10W SET

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steve s
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#31

Post by steve s »

colin.hepburn wrote:Yep for the time being the single EL34 is fine but looking at next project with the view to drive any Speaker :) that's why I keep looking at PSE
my experence tells me the quality is likely to be worse...

better route in my view would be to look towards getting speakers that will work with the single ended output you have.

i have a 6sn7/ kt66 se amp next to me that i built a few years ago for a friend, he was amazed at the detail and clarity. but his speakers did not do it justice.
It makes a very nice sound, really quite good in my lounge, dispite the big hamond transformers.

watts are not everything...
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Paul Barker
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#32

Post by Paul Barker »

pre65 wrote:My 300b amp has a ECL82 driver with the second half cathode follower loaded with a CCS.

Might be worth trying an 811a in that. The 300b heater is an 845/211 Tentlab module so it would adjust, but need a 9v transformer to power it.

Worth a try I suppose, not too much needs changing :)
your DC voltages would be wrong from a CCS load, that is why I said choke.
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Paul Barker
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#33

Post by Paul Barker »

If you don't understand the above, CCS's need the same voltage conditions as resistors. IF the AC swing is 100 volts peak to peak then the DC voltage available across the resistor or the CCS has to provide for it. Whereas an inductive device like a choke or transformer provides the capability by it's inductive properties from just a few DC volts.

Because we are considering slightly positively biased grid connection the dc volt drop across a choke allows for direct coupling the CF to the grid, which sounds good.
Last edited by Paul Barker on Wed Sep 28, 2011 8:36 pm, edited 1 time in total.
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pre65
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#34

Post by pre65 »

In fact, the original circuit did use a choke (100H from memory) and they should still be around somewhere. :lol:
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Paul Barker
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#35

Post by Paul Barker »

that would be great.
steve s
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#36

Post by steve s »

Paul Barker wrote:there is one other really wild thought since it is you. Back in those days there was a OEM amp which consisted of a parallel output stage with dissimilar valves, one a pentode the other a triode. They maintained you got the best of both worlds.

Sounds crazy I know, but there might be something in it. I never really thought hard about it at the time.
hell... thats a new one on me
wonder what that sounded like...

i'll have to think about that one.... best of both worlds ?
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Paul Barker
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#37

Post by Paul Barker »

steve s wrote: wonder what that sounded like...
I immediately though it would be horrible but never tried it.

you had all thes odd ball OEM's with very fixed ideas which diferentiated them from the rest. But quite likely it was a marketing ploy.
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andrew Ivimey
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#38

Post by andrew Ivimey »

Now I appreciate I am not mixing a pentode with a triode outputs but my Monkey is using two very different kinds of 300b and they seem to compliment each other very well! If I had a pair of 300bs I'd try that two of course.
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pre65
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#39

Post by pre65 »

Paul Barker wrote:Here is a Barbour circuit which could be adapted for direct coupling by substituting a choke for the 10k resistor on the cathode follower.

Eric Barbour SV811-10 Design
I see the 811 has no cathode resistor or positive/negative bias applied to the grid, so is that what's called zero bias ?
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pre65
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#40

Post by pre65 »

It would be more convenient to use another amp (not the 300b) for my 811a experiment.

That has a 6DN7 at the front, and the second part is cathode follower, but has a cathode resistor and choke.

Were you suggesting that in order to "drive" the 811a the cathode resistor could be removed, just leaving the choke ?

Here is the circuit as it was.

Image
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Paul Barker
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#41

Post by Paul Barker »

pre65 wrote:
Paul Barker wrote:Here is a Barbour circuit which could be adapted for direct coupling by substituting a choke for the 10k resistor on the cathode follower.

Eric Barbour SV811-10 Design
I see the 811 has no cathode resistor or positive/negative bias applied to the grid, so is that what's called zero bias ?
Well there is 3.25 volts across the filament which pulls the filament positive relative to the grid, and whatever the voltage lift across the choke is to the driver valve. which pulls the grid positive to counter this and overtake it.

You would like to end up at +5 volts or similar, but what you want it 100mA on the output stage and you can add resistance to the choke to create it in one direction but in the other direction you have to add resistance to the cathode.

Not that it matters we are not precise.
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pre65
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#42

Post by pre65 »

So, if I'm understanding your drift (it's possible :wink:) then the 6DN7 driver stage as shown might actually work with 811a ? :)
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Paul Barker
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#43

Post by Paul Barker »

Yes, but your cathode bypass cap on the driver is acting as a hell of a large coupling cap, all for the sake of avoiding the coupling cap prior.

Clever but not my way.

The way this is heading I am going to have to see if I can find the original Eric Barbour article. I just can't remember whether I read it in Glass Audio or in the Svetlana website which has since been largely lost, though remnants remain.

Edit: looked but didn't find it.
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Paul Barker
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#44

Post by Paul Barker »

OK on a google this articlepoints to the eric Barbour 6em7 811-10 design as originating in VTV issue 5, which I can no longer find.

But the article linked above shows a useful mutation which incorporates an interstage. As you have an interstage Phil you could copy this.
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Paul Barker
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#45

Post by Paul Barker »

On google I have found a Harvey Gizmo article on the SV811-10 in which it beat the Western Electric 300b.

"When Mark Conese and I compared the sound of David Berning's new ZOTL single ended SV811 amplifier to the 300B version, we though there was something wrong with the 300B amplifier......and it had brand-new Western Electric tubes. Marco, the pianist, completely agreed with us. The 300B amplifier sounded warm and fuzzy compared to the SV811. The SV811 was much closer to the sound of the Steinway, and the 300B was not!"

It certainly thrashed the pants off the JJ300b in my home during the same epoch. I never realised until today that I was in the company of Harvey with my unpopular opinion at the time.

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