11-07-2019, 08:38 PM
I'm sorry to hear that the transformers are open.
There are some options depending on costs, authenticity and originality.
- Have the transformer re-wound. This can be done by Heyboar. Estimated some $40 each. They will appear as original FWIR the transformers are below the "deck". FWIK the transformers have 3:1 ratio, but there is a chance the 1st AF could have a higher ratio from 4 to 9:1. Only someone who has one original and willing to measure the ratio could help. The winding resistance is good in this replacement.
- A solid-state replacement, recently designed, more info from Robert Lozier of ARF relatively in expensive. Old transformer stays in place. Postage stamp size circuit board nearby. Can be covered with black heat shrink to look like vintage paper capacitor.
- Replace just the winding bobbin with one from ARBE, Yes the power supply maker has made transformers bobbins of 3:1 ratio in three sizes of cores. Go to ARBE-III... Winding resistance is also good
- Hold off, take good sharp images of the transformers and measurements and post ads in the Phorum and ARF classifieds for originals. It will take time...
- Use the A-53 transformer from AES or the Hammond bobbin for Radiola III if the core size fits.. The A-53 is a late model transformer with a saddle strap mount, modern looking. very low resistance tone does suffer. The Radiola replacement has good DC resistance.
- Use R/C coupling, it will work but volume will considerably lower even if "pushing" the tubes. Tone will be good, alas, volume not so...
The 112a tube will use the 135 volts B+ and at least 9 volts "C" bias.
See: http://www.nmr.mgh.harvard.edu/~reese/RC10/RC10-25.GIF
The plate resistance is a good match for an AA5 audio output transformer so a modern speaker could be used...
Good Luck!
Chas
There are some options depending on costs, authenticity and originality.
- Have the transformer re-wound. This can be done by Heyboar. Estimated some $40 each. They will appear as original FWIR the transformers are below the "deck". FWIK the transformers have 3:1 ratio, but there is a chance the 1st AF could have a higher ratio from 4 to 9:1. Only someone who has one original and willing to measure the ratio could help. The winding resistance is good in this replacement.
- A solid-state replacement, recently designed, more info from Robert Lozier of ARF relatively in expensive. Old transformer stays in place. Postage stamp size circuit board nearby. Can be covered with black heat shrink to look like vintage paper capacitor.
- Replace just the winding bobbin with one from ARBE, Yes the power supply maker has made transformers bobbins of 3:1 ratio in three sizes of cores. Go to ARBE-III... Winding resistance is also good
- Hold off, take good sharp images of the transformers and measurements and post ads in the Phorum and ARF classifieds for originals. It will take time...
- Use the A-53 transformer from AES or the Hammond bobbin for Radiola III if the core size fits.. The A-53 is a late model transformer with a saddle strap mount, modern looking. very low resistance tone does suffer. The Radiola replacement has good DC resistance.
- Use R/C coupling, it will work but volume will considerably lower even if "pushing" the tubes. Tone will be good, alas, volume not so...
The 112a tube will use the 135 volts B+ and at least 9 volts "C" bias.
See: http://www.nmr.mgh.harvard.edu/~reese/RC10/RC10-25.GIF
The plate resistance is a good match for an AA5 audio output transformer so a modern speaker could be used...
Good Luck!
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
