10W SET

cressy · Post by **cressy** » Fri Sep 30, 2011 9:08 pm

i found the original circuit for it which is to one im going to build into the "beast chassis" aka the ugly one i built for the 300b, a clever little circuit too, elegantly simple imo
http://www.bonavolta.ch/hobby/en/audio/sv811_2.htm

Paul Barker · Post by **Paul Barker** » Fri Sep 30, 2011 9:35 pm

Ah, that is the one, well done for finding it.

pre65 · Post by **pre65** » Mon Oct 03, 2011 3:04 pm

Would that interstage circuit give as much "drive" as the cathode follower and choke ?

pre65 · Post by **pre65** » Tue Oct 04, 2011 4:00 pm

I found this circuit earlier.

Seems quite simple.

Any thoughts ?

pre65 · Post by **pre65** » Wed Oct 05, 2011 11:38 am

I'm trying to get my head round the interstage 811a circuit, and a couple of things need to be clearer to me.

1) What level of voltage would I expect on the two 6EM7 grids, pins 4 & 1 ?

This is in order to calculate the anode currents so I can sort the PSU out.

2) One side of 811a cathode is grounded (neg side), does that present a problem if using my 4A Tent modules ?

Post by **Nick** » Wed Oct 05, 2011 11:43 am

1) What level of voltage would I expect on the two 6EM7 grids, pins 4 & 1 ?

0v and 0v

2) One side of 811a cathode is grounded (neg side), does that present a problem if using my 4A Tent modules ?

As long as the rest of it is floating no.

Post by **Nick** » Wed Oct 05, 2011 11:44 am

Assume 60ma a channel and it won't be far out.

pre65 · Post by **pre65** » Wed Oct 05, 2011 12:00 pm

Nick wrote:
1) What level of voltage would I expect on the two 6EM7 grids, pins 4 & 1 ?

0v and 0v

Ah, so how can I work out what the anode/cathode current is ?

Curves ?

Post by **Nick** » Wed Oct 05, 2011 12:58 pm

pre65 wrote:
Nick wrote:
1) What level of voltage would I expect on the two 6EM7 grids, pins 4 & 1 ?
0v and 0v

Ah, so how can I work out what the anode/cathode current is ?

Curves ?

Yes.

Post by **Nick** » Wed Oct 05, 2011 1:04 pm

In fact as drawn that circuit will pass something like 80ma and expect the 6em7 to dissapate 30w, so I would personally keep away from it.

Dave the bass · Post by **Dave the bass** » Wed Oct 05, 2011 1:10 pm

Crikey! The larger anode disp is only rated at 10W max and the smaller triode 1.5W!

DTB

Post by **Nick** » Wed Oct 05, 2011 1:35 pm

Dave the bass wrote:Crikey! The larger anode disp is only rated at 10W max and the smaller triode 1.5W!

DTB

Indeed.

pre65 · Post by **pre65** » Wed Oct 05, 2011 1:41 pm

Still confused.

Looking at the first triode, pins 4 - 5 - 6.

Making an assumption that it's biased at -3v, so with a 1.2K cathode resistor that is 2.5ma. That sounds reasonable.

Then 2.5ma through 180K loses 450v, so it cant be that as it only has 430v to start with.

So assume 1.5ma current, makes the bias -1.8V

1.5ma through 180K loses 270v, and a further 84v through the 56K

So anode volts is 430V - (270 + 84) = 76v

But that seems far too low.

1ma would be bias -1.2V and anode 194v, but -1.2v bias seems too low

So is my reasoning suspect, or my maths crap ?

pre65 · Post by **pre65** » Wed Oct 05, 2011 1:51 pm

If having to use 180K as the load resistor is the problem for higher current, would using a CCS on the anode set for 2.5ma and -3v bias with the 1.2K cathode resistor be a (possibly) better way ?

Or, I have got a 100H choke spare in the box.

Dave the bass · Post by **Dave the bass** » Wed Oct 05, 2011 2:40 pm

1st (small) triode of 6EM7 has a high ra ~40K iirc so doesn't really lend itself to choke loading without a hoooooge inductance choke. Remember my little 6EM7 'holiday' amp Phil? That 1st stage is choke loaded but I needed a 500H choke to get any decent LF out of it. Too small and the -3db point is quite high and the LF roll's off quick. There's a long thread on 'choke loading anodes' that covers this very subject on 6EM7.

S'funny you having a go at building this cct as I mentioned the other day because my winter DIY project this year is go at 6DN7-> TZ40 (or 811a or 830B) .

We is idea bruv's!

DTB

audio-talk

10W SET

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