DHT OTL Linestage - Tram 2

[ThorstenL]

Hi,

Originally Posted by kelpie81

I suppose what I'm trying to do is finesse the gain down thereby reducing noise at the speaker level and giving me more usable volume further up the scale if that makes sense. Most cd's I play I don't push the volume much past 12-1 o'clock whereas it was my impression that around 3 o'clock was the optimum. Anyway I'll just keep fiddling with various resistor values, which I did last night ( replaced the the 470r with an 820r ), until I reach an acceptable compromise. Cheers.

I can see your point.

Raising the shunt resistances (to ground from -12dB and from -3dB to -12dB) will increase the level. If the total is raised by around 50% you get around 3dB more level.

Ciao T

[forch]

Thorsten, I implemented your recommendations to install the dropping resistors (total 0.16Ohm) from the power supply and rebiased with the VA 274B and Shanguang 2A3C tube combination.

Now, there is a very slight buzz noticable only a foot or two away from my Zu Druids (>97db efficient). Probably picking up some minor EM. Also noticed that my dimmer switch was throwing noise into the system also, so that is gone. Have some Herbies dampers arriving and have the unit on a set of StillPoints.

Thorsten, I appreciate all the help and hopefully your recommendation can also be used by others. Thanks, Jeff

[ThorstenL]

Hi,

Originally Posted by forch

Now, there is a very slight buzz noticable only a foot or two away from my Zu Druids (>97db efficient).

Good to know you got things sorted.

Originally Posted by forch

Thorsten, I appreciate all the help and hopefully your recommendation can also be used by others. Thanks, Jeff

No worries, glad I could help.

Ciao T

[forch]

Wondering if anybody out there has tried a 6080 in place of the 6AS7 CSS tube? I'm mainly looking to reduce EM between tubes and lower noise even further.

T, is a 6080 even advisable?

Thanks, Jeff

[forch]

For tube rollers out there: as a follow up of my previous email, I bought an octal "socket saver" that raises the socket above the chassis cut out. Wide-base 6080 tubes can be used in the Tram. I have one in use now and it works great. Thanks, Jeff

[DECKY999]

One of the Trams that I assembled developed a fault in the bias supply boards. See the pic. One channel supply is showing red diode next to its 2SA940 transistor. Bias voltage on that side is 16V only. This happened after only 6 months of normal operation.

What went wrong here? Is it possible to get a replacement from Simon?

[ThorstenL]

Hi,

Originally Posted by DECKY999

One of the Trams that I assembled developed a fault in the bias supply boards. See the pic. One channel supply is showing red diode next to its 2SA940 transistor. Bias voltage on that side is 16V only. This happened after only 6 months of normal operation.

Are you sure it's the Bias Module? These very rarely cause any trouble.

Originally Posted by DECKY999

What went wrong here? Is it possible to get a replacement from Simon?

Just return the faulty module for replacements. Hard to say what specifically went, any possibility, something was shorted? It may still work afterwards for a while but something may have taken a knock...

Ciao T

[DECKY999]

I am sorry it looks that I was too hasty as always. The red diode follows one of the valves. It is definitely the valve. I will get some spares today and double check. Thanks.

[ThorstenL]

Hi,

Originally Posted by DECKY999

I am sorry it looks that I was too hasty as always. The red diode follows one of the valves. It is definitely the valve. I will get some spares today and double check. Thanks.

The Red Led is the "cannot control current even though I tried" indication. It basically tells you "Tube dead". If the tubes are under warranty you may be able to get a replacement from DIY.

Ciao T

[DECKY999]

No problems - the tubes are NOS National Union 45s from ebay. Can't really claim warranty on them but they are easy to replace. I will suggest Emission Labs 45 to the owner.