I am currently refurbing an Atwater Kent model 70 with a
L Chassis. AC 110V. I have three questions:
1. The power supply seems to be filtering ok, etc. but seems
to be pulling a lot of current since it seems to get
very hot. It looks like there is a path with about 14K ohms
to ground. Can't find any other abnormal issues
2. The unit seems to pick up local stations very well but
I am not sure how sensitive the TRF models are. There is
no noise until I come up on a station. I get distant
stations but they are very very weak.
3. Does anyone have any information on the tube types used
in the Model 70 that can be used with a tube tester. My
tester will test 40's, 35's etc. but it doesn't have information
on the U225, CX324, etc...

The transformer heating is normal to a point- there are losses within a transformer's windings, in the form of resistance of the small guage of wire, the reactance of the coil winding itself, as well as the magnetic core.

If your transformer is potted in tar, and is not leaking, it "should" be okay.

If it is a concern, or seems like it is warmer than it should be, isolate the transformer electrically from the circuit, and see if a 40 watt light bulb; wired into series in the electrical cord instead of parallel as you might do for a 120 volt pilot light; will light up. If it should light, there may be some shorted windings. If it does not light, there should not be too much to be concerned about.

TRF radios, are not the highest performers, but under some conditions, they can perform better than other designs. Distant stations just are not going to produce incredibly loud signals, but if you are not using a long antenna, going with a longer antenna will improve reception considerably.

TRF designs of that era lack some of the other improvements that we are accustomed to today, so the radio is not going to give you the same loud signals that close radio stations give(5 miles or less), for stations even as close as 20 miles away.

The U225 is the same for all practical purposes as a type "25", and the "CX324" should test as a "24A".

: I am currently refurbing an Atwater Kent model 70 with a
: L Chassis. AC 110V. I have three questions:
: 1. The power supply seems to be filtering ok, etc. but seems
: to be pulling a lot of current since it seems to get
: very hot. It looks like there is a path with about 14K ohms
: to ground. Can't find any other abnormal issues
: 2. The unit seems to pick up local stations very well but
: I am not sure how sensitive the TRF models are. There is
: no noise until I come up on a station. I get distant
: stations but they are very very weak.
: 3. Does anyone have any information on the tube types used
: in the Model 70 that can be used with a tube tester. My
: tester will test 40's, 35's etc. but it doesn't have information
: on the U225, CX324, etc...

Hi

Just something to add.. Atwater Kent used oil type caps in most of their early radios. They may still filter well but often become leaky. Measure your "B+" voltage. It may be low from this loading. After the radio has been in operation are the filters warm? They should remain cool. Higher "B+ voltage will give better reception.

Norm

: The transformer heating is normal to a point- there are losses within a transformer's windings, in the form of resistance of the small guage of wire, the reactance of the coil winding itself, as well as the magnetic core.

: If your transformer is potted in tar, and is not leaking, it "should" be okay.

: If it is a concern, or seems like it is warmer than it should be, isolate the transformer electrically from the circuit, and see if a 40 watt light bulb; wired into series in the electrical cord instead of parallel as you might do for a 120 volt pilot light; will light up. If it should light, there may be some shorted windings. If it does not light, there should not be too much to be concerned about.

: TRF radios, are not the highest performers, but under some conditions, they can perform better than other designs. Distant stations just are not going to produce incredibly loud signals, but if you are not using a long antenna, going with a longer antenna will improve reception considerably.

: TRF designs of that era lack some of the other improvements that we are accustomed to today, so the radio is not going to give you the same loud signals that close radio stations give(5 miles or less), for stations even as close as 20 miles away.

: The U225 is the same for all practical purposes as a type "25", and the "CX324" should test as a "24A".

:
: : I am currently refurbing an Atwater Kent model 70 with a
: : L Chassis. AC 110V. I have three questions:
: : 1. The power supply seems to be filtering ok, etc. but seems
: : to be pulling a lot of current since it seems to get
: : very hot. It looks like there is a path with about 14K ohms
: : to ground. Can't find any other abnormal issues
: : 2. The unit seems to pick up local stations very well but
: : I am not sure how sensitive the TRF models are. There is
: : no noise until I come up on a station. I get distant
: : stations but they are very very weak.
: : 3. Does anyone have any information on the tube types used
: : in the Model 70 that can be used with a tube tester. My
: : tester will test 40's, 35's etc. but it doesn't have information
: : on the U225, CX324, etc...

Hi Aubrey - my experience with AK sets has been that the filter
caps frequently are leaky. since the power supply uses
filter chokes, which are quite effective, it is possible that
you are observing reasonable B voltages, but the filter
caps may be leaking, possibly accounting for excessive
heat from the transformer. Also, I suggest checking bypass
caps for excessive leakage.

good luck - Jim

Hi Aubrey - I thought that the resistance you measured from
the b+ supply to ground sounded way too low, so I checked
a AK model 70 L chassis that I have. readings I got from
rectifier filament to ground was around 400K, but with capacitor
action - which is what I think you would expect.

I think you have a short somewhere in the B+ line, or perhaps
the audio coupling capacitor (between detector and 1st audio)
is very leaky.

good luck !

Jim

: Hi Aubrey - I thought that the resistance you measured from
: the b+ supply to ground sounded way too low, so I checked
: a AK model 70 L chassis that I have. readings I got from
: rectifier filament to ground was around 400K, but with capacitor
: action - which is what I think you would expect.

: I think you have a short somewhere in the B+ line, or perhaps
: the audio coupling capacitor (between detector and 1st audio)
: is very leaky.

: good luck !

: Jim

Jim, thanks for update. I will check out. I haven't had time to
work on this model again since I posted the note. I think
you are correct. Regards.