[Bob]

I have a Crosley Model 5M3. It has a volume control that has a fixed limiting resistance in it. How is this suppose to work? The wiper is connected to ground.
What should I see on an ohm meter connected from ground to each end of the pot as I turn the volume up and down?
Thanks for any help.
Bob

[morzh]

Well, I think it is simply 1) brings the Antenna input closer to Chassis, thus lowering the input signal, when wiper is moved closer to it, and vice versa when away, making it quieter/louder, and 2) changes the 32s' biases (in particular the second one's cathode) by moving them away/closer to the chassis, also changing the gain.

[codefox1]

Seen this before, and yeah, makes no intuitive sense. Selectively shorting out the antenna does lower volume, as does starving the filaments in the front end. You must realize that there were a lot of patent wars and snake oil battery saver salesmen in the olden days.

But there are still enough specimens around to study, if for no other reason than to guess what was going through the minds of the desiners, draftsmen, bean counters, and marketing people of the era, not to mention the patent attorneys, suppliers, pols and financiers.

Nothing has changed. SSDD

[Bob]

I removed the pot. It reads open, so I measured from wiper to one end with it full ccw. As I turn it cw it got up to +/- 40k. Moving the meter to the other end of the pot and it read +/- 170k for a total of +/-210k. The parts list dose not give a value for this pot, just a part # for the pot with off on switch. Do you think 210k would be right for this volume? For some reason I was thinking it should be in the 10k range. I took it apart to see how the "fixed" limit works, and all that is is a positive stop to keep the wiper from going all the way to the end. From what I could tell the "fixed " limit is about 210 ohms to hold a 3 volt bias on the suppressor grid of the I.F. tube.
I think!!! Do they still make pots like this?
Thanks for the help.
Bob

[rghines1]

Did a repair job for a customer years ago on a Crosley "Fiver" that used this circuit, so my memory is fuzzy. The volume control was open as well. Think I used a 5K ohm 2 watt wirewound control. A 10K would likely work too. No audio taper available so used a linear taper instead. Most of the volume control will likely be in the last 1/3 of control's rotation. The taper of the original was likely type II. This is defined as 90% resistance at 50% rotation measured as follows: From the front of the radio, terminals down, measure between the left-hand and center terminals.

The fixed resistance of the original control had to simulated with 1/2 watt resistor between the control and chassis. Don't recall the resistance but likely in the range of 100 to 500 ohms. Without the fixed resistor you got a strange muted region at the low end of the volume control.

A 210K control is far too high since cathode current of the 1st IF stage passes through the control too and would cut off the tube.

The Mallory/Yaxley book shows Mallory part no. E7 for a replacement but no specs are given.

Try contacting Mark Oppat at http://www.oldradioparts.net who has many old radio controls.


MALLORY TAPERS:
#1 = audio taper
#2 = logrithmic right hand taper
#3 = left/right taper (ant., Shunt & Bias Circuits)
#4 = linear taper

Appears another vendor at http://oldradioparts.com has the Mallory E7 control. Does have a $20 dollar minimum.

[Bob]

Thank You Everyone
I'll see if I can get a pot from either one of these guys. I'll post as to how I make out.
Bob

[TA Forbes]

Hello, Bob: one of my "non-Philco" interests is 1932-34 Crosleys.

All I can say is be patient and check EVERYTHING on them..

The early Crosleys were an "affordable" set that used cheap components and crowded them on a small chassis. An especially troublesome component is the cardboard electrolytic filter caps that they wedged unde the chassis. They had a tendency to leak electrolyte. This inevitably caused collateral damage to other components and wiring there.

[Bob]

Hi TA
I have replaced all the caps and resistors. The Radio would play but only at full volume. That is how I found the open control. I want to get one from Play Things of the Past, but he has the flu and asked not to contact him until he updates his site message. I want to get the Mallory E7. I hope it also has the power switch, because I broke the one on the open control.
The radio I have is a 1934.
Bob

[Bob]

Hello
I finally got a volume control. The one I got was a Mallory 6.5K. I install a 270 ohm 1 watt resistor as the fixed resistor. The volume works now.
The problem I have now is that at both ends of the dial all I get is static and noise below 560 and above 1500. Any help would be appreciated.

Thanks Bob

[rghines1]

Are you saying the radio works well in the middle of the dial?

[Arran]

I have an article in a 1934 issue of Radio Craft (or was it Radio News) that documents all of the various volume control circuits and resistances used, they also tried compiling statistics on what percentage of sets used each. Shunting the input of the antenna to ground was a common approach, but there were also various other schemes like controlling the plate voltage on the RF tubes, or in the case of the Canadian Westinghouse Columaire 8 I worked on, controlling the cathode current of the RF and IF tubes. Once automatic volume controls (gain control) became popular most of these circuits disappeared and the circuits became more and more standardized.
I was lucky with the Westinghouse the volume control was fine, and so was the tone control, which was what I was worried about. Sometimes you simply cannot find a correct replacement control and have to modify the circuit to take another, or wait until you find one from a parts chassis.
Regards
Arran

[Bob]

hello rghines1
It works pretty good from 1490 to 720. Only if I connect a wire to the antenna jack and hook it to a conduit pipe. Can't figure out what I need to do. Also the volume needs adjusting as stations are change, I think this is because of different signal strength.
Bob

[rghines1]

Hi Bob,
Have you performed an alignment? This radio has mediocre performance to begin with.

Radio has no automatic volume control (AVC) to level out volume changes as signal strength varies. Therefore you will twisting the volume control incessantly.

[Bob]

Hi
I did an alignment. There are only 3 adjustable caps. I got a lot of the noise to go away by rerouting the power transformer wires. It plays fairly well now.
I still need to attach the antenna terminal to a conduit run to get any stations. Is there a good way to make an antenna that would look good and still work? I found that if I hook up the antenna to the ground hole on my bench receptacle it works great. I am sure this is a true grounded wire because I put in the service and the ground rods. So this gives the radio a lot of wire for an antenna. Any thoughts on this?
Thanks Bob

[rghines1]

Appears dialcover.com no longer has the vintage loop antenna kit. Mainly intended for 1920's radio and look nice. Below is a demo photo found elsewhere on the web.

[Image: http://ts3.mm.bing.net/th?id=H.468754965...5&c=7&rs=1]

I'm sure the ground is good. Just that at RF frequencies you can't be sure what impedance the soil has. Not the same as resistance.