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Old 20th March 2011, 12:43 PM   #81
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Quote:
Originally Posted by JoshK View Post
I'm curious if the Tram II can be ordered set up for 71a (5v filament)?

Josh
It would be good. I asked this:
DHT OTL Linestage - Tram 2

But alas Brian said (IIRC offline) that it was too much work/ not profitable . .
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Old 20th March 2011, 01:11 PM   #82
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by JoshK View Post
Thanks T. Sorry for misspelling your name.

Also, I'm curious if the Tram II can be ordered set up for 71a (5v filament)?
Sorry, no. The 71A does not handle enough current. The heaters are essentially adjustable for a range, depending on heater current.

Ciao T
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Old 20th March 2011, 03:09 PM   #83
Desmo is offline Desmo  Denmark
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@Thorsten: Thanks for helping out with answers...! I have now recieved my Tram 2 and I have a few issues that I hope you can help me with...

1). C16 on the autobias module blows up! I don't have a circuit diagram, so I have no idea what this 100uF, 25V elco is doing, but after a few days it blev up (metal housing was shot of the cap). I hoped it was just a bad cap, so I have replaced it but the new one is beginning to ''lift it's top'' as you can see in one of the attached close up pics. Can you help me with a solution to this..!?

2) HEAT... I run 2a3 tubes and the heat sinks on the DHT supply modules get so hot, that the supplies are getting unstable after +5 hour. Unstable = noise heard through the speakers and low frequency pulsing (woofers flapping) that indicate some sort of low frequency oscillation. I should mention, that I have the preamp located on an open shelf with lot's of ventilation around it. Also worth mentioning is that I have tried with both 0.47 ohm resistors and 0.22 ohm resistors on the input of the DHT heater supply modules, but the modules can't regulate the output to 2,5V dc with the resistors installed.

I have tried a ''proof of concept'' approach to increase the cooling area of the heat sinks, see attached picture, and with the added surface area on the heat sinks the modules does not get unstable, however they still get VERY HOT..!

Can you recommend any solutions besides larger heat sinks and/or fan cooling to solve this problem?

BTW: Wonderful sounding preamp...! The best I have ever had in my system..! I have done a few upgrades:

- All the screw terminals on the boards are removed, so the wires are now soldered directly to the circuit boards.

- 230V ac wire is run in aluminium tube connected to ground.

- Volume control connected in shunt mode, and Vishay naked z foil resistors installed.

- Shinkoh tantalium resistors in the signal path

- Duelund CAST caps in the input

IMHO these updates has lifted the sound quality to an even higher level..!

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Last edited by Desmo; 20th March 2011 at 03:19 PM.
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Old 20th March 2011, 03:12 PM   #84
Desmo is offline Desmo  Denmark
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And here is an overview picture (taken before the Duelund CAST caps and the additional heat sinks were installed).

Click the image to open in full size.
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Old 21st March 2011, 06:30 PM   #85
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Hi Desmo, nice work there!

RE the heat with the 2A3 supplies. They do run hot, I think Thorsten is ok with that. When I switched to 2A3 from 45 I too had a low frequency pulsing. Getting the voltage down with a small value resistor worked for me. I suspect the only way to reduce the the heat is to revert to 45 tubes but I'll defer to Thorsten on this.

Clive
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Old 21st March 2011, 06:58 PM   #86
Desmo is offline Desmo  Denmark
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Hi Clive,

A friend of mine who has the Tram 2 is REALLY struggling with hum when using 45 tubes, this is also confirmed by the European seller: Acoustic Dimension... They can't get the preamp to work at acceptable low hum levels with 45 tubes either. So for now I would like to stick to the 2a3...

I would be OK with the heat as well if the power supply modules did not get unstable because of overheating. As mentioned I have also tried the resistors, but even with 2 X 0.22 ohm resistors the modules can't regulate to 2,5V output. With 2 X 0.22 ohm resistors on the inputs of the power supply modules the maximum DC voltage on the output is 2,2V DC, and that's not enough for the heater in the tubes... I have also tried with just one 0.22 resistor on the input of each module, then the output can be regulated to 2.5VDC, but there is quite a lot of hum...

Last edited by Desmo; 21st March 2011 at 07:11 PM.
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Old 21st March 2011, 07:13 PM   #87
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Hi Desmo,

Nice capacitors...I have some VSF DC for a different application, they are superb. The CAST must be even better.

I've run 4 different sets of 45s with zero hum issues so I don't understand...

I've run 2 different types of TJ and 2 types of old stock tubes. DHT linestages are picky so who knows what's going on.
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Old 21st March 2011, 07:20 PM   #88
Desmo is offline Desmo  Denmark
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The CAST has the same natural sound as the VSF, but are even more transparent. They are very nice..!

I have bought some NOS 45 tubes on e-bay that should arrive soon (ETA depending on, if they get stuck in customs). Then I will try for myself to check if I have the hum issue with 45 tubes...

But again: I wan't it to work with 2a3 tubes..! Actually I have ordered some small (50 mm in diameter) fans, and I'll try to check if one of them inside the chassis running on a slow / silent speed will move enough air to solve the problem. As I see it the problem is not just the rather small heat sinks on the supplies, but also that the ventilation in the chassis could be much better... Cold air can get in easily through the perforated bottom plate, but there is now way for the hot air to escape through the top...
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Old 21st March 2011, 10:19 PM   #89
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I too prefer 2A3, given the tubes I have my 2A3s sound better than my 45s.
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Old 22nd March 2011, 04:36 AM   #90
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Quote:
Originally Posted by Desmo View Post
A friend of mine who has the Tram 2 is REALLY struggling with hum when using 45 tubes, this is also confirmed by the European seller: Acoustic Dimension... They can't get the preamp to work at acceptable low hum levels with 45 tubes either. So for now I would like to stick to the 2a3...
Some recent batches of TJ 45 pick up hum from the rectifier. TJ changed the tube structure over older versions and somehow these hum like crazy in the tram, especially the tube that is closer to the rectifier. You can shield the 45's, the Rectifier or not use TJ's from that batch.

Other 45's generally are quiet, as are 2A3's, however it can depend on the rectifier. Some rectifiers have a very strong magnetic or electrostatic field around them and then any tube in the Tram picks up that hum. For example the Valve Art 2A3 are dead quiet in the Tram.

I have found that the Valve Art 274A are the best rectifiers in terms of being quiet, followed by any coke bottle rectifier 5U4G. The short, stubby 5U4's etc and GZ34 produce hum. The Valve Art 274A may be acceptable even with the "bad batch" TJ 45's.

Ciao T
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