Hi. New to the group (actually this is my first post) so I would like to introduce first myself as an el.eng. working for the last 20yrs on tube amps for music instruments (guitar, bass) - repair and construction. Recently i came across an old (late 60s early 70s) tube PA with tape echo by Blackfield (Germany) type 2020 which is actually the FBT (Italy) Echo PA System Personal 2002 or 1002 (apparently from internet photos they seem to have the same power amp). The system is in a bad shape still transformers seem to be ok. However the output transformer is somehow weird, it has four connections though the PA supports two outputs - 8 and 16 ohms. The system power amp normally wokrs with four EL503 PP (found this info from pictures over the internet) but the one that came to me was loaded with four EL504s - that is a completely different tube.
Trying to find what load this transformer supports and the primary impedance - so that I can use it to some other project, I could not rely on the connections that I've seen because they were clearly altered (someone in the past probably changed them and loaded the EL504s). I measured the outputs with various combinations (applying voltage to the secondary and measuring voltage at primary) and in two occasions it seems to fit (8 and 16 Ohms) for the power tubes used - that is the four EL503s push pull - .with an Raa winding at approximately 1.4k. However a schematic would be of great help in order to verify what i am guessing. Any help would be appreciated.
Attached photos of the PA system (8-16 select switch is missing) and the output transformer with four connections of the same winding and a separate second winding (light green wire) that is connected to a jack terminal labeled "monitor".
Trying to find what load this transformer supports and the primary impedance - so that I can use it to some other project, I could not rely on the connections that I've seen because they were clearly altered (someone in the past probably changed them and loaded the EL504s). I measured the outputs with various combinations (applying voltage to the secondary and measuring voltage at primary) and in two occasions it seems to fit (8 and 16 Ohms) for the power tubes used - that is the four EL503s push pull - .with an Raa winding at approximately 1.4k. However a schematic would be of great help in order to verify what i am guessing. Any help would be appreciated.
Attached photos of the PA system (8-16 select switch is missing) and the output transformer with four connections of the same winding and a separate second winding (light green wire) that is connected to a jack terminal labeled "monitor".
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