Power tube bias and OT load...

[trem]

...in a Fender BF Delx Rev for example.
With no guitar plugged in...all the knobs on Zero...tubes biased at 60%...is there a need for a load on the OT...resistive or reactive.?
At this point...the OT secondary will be shorted and not open... if I am no mistaken.
Thank You

[Jazz P Bass]

My thoughts are that nothing is 'happening' inside the transformer, if there is no signal applied.
Not too sure what you mean by this statement.: 'At this point...the OT secondary will be shorted and not open... if I am no mistaken.'
The secondary is already a very low resistance.
That does not change.
The secondary load is transformed by the winding count & reflected into the primary & the tube plates.
Again, without a signal, nothing is happening.
A transformer only works on a varying current.

[g1]

Not too sure what you mean by this statement.: 'At this point...the OT secondary will be shorted and not open... if I am no mistaken.'

Maybe referring to the shorting jack for the speaker when nothing is plugged into it? If so, and you are sure it is shorting properly (measure with ohm meter), it should be ok to run without signal applied.

[trem]

Sorry.
I meant in my scenario there is no speaker plugged into the speaker jack.
On a BF Fender...I am assuming that means the OT secondary is shorted...and not open...like if there was a speaker cable plugged into the jack...but not plugged into a speaker cab at the other end.
Like it would be if you were biasing the amp...with nothing in the speaker jack.
Thanks

[g1]

Looks like we were posting at the same time. You should be ok, don't push any signal through (would be hard on the tubes) and make sure the shorting contacts on the jack are clean and working properly.

[trem]

Yeah...OK.
I am not tempting fate...or trying to be smarter than I really am.
Was biasing an amp...with a load...like I always do...and just started to wonder if the load was "necessary".?
Thank You

[Enzo]

You are correct, at that moment you don't "need" a load. But what if while servicing the amp, your meter probe slips, and you send a large voltage transient through the amp? Like with a speaker it would make a loud pop or other noise? To the amp that is no different from strumming a guitar. And if unloaded, that impulse could arc your OT. Likely? Probably not, but if you are adjusting the bias on the amp, are you really doing it where no speakers or other loads are within reach? The shorting contact on the jack probably takes care of it, but why develop bad habits? Unless there is some compelling reason otherwise, just plug something into the amp output and be safe. If you already do that, fine.

It's like that safety rope on a climbing wall. You only "need" it when you screw up.

[trem]

Hey Enzo -
Yeah...it was just a theoretical question...was just curious.
I have enough problems in life while acting "normally"...I do not need to give trouble an extra card.

[Old Tele man]

A vacuum tube OT tolerates a "shorted" secondary output much better than it does an "open" secondary output. The reverse situation is true for most direct-coupled solidstate amps, however.

The only time you "really need" a (proper) resistive load is when you're trying to measure output power.