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need Fisher TA-800 resistor value, or bias winding voltage

gadget73

gadget73

junk junkie
Subscriber
Studying the TA-800 schematic because I'm using the transformer for something else. End bells are currently removed for paint and I can't easily hook it up to just measure this. I thought I already had, but either I did not, or I lost my notes.

Trying to work backwards to figure out what this winding's output voltage is.

Schematic bit here

1790204120814.png

so I have DC voltage at the - output of the rectifier at -25v. Some amount of voltage will be dropped across R13. Current through this should be darn close to 0.3 amps. The parts list says R13 is 1K, which means its dropping 300 volts. I find this highly unlikely. C23A is a 30 volt cap so it can't be seeing more than that, which means not more than a 5v drop across R13.

1790204411576.png

Can anyone confirm what the value of R13 is, or I can also work with the voltage coming out of the transformer, or the DC voltage across C23A.

basically just trying to figure out if there will be enough voltage for my bias supply with a bridge or if I need to make it a voltage doubler.

Appreciate any info available.
 
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The DC Heater/Bias supply winding is classically a 25 volt RMS winding on all their vacuum tube amplifiers and receivers that use such windings.

Dave
 
Appreciate it. Kinda figured it was probably somewhere in that zone.

so voltage doubler it is. Just need a bias supply, if its good for 300mA of heaters its certainly sufficient for a handful of mA for a bias network. Building something with TA-800 iron and 6LR8 tubes. Looks like its going to need ballpark -40v if I didn't screw up the modeling too bad. If I did screw it up, its just not that big of a deal.
 
I've been running my TA-600 at work, it hasn't made me in a big hurry to check out the solid state Allied/Pioneer that normally lives here. As a side bonus the line voltage here is 118v, about as good as I could ask for.
 
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