DHT OTL Linestage - Tram 2

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R1 is between C1 and C2 (positive side);
R2 is between C1 and C2 (negative side);

The schematic for the raw dc supply is in the manual, with all the procedures for setting up the regulators, including the raw dc. Please click my name & send some email, if you don't have the manual to hand.
 
Rod,

Please have a look at this picture. So to start off, for 0.15 ohm at R1 and 0.15 ohm at R2, I will need 0.30 ohm in parallel for R1 and 0.30 ohm in parallel in R2.
 

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......JJ 2A3-40s in a Tram.....is the power supply in the Tram adequate for them?

I have no actual experience so correct me if Im mistaken but looking at the data sheets for the JJ 2A3-40s versus standard 2A3, the heater filament load is identical. Most specs are similar except the JJ can be run at higher plate V and A with higher W dissipation like a 300B. So it should handle the Tram2 standard 2A3 load without breaking a sweat.

Whether it sounds good is another thing but having solid plates rather then mesh plates has got to be good for reducing microphonics.
 
Rod,

Please have a look at this picture. So to start off, for 0.15 ohm at R1 and 0.15 ohm at R2, I will need 0.30 ohm in parallel for R1 and 0.30 ohm in parallel in R2.

Hi Peter, You can try 0.3 x2 parallel, but I suspect this value has been optimised for 2A3. You may well get higher voltage, when a 45 is installed, (its 1.5A load is lighter than the 2.5A for 2A3). 240V mains may accentuate it further.

Please feel free to try anywhere from 0.15 to 0.47 for each position, but be sure to check the voltage at the Regulator input - must be 7.0-8.2V for 45, 7.5-7.7 nominal for 2A3 - to get optimal performance and minimal heat dissipation.
 
sjs,

I just looked in Rod Coleman's 'AN_DHT_2A3_V4.pdf' and it details:
The 45 & 46 type is exactly as the 2A3, except R1=0.68R/4W; R2=Not Fitted.

I am a bit confused, as Morten only used 0.68 ohm 12 Watt Mills resistor at R1 for his 2A3 tube. No resistor in the R2 position.

Rod Coleman's circuit for the 2A3 tubes, used for R1 and R2 the value of 0.82 ohms for each resistor.

Can this be clarified by yourself or Rod. Is 0.68 ohm resistor at R1 only for 45 tube and no R2 resistor. For 2A3 tube, use 0.82 ohm resistor in R1 and R2 position??????

Thanks

Peter
 
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R1 and R2 are in parallel in the board so either 1 at the correct value and high wattage or use 2 at double the value at kower wattage. I cant confirm the values as I dont have the amps any more.
So from what you have said about Rods instructions, 45 uses a single 5W 0R68, 2A3 use 2 x 5W 0R82 in parallel or 1 x 0R4 12W ??
 
Replacement knobs for the Tram

I have a lot of trouble keeping my volume knob from falling off. The shaft just isn't long enough for the grub screw to get a good hold.

Does anyone have a fix for this? Ideally, I'd like to get black knobs (I quite like the 'top hat' style), but am confused by the offerings on the 'net. Can anyone recommend something?
 
I have a lot of trouble keeping my volume knob from falling off. The shaft just isn't long enough for the grub screw to get a good hold.

Does anyone have a fix for this? Ideally, I'd like to get black knobs (I quite like the 'top hat' style), but am confused by the offerings on the 'net. Can anyone recommend something?

Sorry your shaft is so short. :eek:

Still if you stop playing with your knob it might not fall off. :nownow:

Maybe just use the remote so you can keep your hands off your knob. :spin:
 
Out of curiosity, has anyone attempted to use an adaptor to try the 4P1L in this preamp? I'd need to look up the op.pt. of a typical triode strapped 4P1L, but I'm guess we are close to the 45/2a3 area. They are cheapish still.

Also, dumb question, but its hard to search this thread at 96pg. I bought a Tram MKII factory made. Which filament regulators were used? Were they Colemans or other?

I see a lot of talk about Coleman regulators in this thread, but I didn't find whether this was a mod/upgrade or part of the kit. Coming in on the middle of the conversation made it hard to parse.
 
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