Series Heaters

[trem]

In the Peavey Amps that do use this scheme, why do they.?
Is there some advantage with series filaments.

Also, in the schem below, Pin-4 of V1A is grounded.
How does that work.?

It is kind of odd. Where they grab the filament supply from the PT, they mark it
AC Fil1
AC Fil2

But they mark the tubes
FIL-A
FIL-B

I appreciate any help with this.
Thank You


https://el34world.com/charts/Schemat.../C30_schem.gif

[Pedro Vecino]

AC FIL is exclusive for the EL84. It must be 24V AC to power the four filaments in series.
FIL A/B they call it (I find the distribution in the diagram confusing) is a -36V DC string to power the six triodes in series. One end is connected directly to ground.
The origin of all this must be to reduce the number of secondaries in the transformer (it only has two), and from there obtain a lot of different voltages for different functions. Without a doubt that must lower the price of the transformer.
This system can be somewhat difficult to understand but in my opinion it is a smart and effective system. Especially if thousands of units are going to be built.

[g1]

The power tubes run off the ACFil's, the preamp tubes run off the DC. Various points of the DC heater circuit are -36V, FilA, FilB, ground.
Probably done for a few reasons. DC heaters can help with hum issues and they can use the -36V supply they already have there. This means a lower current AC heater winding to run just the power tubes.

edit: the main problem with this system is that it makes troubleshooting more difficult, you can't just remove tubes at random like in a single AC heater winding scheme.

[trem]

The power tubes run off the ACFil's, the preamp tubes run off the DC. Various points of the DC heater circuit are -36V, FilA, FilB, ground.
Probably done for a few reasons. DC heaters can help with hum issues and they can use the -36V supply they already have there. This means a lower current AC heater winding to run just the power tubes.

edit: the main problem with this system is that it makes troubleshooting more difficult, you can't just remove tubes at random like in a single AC heater winding scheme.

OK..... I totally missed that
Thank You

[trem]

AC FIL is exclusive for the EL84. It must be 24V AC to power the four filaments in series.
FIL A/B they call it (I find the distribution in the diagram confusing) is a -36V DC string to power the six triodes in series. One end is connected directly to ground.
The origin of all this must be to reduce the number of secondaries in the transformer (it only has two), and from there obtain a lot of different voltages for different functions. Without a doubt that must lower the price of the transformer.
This system can be somewhat difficult to understand but in my opinion it is a smart and effective system. Especially if thousands of units are going to be built.

Peavey and cost savings seem to go hand in hand. Does not make it "bad" just makes it cheaper fro them.

If somebody told me it would be "Cheaper" to make 3 boards instead of one, then connect them with 85 jumpers and then fold the boards into a U-Shape.......... i would think it would cost more

[g1]

If somebody told me it would be "Cheaper" to make 3 boards instead of one, then connect them with 85 jumpers and then fold the boards into a U-Shape.......... i would think it would cost more

I may be mistaken, but that part of it may have to do with the assembly process (how can we make this easier for our robots? ).

[The Dude]

It may or may not be easier for robots to build the board assembly, But, I don't think there's a robot that can stuff that mess into the chassis. So, I can't see how there's any time or cost savings. Those amps suck to work on. The one thing I've learned is to check everything over well before reassembly (check solder, check broken wires, etc., etc.). You don't want to tear one of those amps down more than once.

[SoulFetish]

the main problem with this system is that it makes troubleshooting more difficult, you can't just remove tubes at random like in a single AC heater winding scheme.

This is a total drag. In the cases where amps use a series string of 12V connected heater wiring, I'll bridge pins 4 & 5 with an 82R/5W resistor if I need to keep the amp operational (ie. peavey models and some Silvertone amps)