McTube with power tubes?

[SolderFodder]

Considering basing an amp around the McTube 2 (evidently it's the real one?)

http://www.dogstar.dantimax.dk/tubestuf/mchowit.htm

My question is, can the power supply support a power tube in there?  I think you can get a few milliamps and 240v going.  Shouldn't that be enough to put an EL34 going class A in there?

[MarcoMike]

and then...?

[GibsonGM]

Check the curves for the tube you plan on using. Probably an EL-84, as a guess.  But how about the preamp?
 
You can use a power resistor to determine how much current you can draw before you start "pulling too much" (10% voltage sag?).  Be sure to fuse your primary, you might exceed something on that side!   

[petemoore]

  5e3 pulls sag out of the PT, it gets hot.
  Other tubes which expected their PS to exceed limitations were less successful.
  Pretty much gotta know what you're doing and be ready to smell smoke when pushing a power supply to what could be near or exceed for instance a thermal limit.
  It can be calculated to some degree...but 'what is the load like?' also becomes important...heating time, ambient temperature, cooling...even the bass control can easily be enough to save/break a power amplifier supply that is almost smoking.
 

[sean k]

Add up your filament voltages then add up your HV currents then times them by ten and that how much your first twelve volt winding will be supplying... then take off the filament current and thats what you'll have to rate the second transformer for.

Whats an EL84 filament needs? 860mA? I can't remember so that added to 150mA for the 12AX7 is about 1.01 amps. As for HV the 12AX7 is only 3mA for both at the most but the EL84 would be idling at about 40-60mA so that times 10 is about half an amp so your first transformer would need to be 2A... at 12VAC, though a 1.5 would most probably do it and you then you could get away with the second at 1A though .5A might just do it.

I've made preamps with a single tube and used tow 12V at 150mA so I reckon a 2A and a 1A would allow you an SE EL84, given 1A, 2A etc are generally easier to find than 1.5A or .85 amps. I haven't used the 1.414 and the .707 which you should really use as the 240 will end up at  340VDC so if you need 40mA your going to have to have 1.414 x 10 times that amount of current at the 12 volt side.

[philbinator1]

Where's my free smile dammit!   

[PRR]

EL34 needs 6.3V 1.6A or 10 Watts heater power.

Fred suggests 12V 0.5A wall-warts, 6 Watts each. Already you are over the available power, and also at a wrong voltage.

We could go on, using bigger warts, but EL34 is really a big tube for a junker power supply.

I assume you intend the power tube as a power amp, with an output transformer to drive a speaker? May I suggest 12FX5? It's a real power tube, albeit aimed for 120V 1 Watt performance, and really cheap. Find a 12V 1A wart for the first lump. This can feed both bottles. Either give the 12FX5 raw 12V AC (IMHO, DC is a frill) or diddle R2 smaller to get 11V-12V DC on the heaters. You want one more stage of B+ decoupling between main power to power stage and the power to the preamp stages, see Fender Champ. See 12FX5/60FX5 datasheet for bias and load values.

[SolderFodder]

EL34 needs 6.3V 1.6A or 10 Watts heater power.

Fred suggests 12V 0.5A wall-warts, 6 Watts each. Already you are over the available power, and also at a wrong voltage.

We could go on, using bigger warts, but EL34 is really a big tube for a junker power supply.

I assume you intend the power tube as a power amp, with an output transformer to drive a speaker? May I suggest 12FX5? It's a real power tube, albeit aimed for 120V 1 Watt performance, and really cheap. Find a 12V 1A wart for the first lump. This can feed both bottles. Either give the 12FX5 raw 12V AC (IMHO, DC is a frill) or diddle R2 smaller to get 11V-12V DC on the heaters. You want one more stage of B+ decoupling between main power to power stage and the power to the preamp stages, see Fender Champ. See 12FX5/60FX5 datasheet for bias and load values.

The 12FX5 sounds like exactly what I was looking for.  Thanks.