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Old 27th January 2013, 07:03 AM   #551
kazap is offline kazap  Australia
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I couldnt afford the U52 but acquired a common Tungsol 5U4GB and just need a Tram2 to drop it into. Next weekend could be very interesting.
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Old 29th January 2013, 09:11 AM   #552
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Has anyone had experience with the A1834 (6AS7G or CV2523) GEC or similar tube. They come in straight or curved brown base. See attached pictures for details.

Peter
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Old 31st January 2013, 07:59 AM   #553
Desmo is offline Desmo  Denmark
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I made a small tweak recently...

I don't know about your Tram II's but mine is a pain when it comes to adjusting the 120V anode voltage on the CCS modules. I get it set to around 120V dc, all is good, but then after some weeks the anode voltage start drifting. This is heard as noise when the voltage drops below a certain point. Last time I opened it to re-calibrate the anode voltage it was down at around 90V dc in the left channel. (I should mention, than when adjusting the anode voltage I always let it stabilize for at least half an hour so I'm sure it's stable).

The problem is, that just a change of a few ohms on the trimmer will mean a big change in anode voltage, and it seems that these trimmers can drift a bit over time...

I have now installed resistors instead of the trimmers. In one channel I have an 82 ohm resistor, in the other channel I have 82 ohm // 2k2. The anode voltage appears to be rock solid (at least for now) and there is ZERO noise through the speakers..!!!! With the anode voltage being totally stable at the correct 120 - 125V and the Rod Coleman DHT regulators, the Tram II is now one of the quietest tube preamps I have experienced... Impressive for a DHT running 2A3 tubes

The downside is that it will of course be more work when changing tubes, because fixed resistors needs to be replaced, but since I'm done tube-rolling on the triodes, this is not a problem for me...
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Old 31st January 2013, 10:20 AM   #554
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Morten, there must be a better/stable Trim pot than the one supplied by DIYHIFI Supply. RS Components or Farnell Components. I will have to measure my circuit for appropriate resistors.

thanks for your tweak.

Peter
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Old 31st January 2013, 10:29 AM   #555
Desmo is offline Desmo  Denmark
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The trimmer is a good quality multiturn trimmer, so the ones in the preamp are as good as they get...

The problem is, that the whole resistor is in the trimmer, so even a microscopic change means a big voltage change on the anode. What can be done is a small tweak of the circuit where (for instance) a 75 ohm reistor is used in series with a 10 ohm multiturn trimmer. With this set-up just a little of the resistor is in the trimmer. It would be possible to adjust, the adjustment would be much easier because each turn on the trimmer is much less change in resistance. Any drift would also be much less drift in resistance meaning that the anode voltage is less likely to drop out of ''the zone''.

This little mod means replacing the existing multiturn trimmers with similar ones, just 10 ohm and then making a small mod, cutting a track on the small circuit board to get the 75 ohm reistor in series.

For now I'm happy with the fixed resistor solution, maybe some day I will make the modification mentioned here.
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Old 31st January 2013, 11:07 AM   #556
kazap is offline kazap  Australia
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Quote:
Originally Posted by Desmo View Post
...This little mod means replacing the existing multiturn trimmers with similar ones, just 10 ohm and then making a small mod, cutting a track on the small circuit board to get the 75 ohm reistor in series...
That's brilliant.

This might be a silly question but do you think a 10ohn trimmer will have enough range to change from 45's to 2A3's OK?

Is it possible to mount the trimmer's so the adjustment can be done from the outside without needing to unplug the Tram2?

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Old 31st January 2013, 11:19 AM   #557
Desmo is offline Desmo  Denmark
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Don't know if it's enough range for 45's, but since I don't use them I don't need range for them... The point is, that the smaller part of the total resistance value is in the trimmer, the easier the adjustment will be, and the less it's likely to drift. So if someone needs bigger range then just use slightly bigger trimmer and slightly smaller fixed resitor in series...

If you install multiturn trimmers facing up, drill some small holes in the top of the chassis, and install a voltmeter measuring the anode voltage then you can adjust without opening the chassis... But what is the point? The small mod is to aviod drift and to avoid having to make adjustments...

If you wan't it for easy tube rolling you can of course install this.
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Old 31st January 2013, 12:10 PM   #558
kazap is offline kazap  Australia
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Ive just set up my Tram2 and have a smile on my face. Im just using old National Union 45's and dont have the Coleman regulators in yet but its dead quiet at 150cm from the speakers and sounds great
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Old 31st January 2013, 12:25 PM   #559
Desmo is offline Desmo  Denmark
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There is never noise with the 45 tubes, not with the original DHT regulators, not with the Rod Coleman.

Once again: The biggest benefit of the Rod Coleman regulators is the improvement in sound. The bonus is the lower noise.
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Old 31st January 2013, 12:35 PM   #560
kazap is offline kazap  Australia
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If it ever sounds even better then this Im never going to get off the couch. Thanks for the warning. I must mod the front panel LED brightness so I can see the tube glow.
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