Crosley car radio or “what am I supposed to do with this?”

[scuba]

Let me see if I have this right.


The AC current is induced across the transformer from the primary windings to the secondary ones and is amplified by the windings ratio. When measured from one end of the winding to chassis ground the voltage will be half that of the voltage measured across the windings themselves. This is because the center tap to ground is connected precisely half way through the windings. This AC voltage is then applied to the plates of the rectifier causing their polarity to flip-flop from positive to negative 60 times per second. The cathode, being heated by the aptly named heaters begins to sweat electrons like a swede in a sauna. Each plate in turn attracts the electrons as they go from positive to negative. This drop in electrons from the cathode creates a positive current which flows from the rectifier to and through the primary winding to the plate of the 6K5 output tube. The cathode, once again sitting in its Swedish sauna begins sweating electrons which are vacuumed up by the single plate which is always positive as it is fed by the high voltage B+. Said electron flow being modulated by the grid and screen of the 6K5 since their voltages are being modulated by the Black Magic Voodoo (with a possible pinch of live sacrifice) coming from upstream.

This much I think I understand. My understanding starts to break down with the lack of AC power needed to energize the secondary of the output transformer. Is it possible that a negative current flows from the plate to the opt, combining with the B+ flowing towards the 6K5 to create an AC current that can flow through the 0.01 mf cap thus creating an AC circuit though and back around to the opt? Or does the -DC voltage come from the cathode through the 20, 10, 10 mf caps (one or more of them being smoothing caps?) and on to the transformer circuit creating AC voltage that way? This doesn’t make much sense to me either as the cathode is creating a +DC current and I need a -DC current and only the 20 mf cap is connected to the Cathode and only the two 10 mf caps are in anyway connected to the opt.
Neither of these sound correct to me but I’m currently unable to get past this point as any semblance of understanding just flies out the window.

Please tell me a get part marks for trying.

 

[gadget73]

Its the change in plate current that makes the output transformer work. With a pentode the screen voltage is basically held steady. The grid voltage varies based on input signal. Changing voltage at the grid alters the current flow at the plate, and thats the AC signal that is induced in the output transformer which ultimately drives the speaker.

This one biases by allowing current flow through the tube to pull the cathode above ground potential. It is unimaginatively named "cathode bias". Thats the 600 ohm resistor #39. The grid stays at 0 volts through the 750K resistor 38. Measured grid to cathode, the grid ends up negative relative to cathode. The more negative it is, the less current flows, and the less negative the more current flows. The voltage at any particular moment changes based on whats coming out of the 6SQ7.

 

[trainbuffton]

The tubes are conducting the musical signal which is AC, pulling the current through the transformer.
It's DC at the center tap and both ends of the primary at rest so no actual ac is produced and none gets through.
Start applying signal and the transformer starts to do its magnetic coupling dance and you get current to drive a speaker in the secondary.
Make sense?
The center tap is just a tap off of a reservoir (capacitor) from which power can be drawn.
Capice?

 

[scuba]

varies based on input signal. Changing voltage at the grid alters the current flow at the plate, and thats the AC signal that is induced in the output transformer which ultimately drives the speaker.

If I understand correctly, AC current does not have to be created by alternating polarity but can be generated by fluctuating the current? Does this also mean that current can flow both ways along a wire at the same time? If so, this is really starting to tickle my curiosity bump. I do remember you telling me several years ago the both AC and DC can flow simultaneously down the same wire though I still can’t visualize it.
It looks like the key to unlocking this mystery lies in the multi-section can cap (which is currently wired neg to chassis ground) and how it functions. I’m going to have to think about this and read some more before moving to the input section.

Thanks. I appreciate everybody’s help more than I can say.

 

[scuba]

The tubes are conducting the musical signal which is AC, pulling the current through the transformer.
It's DC at the center tap and both ends of the primary at rest so no actual ac is produced and none gets through.
Start applying signal and the transformer starts to do its magnetic coupling dance and you get current to drive a speaker in the secondary.
Make sense?
The center tap is just a tap off of a reservoir (capacitor) from which power can be drawn.
Capice?

Io ho capito un po, ma non molto.
I’m going to have to dig into the input circuit shortly but right now, I’m still confused about the use and functioning of the multi-section can (20-10-10 mf). I’ll be doing some more reading on that over the next few days.

 

[trainbuffton]

Io ho capito un po, ma non molto.
I’m going to have to dig into the input circuit shortly but right now, I’m still confused about the use and functioning of the multi-section can (20-10-10 mf). I’ll be doing some more reading on that over the next few days.

If you want the rest of the thing I know an englisman who has the Crosley taxicab that this goes in, sitting in his yard...
(This is not an offer to buy or sell its a damn joke, capice?)

 

[scuba]

If you want the rest of the thing I know an englisman who has the Crosley taxicab that this goes in, sitting in his yard...
(This is not an offer to buy or sell its a damn joke, capice?)

With the way this is going, I may have to pay that Englishman to take it off my hands. (That’s only somewhat a joke )

 

[trainbuffton]

Lol

 

[gadget73]

If I understand correctly, AC current does not have to be created by alternating polarity but can be generated by fluctuating the current? Does this also mean that current can flow both ways along a wire at the same time? If so, this is really starting to tickle my curiosity bump. I do remember you telling me several years ago the both AC and DC can flow simultaneously down the same wire though I still can’t visualize it.
It looks like the key to unlocking this mystery lies in the multi-section can cap (which is currently wired neg to chassis ground) and how it functions. I’m going to have to think about this and read some more before moving to the input section.

Thanks. I appreciate everybody’s help more than I can say.

yep, its just changing the amount of current flow. It doesn't really reverse direction in this one, it just swings from close to zero to some considerably higher amount. It does fully reverse direction with AC like what comes out of the wall though. The changing level of current creates a changing magnetic field and thats what couples things over.


can cap with negative to ground is typical. Chassis is the 0v reference, other spots in the supply are some amount of volts positive to that. The multi cap is just several standard capacitors in one physical package, nothing very magical about it.

 

[scuba]

Status update. I picked-up a field coil speaker almost identical to the original one, just 2mm thicker. After wiring it up and putting power to the radio, I noticed that the 6v transformer and the alligator clip wires were getting uncomfortably hot due to drawing an excessive amount of current. I was able to track the problem to the connections to the OPT and electromagnet on the speaker. I had cross wired them. Once corrected the current draw dropped dramatically. I was’t expecting much though I did hope to hear the hiss of a carrier wave at the very least.
I then proceeded to take some voltage measurements at the rectifier and other tubes.
With the step-down transformer producing 6.7 volts from an input of 115 volts from the variac, I got the following results.

6X5: pins 3 and 5 = 197 VAC instead of the 256 volts called out on the schematic
Pin 8 = 259 VDC/240
Pin 7 = 5.7 VDC/5.9
Pin 6 = 5.8 VDC/5.9

6K6: Pin 2 = 5.7 VDC/5.9
Pin 3 = 259 VDC/220
Pins 4 & 8 read as near to zero as may matter.
I did randomly check voltages on other tubes and got no appreciable voltages on them either.

I’m going to put this one aside until I have enough time to study and learn more about electronics and the various components involved. Life is too hectic at the moment with work and ailing parents and family members to help care for.
Never fear though, I have not given up and will prevail in time.

Thanks for all the help.

 

[gadget73]

getting the same voltage on 2 and 7 tells me there is an open on the heater circuit somewhere. One of those will normally go to ground, the other will be 6v. Not sure if that grounds at each tube or what but I suspect thats open, and thats why there is nothing happening. The heater isn't actually flowing any current.


4 is the screen, that should have a couple hundred volts.
8 is cathode, it won't have any voltage if the screen is at 0v or if the heater isn't ding anything.