| Bas Horneman |
Hi all, I was wondering if you could give me some pointers or background on using batteries for biasing my driver stage 6n1p.
I bought the same batteries Gary Pimm uses for his battery biased CCS (CR1225FV / Lithium 3V)
I want to try them on my design instead of the 330 ohm resistor. See schematic.
The voltage across the cathode resistors is 2,6V now. That means around 7,9mA running through the 6n1p. |
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| dhaen |
Hi Bas,
It'll mean the stage gain will go up a bit, because at the moment you have an unbypassed cathode resistor.
I don't know if there will be any sonic benefits. This valve has such a low Ra, and with the active load....
But it's worth a try...
Cheers, |
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| Bas Horneman |
Hi Dhaen,
How about bass? Usually bypassing with a cap improves that. I still think my system needs more bass, even after the improvements after the plate resistor increase, and bypassing the ouput stage with a Black Gate...
So I'm going either bypassed with a cap or battery.
But do you have any idea how many batteries to use in series?
Cheers,
Bas |
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| dhaen |
Hi Bas,
| quote: | | How about bass? Usually bypassing with a cap improves that |
Aha, it depends on why the bass is lacking in the first place.
If it's lacking because of an inadequately sized cap, then a bigger value will bypass down to a lower frequency.
Or,
If an anode inductor (choke or transformer) has inadequate inductance (H), then bypassing the cathode will reduce Ra, and reduce the inductance required to get down to a given frequency.
In the case of a resistively loaded stage with no bypass at all, adding a suitably large value will increase the stage gain over the entire audio band. If the valve is running at a low current, or has a high Ra, it might improve the top end response slightly, by the reduction of Ra.
If that's as clear as mud, I'm sorry ;)
Cheers, |
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| Sjef |
The circuit shown in the picture is a mu-stage. Be careful with battery biasing there bacause the bias point is set by the upper penthode. It's a fixed current system instead of fixed voltage. In a mu-stage you won't find much difference in gain if you bypass the triode's cathode resistor or not because of the anode load (the penthode) wich is very high compared to the triode's cathode resistor.
Battery bias works just fine in anode follower or choke/transformer loaded circuits wich are actually fixed voltage systems. Tubes really like it if you run them in a fixed quiesent current or in a fixed cathode voltage, you can't do both, one factor has to vary with the grid voltage otherwise it's not an amplifier anymore. |
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| Bas Horneman |
Sjef,
You are soo right, about this. I tried bypassing this morning with a capacitor. I could hardly hear a change in volume. It did sound different though. Maybe even better...
What I don't understand though is...the mu-follower determines the current.....so why do we need a cathode resistor at all?
Regards,
Bas |
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| fdegrove |
Hi,
Bas,
You need this to bias the grid of the bottom triode.
Cheers,;) |
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| EC8010 |
| Mu-followers work very well with fixed bias on the lower valve, whether it is battery bias (on grid or cathode), diode bias (cathode), or a PSU to supply grid bias. The gain doesn't change from unbypassed resistive bias, but the power supply noise rejection improves... |
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| fdegrove |
Hi,
| quote: | | The gain doesn't change from unbypassed resistive bias, but the power supply noise rejection improves... |
While this theory is correct,bypassing the cathode R on SRPP circuits will add its' own colouration to the circuit.
It is a given that a mu follower_approaching a CCS_ is still very sensitive to PSU regulation.
I hear,once again,a lot of people dismissing this kind of circuit on the basis of hearsay and a basic misunderstanding of what it can do.
No circuit topology is ever perfect but the next step up to the mu-follower is a CCS loaded stage triode.
How you achieve this is open for debate but I think a few semi-conductors around the top penthode are doing less damage to the sound then a cathode bypass soundwise.
Just my 2 cents,;) |
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| Sjef |
Hi bas, you still need a cathode resistor.
Normaly you set the bias current with the cathode resistor by a given anode voltage. Lets say that the upper penthode is a true constant current source. The bias current is then set by this current source. The cathode resistor of the triode now doesn't set the current anymore but it sets the amount of voltage on the anode of the triode.
What where the audible differences in bypassing the cathode ?
A mu-stage is not the same as a SRPP. |
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| fdegrove |
Hi,
| quote: | | A mu-stage is not the same as a SRPP. |
Yes and no,it is a derivative of the SRPP.
| quote: | | The cathode resistor of the triode now doesn't set the current anymore but it sets the amount of voltage on the anode of the triode. |
Again,yes and no.It primary use is to polarize the grid.
Tie that cathode to ground and you'll see what I mean.
Cheers,;) |
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| 316a |
Hi Bas ,
I only see a problem with using a cathode battery on this if it's a lithium like you stated . The battery must be a rechargeable type . I use NimH (nickel-metal hydride?) for SE input stages and find it an improvement over an LED or bypassed resistor , quieter than unbypassed resistor too . All down to personal taste but it's cheap so maybe try it
316a |
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| Bas Horneman |
Hi 316a,
I thought lithium was rechargeable as well?
Regards,
Bas |
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| 316a |
...I don't think all lithium cells are , best to check before fitting the thing .
316a |
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| Bas Horneman |
| quote: | | In a mu-stage you won't find much difference in gain if you bypass the triode's cathode resistor or not because of the anode load (the penthode) wich is very high compared to the triode's cathode resistor. |
Hi Sjef,
For interest sake:
I read Allan Kimmel again. The bypass cap does indeed not increase gain but does however lower output impedance
| quote: | | What where the audible differences in bypassing the cathode |
Was a very short listening periode but it appeared that the midrange seemed accentuated more than the bottom and top end..providing a seemingly "bigger"" soundstage.
I bypassed with a 2200uF Rubycon. |
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| Joel |
| quote: | Originally posted by Bas Horneman
For interest sake:
I read Allan Kimmel again. The bypass cap does indeed not increase gain... |
Bas, then "Allan Kimmel" is wrong. Bypassing the cathode resistor DOES increase gain, because the tube is no longer subject to degenerative effects - ie. negative feedback from the AC signal presented to Rk. |
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| Bas Horneman |
Hi Joel,
Actually Alan Kimmel's verbatim words were :
"This will have minimal effect on the gain"
I tried this and he is right. Don't forget it is a Mu-Follower.
Cheers,
Bas |
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| Joel |
Bas, I'm sorry - I didn't see that this was a mu follower!
I was referring to a standard common cathode voltage amp. |
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| dhaen |
Bas,
I must admit that I was uneasy when I posted my comment about the gain increase with added cathode bypass cap on this circuit, but actually it is by practical experience.
Perhaps this means that my mu stage is not working right? I'll have to invesigate this further.
Cheers, |
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| fdegrove |
Hi,
| quote: | | Perhaps this means that my mu stage is not working right? |
This is quite possible.
Having built some of these circuits, I can say that in fact adding a bypass cap shouldn't change the gain of the mu-follower at all.
Could it be you made the calculations for your stage with a bypass cap in place?
Cheers,;) |
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| dhaen |
Hi Frank... I'm back:)
I made no calculations:( There is little that I claim is original in my design. I just copied someone else's idea!
But now I must go back to basics, to satisfy my curiosity. I'll report back....
Cheers, |
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| fdegrove |
Hi John,
| quote: | | Hi Frank... I'm back |
At last...I was getting lonely here.;) |
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| EC8010 |
The upper valve in a mu-follower bootstraps the lower valve's anode load resistor, making it (roughly) mu times larger.
Similarly, looking down into the anode, an unbypassed cathode resistor in the lower valve is mutiplied by a factor of (mu + 1).
In any practical circuit, the bootstrapped Rl is so much larger than ra + rk (mu + 1) that the gain does not change when the cathode bypass capacitor is removed. |
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| dhaen |
Frank,
Yup, whisky in hand, running RH linux 7.3 (8.0 was too slow), fully networked, SMB, VM's, it all works!:)
Okagesama'de
BTW, I bought some Cahors yesterday, haven't tried it yet (£3.49).
EC8010,
The mu valve was an EL86 when I checked this, now it's an EL84. As I said, I'll check and report back....
Cheers, |
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| 316a |
...ever thought of trying E83F or E80L in your current source ? (hint hint!)
316a |
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| fdegrove |
Hi,
| quote: | | ever thought of trying E83F or E80L in your current source ? (hint hint!) |
To me the EL86/6CW5 is an almost ideal candidate for this kind of application.
Other than that all professional tubes carry a *5-10* higher price tag I fail to see in what way these would be so superior here...please enlighten us.
Cheers,;) |
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| 316a |
E80L and E83F cost peanuts these days mate ! Take a look on Ebay . Anything thats good enough for mic pre-amps (E83F) must be quiet enough for a mu stage .
316a |
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| fdegrove |
Hi,
| quote: | | must be quiet enough for a mu stage |
Ah,I thought already that was what you hinted at.
Don't know about E-bay price for tubes..I always buy my valves where I can see them and have absolute trade in garantee.
Moreover,professional series penthodes aren't necessarily less noisy than the standard run of the mill stuff.
Low noise and penthode is a bit of a contradiction in terms won't you say?
I must say in all fairness that noise considerations were a major factor for me to stay away from mu-followers in the first place.
Since you point to this factor,I think I was correct in doing so...at least for highly sensitive stages anyway.
Cheers,;) |
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| 316a |
whatever you say Frank . Time for bed now , you've been lurking since about 9.30am this morning , you must be tired yourself . I'll argue further in the morning .
nighty-night
316a |
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| fdegrove |
Hi,
No problem,I work from home most of the time usually 12 to 16 hours a day.
Don't get the impression I want to argue over this...I love to learn from the experienced people.
We all have our diferrent fields I suppose...:cool:
Cheers,;) |
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| 316a |
Morning Frank and all ,
Come to think of it 7N7's favourite the EL822 would probably be the optimum mu stage pentode . The good thing is that Mullards are still available fairly cheap .
316a |
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| fdegrove |
Hi and good morning to you too,
The EL822 seems a good candidate indeed.
I'm not sure whether it was widely used outside the British Common Wealth,maybe 7N7 can tell us more.
I must say I've never seen any in Belgium.:rolleyes:
Cheers,;) |
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| EC8010 |
| The Mullard data sheet describes the EL822 as a video output pentode. Since Mullard was actually owned by Philips, I would have thought that there would have been as many, if not more, Dutch televisions using EL822 than in the UK. |
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| 7N7 |
| quote: | Originally posted by fdegrove
Hi and good morning to you too,
The EL822 seems a good candidate indeed.
I'm not sure whether it was widely used outside the British Common Wealth,maybe 7N7 can tell us more.
I must say I've never seen any in Belgium.:rolleyes:
Cheers,;) |
I wanted to make a pentode sink to sit underneath a 6BX7 differential pair that was DC coupled form a 6SN7.
I realised that for a good sink one required:
A pentode that could handle the power
A pentode with high anode resistance
A pentode with high gm
A pentode with lowish output capacitance
And a pentode with nice flat curves.
I studied the Vade-Mecum and came up with EL822. EL84 would have done but its anode resistance and gm are a bit lower (ra = 40k)
EL822's anode resistance is around 100k and Pa is 12W. Gm is 15 mA/V. I have about eight of them; I suspect that they will be long-lasting and being Mullards, test as they should.
I have heard of its being used in control mechanisms in textile machinery!
It appears to have had no US equivalent, but the Russian 6P15P is very similar in specification and has very nice-looking curves.
7N7 |
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| fdegrove |
Hi,
The closest equivalents to the Mullard EL82X series are the the US made 6CH6 and 6CL6s.
The reason I proposed the EL86 to John instead of the EL84 is based around the same reason you have picked the EL822.
Cheers and thnx,;) |
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| 7N7 |
| quote: | Originally posted by fdegrove
Hi,
The closest equivalents to the Mullard EL82X series are the the US made 6CH6 and 6CL6s.
The reason I proposed the EL86 to John instead of the EL84 is based around the same reason you have picked the EL822.
Cheers and thnx,;) |
Well the EL821/6CH6, look OK until you see the curves; they are not nearly as nice as those of EL822/6P15P.
In reality I expect that the 6CH6 wouldn't make a bad sink, but having seen the curves has put me off;)
7N7 |
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| 316a |
There must be tens of thousands of Brimar 6CH6 kicking about , I have about 30 myself , all ex-government . Most UK suppliers charge about two pounds each for them . Not bad for a UK made near EL84 equivalent
316a |
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| 7N7 |
| quote: | Originally posted by 316a
There must be tens of thousands of Brimar 6CH6 kicking about , I have about 30 myself , all ex-government . Most UK suppliers charge about two pounds each for them . Not bad for a UK made near EL84 equivalent
316a |
I agree with this absolutely - how many Mullards can you buy for that kind of money.
I am surprised that we do not hear more about folk building small UL amps with these; I would think that they would work quite nicely
7N7 |
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| fdegrove |
Hi,
Allow me to cross check worldwide stock on these tomorrow...Tens of thousands may be a little over the top I'm afraid.
If possible at all, you'll get an updaate on the history of these types.
Cheers,;) |
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| 316a |
For a simple base re-wire these 6CH6 would probably fit most EL84 applications quite well , maybe the biasing is similar also . The main stumbling block is the fact that no-one has really heard of the things . Can you imagine the bunch over at the tubes asylum arguing over which shaped getter on their 6CH6 was the best ? They'll use up the world's supply of new old stock EL84 then go on to lousy current production . More than likely in 4-5 years time most of the 6CH6 will be disposed of without ever finding usage in audio .
316a |
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| 316a |
Hi Frank ,
A good pointer with reagrds to 6CH6 stock is Billington Export . Last year they were giving the things away and believe you me they did have tens of thousands of them !
316a |
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| fdegrove |
Hi,
Excuse me..Martin B.?
Peanuts...
I put the man on the map....he's a joke, doesn't know the first thing about valves...
Hold on....
I'll make a few calls tomorrow and you'll have real figures.
For historians,MB was my very first customer and because of him I spent 10 years in the valve business...
Small world indeed,:rolleyes: |
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| 316a |
...are you still in the valve business now ?
316a |
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| 7N7 |
| quote: | Originally posted by fdegrove
Hi,
Allow me to cross check worldwide stock on these tomorrow...Tens of thousands may be a little over the top I'm afraid.
If possible at all, you'll get an updaate on the history of these types.
Cheers,;) |
| quote: | Originally posted by fdegrove
Hi,
Excuse me..Martin B.?
Peanuts...
I put the man on the map....he's a joke, doesn't know the first thing about valves...
Hold on....
I'll make a few calls tomorrow and you'll have real figures.
For historians,MB was my very first customer and because of him I spent 10 years in the valve business...
Small world indeed,:rolleyes: |
316A is absolutely correct; all you had to do is make a phone call and Billington would send you free of charge a 6CH6/EL821
"Possible Audio Type" is the phrase they use I think!
Now for them to be giving stuff away, there must be more than I few about I think. I had one (I think I gave it to 316A!!)
7N7 |
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| fdegrove |
Hi,
| quote: | | are you still in the valve business now ? |
Nope.
Still have the connections though...
Abuse me...:rolleyes: |
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| 316a |
After making quite a few contacts in the UK I can honestly say that for some types such 6CH6 , there are vast quantities . Same goes for Mullard M8162 , I believe the RAF has just released over 100,000 of the things ,more than enough to fill every Fender amp ever made perhaps ? Heaven knows how many E92CC (used in flipflop circuits?) are out there , I have box loads myself , same with EF91 , 6AL5 , the UK government must have wasted soooooo much money . All of the M8136 and M8137 have now gone . It's the oddball types that there really are huge quantities of and some real bargains can be had . For example 12e1's , in various outlets across the globe these can be picked up for as little as $10 / 7 pounds each , a case of '500 quid all-in and you can fill your car with them' . I heard that Langrex had a rather impressive 'wall' of 12e1 a while ago . Same goes for STC 5B/255M . Nobody really uses them and it is a real shame , far better than all this poxy Ei / Reflektor new production which never tests to book specs .
316a |
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| fdegrove |
Hi,
Oh dear...
All the companies you quote know me and I know them...
What's your point?
If you spread the word long enough I can assure you'll be paying twice as much for the same thing tomorrow.
Feeling better?:att'n: |
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| fdegrove |
Hi,
Obviously most people don't have a clue about business.
No offense though.:cool: |
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| 316a |
I'm not paying for any of these , I have enough myself already . I have no need to visit any of these dealers , too many already and not enough space ! As for business , well put it like this , I'm doing very nicely , thank you !
316a |
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| fdegrove |
Hi 316,
| quote: | | As for business , well put it like this , I'm doing very nicely , thank you |
Good for you...just don't disclose too much of it or I'll bite your head off.:cool:
Mr Cutty,;) |
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| EC8010 |
| Billingtons would describe an ME1403 electrometer triode as a "potential audio type" if they thought it would sell a few more units! |
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| fdegrove |
Hi,
As promised I made a few calls this afternoon regarding this nice little penthode.
My "Deep Throat" guy confirms me that there are indeed tens of thousands of these valves around and there is little or no demand for them.
If anyone requires quantity quotes on these or is interested in a group purchase,just let me know.
| quote: | | Billingtons would describe an ME1403 electrometer triode as a "potential audio type" if they thought it would sell a few more units! |
My thoughts exactly.:nod:
Cheers,;) |
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| 7N7 |
| quote: | Originally posted by fdegrove
Hi,
As promised I made a few calls this afternoon regarding this nice little penthode.
My "Deep Throat" guy confirms me that there are indeed tens of thousands of these valves around and there is little or no demand for them.
If anyone requires quantity quotes on these or is interested in a group purchase,just let me know.
My thoughts exactly.:nod:
Cheers,;) |
Frank,
I am not a man of means but if anyone is buying EL822s, put me down for half a dozen - they will never be made again (this latter observation has been my ruination!:rolleyes: )
7N7 |
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