Epiphone Valve Jr. head

I'm sure I'm going to end up with one of those Epi heads soon. I am just trying to be really good right now and watch my spending. I have gone kind of nuts in the last 4 months with 2 new guitars, two new basses, a new bass amp, a new drum machine, and lots of accessories.

Got a question..I am using a 12' 8 ohm speaker. The amp has 4, 8, and 16 ohm out puts. so.... if I plugged the speaker into the 16 ohm out put would it cut down the volume and NOT damage the amp :?: I'm pretty ignorant about such things :lol: --the dog

I have the opposite situation. I have a H&K Cream Machine (8Ohm) and a Fane speaker (16Ohm). Prior to buying the speaker, I mailed H&K to ask them about the output of the cream machine. Their answer was that it was 8Ohms and would tolerate a max of 16 Ohms, but less than 8 was a no-no.
I suggest you ask Epi - using a 16Ohm output to an 8Ohm speaker may void your warranty. If EPi gives the OK, keep the mail safely filed away, you may need it.

I thought that it was safe to drive a larger ohm input speaker with a smaller ohm amp output as long as the differences weren't ridiculously large, but not the other way around. Where's ricochet? We could use a definitive answer. :D

Here is a very good article about mismatching impedences between an amp and speaker (or cab)

Common Misconceptions about Speaker Cabinets

And another great article on Ohms.

All about Ohms

Yes, you can run a 16 ohm speaker or cab off a 8 ohm Speaker Out. But you will lose power. This may be what you want, but on the negative side, you will run your amp harder which will shorten amp life.

Hey Wes, no hurry as I'm waiting for my gear to arrive but wondered if your initial thoughts about settings for reverb were correct after you checked your PB & J pedal. Thanx
Robbie

Thanks Wes ( and all the others ) that was a good article. SO..I can plug my 8 ohm speaker into the 4 ohm out put and the speaker will absorb most of the heat and It won't be as loud( thats what I'm going for) :D BUT If I plug my 8 ohm speaker into the 16 ohm out put The amp will absorb most of the heat and will become TOAST :evil: and I will be crying in my beer :cry: --the dog

I best be saving up for a tube screamer :wink:

Robbie

I am glad you reminded me, I had forgotten all about this. :D I did experiment with my PJ & B.

It is difficult to say what you would like, but this pedal has Mix which seems to give a fullness or depth to the effect. You can go from mild reverb to sounding like an echo coming out of a deep canyon. I myself like to turn Mix all the way up (clockwise). The middle knob is Speed. This controls how fast or slow your repeats are when using the pedal as a delay. This is probably the most important control if you want to use this pedal primarily for reverb. You simply turn it all the way down (counterclockwise). But I found you could turn it up to almost 12 o'clock position and this will sound like reverb as compared to delay or echo. The far right knob is Repeats. When using this pedal as a delay this will increase the number of repeats you hear after the original note.

This pedal also has long and short delay. When you step on the right footswitch the pedal will automatically turn on in long delay. Some complain about this. But I'm sure that some would complain if the pedal turned on in short delay as well. Anyway, it will turn on default at long delay and a green LED lights up. For short delay, step on the left footswitch. The green LED will turn red. To use this pedal as a reverb, you want to use short delay.

With short delay you can get plain reverb or a very good Country slapback tone. Great with a Telecaster.

Using long delay you can get U2 type multiple echos or delays. Good for rhythm or lead guitar.

So, I don't know what you will prefer. I liked Mix turned fully clockwise, Speed turned fully counterclockwise, and Repeats turned fully counterclockwise. This was a good deep reverb tone that I liked.

When your pedal comes in, write back and tell us what settings you like.

Will do and thanx for the info.

Wes, that article about impedance matching is accurate for amps with transistor output or triode tube output. It's not accurate for amps with pentode or beam power tube output. (Basically all tube guitar amps.) The plate resistance of these types of tubes (which is the generator impedance shown in the equivalent circuit diagrams) is far higher than is practical to match with the load impedance of the output transformer's primary. The impedance is selected on the basis of the minimum distortion level. Though the power output generally rises with increasing load impedance, the curve is rather flat, and there's very little difference in the output power of a pentode amp with a speaker impedance of the normal rated value, half that, or double that. The principal difference will be an increased level of distortion from the output stage with impedance values other than the optimal one, and differing percentages of the various harmonics. However, most commercial amps have a large amount of negative feedback built in, which greatly decreases the effects of any change until nearly maximum volume, when the feedback loop loses control. Electronics techs and engineers aren't being taught this stuff these days, and few understand the differences between the different types of tubes, which really are quite different devices in some ways. You've got to dig out the good old textbooks from the tube era.

Ricochet

Then what advice would you give concerning mismatching impedence between speaker and amp?

I know that with solid state amps you are not supposed to use speakers rated lower resistance than the amp's minimum. For instance, you should not run two 4 ohms speakers in parallel (2 ohms) off an amp rated 4 ohms minimum. I know you know this, I wrote this for those who might not know this.

But what about what Smokindog wants to do? run a 16 ohm speaker from the 8 ohm Speaker Out on his Valve Junior?

You've got to write in simple, non-electronic language for most of us to understand.

Actually I want to run a 8 ohm speaker from the 4 ohm out put :D
Ricochet sounds like my dad ( he was a electronics shop teacher back in the 60's) I remember him trying to explain to me back then how tubes work ...whoooosh..right over my head :lol: :lol: :lol: We were going to rebuild a old fender Princeton Reverb but unfortunately he passed away be for we found time to get together to do it ( this was about 10 years ago)
but I appreciate you guys helping me out on this :D --the dog

You could, of course, find a trashed 8Ohm speaker, rip out the cone and wire that into your speaker circuit.

Won't hurt a thing to run a 16 ohm speaker from the 8 ohm jack of the Valve Junior, or even from the 4 ohm. You'll just get more distortion, differing levels of the different harmonics so it'll sound different, and the power will vary very little.

Tube amps are very tolerant of impedance mismatches. The impedance selected as optimum is arbitrary and based principally on the lowest distortion. You'll see considerable variation from amp to amp in the load applied to the tube, anyway. I'm speaking of pentode and beam tetrode output tubes, which most guitar amps have. With triodes the power level varies with the impedance, the most power being transferred when the load impedance (across the primary of the output transformer) equals the tube's plate resistance, but that's full of second harmonic distortion. Normally an impedance of about 2x the plate resistance is used, to give the maximum clean power output. Pentodes and beam power tubes have such high plate resistance that it's not practical to load them with such high impedance, so they have arbitrary plate loads. It seems there's a sweet spot for many of these tubes around what the ideal impedance would be if they were triode-connected. And when they're hooked up in an ultralinear circuit, they're operating as "partial triodes" with a lowered plate resistance, and that ends up being a pretty good impedance range for them. But even with triode tubes, you can run the impedance way up or down with impunity. It'll just sound different, and affect the power output.

What tube amps don't tolerate well is operation with NO load on the output (approaching infinite impedance.) Then the stored energy in the oscillating current in the transformer coils can produce damagingly high voltage spikes in excess of 10KV. Even loading the output with a resistor of ~20x the rated speaker impedance is enough to prevent damage from this, and it's often done. You don't lose enough power across that resistor in normal operation to notice it, but it'll save the output transformer, power tubes and sockets in case you forget to plug in or accidentally unplug the speaker.

Running a tube amp for a short while with the output shorted won't hurt a thing. It'll instantly fry a solid state amp, which doesn't mind if you forget the speaker but will fry if you plug in one of too low impedance.

I found a new forum for valve junior modders. Some one even mentioned ricochet in the forum. I don't think this has been up long, but it looks very interesting :D --the dog

http://www.valvejunior.com/