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Yes magnetized when powered on, and with power tubes (6L6) in.
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Far as I know most all field coil speakers are in series with the b+. Very rare to have one acting as a load on your high voltage. As to the output transformer being mounted on the speaker, I thought that was kind of assumed according to the pictures.
As to pulling the rectifier tube and probing around to measure secondary high voltage and filaments, I'm not sure the OP isn't going to get knocked on his ass from being shocked. Might be better to bring it to a shop who wants to fix it as most will tell him it's BER.Comment
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I was also thinking that this amp might not be the one to cut your repair teeth on. I think a variac and LBL and starting with low, low voltages would be recommended even for someone with experience.Originally posted by mozz View PostComment
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And don't forger, there will be exposed B+ on the speaker wires/OT terminals.- Own Opinions Only -Comment
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I had thought the opposite but have seen both ways.Originally posted by mozz View Post
In series you have big fluctuations in F.C. current unless it is single-ended output.
Originally posted by Enzo
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...or a class A PP amp.Originally posted by g1 View PostI had thought the opposite but have seen both ways.
In series you have big fluctuations in F.C. current unless it is single-ended output.
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I see so few F.C. speakers that I'm sure I was mistaken to believe the parallel 'ballast' arrangement was more common than the series arrangement.
The ones I recall were in old tube radio sets.Originally posted by Enzo
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Yes, some are parallel. I'm talking old tube radios also, guitar amps i have only seen a few field coils. Lets say in a series coil, the coil is 1000 ohms, very popular to be in that ballpark, 500-1000. Even at 2500 ohms, 400v, you are talking 160ma if it is parallel. So chances are if it's a parallel arrangement, the resistance is fairly high to keep secondary current draw to something reasonable. How much current to make the speaker work i have no idea. Once you get to fine wire and lots of turns, the failure rate goes up as mice, old age and temp swings have killed many a old radio field coil. There are guys whom rebuild them, maybe you can do it yourself. I have a Supro pre war with a field coil and have read many times the amp will really come to life if i use a modern speaker, project for me after 1000 other things. With the OP's amp, it would be one of the last things i would work on, first would be getting the amp rebuilt, if it was worth the hassle. He might be better to sell it as-is or do a total BOM to see what the complete cost would be to get it to work. Technician with a multimeter could check the main items in about 15 minutes. The cabinet is a total other story too. Plywood though is a plus if not water logged.
More i look at those pictures, 30's era no doubt.Comment
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Solenoid strength depends on current times turns number (Ampere-turns), so more turns requires less current.- Own Opinions Only -Comment
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I think the OP needs to do a full schematic of how this amp is configured as it is to have any hope with it.Comment
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So I managed to get it working first try, i did 19 caps in 3 hours and used my variac to slowly bring her to life. This was pretty straight forward. Its great and fairly quiet from any noise. Definitely sounds good. All 4 inputs work. Will be looking for the matched tube set soon. Oh, and no shocks, just a small soldering burn on my middle finger
Thanks for helping meComment
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Thanks vintagekiki, i really appreciate it!!Originally posted by vintagekiki View Post
That's all folksComment
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Appreciate, but this field coil wiring would need 4 wires between chassis and speaker assy.Originally posted by vintagekiki View Post
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