impedance question

[mirlo02]

hi guys,for example,in a twin reverb,if i pull of 2 tubes,the impedance is 4k,with the same speaker,but,if disconnect the cathode of 2 tubes,what is the impedance?thanks

[collinsamps]

8 K with two tubes(1 speaker), 4 K with all four(both speakers), if it's stock and wired parallel.

[mirlo02]

thanks collins,my english is bad,but my question is in a amp with 4 tubes,if i disconect the cathode of 2 tubes,the output transformer see the same impedance or double,thanks again

[collinsamps]

When you unground the cathodes or pull 2 tubes you need an 8 ohm load. The primary of the OT is going from 2K to 4K so you need to double the secondary side from 4 to 8 ohms.

[sliberty]

Just to add to what Bruce said - lifting the cathode on the two tubes has basically the same impact as removing two tubes.

[mirlo02]

thanks very much