Hello, I am in the middle of restoring 2 units that need the same interstage transformer. The primary side should read 2K ohms but is open. Secondary is 13K ohms center tapped. Interesting this is the 3rd chassis of this type that I have been into and all 3 have had defective interstage xformers. HUMM design issue? At any rate I know the transformer is a Stancor AU-100 as I found a NOS unit about three years ago and used it restoring the first unit. Any ideas on a substitute? This is a dual transformer type but the output side (primary and secondary) are fine.

Thanks,
Al

Hi Al

You can use a transformer similar to Stancor A53 or A53C if you need a center tapped secondary. AES, www.tubesandmore.com , has part number P-T156. PTOP, www.oldradioparts.com has part number 1017-001 which is lower cost but doesn't have a center tapped secondary.

These audio interstage transformers are often open in 1920's battery radios. Thin wire and corrosion over time cause opens.

Norm

:
:Hello, I am in the middle of restoring 2 units that need the same interstage transformer. The primary side should read 2K ohms but is open. Secondary is 13K ohms center tapped. Interesting this is the 3rd chassis of this type that I have been into and all 3 have had defective interstage xformers. HUMM design issue? At any rate I know the transformer is a Stancor AU-100 as I found a NOS unit about three years ago and used it restoring the first unit. Any ideas on a substitute? This is a dual transformer type but the output side (primary and secondary) are fine.
:
:Thanks,
:Al

Hello again Norm. Thanks for the feedback! My plan is to leave the output stage intact and just "wire-in" the input section. Looking at the schematic it looks like other than grid drive (voltage) and the plate of the second detector (27 tube - 5-6 mAs) this is a lightly loaded device. One thing I am still trying to figure out is that I only have about 1/2 the plate voltage on the tubes? I have recapped the filter assembly and checked the balance of transformers for opens but nothing yet.

Thanks again,
Al

:Hi Al
:
: You can use a transformer similar to Stancor A53 or A53C if you need a center tapped secondary. AES, www.tubesandmore.com , has part number P-T156. PTOP, www.oldradioparts.com has part number 1017-001 which is lower cost but doesn't have a center tapped secondary.
:
: These audio interstage transformers are often open in 1920's battery radios. Thin wire and corrosion over time cause opens.
:
:Norm
:
::
::Hello, I am in the middle of restoring 2 units that need the same interstage transformer. The primary side should read 2K ohms but is open. Secondary is 13K ohms center tapped. Interesting this is the 3rd chassis of this type that I have been into and all 3 have had defective interstage xformers. HUMM design issue? At any rate I know the transformer is a Stancor AU-100 as I found a NOS unit about three years ago and used it restoring the first unit. Any ideas on a substitute? This is a dual transformer type but the output side (primary and secondary) are fine.
::
::Thanks,
::Al

Hi Al

Just add a resistor across the open, primary, winding. I would use 22K rather than 2K. 2K shown is DC resistance. Actual impedance is much higher.

Next connect a cap, .1 mfd will work, from detector plate side of the transformer to either #45 grid. Your transformer will invert this and supply the other #45 grid.

Do you have proper grid bias on your 45's? This is made up by 715 ohm resistor in the filament. If bias is missing tubes will draw way too much current lowering voltage. Would expect grids of your 45's to be near 40 volts negative when measured to filament.

Check & replace other bypass caps. They can become leaky and drop B+ voltage. You might find one getting warm? If you are sure all caps and biasing is ok, try another 80 rectifier.

Norm

:Hello again Norm. Thanks for the feedback! My plan is to leave the output stage intact and just "wire-in" the input section. Looking at the schematic it looks like other than grid drive (voltage) and the plate of the second detector (27 tube - 5-6 mAs) this is a lightly loaded device. One thing I am still trying to figure out is that I only have about 1/2 the plate voltage on the tubes? I have recapped the filter assembly and checked the balance of transformers for opens but nothing yet.
:
:Thanks again,
:Al
:
:
::Hi Al
::
:: You can use a transformer similar to Stancor A53 or A53C if you need a center tapped secondary. AES, www.tubesandmore.com , has part number P-T156. PTOP, www.oldradioparts.com has part number 1017-001 which is lower cost but doesn't have a center tapped secondary.
::
:: These audio interstage transformers are often open in 1920's battery radios. Thin wire and corrosion over time cause opens.
::
::Norm
::
:::
:::Hello, I am in the middle of restoring 2 units that need the same interstage transformer. The primary side should read 2K ohms but is open. Secondary is 13K ohms center tapped. Interesting this is the 3rd chassis of this type that I have been into and all 3 have had defective interstage xformers. HUMM design issue? At any rate I know the transformer is a Stancor AU-100 as I found a NOS unit about three years ago and used it restoring the first unit. Any ideas on a substitute? This is a dual transformer type but the output side (primary and secondary) are fine.
:::
:::Thanks,
:::Al