Print PDF
Favorite
Email
Step 21Finding parts for a build (transformers, etc.)
The "Iron"
If anyone replicates this build, it's unlikely they'll find a 142V transformer. So how to replace that part?
-- One solution is a 230V primary (euro mains), 300-0-300V secondary trannie. If you're in the US, connect the primary to standard US 117V mains, and you've got a 150-0-150V secondary--perfect! However, any filament taps will be halved, so a separate 6V transformer is needed.
-- Try a "universal" isolation transformer--one that has 117 and 230 primaries, and a 117 secondary. Wire that backwards, and tap 230 volts. Then use a "choke input filter"; the choke is first inline after the rectifier, not a cap. that should drop the voltage to less than 210V (vs. 322V for a rectified 230 RMS.) No filament taps, so same as above...
-- Hammond makes an excellent power transformer:
263CX 116VA, sec. 180-0-180, DC ma 250, Fil. #1(rectifier) 5.0v @ 3a ct.
It's 180V, but with a tube rectifier like a 5U4 instead of the SS bridge, the output voltage should be very near 200V. It has a 5V source for the rectifier--a separate 6V filament transformer would be needed...
-- For the PS inductor, Any 4 to 10 Henry inductor will do, but should be rated for at least 120mA @ 250V. New, 4 to 10 Henry inductors are easy to find. The power supply could be redesigned with an initial RC filter, replacing the LC filter (that would be a cheaper option, too.) But that wouldn't be as efficient as the LC setup, and also change the load on the power transformer. Not only would the PT need to be large enough to handle it, it might necessitate changing the resistance values in the power supply also.
NOTE:
Under NO circumstances should an autotransformer be used in place of a standard power transformers. Autotransformers are often used in international voltage converters--i.e., to use U.S. appliances with European wall voltages.
Autotransformers are not isolated, and would constitute a serious hazard in guitar amps.
--A separate 6.3V, 3 amp transformer for the filaments (heaters) will be necessary unless you get lucky and find a trannie with secondaries of 150V and 6V. Again, large current draw for the heaters--2.7 amps @ 6.3V.
-- The Edcor OT is pretty much perfect. Used output transformers are trickier to find, however, due to the lower load resistance of these tubes. It's pretty easy to find OTs for 6V6's, 6L6's, etc., but not for the 50L6 family--except for low-wattage, single tube radios, etc. But that iron is usually less than 5 watts, and not useful for this build.
Tubes
-- Not an issue, NOS tubes are plentiful.
If anyone replicates this build, it's unlikely they'll find a 142V transformer. So how to replace that part?
-- One solution is a 230V primary (euro mains), 300-0-300V secondary trannie. If you're in the US, connect the primary to standard US 117V mains, and you've got a 150-0-150V secondary--perfect! However, any filament taps will be halved, so a separate 6V transformer is needed.
-- Try a "universal" isolation transformer--one that has 117 and 230 primaries, and a 117 secondary. Wire that backwards, and tap 230 volts. Then use a "choke input filter"; the choke is first inline after the rectifier, not a cap. that should drop the voltage to less than 210V (vs. 322V for a rectified 230 RMS.) No filament taps, so same as above...
-- Hammond makes an excellent power transformer:
263CX 116VA, sec. 180-0-180, DC ma 250, Fil. #1(rectifier) 5.0v @ 3a ct.
It's 180V, but with a tube rectifier like a 5U4 instead of the SS bridge, the output voltage should be very near 200V. It has a 5V source for the rectifier--a separate 6V filament transformer would be needed...
-- For the PS inductor, Any 4 to 10 Henry inductor will do, but should be rated for at least 120mA @ 250V. New, 4 to 10 Henry inductors are easy to find. The power supply could be redesigned with an initial RC filter, replacing the LC filter (that would be a cheaper option, too.) But that wouldn't be as efficient as the LC setup, and also change the load on the power transformer. Not only would the PT need to be large enough to handle it, it might necessitate changing the resistance values in the power supply also.
NOTE:
Under NO circumstances should an autotransformer be used in place of a standard power transformers. Autotransformers are often used in international voltage converters--i.e., to use U.S. appliances with European wall voltages.
Autotransformers are not isolated, and would constitute a serious hazard in guitar amps.
--A separate 6.3V, 3 amp transformer for the filaments (heaters) will be necessary unless you get lucky and find a trannie with secondaries of 150V and 6V. Again, large current draw for the heaters--2.7 amps @ 6.3V.
-- The Edcor OT is pretty much perfect. Used output transformers are trickier to find, however, due to the lower load resistance of these tubes. It's pretty easy to find OTs for 6V6's, 6L6's, etc., but not for the 50L6 family--except for low-wattage, single tube radios, etc. But that iron is usually less than 5 watts, and not useful for this build.
Tubes
-- Not an issue, NOS tubes are plentiful.
| « Previous Step | Download PDFView All Steps | Next Step » |
2
comments
|
Add Comment
|
Aug 4, 2009. 7:07 PMisaacnseals
says:
NOS tubes are not always plentiful....trying to find specific less common or popular tubes can become fairly hard. In your design you should use what you have available.
Reply
10
Aug 5, 2009. 8:21 PMgmoon (author)
says:
??? In this case, 6DG6's are VERY plentiful, and cheaper than many classic amp power tubes-- 6V6, 6L6, etc.
Reply
 |
Add Comment
|
