power transformer for a 2a3se amp!

[tubo]

hi,

i have 2 power transformer which has a 300-0-300v 80ma rating. will it be suitable for a monoblock 2a3 se amp? i want to build this circuit.

6C6-2A3

thanks. pls advice

[tubo]

how much current would an rc coupled 2a3se mono amp pull?

[Bas Horneman]

i have 2 power transformer which has a 300-0-300v 80ma rating. will it be suitable for a monoblock 2a3 se amp? i want to build this circuit.

So you have one per channel? In that case they are sufficient. Most SE 2A3 won't use more than 60-70mA.

[azazello]

aprox.....55-65 ma 2A3/in Your case 45:750=60ma, or 52:880=59ma/ + 6-8-10 ma /in Yor case 2-5ma/ preamp. per channel.
It's OK !

[tubo]

thanks guys!

[kevinkr]

Actually it is pretty marginal, unless that 80mA is the rectified dc output current rating of the power transformer.

For a 70mA dc load accounting for power factor in the rectification and first capacitive input filter I would go with no less than a 110mA ac secondary current rating. You can do considerably better than this with a choke input filter where something greater than 90% of the rated current is generally acceptable.

When I first started specifying power transformers for some of my designs and for retail clients I made this very mistake, and ended up replacing a bunch of burned out transformers over the next few months - an expensive mistake.

These transformers would very happily run a 45 amp configured for 2.0Wrms (5K OPT, 35 - 40mA plate current, supply about 300V w/cathode bias, 250V fixed bias) You could use the existing circuit with only a change of the output tube cathode resistor to 1.1K -1.2K or so.

[tubo]

hi kevin,

the 80ma is unloaded! thanks

[boywonder]

Related question: If using a CLC PS with a small value first cap such that the B+ is closer to .9 x transformer secondaries as opposed to 1.41 x transformer secondaries, is this effectively increasing the available current compared to a cap input? In other words, does reducing the first cap value (values that effect a decrease in B+) move the current rating on a rectifier tube chart from the cap input curve to the choke input curve? It would seem so.

[kevinkr]

Originally Posted by boywonder

Related question: If using a CLC PS with a small value first cap such that the B+ is closer to .9 x transformer secondaries as opposed to 1.41 x transformer secondaries, is this effectively increasing the available current compared to a cap input? In other words, does reducing the first cap value (values that effect a decrease in B+) move the current rating on a rectifier tube chart from the cap input curve to the choke input curve? It would seem so.

If you have a very small cap and a fairly large choke, yes, otherwise I would say not necessarily.

[kevinkr]

Originally Posted by tubo

hi kevin,

the 80ma is unloaded! thanks

Umm, that reply makes absolutely no sense at all! By definition that is the maximum load current. There is such a thing as the unloaded output voltage however.

You need to identify whether that 80mA rating is the rectified DC load current or the unrectified AC load current. Should this be the DC rating the transformer is just large enough, if it's the AC rating it is NOT large enough g for use with a standard CLC or CRC based supply (An LCLC supply might be ok) unless the manufacturer was extremely conservative in its design. (Not likely if the transformer is an off the shelf item made in the last couple of decades.)