MOT in speaker crossovers
Another use for the primary pancake carefully salvaged from an MOT is as speaker crossover chokes. They are low loss #14 guage enamelled copper and about 2 mH. If you salvage the I-bar from the E-I core this bar can be inserted into the coil to produce a variable L up to about 5 mH, great for tuning during prototyping!
Another use for the primary pancake carefully salvaged from an MOT is as speaker crossover chokes. They are low loss #14 guage enamelled copper and about 2 mH. If you salvage the I-bar from the E-I core this bar can be inserted into the coil to produce a variable L up to about 5 mH, great for tuning during prototyping!
MOT as plate choke
This may twist your noodle. I have a prototype P-SET on the bench using eight 6080 triode sections in parallel (4 bottles) set up in parallel SET, ultrapath, parafeed coupling and I use a unmodified stock MOT (the primary winding) as the plate choke for the output tube bank. The fidelity is superb! Use the outer end of the winding for the modulation end of the choke, the core end towards the power supply rail.
This may twist your noodle. I have a prototype P-SET on the bench using eight 6080 triode sections in parallel (4 bottles) set up in parallel SET, ultrapath, parafeed coupling and I use a unmodified stock MOT (the primary winding) as the plate choke for the output tube bank. The fidelity is superb! Use the outer end of the winding for the modulation end of the choke, the core end towards the power supply rail.
Re: MOT as plate choke -CORRECTION
OOPS. I meant I used the HV secondary winding as the plate choke.
Frequency response will also be limited by whatever one uses as an output xfmer which in my case wasn't a real ouput transformer either. I'm using toroidal power xfmers.
If it works well, use it I say.
I get pretty much 20 Hz to 40 KHz full power, which is about 20 watts RMS with the toobz running about 225 volts and 50 mA per section, total 400 mA in the plate choke. As I said, fidelity is superb.
I spent A LOT of time dinking with all sorts of different plate chokes and output xfmer impedances and combos of different numbers of 6080's until I hit the magic setup. The fact that I can use surplus MOTs as both PSU chokes as well as ouput plate chokes, and surplus toroid power xfmers as output devices is great from an iron cost perspective. I have full intentions of building this to completion as a stereo amp in a fine case. I have 16 metal can motor run caps (polypropelene and oil) for the output coupling. Actually I bought enough 'output transformers', coupling caps, 600 VA toroidal power tansformers for the PS and NIB 6080's to build half a dozen of these amps.
BTW I tried using an MOT directly as a conventional output xfmer. No HF through it at all.
rcavictim said:
OOPS. I meant I used the HV secondary winding as the plate choke.
Frequency response will also be limited by whatever one uses as an output xfmer which in my case wasn't a real ouput transformer either. I'm using toroidal power xfmers.
If it works well, use it I say.I get pretty much 20 Hz to 40 KHz full power, which is about 20 watts RMS with the toobz running about 225 volts and 50 mA per section, total 400 mA in the plate choke. As I said, fidelity is superb.
I spent A LOT of time dinking with all sorts of different plate chokes and output xfmer impedances and combos of different numbers of 6080's until I hit the magic setup. The fact that I can use surplus MOTs as both PSU chokes as well as ouput plate chokes, and surplus toroid power xfmers as output devices is great from an iron cost perspective. I have full intentions of building this to completion as a stereo amp in a fine case. I have 16 metal can motor run caps (polypropelene and oil) for the output coupling. Actually I bought enough 'output transformers', coupling caps, 600 VA toroidal power tansformers for the PS and NIB 6080's to build half a dozen of these amps.
BTW I tried using an MOT directly as a conventional output xfmer. No HF through it at all.
Re: Re: MOT as plate choke -CORRECTION
Cuts off around 5kHz IIRC. Might go to 10 if you knock out the magnetic shunt (reducing leakage inductance). Such a dual bobbin wound transformer is simply not going to work well.
The core is always good iron stock though. if you are bored enough to wind one...
Tim
rcavictim said:
Cuts off around 5kHz IIRC. Might go to 10 if you knock out the magnetic shunt (reducing leakage inductance). Such a dual bobbin wound transformer is simply not going to work well.
The core is always good iron stock though. if you are bored enough to wind one...
Tim
Re: Re: Re: MOT as plate choke -CORRECTION
I don't think I had bothered knocking out the magnetic shunts for my test. My hopes were that it might work as a guitar amp output xfmer, where a bit of distortion in the OPT is desireable anyhow. My first impression was so bad I dropped further experimentation in this direction.
The biggest drawback I've found with MOTs is the fact that they are welded together. This technique really adds eddy current losses in the core creating much heat when used as a big filament xfmer for example, even with the primary voltage reduced to below core saturation. I guess if they were not welded together they would be as loud as a door buzzer when used as they are in an oven.
Sch3mat1c said:
I don't think I had bothered knocking out the magnetic shunts for my test. My hopes were that it might work as a guitar amp output xfmer, where a bit of distortion in the OPT is desireable anyhow. My first impression was so bad I dropped further experimentation in this direction.
The biggest drawback I've found with MOTs is the fact that they are welded together. This technique really adds eddy current losses in the core creating much heat when used as a big filament xfmer for example, even with the primary voltage reduced to below core saturation. I guess if they were not welded together they would be as loud as a door buzzer when used as they are in an oven.
Sorry to resurrect the R vs ohm flamewar...
When I was working as a prototyper in an electronics workshop we'd nearly be shot for using ohm. 3.6ohm was always written 3K6R. The reason was that a . would not be seen on the various parts buckets (obviously) and if you've seen some engineers handwriting you'll understand why we weren't to write ohm, or omega.
That was professional practice as I was taught it in 3 firms.
When I was working as a prototyper in an electronics workshop we'd nearly be shot for using ohm. 3.6ohm was always written 3K6R. The reason was that a . would not be seen on the various parts buckets (obviously) and if you've seen some engineers handwriting you'll understand why we weren't to write ohm, or omega.
That was professional practice as I was taught it in 3 firms.
Re: Re: Re: Re: MOT as plate choke -CORRECTION
I've got a transformer here that I setup for an isolation transformer (well, almost.. the other primary was from a thicker core and has fewer turns, gets 100V output). It's not too badly loaded, but the core ends up luke warm after a minute or so of run. The windings don't get very warm, so it isn't conduction from wire loss anyway.
Tim
rcavictim said:
I've got a transformer here that I setup for an isolation transformer (well, almost.. the other primary was from a thicker core and has fewer turns, gets 100V output). It's not too badly loaded, but the core ends up luke warm after a minute or so of run. The windings don't get very warm, so it isn't conduction from wire loss anyway.
Tim
Proofreading is good, eh?You cna most likely use the transformer (mostly) intact. I assume you are using it as a power supply choke in either a PI filter or as a "swinging choke" choke-input filter. The high voltage output winding should be just fine for choke duty, especially in your low load situation (100 ma). just ignore the primary and the short filament secondary. The most that you would have to do is to disconnect the other end of the high voltage winding from the core. On some the grounded end of the winding simply goes to a terminal that is screwed to the frame and is easy to remove. Even if you do manage to float both sides of the winding, I would still ground the whole transformer, just for safety reasons. Now if you are having problems isolating the HV winding, have you considered redrawing your power supply with the choke in the GROUND RETURN and just using the tranny as is? this seems like it would work. I would NOT EVER float the whole tranny at B+ except VERY VERY carefully during a quick test! DON'T DO IT!
here is a (very poorly drawn. sorry!) schematic showing the two ways to implement a C-L-C "pi" filter. The version on the left is the "traditional" way, and the way on the right is the grounded choke method. The only thing you need to worry about is that the first filter cap is not grounded, and the power transformer's center tap on the HV winding is not grounded either.
For a choke input power supply with a grounded choke, just connect the choke between ground and the center tap of the transformer, and then just connect the rectifiers and filter cap as usual (the filter cap is grounded this time). It makes much more sense if you think of the entire HV winding and the rectifiers as a two terminal network.
here is a (very poorly drawn. sorry!) schematic showing the two ways to implement a C-L-C "pi" filter. The version on the left is the "traditional" way, and the way on the right is the grounded choke method. The only thing you need to worry about is that the first filter cap is not grounded, and the power transformer's center tap on the HV winding is not grounded either.
For a choke input power supply with a grounded choke, just connect the choke between ground and the center tap of the transformer, and then just connect the rectifiers and filter cap as usual (the filter cap is grounded this time). It makes much more sense if you think of the entire HV winding and the rectifiers as a two terminal network.
An externally hosted image should be here but it was not working when we last tested it.
sorry, i forgot the link!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.