My head amp

Anything to do with the things that make the music we listen to.
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Nick
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#61

Post by Nick »

I have a friend who used to organise tours with people like Chuck Berry. He was renown for being bad tempered and wanting paying in cash as he left the stage.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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IslandPink
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#62

Post by IslandPink »

I believe he was also well-known for not getting off the plane until he was paid another $5000 !
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Mike H
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#63

Post by Mike H »

Paul Barker wrote:
Mike H wrote:Ah right that might be interesting.

Mind you it's sharp cut-off pentode so might get lop-sided waveforms (?)

Not actually used one meself....
Yes I have been doing mental gymnastics trying to predict keeping it out of cut off. Just depends on the input signal amplitude.
I think so. May help not cap bypassing the cathode resistor, in theory at least.

I got 6AC7 pentodes which always look great on paper but have always defeated me trying to actually make them work linearly. Only time I succeeded with cap bypass included was by driving the grid DC coupled direct from the sig gen, which is low impedance output. (Supposed to be 600R). Should have tried other combinations, like no cap bypass, but was running out of time....
 
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Paul Barker
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#64

Post by Paul Barker »

I wasn't planning to use bypass caps.

What is really needed is more voltage headroom, but that is not available.
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#65

Post by Paul Barker »

Nick wrote:I have a friend who used to organise tours with people like Chuck Berry. He was renown for being bad tempered and wanting paying in cash as he left the stage.
I met someone who roadied for Dizzy Gylespie and for Miles Davis. He said Dizzy was a geat guy and that Miles was the biggest racist he ever met. He hated white people and would try never to use them, which wasn't always possible but he gave them a very hard time in such cases as he had to have one on the crew.

Funny that when they get on stage and perform all these things are left behind as their brilliance shines through.

Chuck Bery may be short tempered and demanding but he excelled in his field in his time. He was nice to Eric Clapton on stage, gave him plenty of respect. But in this clip at least he didn't seem to have any respect for Keith Richards. But he was probably unaware that the conversation would one day become public. But it remains that as they both played the only talented star was revealed.
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Paul Barker
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#66

Post by Paul Barker »

OK it is a great success. Sounds much more bluesy than the previous attempt.

It hasn't got any overdrive though.

But the tone is much better. I think the even spread of harmonics with the benefit of keeping the even order and the slight cancellation of the odd order by the pentode VA/driver makes the topology great for timbre.

The 6l6 is running at 246v on the plate 258 on the screen 18v bias 52mA

The 6sj7 119 on the anode 108v on screen care of a 110k load biased at 3.9v 2mA This keeps it out of clipping and grid 3 is grounded because it isn't internally connected. The 6sj7 doesn't go to cut off with my Samsung Galaxy SII as a source played maximum output. I would say that this 6sj7 stage is worth experimenting with. I know it has beeen done before. I havn't done it, and I like what I hear.

The screens are supplied by a cascade of VR tubes a 108v and a 150v so the 6l6 gets fed from the top and the 6sj7 picks up at 108v.
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#67

Post by Paul Barker »

out of interest plugging in the 6550 pulls more current 57mA and pulls down the ht voltage accordingly. Sounds just as good. No more power to notice.

EL34 only pulls 14v across 340R and so ht is 250. Doesn't sound as full as the other two, which is a surprise. Requires a supressor grid connection from pin 1 but I put one in anyway because the beam tetrodes are internally connected have pin 1 removed and the metal ones have the can grounded at pin 1.

6V6 comes out best performer and just about sits there at the right operating point. 250v 14.5v 45 mA with 250 on the screen should provide 4.5 watts.

So 6V6 is the keeper.

Eventually I might make a gender changer and try the el84 which with greater mu should get the necessary drive to overdrive it. All the former valves keep out of overdrive.
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#68

Post by Paul Barker »

OK so what attracted me to the design was

1/ two stages both pentode for cancellation.

2/ single ended so retains the even order harmonics for a correct timbre.

3/ the possibility of what Nick driected me to which was plan for distortion coming from output stage rather than overdriving a pre stage.

1/ and 2/ are ticked clearly it is a whole lot better than the other attempt for timbre. with the previous design I had way more preamp overdrive but it didn't sound nice.

Box 3/ is not quite ticked, need more drive to get the 6v6 into distortion.

What I like musty not be lost so I can't use a single inverting stage between the two pentodes. Neither can I add a gain stage before the 6sj7 as that would send it into cutoff. If I~ had more HT I could drive it a bit harder, but let's see what we can do with my 270v. First thoughts are CF buffer. this would pull more gain from the VA as a perfect impedance coupling (when DC connected on it's input), and drive more into the output stage. I don't add any coupling caps, and no other extra caps, so it should be all gain. This may be sufficient in itself.

Of course if I wanted a tone stack it could drive it. but I don't.

Further more there is an option to convert the output to provide damping while retaining the timbre with a second cathode follower after the 6v6. That is to say Cf output stage using say parallel 6as7. Retain the timbre of the two pentodes but get better damping and better drive without any feedback (except the positive local feedback inherent in the CF's.)
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Mike H
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#69

Post by Mike H »

Paul Barker wrote:6V6 comes out best performer and just about sits there at the right operating point. 250v 14.5v 45 mA with 250 on the screen should provide 4.5 watts.

So 6V6 is the keeper.
A-ha!! It not bad the ol' 6V6, that blues player corresponent I had likes 'em, in Fender Champ :D
 
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#70

Post by Mike H »

PS: gonna hafta have another go with it as a driver....
 
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#71

Post by Dave the bass »

Paul Barker wrote: But it remains that as they both played the only talented star was revealed.
I agree.

That drummer is excellent.

DTB
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#72

Post by Paul Barker »

Dave the bass wrote:
Paul Barker wrote: But it remains that as they both played the only talented star was revealed.
I agree.

That drummer is excellent.

DTB
I meant the Pea Hanna :roll:
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#73

Post by Dave the bass »

Paul Barker wrote:
Dave the bass wrote:
Paul Barker wrote: But it remains that as they both played the only talented star was revealed.
I agree.

That drummer is excellent.

DTB
I meant the Pea Hanna :roll:
Sure, the Pianist is good, pays attention for cues but that drummer is the star. Listen to his click, that's tight, really tight. Says next to nowt, just plays very well. Maybe its a bassist thang!

DTB
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#74

Post by Paul Barker »

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The Stratmangler
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#75

Post by The Stratmangler »

Ferget all them fancy caps.
They'll screw the sound up.
What was availible back in the late 1950s - them's the ones to go fer 8)
Chris :happy3:
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