I am having trouble figuring out why the Express is rated at 35 watts with a pair of fixed bias EL34's. I'm also a little puzzled by all of the schematics showing EL34's AND 6V6 tubes, but I am assuming that with the 6V6 tubes you switch to a different speaker tap, right?
But the wattage thing has me stumped.
What am I missing?
why 35 watts?
Moderators: pompeiisneaks, Colossal
Re: why 35 watts?
What are you missing? The primary impedance of the OT, for one thing. We tend to run 5K-6.6K while the datasheet shows 45watts at our voltages using a 4K load.
We're running at least 50V less than most amps with '34s. We're using NFB (presence loop), higher output impedance, 1K or 1.5K screen resistors... admittedly, 35watts is a low end estimate, but I would guess it's about right. Now that you mention it, I kind of want to build a load box and test mine to see what it really does.
As for 6V6, sometimes I just bias the things and go to town. Same taps and everything. They don't seem to have a problem running in the mid300V range for less than 20W out, and I can do the 400V thing with JJs and not worry too much. I do like to run them with twice the load selected so I'm reflecting 10K, though, as it does change the character somewhat for the better. Datasheets for 6V6 show 8K at 300something volts, so it's more in tune with the trainwreck philosophy of slightly higher than normal impedances.
We're running at least 50V less than most amps with '34s. We're using NFB (presence loop), higher output impedance, 1K or 1.5K screen resistors... admittedly, 35watts is a low end estimate, but I would guess it's about right. Now that you mention it, I kind of want to build a load box and test mine to see what it really does.
As for 6V6, sometimes I just bias the things and go to town. Same taps and everything. They don't seem to have a problem running in the mid300V range for less than 20W out, and I can do the 400V thing with JJs and not worry too much. I do like to run them with twice the load selected so I'm reflecting 10K, though, as it does change the character somewhat for the better. Datasheets for 6V6 show 8K at 300something volts, so it's more in tune with the trainwreck philosophy of slightly higher than normal impedances.
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MooreCowbelle
- Posts: 81
- Joined: Mon Mar 20, 2006 5:03 am
- Location: Tacoma, WA
Re: why 35 watts?
Moose,
Let me get this straight - If my wreck has 6V6's, and I have a 4ohm cab, I should run with the 8ohm secondary?
With the 6V6's, is it 'better' to use the 5200 or the 6600 tap?
Let me get this straight - If my wreck has 6V6's, and I have a 4ohm cab, I should run with the 8ohm secondary?
With the 6V6's, is it 'better' to use the 5200 or the 6600 tap?
Re: why 35 watts?
heh i was reading recently eddie VH was running his stock super lead 100 watt plexi into a 20 ohm power resistor ....but with the variac turned down so it's comperable to a 50 watter (same preamp schematics and the extra output tubes and bigger trannies)...so he's running the power tubes way under biased.....right? then he sets the output transformer to 8 ohms, lol!
'cause like the power tubes are barely on...oh and all this was before attenuators and he heard that the old marshalls were to run at 110 v instead of 120 v and of course it was a bit quiter ...lower B+ voltages.
also the airbrake is reported to want you to set your output transformer to 8 ohms (but that's to match the impediance of the airbrake going into a 16 ohm cabnet...which is about 8.9 ohms on first attenuation then goes up from there to about what ..20 ohms on lowest setting?)
i guess my point is, besides nothing we are doing here is technically right (engineers built amplifiers to NOT distort) ,all the 'mistakes' are perhaps leading us to better mangle the tone to our liking...that is as long as you don't smoke your amp ...hehe.
'cause like the power tubes are barely on...oh and all this was before attenuators and he heard that the old marshalls were to run at 110 v instead of 120 v and of course it was a bit quiter ...lower B+ voltages.
also the airbrake is reported to want you to set your output transformer to 8 ohms (but that's to match the impediance of the airbrake going into a 16 ohm cabnet...which is about 8.9 ohms on first attenuation then goes up from there to about what ..20 ohms on lowest setting?)
i guess my point is, besides nothing we are doing here is technically right (engineers built amplifiers to NOT distort) ,all the 'mistakes' are perhaps leading us to better mangle the tone to our liking...that is as long as you don't smoke your amp ...hehe.