[Eric]

I have a Crosley 148 and I think I'm pretty close to getting it fully functional (I think) it was completely dead when I started but I'm stumped so here is my data.

socket voltages going across the way the print is laid out. Vol was at max the gang was closed

58osc - 249, 112, 44, 2.6, 2.5

58IF - 288, 153, 0, 4.2, 2.5

57det - 180, 64, 0, 16, 2.5

42op - 257, 272, 0, 22, 6.9

The ones that stand out to me is the 57 both the screen and bias are very high?

I've changed all the caps and resistors the vol pot goes from 170ohms to 5.3k looked at posts on the antique forum and this looks to be correct

I checked for open coils and they look good

when I connect the ant I I get tone like it was hooked up to a sig gen but faint and only when the vol is about 1/4 if I go higher it goes away.

If I connect a ant wire to the grid cap of the 58osc (also top of gang) I get stations the vol has to be turned up more than 50% and even at max it is not as loud as it should be.

Any ideas on what to look at next??



Riders Volume 3 - CROSLEY 3-26

http://www.nostalgiaair.org/Resources/276/M0003276.htm



Eric

[Radioroslyn]

Hi Eric
There is something funny going on here. All of your tube are 2.5v heaters except for the 42 it's 6.3. I'd replace the 42 with a 2A5 as it has the right heater.
Terry

[Eric]

Hey Terry
All my paper work says it's supposed to be a 42 even the socket is labled 42 infact all the sockets are labled with the tube numbers, and the heater voltage is correct for a 42 I get about 6.8. Besides I don't think I have 2A5 and wouldn't the higher heater volts burn it up?

[LedHed]

Please ignore.

[Radioroslyn]

Well if you've got 6v there then the 42 is ok. I must have missed something when I took a quick look the diagram. Is the 22v on the 42 + or - ?
Terry

[Eric]

The 22v is positive
The 5.8 on the 57 Bias is almost 3x what it should (16) be is this a problem?

[Mondial]

Something does not seem right in the 57 detector stage. If there is 16V on the cathode, there is effectively -16V on the control grid which would put the tube way beyond cutoff. The tube should be biased just before cutoff (5 or 6V) so that positive peaks of the signal will cause the tube to conduct and rectify the RF, producing audio in the plate circuit. With 16V of bias it takes a very large RF signal to produce any audio, which seems to be what you are experiencing.

If the 40K resistor in the cathode circuit is ok, then I would probably say the 57 tube is bad ( gassy) which is causing the tube to conduct more than it should, allowing more current to flow through the cathode resistor. This would increase the bias past what it would be under normal operating conditions.

Do you have another 57 you can try?

[Eric]

I will recheck the 40k and will see if I have another 57 I take it that a gassy tube would not show up on a tube tester?. What you have explained makes a lot of sense to me in what I'm hearing.

[Eric]

Terry
The resistor was 48k and changed now 38K but no difference
I have another 57 but baffled by the results with the meter neg lead on 5 cathode here are the two
Screen volts high and neg on all the bias readings ????
tubes plate scr sup bias
57 orig 172 55 0 -13.5
57 used 217 140 0 -8
Went back and took new volts keeping neg on 5 cathode
58 osc 241 108 -42 -2.6
58 If 278 147 0 -4
42 246 262 0 -20
Do I have something backwards??

[Mondial]

Your new readings look reasonable. If you put the negative meter lead on the cathode and the positive to the chassis to measure the bias, you will get a negative reading since the cathode is positive with respect to the chassis.

Keep in mind that the original voltage readings on the schematic were taken with a relatively low input resistance mechanical analog meter, which loaded the circuits and made the readings seem lower than the actual voltage at the point being measured. A modern DVM will usually have a 10 meg input resistance, so the voltages will seem high in comparison when measuring high resistance circuits like the 57 screen grid pin, fed by a 3 meg series resistor.

The voltages with the replacement 57 seem more like what they should be. Do you notice any difference in performance?

[Eric]

I agree but the Screen at 140 when it calls for 40 I would think is a problem?

Nothing has made any real diff was playing with the ant coil and when I clip an ant wire to where it connects to the grid cap and top of the gang it plays fine I'm beginning to think I have a problem with this coil even though I read Resistance 11 and 3 ohms on the two coils....?

[Mondial]

Yes, if you are receiving stations with the antenna connected to the grid cap of the 58 mixer/oscillator but not when you connect it to the antenna terminal, there is a problem with the antenna coil or associated circuit. You might check the .1 uF bypass cap connected to the cold end of the antenna coil secondary. If it is open, the coil will be floating with respect to RF ground.

As far as the detector screen voltage, 140V is about what I would expect there. Remember, the 57 is biased at cutoff, so with no signal very little current flows in the screen and plate circuits. With very low screen current the voltage will rise, only limited by the 3 meg series resistor. I would not take the voltage measurements too seriously. The voltage chart shows different screen voltages on the 58 mixer/osc and the 58 IF, yet the schematic shows the two tubes screens tied together, so how could the voltages be different?

Assuming the schematic voltages were measured with a voltmeter with a 1 mA meter movement typical of the era, with a 500 V full scale range the meter input resistance would be 500k. If you try to measure the screen voltage at the 57 pin, you are creating a voltage divider consisting of the 3 meg resistor connected to the 260V supply and the 500k meter resistance. So even with the tube out of the socket you would never measure more than 260V x 500k/3500k, or about 37V at that point! This is a worst case situation, as most measuring points do not have a 3 meg source resistance, but it does illustrate that unless the type of meter used is specified, the voltage readings are questionable at best.

[Eric]

The .1mf is good I'm going over the wiring again I'm going to make a clean copy and use a red pencil and trace everthing in that ckt don't know what else to do at this point

[TA Forbes]

Check the wires that pass through the underside of the chassis to the tuning cap for short to chassis. Crosley was notorious for issues under the chassis due to inexpensive components closely mounted together.

[Eric]

Everthing under the tunning cap looks good. Have retraced the wiring up to and including the OCS coil and it looks good(no opens) ....But on the diagram the coils are not the same length which tells me they should not be the same Ohm value when I checked them I got 7ohms on each coil am I correct in my thinking??