Plate load Z

[lowell]

Hello,
I'm running some ideas for different output designs through my head and am not too educated on plate load impedances. Where can I find info in what primary impedances of OT I should use w/ certain tubes... I'm also assuming that p/p s/e and class of operation all play a role too.

[stokes]

A tube manusl will give you the plate load for that particular tube.Not all amp makers run the amps exactly as stated in the tube manuals.For instance Fender usually ran a pair of 6V6's at about 6600ohms,6L6's at about 4200ohms primary impedance.You can run them as you please,but tube life and sound quality will be an issue.And remember,the tube manuals werent written for guitar amps.In a Hi-Fi application you want exact reproduction in sound,guitar amps are more forgiving,and actually want some amount of distortion,so usually close is "good enough".

[Enzo]

And also tube manual specs were writeen for designs that were to politely use the tube for lengthy periods reliably - like TVs and table radios. The specs are not intended for guitar amp applications where we drive them to death and expect to replace them once a year or more.

[hasserl]

Speed Racer from the old Ampage bbs once posted this info on common guitar amp primary loads that I saved (I think he also had it posted on the old OEI website):

Amplifier Primary Impedance

Marshall, 50W 2xEL34 3,400 Ohms

Marshall 100W 4xEL34 1,750 Ohms

Marshall JTM45 2xKT66 8,000 Ohms

Vox 30W 4xEL84 4,000 Ohms

Vox 15W 2xEL84 8,000 Ohms

Fender 50W 2x6L6 4,100 Ohms

Fender 100W 4x6L6 2,000 Ohms

Tweed-Spec Cathode Bias 6L6 p-p 6,600 Ohms

Matchless 15W 2xEL84 4,000 Ohm

Matchless 30W 4xEL84 4,000 Ohms

Park 50W 2xEL34 5,000 Ohms

[lowell]

nice thanks guys!

[Old Tele man]

...the 'general' rule-of-thumb with power beam tetrodes and pentodes is that Z.pri should be between 1/6th and 1/8th of the TUBE's dynamic plate resistance ( rp ) value, with the LOWER Z.pri value yielding lower %THD and the HIGHER Z.pri value yielding higher output POWER...and, anything between those two values is acceptable, depending upon the "goal."