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Old 5th January 2011, 11:18 AM   #761
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Thanks Rod,

you got my order. I'll try them in my 801A line stage

Thomas
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Old 5th January 2011, 12:36 PM   #762
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Hi Thomas,

I'd be very interested in your findings for the benefit of everyone using filament bias.

Andy
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Old 5th January 2011, 01:10 PM   #763
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Hi Andy,

I will test them in my 801A linestage which is currently cathode bias, not filament bias

In my 'commercial' designs I only use filament bias if the customer explicitly requests it, due to the excessive heat dissipation (with tubes like 801A).

I will consult with Rod after I tested them before I write anything. No matter what will be the outcome, keep in mind everybody is biased, including me, so I encourage people to try and listen for themselves. Also what is better in one set up might sound worse in another.

If someone wants to do the comparison himself, I can offer the filament chokes on a loan basis. So no risk, just shipping costs.

Since filament bias seems to gain popularity, I will write up an article on my blog about it sometime soon. Speaking of filament bias, have you also tried the next step beyond? Filament bias with 'DirectPath'? A gain stage based on UX201A absolutely without capacitor in the signal path.

Here ist the schematic:

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The PSU:

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A foto:

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PSU:

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Maybe it's time to rebuild this in a new chassis ...

Best regards

Thomas
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Old 5th January 2011, 01:24 PM   #764
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Thomas - did you play with Meccano as a child?

Andy
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Old 5th January 2011, 01:38 PM   #765
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Hi Andy,

Quote:
Originally Posted by andyjevans View Post
Thomas - did you play with Meccano as a child?
Many people ask me that ... This is my old style to build things. I still like it for quick prototype builds.


This is how my stuff currently looks like (boring, I know)...

Linestage with 801A and LCR Phono with EC8020:
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A pic of some amps demoed at ETF09:
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Closeup of 801A power amp:
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300B with switchable filaments AC/DC:
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Best regards

Thomas
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Old 5th January 2011, 02:56 PM   #766
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Very nice!! I'm pleased to see that the cases have sturdy handles. You must be keeping Mr Lundahl in business!

Intriguing concepts you come up with - really original and creative.

Andy
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Old 14th January 2011, 06:19 PM   #767
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Smile Starting 26 preamp

Hi,

Received today the tubes, I will use Salas Shunt High Voltage regulator (can I share for the 2 tubes or I need one reg for each tube?) for B+ wich current I need to adjust? & Rod Coleman for heater filament (I suppose I need two, one for each tube?), could you remind me the last schematic (I have page 36 post 353), it's the last? I mind that with SSHV don't need plate choke right?

Attached a photo with the 3 tubes Cunningham 26, someone could do a look to see if all three are good?

Cheers

Felipe
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Old 14th January 2011, 06:43 PM   #768
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Merlin,

you could use one or two SSHV, but you need either a plate choke or a plate resistor, I use two SSHV and plate chokes. Also one of Rod' s fillament per channel, with a separate transformer, around 30VA each.
Regarding tubes, you never know if you don' t try. I did' t have good luck with RCA, and then I had 4 Sylvanias, and after a while one of them had strange noise and I replaced it. But so far I like the sound of Sylvanias better.
You could start with cathode bias and around 150V B+. I use battery bias now.

Last edited by vgeorge; 14th January 2011 at 06:45 PM.
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Old 14th January 2011, 08:13 PM   #769
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Quote:
Originally Posted by vgeorge View Post
Merlin,

you could use one or two SSHV, but you need either a plate choke or a plate resistor, I use two SSHV and plate chokes. Also one of Rod' s fillament per channel, with a separate transformer, around 30VA each.
Regarding tubes, you never know if you don' t try. I did' t have good luck with RCA, and then I had 4 Sylvanias, and after a while one of them had strange noise and I replaced it. But so far I like the sound of Sylvanias better.
You could start with cathode bias and around 150V B+. I use battery bias now.
vgeorge,

thanks for support, I have a lot of questions without answer:

Tx for B+, value in volts & power needed to adjust 150V, wich current to use only one SSHV?
Tx for Rod Coleman heater filament, value in volts & power needed or better shoul I ask to Rod?
Sorry my ignorance, cathode bias is a resistor or a resistor bypassed with a cap, values?
It's absolutely mandatory the Tx in a separate box?

Cheers,
Felipe

Last edited by merlin el mago; 14th January 2011 at 08:15 PM.
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Old 14th January 2011, 08:30 PM   #770
vgeorge is offline vgeorge  Greece
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As you need to burn around 25mA on the shunt plus 6 mA per channel, total 42 mA for one shunt minimum.
Rod will tell you everything about his regulators in a very detailed manner.
You could start with a 1,8kohm to 2.2kohm bypassed with 470uF on the cathode.
If you don' t use a seperate box for transformers be sure to decouple the tubes from the chassis.
For me there was not enough space to put all the caps, chokes and transformers in a single chassis anyway. I am going to transformer coupled soon.
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