to drop voltage or not?

[bnew63]

I have a 380-0-380 larger PT
I also have a 290-0-290 smaller(Removed from a hammond amp)
You can see from the diagram That I need 290
Is it better to drop the voltage on an oversized amp or use the smaller one.

Also how many amps is needed for this size of amp

[HotBluePlates]

If it were me, I'd drop 2 output tubes and use the 290-0-290v 15w PT.

[imaradiostar]

^ what he said.  Path of least resistance.

If the goal is really a higher powered amp why not try the bigger PT but use some different output tubes? An output transformer from a low voltage high current 4x EL84 stage should be happy with a wide array of other tubes. You could try a pair of almost any normal 6 volt output tube- 6l6, el34, etc.

Here is a thought- try a quad of EH 7591a's. They'll bias up somewhat like EL84's but only consume a touch more filament current. If the amp was good for 36 or so watts with the EL84's the 7591's with the plate voltage around 450 should easily do closer to 50 watts, assuming the PT can handle it.

You can always sub in a 5u4 to lower plate voltage give the amp a little more sag- depending on where your voltages end up this could be a lifesaver.

Jamie

[bnew63]

Thanks Guys
Can I use the same preamp and just go to 6V6 with the 380-0-380,or does that require a great deal of redesigning.I'd like to stay in the 30-40 watt range
I'm still new at this and am not looking for anything too complex at this point

The Hammond PT from the 15watt amp was an earlier build that I was not happy with so it may be able to handle a larger amp.

Whats the best way to create a dummy load to see if this PT can handle it a certain load?
Also can a choke be used to reduce B+ voltage.

Brian

[Tiny_Daddy]

I would consider the JJ 6V6S, rated at 500V plate. The 6V6S costs less than 7591 and looks about the same.

[bnew63]

I managed to get some info on the smaller hammond 290-0-290 PT
It came out of a hammond organ model# H-AO-29-13  or model M 111
It ran 1 BU4
         2 6V6
  and  8 various preamp tubes.

[imaradiostar]

I would consider the JJ 6V6S, rated at 500V plate. The 6V6S costs less than 7591 and looks about the same.

Good suggestion- I only recommended the 7591 because they'd do OK cathode biased because they would only require minimal grid bias and would make a ton of power in an EL84 hole. 6v6's will want to see bias and input levels more along the lines of a big bottle.

If you were to use JJ 6v6's you might consider using 4 of them. It's unlikely you'd need much in the way of preamp changes- 6v6's require a little more drive but I'd leave it as is first to see how it goes.

You could weigh and give the dimensions and I'm sure we could put a good guess to the power rating and appropriateness of each.

Were the listed voltages ones that you measured or ones that they're "supposed" to produce?

jamie

[Tiny_Daddy]

7591, that's true and I have used them more than 6V6S.

[bnew63]

290 was the measured voltage.