2xReeves "Vintage Purple" speakers in series with

[traktop]

I´ve got a 73´DR-103 which I´m playing at half the power, (just 2 output tubes), on a 2x12, 16ohms cabinet, (series wiring), so in order to match the speakers load, the amp tap is at 8ohms. Given that the reeves vintage purples run at 16ohms each, the series wiring would make the amp see 32ohms, so my understanding is that returning the amp´s tap to 16ohms would match the cab load...
Is that correct? Would it be dangerous for the OT? Would the sound "suffer"? Did someone try something like this...?
Best regards, Gilberto.

[xtian]

** corrected below **

[sluckey]

Danger! If your amp normally wants to push against 16 ohms (16 ohm tap) but you remove two power tubes, you need to reduce the load by half to 8 ohms. Sounds like you've got a 1:4 mismatch which is a recipe for disaster.

I think you have that turned around?

[xtian]

Always fine with being corrected. Please explain.

[sluckey]

When you remove a pair of parallel tubes on the primary, the impedance increases. Therefore you need to increase the impedance on the secondary as well.

Just think of the parallel tubes as two parallel resistors. If you remove one of the parallel resistors the total resistance increases. If the resistors are equal value, then removing one will cause the total resistance to double.

[JazzGuitarGimp]

Hi Traktop, your assertion is correct: remove two tubes (make sure they are not both on the same half of the OT primary), set the amp's output impedance to 16R, and connect a 32R cabinet. You're good to go.

[xtian]

Just think of the parallel tubes as two parallel resistors.

That's very helpful. Thanks.

[Stevem]

Pulling two tubes and dropping the heater load by near 4 amps will raise the other tubes heater voltage by enough to may be make the amp sound harsh and brittle, and will also kick up the B+ voltage a tad!
I would place the tubes back in and add a switchable 25k 1 watt resistor in those tubes cathode to ground connection to cut them out!

[traktop]

Hi Traktop, your assertion is correct: remove two tubes (make sure they are not both on the same half of the OT primary), set the amp's output impedance to 16R, and connect a 32R cabinet. You're good to go.

The 2 remaining tubes are the inner ones, so I think is ok.
Thanks, Gilberto.

[traktop]

Pulling two tubes and dropping the heater load by near 4 amps will raise the other tubes heater voltage by enough to may be make the amp sound harsh and brittle, and will also kick up the B+ voltage a tad!
I would place the tubes back in and add a switchable 25k 1 watt resistor in those tubes cathode to ground connection to cut them out!

I did´t hear the amp sounding harsh or brittle after pulling 2 tubes, however, I didn´t know about that could be dramatic for tubes. All tube sockets have a resistor on it, (maybe they are for biasing tubes, I don´t know.)
Cheers, Gilberto.

[traktop]

Pulling two tubes and dropping the heater load by near 4 amps will raise the other tubes heater voltage by enough to may be make the amp sound harsh and brittle, and will also kick up the B+ voltage a tad!
I would place the tubes back in and add a switchable 25k 1 watt resistor in those tubes cathode to ground connection to cut them out!

I did´t hear the amp sounding harsh or brittle after pulling 2 tubes, however, I didn´t know about that could be dramatic for tubes. All tube sockets have a resistor, (maybe they are for biasing tubes, I don´t know.)
Cheers, Gilberto.