DHT OTL Linestage - Tram 2

[Desmo]

Originally Posted by kazap

NOS RCA JAN VT-95 2A3

I wonder if I need to install the Coleman regulators when the Version3 regulators can handle the 2A3 load reliably? Has anyone updated the Version3 regulators to the Coleman and heard a difference? Thanks. Being so inexperienced I really appreciate the guidance.

Yep, I also bought two pairs of those RCA tubes... None of them really work in the Tram II (maybe I was just unlucky)... With some of them I have hum, with others there is so much microphonics, that they are useless.

Regarding the DHT regulators: To my knowledge the circuit in the new V.3 regulators is the same, as in the previous versions, only the cooling capacity is upgraded (I might be wrong, but it looks like this from the pictures)... Meaning, that the increase in sound quality with the Rod Coleman regulators should the same. And again (I know I keep repeating myself): This is the biggest sonical improvement I have yet made..! Bigger than going from standard tubes to the 2A3/SE, bigger than any cap upgrade or what ever one can make. The improvement in sound with those regulators is massive... And as a bonus, the noise is gone too...

The difference in sound quality is not because of cooling area, it's because the Rod Coleman regulators uses a totally different technology.

Regarding the V.3 regulators that now come with the Tram II, then I'm positive that the preamp will now run stable with those. Because the only reason for the problems with earlier versions was, that the heatsinks got too hot when using 2A3's. Look back in the thread, there is loads of info and discussions on this...

So to your question: No, you don't need the Rod Coleman regulators to have the preamp run stable. You need them if you want the best sound...

[kazap]

Originally Posted by Desmo

Yep, I also bought two pairs of those RCA tubes... None of them really work in the Tram II (maybe I was just unlucky)... With some of them I have hum, with others there is A LOT of microphonics.

I should have asked you first before buying them.




I wonder if you got the actual VT-95 military versions? I hadnt seen anyone mention the VT-95 so thought it was worth a punt:

"the VT-95 look just like the 2A3 but they sound very different... being more focused with sharper imaging while pushing music to the back of the stage and allowing vocals to move to the front...music has wider dynamic range, good detail and impact. Precise but still relaxed..." EDITED.

Obviously that description has nothing to do with the Tram2 but is intriguing. Time will tell.

Originally Posted by Desmo

..the increase in sound quality with the Rod Coleman regulators is the same...

Thanks - will definitely install the Rod Coleman Regulators then. They are also very affordable making them great value.

Morten, Im also wondering if I should try your Dueland CAST mod but the expense is a hurdle for me. Are there any other capacitors that come really, really close in sound quality; or are the CAST's out in a class of their own? Thanks again.

[ptashton]

The VT stands for:

vacuum tube
n. Abbr. VT
An electron tube from which all or most of the gas has been removed, permitting electrons to move with low interaction with any remaining gas molecules

This was a second World War US Miitary designation for tubes used in their equipment. Even today, the US Military will procure parts/spares from the OEM at large quantities and have their own Part No. designation. The part manufactured has to be to a specification desigated by the US Military. The specification might require the 6DJ8 plates for example to be extremely closely matches for it's peice of equipment to operate within it's operational parameters. Since the Tube Manufacturers in their hay day made tubes to high tolerances with materials that would withstand higher voltages, they would just restamp the civilian tube Part No. to a Military Part No. VT or CV designation. Most of the time the tube will have both the Civilian and Military Part No. on the tube. The VT or CV tube most of the time was nothing special. Only when the manufacture was required to produce a close tolerance tube, then it was special. That's all.

[kazap]

Originally Posted by ptashton

... The VT or CV tube most of the time was nothing special. Only when the manufacture was required to produce a close tolerance tube, then it was special.....

Thanks for clarifying that but at least if we buy VT designations we know its origins were at least a factory tested and selected tube for superior performance, with the normal designation possibly lower performing and re-badged possibly even worse. Maybe.

[ptashton]

Hugh, you still pay for the special selected tubes. Unfortunately with tubes, if you get into what is the best tube for your audio equipment, you could purchase many tubes to find the right one for your audio system. It ends up to be the synegy. With tubes you can fine tune your sound. It my take several attempts to get it right. It's all time, effort and of course money. It's people like Desmo who are an extremely knowledgable and helpful to put you on the right track.

Peter

[Desmo]

I'm no tube expert, so I can't tell if VT-95 are different than other. What I have learned is to stop reading all the nonsense on the Internet (well knowing that I participate myself). I have learned, that the only way to learn is to experiment by buying a lot of different tubes and/or to listen to friends with experience whom you trust. I have tried both, the first way is the most expensive, brings up the number of tubes sitting in the box with your spare tubes. The second way, listening to friends, is cheaper and the result is tubes that works and sound good...

I looked in my tube box, and I do have a pair of VT-95. I was told, that they are identical to other RCA 2A3 double plates. They also look 100% the same in their internal structure and they sound the same. Non of these really work in the Tram II though (two are extremely microphonics, two results in hum. The hum can be fixed with grounded metal containers over the tubes, but I don't want that). The sound is OK, you can read my impression of them here: Tram 2 45 tubes I think that they are almost as good as the better current production tubes like Treasure and the JJ's that Bjarne uses. But since the RCA cost the same (or more) then I see no point in using them since they are so unreliable...

Why pay for something old and unreliable, when you can reliable tubes for the same money, that sounds better..? Personally I believe the answer is the ''storytelling'' about NOS tubes being SO MUCH better, and new production tubes from China being SO BAD... Well, if hearing is believing, then that is not true (for me). I'm done spending money on NOS triodes for the Tram II...

Regarding the caps... Again: It has been asked and answered several times during the tread. So please read and find the answers, otherwise we keep filling up the thread with the same again and again... The short answer though: Upgrade the output cap first, that gives the biggest improvement compared to the input caps, and the 2,2uF tinfoil Obbligatos needed are not that expensive...

[kazap]

[QUOTE=Desmo;3302834] I'm done spending money on NOS triodes for the Tram II...[QUOTE]

me too thanks to you... Music First 2A3SE next

[QUOTE=Desmo;3302834] Upgrade the output cap first, that gives the biggest improvement compared to the input caps[QUOTE]

got it thanks very much for all your help

[ptashton]

Hugh, next is to place an order for a Tram2 with eight extra Obbligatos 2.2uf Tinfoil caps. You can find these caps at Obbligato 2.2uf/250vdc Tinfoil/film Coupling Cap | Diy HiFi Supply

Peter

[kazap]

Originally Posted by ptashton

Hugh, next is to place an order for a Tram2 with eight extra Obbligatos 2.2uf Tinfoil caps......

thanks Peter.. I appreciate that precise info that a beginner like me needs

Ive been looking at installing the Rod Coleman Regulators so here's some ideas I hope might help you a little with your installation designing:

Rod Coleman recommends using the chassis side wall as the heat sink as per the photo below and writes:
"If the chassis is made from 3mm thick Aluminium, or thicker, and exposed to he outside air, the performance will be excellent. To test this claim, a regulator was set up to supply ... filaments running 3.3A, mounted on some scrap 3mm Aluminium, 275mm x 100mm ..... The high power heater can operate with this heatsink indefinitely, and only reach about 45 deg C.....
Temperature Effect. You will notice that the current falls back a little after 5 - 20 minutes. This is because of the temperature coefficients in the transistor junctions, and the sense resistor. Use better heatsinking if you wish to minimise the difference between cold turn-ON current & steady-state level."

I think the design rationale in using the chassis side wall as the heat sink for the Regulators is brilliant as
a. its simple
b. it will tend to transmit heat out of the case compared to mounting heat sinks under the tubes
c. it might minimise any stray electrical fields from affecting the tubes/wires and thus aid in keeping the noise floor lower?

I wonder if this installation into the Tram2 chassis can be optimised via:

a. removing the epoxy paint on the chassis inner side wall to achieve a smooth raw aluminium exposed surface to maximise heat conduction transfer

Either mounting the transistors using heat conducting tape

OR better still: screwing the transistors into the side wall if you have a deft touch so as not drill though the chassis (perhaps wind tape around the drill to build up a 2mm wide collar allowing a safe drill depth 1mm shorter then the case thickness).

Use a copper shim for best heat transfer between the transistor and chassis and plenty of Thermal conducting CPU paste between all surfaces.

b. sticking heat insulation tape to the inner chassis wall adjacent to the transistor mounting; with the aim of minimising heat transmission back inside the case

c. optionally sticking heat sink fins on the outside of the case (if you don't like the look or they don't drop temperature appreciably just pull them off)

4. Put aluminium shielding on the inner side of the regulators to minimise stray electrical fields and further minimise radiant heat transfer - the fins of that linked heatsink will need to be flattened back with a hammer leaving just the top fins as a mounting base to the underside of the top plate. The inner vertical surface should have the thermal-electrical insulation tape glued to it.

Please let me know if any of this is mistaken? I haven't actually tried it and I am just a beginner.

Cheers
Hugh

[Desmo]

Originally Posted by ptashton

Hugh, next is to place an order for a Tram2 with eight extra Obbligatos 2.2uf Tinfoil caps. You can find these caps at Obbligato 2.2uf/250vdc Tinfoil/film Coupling Cap | Diy HiFi Supply

Peter

Yes, those are the ones for the output caps I will recommend getting ten extra though, to get six of them in each channel...