Choosing which B+ Nodes to Drive 1-Tube Reverb in AB 763 Deluxe Lite

[fiftynine]

Can anyone tell me the criteria used to choose B+ nodes? Why is V1a usually the last node? I see the voltage dropping across each successive resistor but it's not a huge amount. Is the filtering increasing? Is that what's important?

It's just the 2 supplies I need to choose; one to the standard Fender reverb tranny (V2a) and V2b.

Ta.

[PRR]

> Is the filtering increasing?

Yes.

Over-simplifying:

Wall-power is BIG buzz. We can filter the buzz, but that costs money. And more money for higher currents.

The last (Power) stage has BIG signals, draws BIG current, and can tolerate significant B+ buzz.

The first (input) stage has small signals, can't tolerate B+ buzz, but does not need much current.

Change of topic. Your water supply is dirty (my well leaks dirt). You need 100 gallons to flush toilets, 10 gallons for bathing healthy adults, 1 gallon to wash and water a newborn baby. The toilets can flush with dirty water. The adults like clean water. The baby needs VERY clean water.

Do you use a super-duper filter to clean ALL the water to baby-quality? It would clog every day or be as big and expensive as a house.

You run a trash-screen first, so the toilet water isn't gross-brown before you do business. Then you run a paper filter to knock down the visible scum so that adults come out cleaner. Finally the baby-water only goes through a super-filter so nothing annoys or sickens the lil darling.

Same thing in your amp. The 6V6/EL84 get nearly raw buzzy DC, several volts of ripple. That's like filtering the toilet water so you hardly see the dirt. The amp has other stages which need cleaner power but not so much current, little filters do this job economically. (unlike water filters) A cascade of power filters can clean-up to any desired cleanliness, even clean enough for the small but precious signal from your guitar.

> the 2 supplies I need to choose

The reverb driver (transformer) IS a "Power" stage. It may be 1/100th the power of your 6V6es, but that's still 10X the power of any other stage. And reverb driving is not real hum sensitive; the RT and the spring drop bass. You would probably take reverb driver power from your second dirtiest node, typically 6V6 G2 node.

The reverb recovery is actually the -weakest- signal in the amp. Pickup is 20mV-200mV, reverb recovery is often under 10mV. This stage should get the cleanest power in the amp, typically the same node used for your pickup input stage.

[fiftynine]

Ha ha. Great analogy. Loved it.