SE 6v6?

[golana]

Very cool all-octal schematic. I'll build one this week.

While we're on the topic, could you suggest something for SE 6BM8 with the same topology?

Please post back, I'm sure i won't be building for at least a week.

 

[Kegger]

Nice Kegger!
Can you go on for a line or for on your thoughts on differences better or worse.
I know I've heard you say you liked the AT7's really well before, but differences?

I'm not sure what your asking..:scratch2:

BUT, 12at7's just happen to have good parameters to fit a wide range of circumstances for me.

I have a set of parameters I "try" an stay in with small signal tubes, mainly plate resistance and
the gain of the tube, I prefer to work with ones that have a plate resistance less then 20K as It
most often lends it'self to get a decent load onto the tube while still providing adequate current
and voltage to the plates with reasonable supply voltages, as you go up in plate resistance and
the load required by that tube to perform well you really start to "need" that much higher power
supply voltage to get decent current plus plate voltage onto the tube, the 12at7 has the largest
gain of the usual suspect dual triodes while staying under the 20k plate resistance so it tends to
work rather nicely technically in a lot of circuits. (9AJ pinout 6AQ8/ECC85 is quite good at it to)
(these are MY design parameters, others may think differently)

The 6sl7 has an slightly higher gain then the 12at7 but it's plate resistance is double the 20k mark
so when loaded pretty well (plate load resistor) you loose a bit of voltage and or current the tube
can get from that power supply, it's output impedance goes up an it's "drive" suffers as well there.

Now for here driving a 6v6 or an el84 or even a 7868/7591 there drive requirements are pretty low
meaning easy to drive, the 6sl7 would have no problem, but I really wouldn't want to use one with
an supply voltage of less then 310v-350v you mentioned to keep the current and voltage "decent"

Also in this circuit with that "schade" style feedback and that higher impedance of that 6sl7 circuit
the actual feedback ratio goes up from it, that is why the feedback resistor has gone up to try and
compensate or shall we say even it up to what the 12at7 would of provided. (that's what I did here)
(should be about 1v input to drive the amp to full power, in other-words not to sensitive for preamp)

Hopefully that answers your question, if not, well then, bite me, :twak::guitar:

 

[golana]

Hah, hope they add sprinkles on your ice cream!

 

[Squidward]

Would a 6SN7 be a better fit for the circuit than a 6SL7? It has a lot lower plate resistance, lower than the 12at7, even. It and the 12AT7 seem a lot closer than the 6SL7, which sort of looks more 12AX7ish.

 

[Kegger]

Since were running the output in pentode and we "need" the fair amount of feedback
in that config the 6sn7 doesn't have good gain in a 2 stage amp to drive full pwr easy.
(in that setup the 6sl7 should actualy work pretty good driving the 6v6 an or the el84)
(the 6sn7 would work, you'll need over 2v input to do it, not passive preamp "friendly")

I try to keep input voltage required to drive amps to full pwr at less then 2v, that way
any passive pre should work, at the same time I try an make it so it takes at least 1v
to do it so any active pre isn't to sensitive to where you can barely touch the volume.

-------------------

From my perspective I wouldn't really call the 6sn7 or the 6sl7 any closer to the 12at7.

6sl7 gain of roughly 70, plate resistance of say 40k

12at7 gain of roughly 60, plate resistance of say 15k

6sn7 gain of roughly 20, plate resistance of say 7.5k

So yah the 6sl7 an 12at7 are close in gain but the 6sl7 twice the plate resistance, but
the 6sn7 has 1/3rd the gain and half the plate resistance, so which one is really closer.

 

[golana]

That's pretty much how I read it elsewhere. You need a little grunt of a tube in that position.

Would the SL7, be better off in the RH807. Driving a 6L6 or similar, where you could ramp up the
voltage a bit more. We know it wants more, from the resistance.

 

[Kegger]

The reason the 12at7 works in both the el84 and the 807 is just what you said,
we have more power supply voltage, we get more current and voltage available
in the 807 circuit, just like you would on a 6L6, which yep means the same thing
for the 6sl7, a little more current for it and it can drive the 807, should work well.
(goes from roughly 1v sensitivity to drive the 6v6 to roughly 1.7v for the 807)

 

[Kegger]

Updated tweak to the 6BM8 in post 19.
(I still want to list voltages there, an will)

 

[analog addict]

Am I missing something?

Updated tweak to the 6BM8 in post 19.
(I still want to list voltages there, an will)

Is there a rectifier/PS for this one, or are you using the RH supply?

 

[Kegger]

In that post I mention,
"(an isolation power tranny with a voltage doubler should give you decent B+ as well)"

--------------

As that tube wants an much lower voltage then an EL84 does, or any other RH supply.

I believe VictoriaGuy is finishing building one and is going to do an thread, he may post
a supply suggestion in there, but 220-230v is what your after here with the 6BM8 tube.

 

[brians7]

Well I forgot I had a similar setup going, so I tweaked it a bit..

This should be a good working version using the 6SL7 if you decide to do it..
(about 1v to drive it full pwr, an same amount of feedback as the 12at7 circuit)
.
.

Hi Kegger

Could I up the B+ to say 350 to 375 and replace the 6v6 with a 1625 and 6sl7 with a 12sl7 in this circuit? Also what changes would need to be made for UL Thanks Brian

 

[knockbill]

I'm going to make an amp following the RH84 schematic but with the 6V6 real soon.

I will watch this thread with interest.

hi guys,,

where is this schematic? did i miss a thread?

thanks,
john

 

[cubby01]

The rh84 schematic? Just do a web search on "rh84". It should be evident right away, but if not switch to image search.

 

[Kegger]

Yes to all the above..
(also several people asked for it, and built it as well with very good results)

Your mileage may vary,,, as with all things...

 

[Kegger]

"Originally Posted by Brian7

Hi Kegger

Could I up the B+ to say 350 to 375 and replace the 6v6 with a 1625 and 6sl7 with a 12sl7 in this circuit? Also what changes would need to be made for UL Thanks Brian"

-----------------------------

The 6SL7 has no problem driving the 6V6, EL84 or even other small tubes to full power..

The 1625 is more like a 6L6, requires more drive, not the best choice to use the 6SL7 for it.
(but yah it would work, just not an superior option is all, but overall not bad)

Cheers..

 

[brians7]

Hi
I had no idea that the the 12at7 could be heated with 12.6V. How would one wire the heaters for this? Looks like a RH-1625 is in my future. Thanks Brian

 

[gadget73]

For 12v operation you use pins 5 and 4, pin 9 remains disconnected. For 6v operation, connect 5 and 4 together for one side of the heater circuit, and pin 9 becomes the other side. 12AT7, 12AU7, 12AX7, and probably others in that series work the same way.

 

[vveltvictor]

I'm sure we could figure something out, let me look at the pdf's and I'll post something.

-----------

EDIT: Posted is schem for 6BM8 that should work well I think for that tube in this setup.
(an isolation power tranny with a voltage doubler should give you decent B+ as well)

Recent tweak, to "optimize" the driver section a bit. (second schematic)

Hello,
I just built Kegger's RH style 6BM8 amp (second schematic) and it's an impressive performer. Previously I built the 6V6/6SL7 version and it turned out great using Edcor GXSE10 OPT's. However, with the 6BM8 amp I'm getting some saturation distortion on hard bass transients using the same model Edcor's. I swapped in a pair of James 6123hs OPT's and they sound fantastic with this amp, plenty of bass with no distorion at all. However, I want to save those OPT's for another project so I'm wondering what other transformers would be a good match for this amp. I thought the 10 watt Edcors (80mA) would be enough, but it's not working out that way. Any ideas why or what I should try next? My B+ is exactly 225v as specified in the schematic.

 

[Kegger]

That sounds odd on the swapping outputs and it's fine.

You shouldn't be saturating the Edcors, unless it's really low notes and it's just the performance of that inexpensive output.
(could experiment and lower the value of the coupling cap, may try cutting it in half and go from there)

 

[primosounds]

Not the ones I have now, IIRC they're Zenith 5K that ran 84's.
I'm going to build the RH version to have something to do here.
I've been watching and bidding on SE/5K, I will in the future play with these several more times.
6V6's are so good, I could stick my foot in them.

I have built a few rh amps, the one on the left is a high power version. Anyway you can use the RH "universal" schematic for the 6v6 with a 6sl7 or 6sn7 driver. The one in the pic follows that schematic but it uses fixed bias. The real important part is to make the power supply as close to the design as you can at least in terms of 2 inductors. Also if you have say 8 watt output trans you can run 6l6 as well for another 2 watts of power. I have made the universal amp with a switch on the fb resistor to go from 6sl7 or 12ax7 with 200k anode to anode resistor to 100k resistor for 12at7 or 6sn7 driver tube. It was hard to know which way i liked more. Sometimes i even forgot to switch the resistors for different driver tube and the sound was not overly affected. Anyway it is a great sounding circuit.