio indicates that the B+ should be 135 volts. When I measured it, I got 187 volts - a little over 50 volts difference. The radio seems to be working very well. But should I be concerned with the voltage difference that I measured? And if so, are there suggestions on what I could do to adjust this to more closely match the value on the schematic?
Thank you. Mark

Are you sure the schematic is correctly read as 135 instead of 185? A bit of fuzzy reproduction/copying or even a typo in the original draft schematic might explain the difference. 187 is insignificantly different from 185. If you post the schematic and parts list we may be able to determine from the other parts whether 135 or 185 is more likely the correct number.

When the radio was made and the paperwork issured, pay attention to what kind of voltmeter they used to go by.

What is the working voltage rating of the original Electrolytic capacitors?

Very good point. It won't account for 50v worth of difference in this case but it's worth remembering when small differences are found.

Schematics:
https://www.tubesandmore.com/schematics ... -co/62-288

Parts list says the filter electrolytics are 200v rated.
And the print is clearly 135v on the B+.

Then again...
The schematic's power transformer BE104-100B crossed to a Stancor replacement P-6011 which is listed as 700 VCT @ 70 mA.

Note that the speaker field coil is 2000Ω in the negative side of the power supply, and has a significant drop across it. Total B+ from the + side of the electrolytics to the CT of the transformer is more than 135 volts, but less than the voltage rating of the electrolytics.

With today's higher line voltages and new modern electrolytics, I'm not too concerned if the B+ is about 20% over specs. But in this case it's higher than that.

You can check the bias on the 6K6 grid and see if it's reasonably close to specs, and you can try a different 6K6 as that is the major load on the B+ in this set.

I'd check the filament voltage on the tubes, and see how close to 6.3VAC that is. If it's high by the same proportion as the B+, then you might want to take steps to reduce the AC line voltage a bit.

The schematic says measurements were taken with a line voltage of 105 vac. A modern day line voltage of 120 vac may give up to ten extra volts or so in B+. I'd like to know where B+ was measured, which points for both leads of the meter. The type of meter (ohms per volt sensitivity) will have less affect in accuracy at a low impedance spot such as the the filter cap area and is more likely to show up in high impedance areas like the plate load of the IF. transformers. The filter cap rating seems plausible as a clue toward "correct" B+ but what has me most skeptical is the voltage on the target of the eye tube. Voltage here is 135 vdc which would make for a dim green glow. One unknown here is the voltage drop across the field coil.

6U5 datasheet says target range is 100v min to 285v max. So, maybe there WAS a typo & 135 should have been 185??

EDIT:
Over at this site a restoration noted the 6U5 was "very bright".
https://philcoradio.com/phorum/showthread.php?tid=19308

I've had a few of these over the years, and even a brand new eye tube is not particularly bright in them. I don't know if I saved any notes about the B+ voltage not matching the schematic though.

Ain't happnin..

Assuming it's correctly calibrated, no chance the B+ will read low on a older VOM or high on modern solid state meter. If you're talking about a bias, AGC, etc voltage, yes.

How are you measuring this? It should be 135 volts from the B+ bus to the chassis. There's another 100 volts or so of drop in the speaker field coil, which is in series with the center tap of the power transformer HV winding. Your 187 volts actually sounds a little low, but that would depend on where you are taking the reading and how much current the set is drawing.

The math is as follows: a 5" speaker will need about 5 watts of power in its field coil to work successfully. Then 5 watts / 2000 ohms = 0.0025 amps squared, square root of that gives 0.05 amps (50 mA) as the expected field current. Then 2000 ohms x .05 amps = 100 volts dropped across the coil.

If you are reading 187 volts from the B+ bus to chassis and everything else is in good order, then I would suspect that either somebody changed the speaker and used one with the wrong field coil resistance or yours is partially shorted.

I appreciate all of the help.
I measured the B+ voltage from pin 2 of the 5Y3 to chassis. There are only two or three other voltages listed on the schematic. One is 75V on pin 4 of 6A8G tube - I measured 96V. Another voltage is on a wire leading to pin 5 of 6K6G tube at -10V; I measured -8.5V. The parts lists the electrolytic caps at 5MF at 200V and 5MF at 250 volts. The 6K6G tube is a little weak (replacement on order). Again, the radio is working quite well, but it just bothered me that there was such a discrepancy in the B+ voltage.

Im working on a zenith 12-s-266 right now and ALL of the voltages are high. My line voltage is 123.
You can make an autotransformer from an ordinary wall wart to your lower your voltage to the radio. This will drop ALL of the voltages. I find that a 9 volt wall wart will reduce about 11 volts then to the radio, a 12 volt about 14 volts. I find that if you use 2.0 times the radio wattage on the wall wart it wont even get hot. So a 70 watt radio needs an 1200 milliamp or or so for the wall wart guts.

Once you get past the learning curve they go together fast.

Bill

He can also use a 28 ohm 50 watt wire wound power resistor on the AC return line. I lowered the voltage on an 8S463 by 10 volts using one. Mouser carries them for about 5 bucks.

How warm does that 28 ohm power resistor get ? Thanks

I can't answer that, because I had mounted it on the inside of the chassis. I can tell you though that the PT only gets warm, even after the set being on for a length of time.

I note on page 2 from the tubes & more link that its a 1000 opv meter and that one quotes 110-120v. Confusion seems to be maximum when the choke is in negative. On B+ both an analogue and digital meter should read the same. Chassis will be positive relative to the centre tap and the voltage at the rectifier will be higher than the working voltage that the tubes are running at.

The voltage between chassis and CT is usually that of the output tubes g1 bias.

Marcc

I corrected the size and watt vs miiliamp statement to better reflect reality

Bill