Future plan for 300B XLS amp

simon · Post by **simon** » Sun Jun 01, 2008 11:12 am

Which valves did you use in the Aikido Andrew?

I remember Dave D posting that he'd tried the Aikido 300B circuit on John Broskie's site (ECC83/ECC82 or 81 think) and really rather liked it. I got the impression he preferred this to what he had been using. Don't know where Dave is at now though.

Andrew · Post by **Andrew** » Sun Jun 01, 2008 11:35 am

I also believe that was Dave D's opinion.

I used an 83 into a triode connected C3g, here's a copy of JB circuit diagram, (courtesy of JB). I ended up with a tad over 320v B+, 2k I think on the cathodes of the 83's and 8k2 on the cathode of the C3g, this is what we heard at Witham last Sept, but at that point I only had 250v B+. It was better with > 300v.

I keep thinking around this topic, and I may just have to fork out for a decent pair of 83s. I would then use 6N30,6N6P,5687 in place of the C3g, probably using both triodes one on top and one below the interstage as the lower triode gives marginally lower distortion figures than the resistor.

My big negatives on this circuit are

a) I'm not really using the choke loading of the interstage tx to full advantage.

b) ECC83

c) low sensitivity really, it needs the full 2 volts input

And I keep asking myself, can an Aikdio really swing 160v p to p? I still don't think I managed to drive my 300B to full power with this circuit. I guess it can but....

Suggestions welcome, I am in need of inspiration.

-- Andrew

Andrew · Post by **Andrew** » Sun Jun 01, 2008 2:23 pm

In some ways I'm quite tempted to take a closer look at this, despite the cap, as the extra swing-ability on the output valve could be very welcome.

-- Andrew

Andrew · Post by **Andrew** » Sun Jun 01, 2008 3:42 pm

My big negatives on this circuit are

a) I'm not really using the choke loading of the interstage tx to full advantage.

Anyone care to comment, I wonder if I have this correct now?

-- Andrew

IslandPink · Post by **IslandPink** » Tue Jun 10, 2008 9:17 pm

Dave's been round the houses a lot with his opinions about the best Aikido combination. I can't remember where he settled in the end . He didn't like the ECC40 for some reason .

Meanwhile...I have my chokes !
'Just' need to make some space on the breadboard for them now .

Will need a few hours clear for faffing, at the weekend I think .

MJ

IslandPink · Post by **IslandPink** » Tue Jun 17, 2008 10:24 pm

New chokes installed and mods done . We now have 'Phase 3B ' !
Very nice so far , even after about 5 hours usage . More tonal colour , more presence , dynamics probably a touch better . Those pianos have never been more realistic .
Pics and more comments to follow .
MJ

IslandPink · Post by **IslandPink** » Thu Jun 19, 2008 10:26 pm

New breadboard with chokes on left of 45's .

IslandPink · Post by **IslandPink** » Fri Jun 20, 2008 2:51 pm

It's very good in many respects, compared to the half-way-house one with the resitor load.
More realism, more presence, better tonal colour .
Seems to go pretty low in the bass too .

Have slight misgivings about the bass though . Seems to be a bit 'lumpy' or awkward at times . Maybe a timing issue - cause not clear . Will see how it goes in next two weeks then maybe Nick can help with some tests.

Mark

IslandPink · Post by **IslandPink** » Mon Dec 01, 2008 9:14 pm

OK, I'm back with the C3m driver now .
Will post another pic to confirm this

It's been a very close call, but longer term listening with the DHT circuit seemed to show a bit less refinement in the treble and some slight timing issues in the bass . With the pentode-driven amp, at first it seems a little less weighty in the bass, but actually bass lines are easier to follow and I think the bass is actually a little better . Midrange is different between the two, but not decisively better either way. Tone in the treble is better with the pentode driver .
Overall the C3m driver version seems more 'together' and wins by a short head...for me .
It's a great and simple circuit though . Top marks to Verdier / Thorsten / Doddington .

MJ

dave dove · Post by **dave dove** » Sun Dec 14, 2008 1:25 am

hey mark

that wasn't a bad amp was it...

that c3m cct is real good

i got stuck a while ago 'cos i'm pretty happy with mine
and i got other fish to fry....
6072 cap coupled to 6n6p>6n6p aikido into 300b
nick's ecc40 cct
as much current through the 6072 as it'll reasonably take
and a fair bit through the 6n6ps too

sounds good enough for me
though i have been left behind with both sources and speakers
you guys have been cooking up some real beauties there....

dave

simon · Post by **simon** » Sun Dec 14, 2008 10:21 am

Good to see you're still about Dave

. I for one miss your posts.

IslandPink · Post by **IslandPink** » Sun Dec 14, 2008 1:19 pm

Hi Dave

I agree you have no need to work further on your amp

It sounded excellent when you came round last time . I think both of us have explored what's possible with the Super 300B's and got as much as we can from them .
What I want to do now is concentrate on more efficent speakers, since I still crave the treble tone you get from smaller valves , 2A3's and smaller , which does not seem to be possible from 300B .

Mark

dave dove · Post by **dave dove** » Sun Dec 14, 2008 3:24 pm

except that i was so appalled with bass
i rebuilt the 6072 stage
as soon as i got back from yours
hence giving the 6072 loads of current
without going OTT
sounds much betterer now
am forced into a PSU rebuild soon
so improvements all round again i hope

dave

steve s · Post by **steve s** » Sun Dec 14, 2008 5:02 pm

IslandPink wrote:OK, I'm back with the C3m driver now .
Will post another pic to confirm this
It's been a very close call, but longer term listening with the DHT circuit seemed to show a bit less refinement in the treble and some slight timing issues in the bass . With the pentode-driven amp, at first it seems a little less weighty in the bass, but actually bass lines are easier to follow and I think the bass is actually a little better . Midrange is different between the two, but not decisively better either way. Tone in the treble is better with the pentode driver .
Overall the C3m driver version seems more 'together' and wins by a short head...for me .
It's a great and simple circuit though . Top marks to Verdier / Thorsten / Doddington .

MJ

Hi mark, nice to see you back
just one point, as a bit of a triode addict...

i would guess there is a good reason for the distortion...a thickend up bass( hope i'm reading your comments correctly) and a not so clean top end are sure signs of something not quite right...

steve

IslandPink · Post by **IslandPink** » Thu Feb 12, 2009 5:53 pm

Hello Steve
Please elaborate ...
The differences were subtle . I didn't say anything about distortion , just that there was slightly more tone and refinement at the top end with the pentode . The bass was also a bit out-of synch with the rest ( subtle effect again ) at times .
I was a little surprised at the result, after all the talk about DHT-DHT amps, but there's no technical reason why a high-transconductance pentode is not a good technical solution to driving a moderate-sized valve like a 300B .... as long as grid current is low of course. It has the advantage of needing very little to 'support ' it, compared to the 45 ( in my version ) where the 45 had a choke load and obviously a cathode-bypass cap , neither being needed by the pentode.
I still wonder if I might have been limited by the ECC40 front end, but Nick was very happy with them in his experiments .
Trust me I am very concerned about low-level subtle details, midrange tone and natural presence in what I listen to .

Mark

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Future plan for 300B XLS amp

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