Son of 6EM7 Heaven

simon · Post by **simon** » Mon Oct 01, 2007 12:35 pm

Andrew wrote:With 6EM7 you need to have a largish cap on the cathode bypass, say 47uF on the Barker/Kaufman design.

And 250V rating too, so the usual-suspect Blackgates are out. Guess that leaves Solen or a motor run as obvious candidates, with a bypass probably, unless anyone has alternative ideas?

Toppsy · Post by **Toppsy** » Mon Oct 01, 2007 1:13 pm

In fact it may be time to invest in some 5k amorphous OPTs from AE;

Andrew,

if you decide to invest in these could you please order a pair for me. I think it's time for me to cut my teeth on a first amp build and the 6EM7 seems right for me to have a go at.

I don't count the 300b/gm70 amps as my fist amp build as I only really built and assembled the finished carcasses. Nick did all the hook up wiring and testing etc. and rightly so with such high voltages.

Colin

Andrew · Post by **Andrew** » Mon Oct 01, 2007 1:14 pm

I'm unable to phrase a counter argument, to Nick's point, perhaps due to lack of understanding, I need to digest this some more. I will say this might be a case of the pentode's missing gain

The LCR remains on the shelf for the time being as being a step too far!

However, I'm hoping understanding comes as I build. I will say that Spice seems to give similar gain for both topologies, tho' the CCS version rolls off quicker at the bass end. Now, I had assumed that this roll off was the parafeed LC combo, perhaps that's not the case.

The 300B now haas 330v on the driver and 2k resistor in the 83/5751 cathodes, it seems meuch better for it. I hope to listen more tonight. I regret not doing this before Witham and when it was first noted before Owston; these do's really are of great help!

cheers,

-- Andrew

Post by **Nick** » Mon Oct 01, 2007 2:16 pm

The CCS thing was just something that struck me as I read your post, just how much effect it will have I don't know, its still worth trying IMO.

The other options to avoid the cap are to cap coule like my gm70 driver, or maybe a split power supply.

Dave the bass · Post by **Dave the bass** » Mon Oct 01, 2007 6:39 pm

Thats my 6EM7 PSU Simon.

What program do you Gents use to draw Electronic ccts BTW?

DTB

simon · Post by **simon** » Mon Oct 01, 2007 6:46 pm

Thanks Dave. You've got quite a bit more C in there than me - I'll have a play with PSUD, see what I can do with the bits I have. I use AutoCAD, perhaps a sledgehammer to crack a nut, but I have it so that's what I use.

Post by **Nick** » Mon Oct 01, 2007 7:31 pm

When I want to be neat, I use the schema drawing part of expresspcb

http://www.expresspcb.com/

I have a set of valvie symbols that you can add to it. I think its from Duncans amp pages.

simon · Post by **simon** » Mon Oct 01, 2007 7:52 pm

This little amp is remarkable. I was going to administer some surgery on the power supply but couldn't turn it off, the music pouring forth is so captivating. How can such a weedy 1W of an amp produce deeper and more extended bass than 8W of 300B or 4W of 2A3? And it's making more sense of some of the more rubbishy recordings I have; the good ones sound sublime.

Colin, this is a great amp to build as it's so simple and sounds so great. I'll send you the "loaner" 6EM7s if you want to build it. But you'll need efficient speakers to get the real magic...

I really do need to build the Dodd Spec to compare, but right now I'm thinking I need to build a keeper.

colin.hepburn · Post by **colin.hepburn** » Mon Oct 01, 2007 8:09 pm

Hi All
I like the idea of this amp so 6em7 and fostex 126e 93db back loaded frugal horns in room size 15ft+ 10.6 ft good enough or not for 1 Watt

pre65 · Post by **pre65** » Mon Oct 01, 2007 8:19 pm

Dave the bass wrote:Thats my 6EM7 PSU Simon.

What program do you Gents use to draw Electronic ccts BTW?

DTB

Hi Dave-were you able to calculate (or simulate) the end result using those caps/resistors across the HT (after the choke) or did it just "evolve" ?

What HT did this power supply give you ?(ps can see it on the circuit-doh !)

Just for interest,you understand !

Dave the bass · Post by **Dave the bass** » Mon Oct 01, 2007 8:30 pm

Hi Philip,

Nope it was just a build and see how it worked TBH. After BOBA it was only the 2nd PSU I'd ever built from scratch so I just went by Nicks advice firstly and then just farted about. First incarnation was just the CLC bit, I added the RC bit on as there was a little bit of hum and I wanted to see what would happen if I added an 'R' and a 'C bit on the end, lo and behold the hum vanished and after further input cap tweakage got the HT to 325 ish Volts.

Anyone would think I don't know what I'm doing....

DTB

Andrew · Post by **Andrew** » Mon Oct 01, 2007 8:35 pm

Nick wrote:When I want to be neat, I use the schema drawing part of expresspcb

http://www.expresspcb.com/

I have a set of valvie symbols that you can add to it. I think its from Duncans amp pages.

I use Linear's LT Spice, again a link from Duncan Amps, Google should find it.

cheers,

-- Andrew

Dave the bass · Post by **Dave the bass** » Mon Oct 01, 2007 8:52 pm

Thanks for the replies about tidy cct diagrams, I tried the spice on before on the works steam powered PC but it wouldn't have it, I'll try again here at home. The PCBexpress one I'll try too.

Ta Nick and Andrew

DTB

andrew Ivimey · Post by **andrew Ivimey** » Mon Oct 01, 2007 10:20 pm

You know, now we've ditched DHTs as being frankly second rate, there is a way, just one way of improving things ..... 6EM7 ain't bad - gawd knows I've been trying to give them away but ecl82 aka Doddington Special - two watts of joy!!!! No, I know that is too much right now but in time, dear friends you will realise just what can be gained from a few chokes here and a couple there (even if they aren't quite the right value).

onwards and upwards!

simon · Post by **simon** » Mon Oct 01, 2007 10:27 pm

colin.hepburn wrote:Hi All
I like the idea of this amp so 6em7 and fostex 126e 93db back loaded frugal horns in room size 15ft+ 10.6 ft good enough or not for 1 Watt

T'other Colin,

I'd guess "probably". Depends on how loud you listen. My 208s are 97dB and there's plenty of volume in a similar sized room. You might be pushing it a little more, but I'd guess you'd be okay.

audio-talk

Son of 6EM7 Heaven

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