Orange Rocker 30, not so 30...

[mikeboone]

I had posted a while back about putting a bigger sized OT in in my Orange Rocker 30. I put a 50W Plexi style replacement OT and its now considerably louder than it was with the stock OT, which is much smaller physically.

So I was thinking more iron, better efficiency, louder and I am pretty sure that's close to accurate.

So, then I decided to measure the power out by calculating it from the plate to cathode voltage, cathode voltage, bias resistor. I double checked on Webers bias calculator and I was on the right track. With the new transformer I am running the tubes at 22W per tube at idle. So, I thought that was insane and I was going to kill those tubes so I put the stock OT back in and got the same exact result.

So, in its stock configuration is it 44W being throttled to 30ish watts of perceived output by the smaller OT?

I did some digging and found some info on the Matchless Chieftain and Bad Cat Hot Cat 30 and found they too are running the tubes that hot as well.

Am I missing something or are these amps destined to eat tubes???

[JoeM]

Sounds like your measuring the tubes dissipation, not the power into a load.

[mikeboone]

Good point, I hadn't considered that. How can I measure the power into a load?

[Mick Bailey]

The power into a load varies with frequency. I stick to a 1khz sine and use a resistive dummy load the same as the speaker impedance. Measure the RMS voltage, square it and divide by the resistance. If you have a scope you can also see when it clips or if there's any distortion (crossover or otherwise). If you can stand the volume you can dispense with the dummy load and more accurately measure straight off the speaker - I have a pair of RAF marshalling ear defenders for this job.

Tubes have a fairly short life in these amps due to running class A. I've tried to re-bias them to run cooler but all it does is produce crossover distortion.

[Enzo]

I would think it was not because they were in Class A so much as it is that the Class A circuit they find themselves in is demanding way more of the tubes than they were intended for. In other words don;t make amps with EL84s where 6550s ought to be. Class A amps do run their tubes at close to full dissipation, but the designer determines what that dissipation might be and underspecs the tubes.

COnsider that your new transformer might be louder because it has a different turns ration than the old.

[mikeboone]

Thanks for the info guys... I have only been messing with tube amps for about 5-6 years. I read a lot but often times don't really get it right away. It takes years of tinkering, failing (a lot), succeeding (sometimes) to really absorb this stuff.

I come from an RF/Satellite comm's background where everything is now digital and SSPA's are, well, SS... The art of tube technology was abandoned for the most part by tech school curriculums in the 80's.

[Amp Kat]

Especially around our neck of the woods and more so in you're neck of the woods which is actually one of my favorite places. There are only a handfull of us tube techs in Baton Rouge and very few in the N.O. area.

On the amp issues I was surprised you actually heard a dynamic difference in those trannies and as Enzo said it was probably due to impedance differences. If you ohm out the primary OT winding from either CT to each leg or across the whole winding should yield some differences. That the plate voltage and Cathode resistor are the same would yield the same amount of power. Dropping the Cathode resistor some would dissipate more heat incresing the wattage and raising the Cathode resistor would drop less voltage across the resistor therefore less power. So basically the Cathode resistor sets the bias just like the negative grid bias would do in an AB1 Push Pull amplifier.

[mikeboone]

Yes, you are correct sir. There aren't many people around these parts that do this work. I live in Chackbay, which is just north of the middle of nowhere... I have people calling me from all over needing repairs, including a major blues artist and another Grammy winner. I am getting better at it thanks to you guys in this forum. I don't really charge very much, especially since most of the time I have to comb through this forum to figure out what the heck is going on.

I do it for the education mostly.

The overall tone of the amp did not change much, it just extended the clean headroom a bit. The reason I did it, is because it sounded a little thin and washed out at gig volumes. Now it has a punchier and thicker presence that cuts through a mix like a chainsaw.

It didn't stop there... There are a few things I wanted to change about the amp but didn't want to hack at a PCB repeatedly. So I found a schematic (home made) and verified the component values against my stock amp.

I built a clone of the Dirty Channel so I could tweak it easier. Its great. The Orange is a little muddy in places so I changed a few capacitance values here and there to tighten up the bottom end. I also added a switch to select between cathode and fixed bias. I hooked it up to a Marshall 4x10 loaded with Greenbacks. Its ridiculous.

[Amp Kat]

Yes, you are correct sir. There aren't many people around these parts that do this work. I live in Chackbay, which is just north of the middle of nowhere... I have people calling me from all over needing repairs, including a major blues artist and another Grammy winner. I am getting better at it thanks to you guys in this forum. I don't really charge very much, especially since most of the time I have to comb through this forum to figure out what the heck is going on.

I do it for the education mostly.

The overall tone of the amp did not change much, it just extended the clean headroom a bit. The reason I did it, is because it sounded a little thin and washed out at gig volumes. Now it has a punchier and thicker presence that cuts through a mix like a chainsaw.

It didn't stop there... There are a few things I wanted to change about the amp but didn't want to hack at a PCB repeatedly. So I found a schematic (home made) and verified the component values against my stock amp.

I built a clone of the Dirty Channel so I could tweak it easier. Its great. The Orange is a little muddy in places so I changed a few capacitance values here and there to tighten up the bottom end. I also added a switch to select between cathode and fixed bias. I hooked it up to a Marshall 4x10 loaded with Greenbacks. Its ridiculous.

Sounds like you are well on your way and yes I've been to Chackbay and it's a really cool place. Me being a pure coony I feel right at home
If you need anything feel free to send me a PM anytime and I'll do what I can.

[g1]

If your working on amps one of the most important tools is a scope. You wanted to measure power output, you can do it with a meter and a load, but you can't see how distorted the output is. A scope will show you this.
Doesn't matter how cheap or simple, as long as it will show you a proper waveform. Then you can use it for signal tracing to find faults.
You can always measure the voltage with you meter, but being able to see the waveform will save you incredible amounts of time.

[mikeboone]

That is very good advice and I should follow that as it is my own advice to guys who do work for me in the field. I am constantly on their butts about using a spectrum analyzer to point satellite antennas rather than using a signal meter. When I was running oil rig to oil rig in the Gulf setting up and repairing satellite comm's for voice and data, my spec an was my most prized possession for dish point and troubleshooting link quality issues...

Shame on me!

[Mick Bailey]

There aren't too many amps that run EL34s in class A. I've found that the Orange cooks and blisters the bases after a short while. Out of interest, the locations are already on the PCB for fixed bias.

Perhaps the replacement transformer has better low frequency performance.

[mikeboone]

I will have to take a look inside to locate the fixed bias locations. I read a thread in the Orange forum that suggested the same thing.

FWIW, the Rocker 30 clone I built sounds strikingly similar to the real thing. I added a cathode/fixed bias switch out of curiosity. The differences are very subtle and more evident when playing overdriven tones. It is more touch sensitive and has a really sweet feel. BUT all of that is lost in the mix in a live/club setting, you just cant tell the difference. In full on high gain there is no difference, I didn't expect there would be. It actually louder since the tubes are biased hotter in cathode bias.

With that said, I think the amp is better off in fixed bias. It will save tubes and the whole amp runs cooler which should mitigate heat related failures.

I would tend to agree with you that the replacement OT has better low end response. Its tighter all the way around.

And I didn't buy this amp or build the clone for its lower gain, overdriven bluesy tones... I have Plexi and a Blackface clones I built that do that exceptionally well. This one is for rockin' out!

[Amp Kat]

I will have to take a look inside to locate the fixed bias locations. I read a thread in the Orange forum that suggested the same thing.

FWIW, the Rocker 30 clone I built sounds strikingly similar to the real thing. I added a cathode/fixed bias switch out of curiosity. The differences are very subtle and more evident when playing overdriven tones. It is more touch sensitive and has a really sweet feel. BUT all of that is lost in the mix in a live/club setting, you just cant tell the difference. In full on high gain there is no difference, I didn't expect there would be. It actually louder since the tubes are biased hotter in cathode bias.

With that said, I think the amp is better off in fixed bias. It will save tubes and the whole amp runs cooler which should mitigate heat related failures.

I would tend to agree with you that the replacement OT has better low end response. Its tighter all the way around.

And I didn't buy this amp or build the clone for its lower gain, overdriven bluesy tones... I have Plexi and a Blackface clones I built that do that exceptionally well. This one is for rockin' out!

You don't have to run those tubes that hard in Cathode bias mode. That resistor on the schematic is 120 ohms which is really low for a cathode bias resistor and I'm also not sure it's true class A unless the plate voltage is 250 volts or lower. Upping the resistor to about 220 ohms could get you closer to a more lower % wattage dissipation and probably not a lot of difference in tone and you have the cathode bypass cap to change a tad in case the frequency response changed a little.

[mikeboone]

My cathode resistor is actually 300 ohms to get it to where it is now. My plate voltage is way higher than the stock Orange. I built this amp with stuff I had on hand instead spending a bunch on a hunch. I need to either buy a bunch of values and tinker or perhaps a high powered variable resistor.

I don't know enough to say whether or not these style amps are class A or not. The opinions vary. But I do know what my ears tell me and I think they sound pretty sweet for cleaner tones. But again, that gets lost in the mix at a gig. I think it would make a great studio amp.

I am thinking of building a single ended amp with a Plexi front end just to see what a genuine class A amp feels and sounds like.