Simul Class C+

Forgive me if this has been addressed. I've had my DRG for a very long time and I never pursued this. People with Simul Class rave over the tone but with mine, when I engage SC, it just boosts the volume a little. Nothing to rave about. What am I missing here? Did I get a lemon OT? You would think after engaging SC , it would be like stepping on a pedal to change the tone or something.

I could be way off as I’m no expert on the nuances of the transformers but I think the raving is about the simulclass in general whether switched to Class A or Simul. The tone that poweramp provides is different to a 60, 60/100 etc irrespective of the setting.

I haven’t heard an SRG or HRG in person but if using the JP as a proxy for the HRG (assuming they sound close) I find the DRG to be squishier and sweeter. A touch less abrasive and I personally prefer the DRG to 60/100 based purely on this comparison.

Between the two switches on the DRG I personally find the DRG switch adds volume and power potentially more punch in the low end. Similar to the difference between triode and pentode. That’s what I hear anyway. I generally have mine in Class A but switch every now and then.

It would also depend on what tubes you have in the outer sockets. With the DRG’s option to run 34s on the outer pair it changes the tonal characteristic as a whole, again irrespective of Class A or simulclass setting. The differences between DRG and HRG might be less pronounced if running all 6L6s in both amps. I run winged C 34s in my outer set and I love what that brings to the amp.

That said, each have their own favourites. Some rave about the HRG, some about the export transformers, some of Coliseum, Doug West - the non GEQ etc etc. There’d be variability between each subset as well.

I think the tubes used would make a big difference. The recommended 415 6L6 in the inner sockets and some of the Siemens EL34 valves in the outer sockets is good. The class a does not sound like a quiet Simul-class, it has its own thing going.

Fairly good thread here discussing some of the differences.

https://www.rig-talk.com/forum/viewtopic.php?f=3&t=124080

So if I got this right

DRG:
Class A: All tubes in Class A (4 x 6L6 or 2 x 6L6 + 2 EL34)
Simulclass: Inner pair class A/B, outer pair Class A

HRG:
60w: 2 tubes in Class A/B (2 x 6L6)
100w: All tubes in Class A/B (4 x 6L6)

SRG:
60w: 2 tubes in Class A/B (2 x 6L6)

So my comment of running all 4 6L6s in a DRG maybe being similar sounding to an HRG does not hold up and the point that a DRG sounds different regardless of switch would be accurate with tube type and actual tube selection also having an impact.

Aside from volume, I hear more low mid and feel more power in palm mutes.

I have tried many combinations of tubes. I'm currently using Sylvania 415's in inner sockets with 34's in outer. I have yet to hear any difference. But, soooo many things come into play. Pick, fingers.... All the way down to speakers. Something that I didn't factor in is that I don't crank it up enough to bring the power section in.

Yeh I run mine pretty low as well. The difference to me between class A vs Simul is subtle. Less than I would expect the difference between DRG to HRG to be. But yeh. Too many variables to pinpoint and it’s all subjective as well.

Thaymz said:

Fairly good thread here discussing some of the differences.

https://www.rig-talk.com/forum/viewtopic.php?f=3&t=124080

Click to expand...

Excellent link, thanks for posting

So if I got this right

DRG:b
Class A: All tubes in Class A (4 x 6L6 or 2 x 6L6 + 2 EL34)
Simulclass: Inner pair class A/B, outer pair Class A


The above is incorrect:
When switch is in class A position ONLY the outer pair of tubes are operating. The Inner pair of Class A/B tubes are turned off. Hence the slight volume boost when switching from Class A (outer pair only ) to Simul Class (all 4 tubes operating)

The inner pair of tubes are wired pentode ALL the time. The pentode triode switch only affects the outer pair (class A) of tubes by changing them from pentode to triode operation. This is true whether amp is in simulclass or class A mode.

Great link. Thanks! I wonder what a SC would sound like if engaged, would only run the inner pair. Off topic, anyone know how to install a bias pot in a C+ ? I've been reading up on MPD and biasing. The average MPD is 75% on power tubes. Some ppl think that's to high for Boogies and makes them sound muddy. I did the equationthanks to Boogie Babies) 6l6= 30watts, EL's= 25 watts. Take tube, divide that with the plate voltage. Take that and multiply by .75 (75%). Drop the zero and that is where your bias should be. I did it with my C+ at 514v plate voltage and got -43vdc. But the amp has a fixed bias of -48. I'm a bit confused here because how does one know the MPD of any given tube? That would explain why some tubes run hotter, even red plate a little, and some run cooler. My plate voltage was never that high. Years ago it was always 469v. I have no idea as to the increase. Self adjusting amps are cathode biased. There is a one meg resistor across the cathode and pin 5. Pin 5 is the control grid (bias). So is it a self biasing amp or is it a fixed bias amp? Can ya tell I'm confused? Where is BB these days when you need him. JB32 as well.

Think of it this way. In the SC amps, the SC Class A tubes (in Triode except for the MKIII green stripe) provide the tone. The inner A/B pair just provide more horsepower when engaged.

Since it's triode, it'll be more soft & smooth than a pentode amp.

Here's a couple examples I have-

DR C+ (triode) https://youtu.be/G6zI-fVggTo?t=292

SR C+ (pentode) https://youtu.be/j5G729T4Jwg?t=152

Would appear a bit more complicated than I thought. There's no commentary on the c+ specifically but great insight into Class A and simulcasts.

https://mesaboogie.zendesk.com/hc/en-us/articles/225099807-What-is-Class-A-and-how-does-it-differ-from-Class-AB-

Im a bit confused. On the face plate of my C+ SC, the power switch says half power or SC. When I choose SC the inner tubes are engaged. So, if im mis understanding, you are saying that SC should be the outer sockets? help me out here. I've had this amp since 1984 and was never impressed with my SC mode. No tone enhancement just a slight increase in volume. Is my amp wired wrong? Thanks, Jim

The outer tubes are Class A on SC amps, except for the KRGs where it's the inner pair. When you pull the chassis what code is written on the side? Can you provide pictures?

It's DRG. I have picts but don't know how to upload them . But I can tell you how the OT is wired. There are two striped leads going to the plates of outer sockets. Two solid color leads going to inner socket plates. The inner sockets have diodes to plates to ground. Pin 4 has the 470 ohms going to B+. The outer sockets have the 470's going from plates to pin 4. And of course all of sockets have the bias resistors on pin 5. The SC switch lead goes to inner sockets to ground. My plate voltage to me, is on the high side. Around 515v. Don't know why. I have the 105 PT.

1985 Mark II C+ :

Basic settings for smooth jazz and for regular rock with sustain.

Posted long ago but no banana.

I posted long ago abt sustain but it didint seem to work. JUst the amp and the guitar...dont use boxes.

Also, tried to donate but cant using paypal..other way?

Best and Xo to all

RR

My two 105s were 505v & 515v. My KRG PT is 540v! Just run good tubes & don't sweat it.