Stuck on where they should go

[N3DRB The Derb]

Timmy and AHE told me that I had better do the hum pot or the 100 ohm rx's to ground trick on the amp or I would get hum no matter what.  OK. I have some 100Ω@ 3W resistors. please take a look at the relevant part of the circuit  attached and show me where these center tap rx's should go. I would lift the ground off of "B" and connect a 100 ohm rx to each side with both of other ends of them grounded to chassis ground or taken back to B minus where the filter string starts?

which side of the fil chokes get the rx's, the side going to the tubes; or the side going to the transformers?

I honestly have no idea. 

[The Slab Bacon]

Timmy,
          the resistors should be somewhere around 25-30 ohms each and around 10w each. 1 leg of each resistor should hook to each leg of the filament supply BEFORE the filament choke and the other ends of each resistor tied together and grounded. (or tied to the switching relay that disconnects the cathode in standby that I put in it) this creates an "artificial center tap" for the filament supply.

However............. that amp also uses the filament supply for the operating bias for the tubes. So lifting the grounded leg of the filament supply will probably cause some biasing issues. so if you do that, you will have to come up with another arrangement for the biass supply.

If you want I can send you the resistors and a very small fil trans for the biass supply. Call me over the weekend on the yellafone to discuss it.

However, I would fire it up on the air first and see if you have a hum issue or not. If you dont have a hum issue then dont worry about it!! You may not even need to do it at all. the only way you will tell is to test run it and see.

                                                                 the Slab Bacon
 

[N3DRB The Derb]

good point. I think I'll hook it up and see what happens.

I am at the point where the tube sub chassis goes back in, the tubes go back in, the tube suppressors get refitted, and the nichrome wire suppressors that goes over to the DC blocking cap mounted on the plate cap gets soldered. All the wiring underneath done. All DC connections made.

Lets see what I can get done. some pix to follow....

[k4kyv]

If there is  hum, first try reversing the filament connections to two of the tubes (swapping leads to pins 1 and 4).  Assuming identical physical construction of the filament structure of all 4 tubes, the slight hum introduced by two of the tubes should cancel that of the other two.

I am not sure what note 7 accomplishes, since it isn't evident from the schematic.  Do the 572B's need negative grid bias?  If reconnecting the diode for these tubes puts the grid at zero-bias ground potential, then you could go ahead and use the tapped resistance and not worry about the bias.

[N3DRB The Derb]

it is SO COLD in the shack.

that little space heater in there not heating up much space. ....working continues......