help with heater supply

[NFXP]

I have an interesting amp Bogen J1623, there are 2 center tapped 9vac windings for heater filament supplies but the amp runs all 6.3v octals. The amp was designed to run off a 6v or 12v battery or 120v mains by using different plugs. Heres the schematic, what a headache.



Im converting the amp to guitar but keeping the original tube configuration, its completely stripped of the original circuit and ready for a complete redo. I don't know how I should tackle this to make the heaters run the right voltage.

[Enzo]

I see two power transformers, one has the primary and HV plus two center tapped, the other has primary and two center tapped. That is four center tapped. All four make 9v?

Also, is that 9v unloaded? What does it drop to when all seven tubes ar installed?

[NFXP]

I see two power transformers, one has the primary and HV plus two center tapped, the other has primary and two center tapped. That is four center tapped. All four make 9v?

Also, is that 9v unloaded? What does it drop to when all seven tubes ar installed?

I don't have the second transformer. Just t379. blk/red gets 117v. Then with a multi meter and no load I measure 9vac on each secondary on the left side, or 4.5vac x4. I haven't hooked up all 7 tubes et

[Enzo]

Your 9v winding may fall to 6v under load.

You say the thing is gutted. Did you leave the heater wires?

[NFXP]

Your 9v winding may fall to 6v under load.

You say the thing is gutted. Did you leave the heater wires?

No I just have a pic from before I gutted it, all heaters were hooked up in parallel, but how they were hooked up to the pt I can't see. Someone already hacked and slashed it when I got it so It wasn't hooked up like the schematic anyway.

[NFXP]

Just checked again found a pic that shows one end of each 9.4v winding not connected. Therefore it was running on the center taps at 4.5v maybe paralleled I can't see exactly. Again it was hacked so I don't think I want to run it that way. There has to be some comination to get it running right. I thought running both 9.4v windings in series then running the tube heaters in series with 3 levels. I don't know if that's a good idea or if there's a better or easier solution,

[g1]

Do you have that jumper connector, or have it all wired as such? The t379 org & blk get connected via the connector.
From ylw to grn you should measure 12.6V, but that is with 117V in, and fully loaded with all the tubes, the pilot light, and the 20-7W & 68 1W ballast resistors.

[g1]

So your readings make sense, and they are using 3 out of 4 of those windings to get 12.6V (you are measuring 13.5V unloaded).
You can't get 6.3V out of there unless you use voltage dropping resistors.

[NFXP]

So your readings make sense, and they are using 3 out of 4 of those windings to get 12.6V (you are measuring 13.5V unloaded).
You can't get 6.3V out of there unless you use voltage dropping resistors.

I don't have that plug or any of the original circuitry. I'm going to run fused and switched 117v to the blk/rd winding. If I use 3 of the 4 sections I will get 9.4v + 4.5v so just under 14v. If I run the tubes heater in pairs I could get close.

[NFXP]

this is what I came up with. I know enough that the heater draw of the filaments have to be equal when in series, but I don't know if theres anything else I should add or do. I want this to work properly without hurting any tubes or the transformer, this is a 60 year old amp and tubes aren't cheap.

[g1]

That's pretty much how they did it. They used that 20-7W to correct for balance between the top and bottom sets.
They had the center of the two sets tied to a +DC for elevated virtual ground. You will need a virtual ground of some sort.
If you end up with more than 6.3V per heater you can use small series resistors coming off the heater windings.

[NFXP]

so if I hook it up per the original schematic where would I hook up the line with the question marks. my project is to clone the power amp section of bassman 5b6 schematic. its cathode bias and I don't know where to connect that line, or if I can keep it separate from the power amp and connect it some other way.

anyways this is what I see without the big connector and the vibrator connections.

[g1]

You could run that point to the power tube cathodes. Many circuits elevate the heaters that way.

[NFXP]

You could run that point to the power tube cathodes. Many circuits elevate the heaters that way.

dang that means I have to set up the whole circuit before I can test the heaters. id rather set up the heaters, then I can check my voltage out of the rectifier. Do I want to elevate the heaters? i might have to lower the voltage already. is there another way?

[g1]

Just ground it for testing.