Slaved clip on halloween with Jnew

[Jeremy1283]

I'm scared at how alike we're thinking right now. When I did this clip of SGMAD:

http://www.soundclick.com/bands/page_so ... D=12585071

I used that same E chord and rolled back Vol I until I realized about the same rate of decay as the album. I actually still have a little more sustain I think but that was the barometer I used. I think Vol I was on about 5. It was pretty loud when I did this so some of the speaker smashing is going on and I had to smack down on the strings as well but I think it's a good example of what we're talking about.

Your tone hear is killer james. Amp and cabinet cranked. If i do this live i will be the only one heard. LOL

[jnew]

Thanks. I'm loving it because everything is on 10 and I do have the 330uF on V2. I don't know how to make the amp sound this way with Vol I on 10 but I don't really care about that. I care only for the knowledge of understanding how and what keeps an amp stable to be able to do it but I definitely don't need more volume or gain so Vol I on 5 or 6 is just fine by me.

And BTW, a delay before the head sounds killer like this.

[rgorke]

I'm scared at how alike we're thinking right now. When I did this clip of SGMAD:

http://www.soundclick.com/bands/page_so ... D=12585071

I used that same E chord and rolled back Vol I until I realized about the same rate of decay as the album. I actually still have a little more sustain I think but that was the barometer I used. I think Vol I was on about 5. It was pretty loud when I did this so some of the speaker smashing is going on and I had to smack down on the strings as well but I think it's a good example of what we're talking about.

Is this slaved?

[jnew]

Yep. All controls on 10, Vol I on 5, Vol II on 0, OPT on 8 ohms, 20 ohm load resistor, line out with the Jenesen 4:1 step-down, through a Digitech TSR-12 ( mainly to see a level meter) and then into the Peavey Classic 50/50 pwr amp and pretty loud. There's something to note here and I've mentioned it before. The OPT transformer is a Mercury Magnetics, O45RS-L. This was designed for 6L6/KT-66 type tubes with a 6.6K primary. Unlike a typical 3.4K primary. I'll let the more intelligent types chime in on the details of differences but it is a big part of the overall equation with this little POS JTM-45 re-build. Here's some great info on it:

http://www.mercurymagnetics.com/images/ ... 45RS-L.pdf

I wish plexified was around on this. He'd be able to nail down exactly what's going on. It might not be anything more than the simple mis matching of an 8 ohm amp into a 16 ohm cab, but then again, I'm kind of doing that anyway but using a 20 load resistor. So something must be different.

[vh junkie]

Looking at the wiring choices I am guessing that the OT is hardwired at 8 ohm? Which primaries of the OT are wired to the power tubes? Are you using EL34s/6CA7s?

[jnew]

Yep. 8 ohm only with no other options. Big bottle 6CA7's are the power tubes and the primaries are wired 6.6K. How does this all translate?

[vh junkie]

The mismatch you are describing is going in the same direction as running a 100w amp on 8ohms into a 16 ohm cab... but it is going WAY in that direction. The way to look at this is: what impedance is the load (speakers) and the OT "reflecting" back to the primaries (and of course the tubes). Let's look at some examples starting with ones we know.

Running a 4 tube El34 Amp with into 16 ohms with the selector set at 8 ohms:
1700 ohm primary, 8 ohm secondary, with 16 ohm load
1700/8 is the imp ratio = 212.5
212.5 x 16 = 3400 ohms reflected back to the 4 power tubes
3400 is twice the 1700 the tubes would normally see. We have all run this way, so doubling the reflected impedance must be OK, right?

Note that while the 3400 is twice what the 4 tubes would normally see, it is exactly like what 2 tubes would like to see. That's why the common wisdom is "pull two tubes, turn the selector down to 8, and leave the 16 ohm cab".

Now lets look at your setup:
Running a 2 tube El34 Amp with into 20 ohms with the selector set at 8 ohms:
6600 ohm primary, 8 ohm secondary, with 20 ohm load
6600/8 is the imp ratio = 825
825 x 20 = 16500 ohms reflected back to the 2 power tubes
This is 4.85 times the 3400 ohm load we would expect! We said that twice as much was OK... but this is more than double that...

Of course we are not taking in to consideration the following:
You are using a purely resistive 20 ohm load (likely would equate to a smaller reactive load?)
Different plate voltage that would be in effect depending on you PT.

Interestingly, running at 16 ohms into a 8 cab would work nicely here:
6600 ohm primary, 16 ohm secondary, with 8 ohm load
6600/16 is the imp ratio = 412.5
412.5 x 8 = 3300 ohms reflected back to the 2 power tubes

[jnew]

Holy shit. Well, can't be all bad. I've been doing it since 07 and the amp has never even had a hiccup about it.
There are 8K and 9K primary options for this as well. I'll revisit your last post and try to understand how those options might react.

[jnew]

OK, so nevermind the 8K and 9K options. It goes even further into extreme mis-match territory. So, if I have my math going correctly, I could use the 6.6K primary, the 16 ohm secondary and a 16 ohm load. That puts the whole ball game at 6600. That's alot less than the 16500. This would have to have a significant influence on the tone. And I like my amp the way it is. Food for thought.