Heaters

[Lee S]

Hi all.

Am thinking of reducing the iron count inside my amp. I have currently got 2 x 2.5v traffos for the filaments of either the 56s or 27s. I am also using about 600mA of a 6.3v 6A heater winding on my mains traffo. I would like to rectify the 6.3v supply and use that for all four valves. How to do it though. I can obviously rectify and filter down to 6.3v for the 6J5Gs, but what about the 56/27s? I need 1A for a 56 and 1.75A for a 27. I would like to be able to use both, so would it be wise to run them in series, thereby only having to "get rid" of 1.3v at 2 or 3.5A or would it be better to run them in parallel and drop 3.8v across something? Also if tweaked for 2.5v at 2A for the 56 , would I get terrible voltage drop running the same circuit at 3.5A for the 27s?

I was thinking of a basic bridge rectifier pack followed by a C-R-C for the 6.3v. Could I just then tack on another -R-C to drop it for 5v (if in series) or 2.5v? Would I need some kind of switchable load to change between the low currrent/high current circuit? Would a voltage regulator be better or is trying to get that much current through a reg asking for trouble?

Any other comments/ideas?

Thanks,

[Nick]

Replacing the 56 with a 76 might simplify that part.

[Lee S]

It would indeed Nick, but how would I then be able to try a 27? It is at the moment a 56 -> 6J5G -> 2A3. I would like to be able to swap the 56 for a 27 now and then, but as the 27 is a mesh plate, it is a little susceptible to hum. I chose the 56 over the 76 as it allows me to swap between the 56 and 27 with the same heater supply. It was all done to be able to listen to both valves and decide between them, but I am thinking that a lot of the hum I get on the 27 is down to the AC heaters and the solid plate 56 is a lot quieter. I was hoping a change to DC would quieten things down a touch with the mesh plates.

Let's say I wanted to keep the 27 in permanently, what's the best way to get 2.5v 1.75A DC for two valves from a single 6.3v 6A winding?

Thanks,

[Mike H]

Are these DHT's?


Cos don't think you can heat 2 DHT's from a single common source.

I could be talking cobblers of course

[Lee S]

No Mike.

They are just indirectly heated triodes.

[Nick]

You could use a Hammond 195P5