11-09-2015, 02:00 PM
I have this old Ekco AC18 HT Unit from 1930 and I'm keen to:
1: Reverse engineer it, and;
2: Get this one operable.
I'm hoping I will be able to get some information and advice here.
In terms of reverse engineering it looks like quite a simple affair, just seven components, and so I'm hoping it won't be too difficult. Just a case of identifying the components and drawing a circuit I hope. I've attached a few pictures with the components numbered. Four of the components are clearly visible and underneath the socket-plate there appears to be just three more. That's all I can see. I don't recognise some of them though and the others I am taking a stab at. There is also a set of sockets underneath the unit in the base and I can't see where they go. I think the components are:
1 = Transformer (ratings?)
2 = Choke? (rating?)
3 = ?
4 = ?
5 = Dry electrolytic condenser 4+4 mfd and 300 peak volts. (what does 4+4 mfd mean? I've not come across that before)
6 = Resistor (value?)
7 =Resistor (value?)
In terms of getting it operable I think someone must have at least considered using it in the last 30 or so years because it has a modern mains cable fitted. I have read a thread on another forum where someone has just plugged theirs in and starting using it, but I'm not quite so brave or gung-ho. I also don't want to risk permanent damage to the unit either. Do you think it's safe to apply power using my variac and lamp limiter and then try to reform the capacitor in circuit using same? Any advice on the methodology and safety checks will be appreciated.
Operation and Specs (I believe are as follows):
MODEL A.C. 18 - Suitable for receivers not requiring more than 18 milliamps.
HT only unit using wander plugs to connect receiver to the mains unit. There is an additional selector plug which goes from the socket marked VAR to either H, M or L.
HT negative of the receiver goes into the "NEG" socket of the unit.
There is a choice with the HT positive according to the voltage required. If 120/150v is needed then the "120/150" socket is used and the setting of the H M L socket using the selector plug doesn't matter as the supply is taken straight from the transformer.
If 50/80v is needed then the "50/80" socket is used. I believe this lower voltage is obtained using a tapped resistor to drop the voltage rather than a tap on the transformer. Because of this the voltage varies with the current taken by the set, so three different tappings on the resistor are available for High, Medium and Low current and these are chosen by the H, M and L positions of the selector plug. For example, a 1-valve set will probably require the L position and a 4-valve set the H position.
The two sockets at the top with "SG" between them are only for use if the receiver has a screen-grid or pentode valve which needs its own supply, and there are two sockets marked "H" and "L" to select high or low voltage. Early screen-grid valves will probably take the lower voltage and pentodes the higher.
S.G. Tappings
H-70-85 volts at up to 1½ m.a. for screen of screened grid valves.
L- 60-70 volts at up to 1½ m.a. for screen of screened grid valves.
(If more than one screened grid valve is used it is usually necessary to use socket H.)
50/80 Volts Adjustable Tapping. Adjustable between 50 and 90 volts at up to 3 m.a. according to position of bridge (H.M. or L.).
120/150 Volt Tapping (with other tappings in use). 120 volts at approx. 14 m.a. up to 150 volts at approx. 9 m.a. (If the 50-80 volts tapping is not used, then 120 volts can be obtained at approx. 18 m.a. up to 150 volts at approx 13 m.a.
Low Output.- With mains voltage Connector Screw in base of Unit inserted into screw socket L instead of one of the mains voltage sockets, the output of socket 120/150 is reduced to approximately 100 volts at 14 m.a. up to 120 volts at approx. 10 m.a. with other tappings in use.
Thanks in anticipation
Nick
1: Reverse engineer it, and;
2: Get this one operable.
I'm hoping I will be able to get some information and advice here.
In terms of reverse engineering it looks like quite a simple affair, just seven components, and so I'm hoping it won't be too difficult. Just a case of identifying the components and drawing a circuit I hope. I've attached a few pictures with the components numbered. Four of the components are clearly visible and underneath the socket-plate there appears to be just three more. That's all I can see. I don't recognise some of them though and the others I am taking a stab at. There is also a set of sockets underneath the unit in the base and I can't see where they go. I think the components are:
1 = Transformer (ratings?)
2 = Choke? (rating?)
3 = ?
4 = ?
5 = Dry electrolytic condenser 4+4 mfd and 300 peak volts. (what does 4+4 mfd mean? I've not come across that before)
6 = Resistor (value?)
7 =Resistor (value?)
In terms of getting it operable I think someone must have at least considered using it in the last 30 or so years because it has a modern mains cable fitted. I have read a thread on another forum where someone has just plugged theirs in and starting using it, but I'm not quite so brave or gung-ho. I also don't want to risk permanent damage to the unit either. Do you think it's safe to apply power using my variac and lamp limiter and then try to reform the capacitor in circuit using same? Any advice on the methodology and safety checks will be appreciated.
Operation and Specs (I believe are as follows):
MODEL A.C. 18 - Suitable for receivers not requiring more than 18 milliamps.
HT only unit using wander plugs to connect receiver to the mains unit. There is an additional selector plug which goes from the socket marked VAR to either H, M or L.
HT negative of the receiver goes into the "NEG" socket of the unit.
There is a choice with the HT positive according to the voltage required. If 120/150v is needed then the "120/150" socket is used and the setting of the H M L socket using the selector plug doesn't matter as the supply is taken straight from the transformer.
If 50/80v is needed then the "50/80" socket is used. I believe this lower voltage is obtained using a tapped resistor to drop the voltage rather than a tap on the transformer. Because of this the voltage varies with the current taken by the set, so three different tappings on the resistor are available for High, Medium and Low current and these are chosen by the H, M and L positions of the selector plug. For example, a 1-valve set will probably require the L position and a 4-valve set the H position.
The two sockets at the top with "SG" between them are only for use if the receiver has a screen-grid or pentode valve which needs its own supply, and there are two sockets marked "H" and "L" to select high or low voltage. Early screen-grid valves will probably take the lower voltage and pentodes the higher.
S.G. Tappings
H-70-85 volts at up to 1½ m.a. for screen of screened grid valves.
L- 60-70 volts at up to 1½ m.a. for screen of screened grid valves.
(If more than one screened grid valve is used it is usually necessary to use socket H.)
50/80 Volts Adjustable Tapping. Adjustable between 50 and 90 volts at up to 3 m.a. according to position of bridge (H.M. or L.).
120/150 Volt Tapping (with other tappings in use). 120 volts at approx. 14 m.a. up to 150 volts at approx. 9 m.a. (If the 50-80 volts tapping is not used, then 120 volts can be obtained at approx. 18 m.a. up to 150 volts at approx 13 m.a.
Low Output.- With mains voltage Connector Screw in base of Unit inserted into screw socket L instead of one of the mains voltage sockets, the output of socket 120/150 is reduced to approximately 100 volts at 14 m.a. up to 120 volts at approx. 10 m.a. with other tappings in use.
Thanks in anticipation
Nick
