[OZ4]

This thing is a strange unit or maybe its just me. I can't figure out what the control voltages should be. Because the volume control varies the bias on the rf and if sections along with the automatic gain control I am lost. It does receive at a very narrow spot on the volume control but not very well and its unstable. I have a copy of the riders docs. but they don't help here. Does anyone have any info about the agc on this unit? It would much appreciated'
Chris

[codefox1]

Post link or schematic here. Some of these sets had really bizzare setups where volume controls were really filament voltage regulators, and stuff like that.

[OZ4]

The schematic I have is from nostalgia air (http://www.nostalgiaair.org/Resources/480/M0001480.htm) and has a lot of voltages listed but these were taken with some old voltmeter that loaded the circuit so they are only so good. There is nothing about volume setting or signal level. I do understand that the volume control should reduce the gain of the circuit. And as it stands there seems to be too much change in voltage and bias. So without any point of reference where to start?. The voltage divider of the power supply is fine. And of course I changed almost all the capacitors' checked the continuity of the coils and all checks good. There is a double layer of windings on the oscillator coil with some sort of insulator in between but it looks good no green stuff.

[Radioroslyn]

No wonder they out of business in '36. I replace the '24 and check the resistors around it.

Terry

[TA Forbes]

Have you verified that ALL the cloth resistors are good? This is one of the most common problems with the AKs from that period. The 670 ohm flex between the low end of your volume control and ground would be a prime suspect.

Agree with Terry problem may be vic 24 control tube. Make sure that someone did not replace the 24 with a 35/51 in the past. These tubes can replace each other in some circuits and not in others. Additionally check/confirm the 550 ohm volume control itself. As a former "AK guy" I probably replaced the volume control on 25% of the AKs from this period that I worked on.

I would not read too much into what the voltages are supposed to be IAW the schematic. These sets were not precision pieces of equipment.

Good luck and keep us posted. Between "wanna-be technicians" like me and real deal experts like Terry, you should find what ails your set.

[OZ4]

Funny you should mention that. It seems that somehow one of the 35 tubes and the 24 got switched. I just figured this out after doing a closer inspection and about three days work. As for the volume control it measures 598 ohms and the cloth resistor at the lower end measures 675 ohms. Both of these seem acceptable and I have measured all the resistors and have replaced a few. However the back of the vol control is missing and so the power switch. If anyone knows where to obtain one please let me know.

So after all this it works better but the lower half of the freq band is weak to missing. I have done the usual peaking and tweaking but without an alignment procedure is more like diddling and twittling. As for the tuner I have blown out the crud and cleaned the little brass spring contacts. Oh and I found that a piece of 5/16 inch fuel line replaced the rotten tire for the tuner drive very nicely. But still it needs something. Thanks for any help, I will keep at it.

[TA Forbes]

Here are some links that may help:

http://www.atwaterkentradio.com/

http://www.atwaterkent.info/

[Radioroslyn]

TA is correct as the grid bias is different for the 24A than the 35/51 tube. If it did have a 35 in that socket it very well could cause that sort of issue.
Terry
ps.
WELCOME TO THE PHORUM!!!

[AI2V]

Your problem will probably be resistors. Those colorful ceramic resistors are notoriously unreliable and usually way out of tolerance; I always change them all- it's just not worth the hassle of continually repairing the radio(s).

The low value resistors are equally lousy; these look like wires with sleeving and have solder lugs crimped on the ends. These are very intermittent and I always change them too with modern resistors (half watt is fine in most cases). When you replace these you often need to add new ground lugs so that you don't have ridiculous lead lengths. Don't worry about placement either; these AK's are not VHF or UHF. Just put your new components wherever they fit nicely and with neat shortened leads.

[OZ4]

A quick update. I ordered a NOS 24 tube and tripled checked the resistors of all types with little success. So next is a NOS 35 tube. Sure wish I had access to a tube tester.

On a more positive note I did figure out how to get accurate voltage readings that jive with the riders chart. I just needed the right load. It took reviewing my old textbook on how meters work and the spec from the riders chart of 1000 ohms/volt. Now with a 250v scale that comes to 250k duh. Ok so I hung a 270k resistor on my digital meter as a dummy load and the readings were right on.
Chris

[Arran]

With regard to voltage readings sometimes the schematic will tell you what percentage of possible error to expect in that they could not account for differences in line voltage and in volt meter calibration. The older ones would often tell you how many ohms per volt the meter used to compile the readings would have loaded the voltage down.
However it's been my observation that most voltage charts from the mid 1930s onward appear to have been compiled using a VTVM as the readings seem to be pretty close to what my DMM reads. A VTVM is something which any good factory or electrical engineering lab would have had at that time, in such cases the volt meter would not load down the voltage reading much if at all.
Regards
Arran

[codefox1]

For the few cents apiece, replace the resistors, all of them. Capacitors as well. Make sure tubes are in their right place, correct and patent. VTVM or modern digital voltmeter will always read high on signal voltages. Reason is that load imposed by the meter is almost negligable, but old time meters did serve as voltage dividers, and back then that's all they had.