Should i worry?

[iknowjohnny]

I asked this in the thread that i started about 6l6 vs el34 but i don't think anyone is visiting that thread anymore. But i'll make this short. Tried a 4k heyboer in the amp today, same one i've used in the past. But don't care for it. I just prefer the 3.6k mag comp OT. But i want to know if the amp will be reliable and safe with a 36k load or if not what if anything can i do to make it so? I could go with a mag comp fender OT at 4.2k i supposed, but maybe it's the higher impedance that i didn't like about the tone of the heyboer, and if thats the case them i'm not likely to find a 4.2k OT any better and probably worse. So is there any way to stay safe with the mag comp OT running 6L6 off 3.6k?

[Phil_S]

Not enough info. What's your plate voltage? Two power tubes, right? What's the wattage rating on the OT in question?

[Cliff Schecht]

You're fine. Although you aren't in the optimal loading range, you can easily adjust the bias as needed to keep things in order. Learn how to use a transconductance chart to calculate the bias you need! Merlin's website is a good place to start.

[iknowjohnny]

So what, bias lower than normal? I'll see if i can find and understand whatever i can find on merlin's site. Its 2x6L6 at 3.6k, plates are 465, OT is a 50 watt marshall style. Someone said 6l6 ranges from 3.8k to 8k something. So i'm out of range. If i can just bias low that would be fine since i'm already running 8-10 ma under what webers bias charts shows to get 70% for 6l6 at 465v.

[Cliff Schecht]

Your screen voltage would help as well. But with the standard GE 6L6GC curves, a 465V B+ and a 3.6k transformer I calculate a -40V bias for pentode operation and something like -45V for triode operation (screen at about the same potential as the plate). What bias are you running now?

Just for note, the lower your transformers impedance the more clean headroom you'll get before you clip the power stage.

[ToneMerc]

I asked this in the thread that i started about 6l6 vs el34 but i don't think anyone is visiting that thread anymore. But i'll make this short. Tried a 4k heyboer in the amp today, same one i've used in the past. But don't care for it. I just prefer the 3.6k mag comp OT. But i want to know if the amp will be reliable and safe with a 36k load or if not what if anything can i do to make it so? I could go with a mag comp fender OT at 4.2k i supposed, but maybe it's the higher impedance that i didn't like about the tone of the heyboer, and if thats the case them i'm not likely to find a 4.2k OT any better and probably worse. So is there any way to stay safe with the mag comp OT running 6L6 off 3.6k?

When it comes down to it you don't know exactly what any of those transfomers are, as far as you know that 3.6k could actually be a 3.4K, besides impedance is dynamic. Some of the best tones have come from combinations that are not paper perfect.

Run it at 3.6K and be done with it, it won't be any less reliable or safe.


TM

[iknowjohnny]

Thats where it is now, right at 40 not taking the screen into the calculation. I usually figure about 5ma for them. So i figured i'm low. But like i said i'll go lower if thats going to make it much safer.

[JamesHealey]

Don't worry so much that mismatch will be fine! Might chew up tubes a bit faster but will be fine just check you're not over bias limit for that tube.

[rp]

Just for note, the lower your transformers impedance the more clean headroom you'll get before you clip the power stage.

Cliff, maybe you and others here can expand on this. What I culled from the web (from posts) is that raising the pZ lowered distortion and decreased power and, I'd figure, raised headroom. So you'll see Hifi amps w/ 6L6s or El34s typically using 6.6K or even 8K as more clean outweighed more power.. On guitar amps where people were willing to sacrifice more distortion for more power you see designs typically using 3.4K to 4.2K.

This to me explains the early Marshalls, they sourced off-the-shelf Hifi iron at first and ran 6.6-8K but then later used their own custom iron designed for more power and voiced more specifically for guitar and distortion and went down to 3.4-4K.

I'd like to get the final word on this, or at least better understanding, as it's an important factor for voicing an amp.

[JamesHealey]

higher primary gives less headroom but wider frequency responce.
Lower primary gives you more head room but narrower bandwidth

[iknowjohnny]

I love simple to the point explanations like that ! thanks.