New Fisher 400

-16.2 is way too low. Get a 10K trimmer pot, tie the wiper lead to one of the outer leads and then set it for the resistance that R35(or whichever it was that you pulled to change to 1K) WAS ORIGINALLY and install it in place of the 1K resistor. Once all the other work is done, including the cathode resistors, grid return resistors, and screen resistors, then we'll show you how to check and adjust the bias using actual tube draw vs a generic voltage. It's more accurate, and enables you to dial in the tubes to a better working level. Until then don't mess with it, please.

With you running it @ 117V, check the V8-9-10-11 heater voltages. 12.6v is max. per tube. FISHER Ran the heaters slightly starved at around 11.6 to 12.2. IIRC. Personally I run mine @ 12.3v. Adjust your input voltage to get the desired heater voltage.

Limiter is supposed to get very hot. NORMAL.
 
OK, the metal bone kit had 4 resistors for r35, I used the 470 ohm. The voltage at pin 2 across the outputs was equal at -20.2. It stated in his instruction that the other 3 resistors were to substitute to try and get the voltage as close to the fisher manuals -17 v. So..... The a 10k trimmer pot sounds like a better idea for sure. I will check the heater voltage and get back.
Which pin is the heater checked at?
 
Each tube type has different pins that are heaters. On the 12ax7 4-5-9 are the heater pins as it can be used for either 6.3 or 12.6v heater voltage. In this case it's 12.6v DC. FISHER Historically ran the heaters "COOL", from 11.6 to 12.2 or so. Anywhere in that range is good. Change the voltage at the variac until you get a voltage in that range you are comfortable with. Write it down and then maintain that voltage +/-1V @ the variac. Check at either 4 or 5 following the schematic.
 
Why doesn't Metalbone give out 10K trimmers? Seems like a better solution than trying four different resistors.
 
Back to the switch install, the previous burnt out switch had some jumpers soldered across a few pins on the back. When I soldered the new switch I was not sure if these jumpers were put on to keep the unit powered up when plugged in? I did not put them back on the new switch and all seems good... Switch works as it should. Was there a jumper wire originally??
 
OK, my old switch was HotWired . good ! My new on/off works perfect. Do the old switches literally burn up? I cleaned the defective unit and it actually looks pretty good ( had a burnt carboned coating ) , but I promised to send it back for some TLC and repurposing. Keep them alive!
 
Put a CL-80 thermistor is series with the PT primary. Does a slow start-up easy on the switch. Best preventative measure is to leave it turned-on but switch it from a multi-outlet surge strip.
 
Also have a 400 hotwired to bypass the on/off switch. Replacing the switch with the NOS is my next challenge. Just working up the courage.
 
Wasn't too difficult , the hard part was getting the back cover apart. Mine was soldered on the top and bottom. I used a flat screwdriver from a glasses kit that was really small to pry apart the tabs. Check out the sticky at the top of Fisher forum. www.oldradioparts.net
This is the link for where I got the switch.
 
Restuffed cans, but having a small issue with c57.... Had a bit of a chip out on the side where the indicating symbols are and now I can't make out which capacitor goes to what pin?? ( never took a pic....I know) ..... I will look at schematic but thought I would check in
 
Take and post a picture of what you have now. take a close up of the bottom end ofthe CAN CAP so we can see the shapes.
 
They flaked off the bottom, the shapes that is, but I managed to figure what goes where. I'm trying to measure those heater voltages on the 12ax7's, are they taken at pin 4 or 5?? Also running the unit thru my buck tranny the output at pin 2 is. -17.4 ! Across the board! Everything is running cool to touch so far. Sounding very nice!!
 
Try either. Find the tube with 5 to ground. you'll get ZERO @ 5 but about 12V @ 4. Then Go back one tube and that 5(2nd tube) will be the same as the 1st tubes pin 4. And the pin 4 for the 2nd tube should be about 23-24V. The voltage drop across the tubes should be close to equal as possible.

Can you be a teeny bit more specific on -17.4v @ pin 2??? Pin 2 of what??? I know what it is but the poor guy 10 years down the road who's reading this trying to get his 400 may not know. So being specific helps YOU, us, and future members and readers.

I would rather have you check current draw at the 10 ohm resistors on pins 3 of each tube. Red probe on tube socket end and black probe to a chassis ground. Write down the tube # and the millivolts. Convert to ma by dividing by ten. So for example 320mv = .032ma. Multiply that by the voltage on pin 9 to get wattage per tube. This is a better indicator of tube performance in that equal ma draw across the board is ideal. Using the voltage to set the bias can have the tube draw's all over the place, making one tube of each pair working harder than the other. Equal load's across the output tubes produce, less distortion, less heat, and less strain on the rest of the circuits. HOWEVER if the original bias circuit is still in the unit, -17.4 should be ok. But still take the readings on Pin 3 to determine how far out or how close they all are.
 
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Output tubes the heaters are pins 4 & 5. The output's are AC heaters so it doesn't matter which one is checked. Red probe to pin 4 or 5. black probe to ground . If you get 1/2 of voltage, then black probe to the other pin. (That's alright I just woke up!).
 
OK update. Restuffed those cans after cutting them down with a new hacksaw blade, 10" 24 tpi DeWalt blade. Used silicone inside the can after cleaning them out. Used a heat gun to get the gunk out better! Used some cheap epoxy from the dollar store and voila! Fired it back up with dbt and good to go!! So I have been checking my voltages and was hoping for any feedback from the pro's??
CR1 negative lead from rectifier : -27.1v
After R35 drop. : -18.1v
V14 output tube
Pin1 341.8v
Pin2. -17.7dcv
Pin3. 150mv
Pin4. 2.99 acv
Pin5. 2.98 acv
Pin6. -17.7dcv
Pin 9. 396 dcv

All the outputs essentialy measured the same across all pins.....( V15,16,17) as V14

C56 Can cap 396 dcv

C52A. - 233.7 dcv
C52B - 288 dcv
C52C - 319.7 dcv
C52D - 341 dcv

C57A - 179 dcv
C57B - 186 dcv
C57C - 194 dcv

Anything seem out of place??
 
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