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Old 11th June 2011, 02:57 PM   #181
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by beardman View Post
Hi Thorsten
i have tried it 2 times with my heater---where the sound died---first a little under 2,4 dc and then 2,6dc-----first with 2.7 it got stable in sound---is it the regulator that goes to zero with that low volt ?
Just to be clear, there was 2.4V across the heater (at the tube socket), the heater where glowing, the other voltages (anode, grid, bias across 12 Ohm to ground) where all OK but you lost sound completely?

I will try to replicate this.

Ciao T
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Old 11th June 2011, 04:23 PM   #182
diyAudio Member
 
Join Date: Jan 2005
Location: a littlee town in western denmark
Hi
the 2.4 vdc was messured without any tubes---so is the 2.7vdc---it is the first thing to do before installing the tubes---when this volt get to low my tram lost sound---
messured direkt on the heater out
best bjarne
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Old 11th June 2011, 05:27 PM   #183
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by beardman View Post
the 2.4 vdc was messured without any tubes---so is the 2.7vdc---it is the first thing to do before installing the tubes
The 2.7V setting should be in the manual.

There is a 0.1 Ohm resistor on the Filament supply, with a 45 it will drop 0.15V, with a 2A3 0.25V. There is probably more than 0.1 Ohm in total losses in the wiring to the socket as well.

So yes, at 2.4V without tube you are likely below being able to operate the Pre.

Best is to measure the heater voltage directly at the tube pins (this way even the socket resistance gets excluded) and set this to precisely 2.%V with your actual tubes in place. The setting without tube is meant to get you to the ballpark, so it is safe to plug the tube in.

Ciao T
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Old 11th June 2011, 06:04 PM   #184
diyAudio Member
 
Join Date: Jan 2005
Location: a littlee town in western denmark
Hi Thorsten
thanks for this advice, i will set my heater to 2.96v
have you try some EML tubes .and how do they sound---?
best bjarne
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Old 11th June 2011, 09:49 PM   #185
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Join Date: May 2003
Location: UK
Why not find a way to support the Tram upside down with the tubes in place and then set the heaters to 2.5V?
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Old 12th June 2011, 06:51 AM   #186
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by beardman View Post
thanks for this advice, i will set my heater to 2.96v
Please do not do that.

Take the knobs from the Tram and place it on a piece of foam, face down. It will stand quite safely that way, resting on the transformer and face.

Then you have access to the underside with tubes fitted and you can adjust precisely.

If not, stick to the 2.7V, I worked these backwards with several different sets of tubes (both 45's and 2A3's) for the best compromise.

Ciao T
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Old 12th June 2011, 05:26 PM   #187
diyAudio Member
 
Join Date: Jan 2005
Location: a littlee town in western denmark
Hi all
i have now reset my heater and the anode volt---
one channel was 122 vdc---the other was 100vdc
not so easy to ajust precice on 120 vdc
maybe a better 10turns variable resistor will be easyer to ajust---
any comment on this ?
best bjarne
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Old 12th June 2011, 07:30 PM   #188
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by beardman View Post
i have now reset my heater and the anode volt---
one channel was 122 vdc---the other was 100vdc
This was probably okay, normal tube variation can account for this and it is okay.

Quote:
Originally Posted by beardman View Post
not so easy to ajust precice on 120 vdc
I think manual states +/-5V or even more, it is not neccesarry to be a absolutely precise.

Quote:
Originally Posted by beardman View Post
maybe a better 10turns variable resistor will be easyer to ajust
It has more to do with the time constant in the bias system.

I personally set the voltage once, very slowly and then monitor over the next ten minutes or so and adjust the voltage in small steps as it drifts.

Ciao T
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Old 12th June 2011, 07:40 PM   #189
diyAudio Member
 
Join Date: Jan 2005
Location: a littlee town in western denmark
Hej
my variable resitor is not easy to turn ,without to much variation--even a tiny turn give to much---there for i think a 10 turns will be a little more easy--
best bjarne
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Old 12th June 2011, 07:54 PM   #190
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by beardman View Post
my variable resitor is not easy to turn ,without to much variation--even a tiny turn give to much---there for i think a 10 turns will be a little more easy
The resistor on the CCS is an 18 Turn one and as long as you try to get 120V +/-5V the action is quite okay. If you try to get 120.00V exactly, then yes, it may be too sensitive, but such accuracy is not really needed.

Ciao T
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