50w 183?

[Oddvar R]

Hi. Just thinking about making the 183 into a 50w amp. Is there anything else than just omitting two output tubes from the circuit?

[10thTx]

Compare the bias circuit of a known Dumble 50w amp using the tubes you're gonna use (6L6,5881,EL34,KT66, etc...) and contrast that with the 100w 183 bias circuit.

With respect, 10thtx

[Oddvar R]

Are there any 50w layouts around?

[pompeiisneaks]

They'd literally be the same w/o the extra tubes and a specifically different OT to support the different required plate load, thus 10thTx's point.

Power Amp side everything is equal and you just adjust the OT for the number of tubes, you could even possibly do 150W with 6 tubes but you'd need to beef up the PT likely for more heater current and HT current for the extra tubes

4x power tubes just require 2 more sockets, 2 more grid stoppers, 2 more screen droppers, and a bit of jumper wire for the OT primaries to share the load on each side. Then the OT of course. If you're doing 2, just omit the xtras.

~Phil

[norburybrook]

you're forgetting that to keep the same feel of the amp you would need to half the main filter cap values.



M

[martin manning]

...and adjust the GNFB resistor.

[pompeiisneaks]

I stand corrected, those definitely both make sense. Although filtering usually in dumbles is pretty stiff already, I don't think adding more power filtering is 'horrible' in that case no? yes?

The GNFB would definitely change the tone of the amp and needs adjusting, my apologies . It's based on the actual OT impedance ratio right? Something I still have yet to figure out fully. I've seen people showing the calculation to adjust for different taps etc, but still have never seen a super great explanation of it.

~Phil

[Oddvar R]

...and adjust the GNFB resistor.

What would be recommended here?

[martin manning]

For half the power into the same speaker load, the voltage is reduced by a factor of 0.707, so I’d start by reducing the FB resistor by that factor. You may want to experiment with that, though.

[10thTx]

I looked thru my D files and found these 3 schematics. Maybe something of use in there helping with bias, NFB, etc.....

With respect, 10thtx