Mixing Circuit for EL34 , 6L6 Power Amp Stage

[Jack1962]

does anyone here have a schematic for a power amp section using 6L6 and El34's with a mixing circuit to mix the 6L6 and EL34 combo?

[kagliostro]

No, for 6L6 and EL34 no

but you can use a mix of the architecture of the Mesa Boogie Blue Angel and of the Egnater Rebel 20

something like the other schematic

K

[HotBluePlates]

For how many output tubes total?

[Jack1962]

for 2 EL34's and 2 6L6's using a single long-tail pair to feed them. I got this idea from the Egnater Renegade .

[tubenit]

I would have a separate cathode and resistor set up  for the 6L6 .................... and the EL34.

And then I would use Geezer's  cathode biased attenuation idea.  That would definitely give you a variety of dialing tone combinations. I've used this on several amps and thought it worked quite well.

http://www.el34world.com/Forum/index.php?topic=4437.0

With respect, Tubenit

[HotBluePlates]

for 2 EL34's and 2 6L6's using a single long-tail pair to feed them.

I would do it like Kagliostro's posted modded AC30 (last schematic). Post phase inverter master volume, one ganged-pot per output tube type.

If you're gonna use cathode bias, then Tubenit's suggestion is probably best.

[Jack1962]

The master volume pots on the modded AC30 do look like what they are doing with the tube mix circuit . Bruce Egnater has drawn his relay circuits very strange. I have attached the schematic I am looking at so that everyone can see what I am talking about, Pssst don't tell Egnater 

[HotBluePlates]

Yeah, the relays and the mix card drawing is a hot mess. Fine for figuring out signal path on a given board but not so helpful with seeing overall circuit function.

The Egnater circuit is different from the Vox circuit; you can't have any setting with drive to both sets of output tubes full-up. In other words, the maximum output power is basically the power output of one of the tube pairs.

The other wrinkle is it looks like Egnater uses a 4-gang pot (so all 4 are VR5, and only for a single channel), so SCN14 & SCN15 are the connectors one of the channel Mix knobs interrupts/mixes, while SCN14A & SCN15A is for the other channel.

The relays RL5-8 look to me like they facilitate footswitchable channel selection, but I'm getting so cross-eyed looking through everything I'm having trouble finding the source of D7 to be sure.

[kagliostro]

Thanks Jack1962 for posting the Renegade schematic

it is always interesting to study the solutions adopted in commercial amps

the way the schematic is draw make it difficult to be read

I'm still trying to identify on it switch n. 3 and switch n. 11

whose purpose is to change the power level from 18W to 65W independently for each channel

http://www.egnateramps.com/manuals/RenegadeManual.pdf

BTW do you know if is possible to find a link about the footswitch ?

K

[Jack1962]

Yeah, the relays and the mix card drawing is a hot mess. Fine for figuring out signal path on a given board but not so helpful with seeing overall circuit function.

The Egnater circuit is different from the Vox circuit; you can't have any setting with drive to both sets of output tubes full-up. In other words, the maximum output power is basically the power output of one of the tube pairs.

The other wrinkle is it looks like Egnater uses a 4-gang pot (so all 4 are VR5, and only for a single channel), so SCN14 & SCN15 are the connectors one of the channel Mix knobs interrupts/mixes, while SCN14A & SCN15A is for the other channel.

The relays RL5-8 look to me like they facilitate footswitchable channel selection, but I'm getting so cross-eyed looking through everything I'm having trouble finding the source of D7 to be sure.

The bias on both set's of tubes according to egnater are set at 65 watts (basic ohms law) , on the control panel there is a mix pot for the clean channel and one for the drive channel. I do have to agree however there is no way that you can send that much power to the OT. Yes RL5-8 do control the channel selection. What I was wanting to do is to use just 1 tube mixing control , the way Bruce did it is really cool and this thing has great tone but way to may tweaker knobs for me lol.

[Jack1962]

Thanks Jack1962 for posting the Renegade schematic

it is always interesting to study the solutions adopted in commercial amps

the way the schematic is draw make it difficult to be read

I'm still trying to identify on it switch n. 3 and switch n. 11

whose purpose is to change the power level from 18W to 65W independently for each channel

http://www.egnateramps.com/manuals/RenegadeManual.pdf

BTW do you know if is possible to find a link about the footswitch ?

K

the purpose of change from 18 to 65 watts independently who knows????????
I doubt if there is any link about that footswitch itself , I opened it up and checked it and there is really nothing special there most of the real switching is do with that footswitch circuit (digital by the way) on the power amp board.

[kagliostro]

This morning I tried to go deeply on the circuit between the PI and PA (the 4 relais)

looking to the schematic I see the coils of the 4 relais in parallel, so they switch all at the same time

following the signal what I can see is that the signal from PI reaches all 4 power tubes

at the same manner in both the positions of the switch on the relais

This seems very odd to me, please someone can say something about this ??

Many Thanks

K

[HotBluePlates]

looking to the schematic I see the coils of the 4 relais in parallel, so they switch all at the same time ...

Yes.

... following the signal what I can see is that the signal from PI reaches all 4 power tubes ...

Not at the same time.

SCN14 does not connect directly to SCN15, which is how it looks on the schematic. SCN14 connects to CN14 on the Mix Card, then the output of the Mix circuit goes to CN15, which connects to SCN15, and then on to the output tubes.

The same happens for SCN14A and SCN15A, with another, separate Mix card, which is not shown on the schematic but is implied.

It also really helps if you redraw everything on a blank page showing the output of the phase inverter to one position of the relays, then out of the relays to the connectors, to the Mix card circuit, back to the other connectors, through the 2nd relays and to the output tubes. Then you will see how the mix circuit works.

Bottom line, this is a very complex way to give each channel its own Mix knob and Mix setting.

[kagliostro]

Thanks HotBluePlates

Now all this thing has more sense, I think I'll try to follow the signal path using your explanation

---

Today I give also a look to the circuit from SCN11 to the VVR that supplies the plates of the PI

and also there there are some "difficulties" on understanding what happens

I see the + voltage that supply the coil of RL1 going (through R44 & R50) to the base of Q7

Q7 & Q8 are in darlington configuration and when Q8 conduct, the gate of TR1 is connected to ground through

R69 but there are also C46 & C40 to consider on the equation and .............

I didn't understand well how that part of the circuit acts, I can guess that the VVR is acted as to have on the plates two distinct B+ voltage levels, but concerning the details I'm lost

K

[Jack1962]

I was incorrect about the biasing of this amp , the way they are pulling off the output power of these 4 tubes is they are biased at 1/2 power. Yes this is probably one of the most complex amps I have worked on , due mainly to the way the schematic is drawn. I have fixed what the amp was brought in for (bad bypass cap on the cathode of V1) I think Bruce could have built a amp with the same tone without making it this complex , I also believe the schematics they are working off of aren't these .

[HotBluePlates]

I was incorrect about the biasing of this amp , the way they are pulling off the output power of these 4 tubes is they are biased at 1/2 power. ...

I don't see it like that at all.

The way the Mix circuit works, you can get full-drive to the 6L6's only, full-drive to the EL34's only, or half-drive to both 6L6's and EL34's. You can also blend smoothly between any of these 3 points.

What you cannot get is full-drive to 6L6's and EL34's at the same time. That's why it's 4 output tubes but only 65w max output.

[kagliostro]

I've redraw the PI PS part of the schematic

this way it seems more comprehensible

K

[Bruce Egnater]

The Egnater schematics are a bit confusing because they are redrawn by the manufacturer and they squeeze it all onto one page. There is an omission that may confuse you on the tube mix. The four ganged custom pot is also center tapped so when the pot is at 12:00, there is no attenuation. You are essentially reducing the signal when panning away from that pair of tubes. In the center, the signal is full on to both sides. Hope this clarifies it.
Also, FYI we are offering another one of our rare, two day amp building seminars near Detroit, Michigan on April 26/27, 2014. Go to detroitschoolofrockandpop.com/egnater/ for info.

[kagliostro]

Many thanks for the explanation Bruce

Also, FYI we are offering another one of our rare, two day amp building seminars near Detroit, Michigan on April 26/27, 2014. Go to detroitschoolofrockandpop.com/egnater/ for info.

 

Simply Fantastic

Unfortunately I live in Italy  

K