DHT OTL Linestage - Tram 2

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However, the motivation for this post is that, when no music is playing, i can now hear a low level oscillation/feedback type whine that appears occasionally

Hi all, just a quick update to say that i have determined that the 'oscillation' noise in my Tram2 is the (Coleman regulator) cooling fans kicking in.

At this stage I am not sure whether its caused by EM radiation from the fan supply wires, or from the fans themselves, or noise injected back down to the supply from the fan motors (maybe the most likely?). I suppose the easiest first step is to try to shield the supply wires and see if that makes any difference.

Incidentally, my friend's Tram2 that does not have this problem has (cooling) holes drilled through the top of the chassis in addition to the fans: I wonder if the holes might be enough to stop the fan from coming on?

I note that my fans only stay on for something like 20-30 seconds... I suppose a possible work around might be to test the actual temperature of the regs at equilibrium and see if can avoid the fans kicking in at all during normal operation!

- richard
 
Thanks Morten, i bet you are correct: the character of the noise does seem consistent with vibration of the tube components!

Also, i had never noticed the noise until I started using an EML rectifier tube, so maybe it's vibration of only that rectifier tube that's causing the noise...!

- richard
 
I used a fan under my Tram2 in the heat of last summer with early stock regulators. But the fan was powered on all the time, was powered with a linear 5v low noise supply plugged into a different outlet form the preamp, was a very low noise 12V design, had special bearings and was mounted via silicon to isolate direct vibration. It was noise free via the speakers and from 40cm away.

I think the airflow from drilling extra holes to get cooling via passive convection could be optimised using a chimney effect. The top transformer cover gets warm enough to likely augment updraught by attaching copper tubes with thermal paste around the back of the transformer cover.
 
Coming very late to this thread but hope someone here can help ....I've picked up a Tram2 (already built) ...

However it has no remote and I have no idea what remote I should buy to work with it.

Any suggestions on a simple remote to operate it? (ideal would be just with input selection and volume control but any remote at all really would be great).

If anyone has a pointer to something in particular (say on Amazon or eBay) that would be ideal.

I'm actually pretty short of remotes in here, I don't have a TV or DVD player any more (haven't had for years) so the only remote in operation is the one for the CD transport.
 
Bob Magaletta [Magz] has done some work on quiet fans - maybe will help:

Thanks Rod: i'll check it out!

However it has no remote and I have no idea what remote I should buy to work with it.

Easy, as noted above, any universal remote should work (i use a Logitech Harmony 1). For codes, also see this thread: http://www.diyaudio.com/forums/diy-hifi-supply/192057-tram2-remote-code-logitech-harmony.html [EDIT: ah, i just noticed you already posted on that thread...]

Finally, diyaudiosupply probably still have the $20 remotes that they supply with the Tram. You could try contacting Simon. I seem to recall you can also buy them on eBay, but it would be easier to buy one from Simon, pre-programmed.

- r.
 
Well.....Finally I have my very own Tram. At the moment it is a 2 box affair with separate transformers for the B+ and heaters etc. Thankfully I have no hum (my biggest worry). I was picking up some mechanical noise from the fans however I have now devised a way to keep them isolated.

I have, with the help of the generous posts of members in this forum implemented the following:

TJ 2A3 SE output tubes (thanks Morten :))
Chatham 5998 Mu (others on order)
Emission Labs 5U4G

Coleman regs with Mortens upgrades (thanks Morten :))
Duelund CAST input caps (thanks Morten :))
Obligato 2.2 X6 output caps (thanks Morten :))
SHINKOH Resistors throughout (thanks Morten :))

I could feel my heart in my throat and my stomach turning on first connected turn on and initially the left channel was out........ I traced it down to a faulty resistor in shunt mode. All fixed and sounding wonderful. Now for the burn in.

Thank you again

Greg
 
Headphones - Tram mk2 question

Pardon my limited knowledge, but is it possible to use Headphones, Sennheiser HD 650 (impedance 300 ohm), directly from the Tram mk2 output? If not, does anyone have a suggestion of a modification, external converter etc. Do I need a separate headphone amp?
Regards, Mats Falck
 
I have the Marantz remote RC5200SR. It works selecting the TUNER function. For coding select any Marantz AV Receiver eg SR-7200 or SR-4200 should work and are in the Logitech database. Enjoy.

Hi all, for the record i finally sat down and tried several different amplifier and AV receiver brands and models to get the input selector working.

The SR-7200 does not work, but the SR-4200 AV receiver does! So now for the first time I have both volume AND input selector working! (I could not get any of the Rotel, Philips or Marantz amplifiers remote codes to do this).

Thanks kazap!
 
hello Peter,

I assume you mean the R1 and R2 in the raw-dc supply that feeds the regulator (and not R1/2 of the regulator PCB itself).

0.15 sounds OK as a start, but the only thing we care about is to get the dc voltage supplied to the Regulator at about 7.5V-7.7V (measured at the regulator PCB).

You can increase from 0.15, if the voltage is too high (which will burn more heat is the regulator pass transistor) or adjust lower for more voltage.

The resistors can be equal or different values.
 
Rod,

Thanks for your response. Yes, I am talking about the raw-dc supply. I am after the configuration for these two resistors. On Morten's picture, there are two resistors for R1 and two resistors for R2. What would you recommend using for example: 'say one resistor for R1 at 0.15 ohm at 10 watt'. Thanks

Peter
 

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If you are using the 7.5V winding on the TRAM2, then the values that Morten used should be your starting point, so yes, R1=R2= 0.15 10W wirewound.

When you have built and installed the Regulator and raw dc, please measure the raw dc's voltage at the Regulator PCB, when it is adjusted so that the 2A3 filaments have 2.5V across them. The volage must be 7.5-7.7V on a TRAM. if it is outside this range, reduce R1 to increase voltage, or decrease R1 to get a lower raw dc voltage.

One can't predict the exact value of resistor, because it depends upon the small resistances (parasitics) of the rectifiers, ESR of caps, trafo, wiring.
BUT - it's only with a 2A3 that so much fuss is called for: with 45, or other lower current filaments, the raw dc can be anywhere from 7.0-8.2V
 
Rod,

Thanks for your info.

On the Regulator PCB, Morten used a 0.47 ohm 2 watt Mills resistor for R1 for his 2A3 tube. I am using 45 tubes. Will this 0.47 ohm resistor be ok for the 45 tube???, or if not what should I use.

Just to clarify on my previous question, I only need to use one 0.15 ohm 10 watt resistor for R1 and the same for R2. I just wondered why Morten has two 0.15 ohm resistors for R1 and the same for R2.

Thanks
 
Hello
I can se on the skematic from Rod, that you shall use one 0.68ohm on the regulator

a good idea is to buy some different resistor value for the input to coleman regulator--
i use 0.18 ohm (2 pieces like Morten)--it depent on what is the volt from net ..here by me in Denmark i have 232 v ---maybe you have 240 or 220v
Best Bjarne
 
Peter, Yes, Bjarne's advice is good. Buy as few cheap 10W ceramic wirewound resistors 0.1 to 0.68, to fine tune the raw dc voltage.

If you want to use a 45 only, and 240V mains, you may need R1=R2=0.47 as a starting point.

Then if you need more voltage, drop one of them to 0.33. For lower voltage, raise one to 0.68 (or just add another 0.1 in series).

If you have it all connected now, what is the raw dc measuring?
 
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