New amp design

[überfuzz]

Oh, I didn't see that you posted all nodes. Judging by the plot I'd say you got yourself a mighty find filter.

[Pdavis68]

Really? A 10V swing is okay filter-wise? Yeah, the later stages are much smaller. What's a reasonably swing on the 1st stage preamp, because I might want to reduce the C3 and C4 a bit (save myself some 47uFs).

[eschertron]

Really? A 10V swing is okay filter-wise? Yeah, the later stages are much smaller. What's a reasonably swing on the 1st stage preamp, because I might want to reduce the C3 and C4 a bit (save myself some 47uFs).

You don't show a load on C1, so the ripple there is invisible to the amp. C2 is connected to the first load (plates?) and is about 1 volt. Plenty good for a any amp, including single-ended. Probably overkill for a push-pull. And when I say overkill, I'm speaking as if you'd mass-market the design, since the bean counters will say cut back on the big e-caps

There are many - especially those familiar with vintage amps from the early days - who will say there is such a thing as too much filtering. Ignoring real current limits when using tube rectifiers, I don't see anything wrong with stiff filtering. The true test of the PSU is keeping nodes from interacting, and controlling the voltages at the stages where a particular HV is desired.

As mentioned before, I try to plot my voltages at an idle state, and at a full-power state, to see where the sag will take things. I also started this thread http://music-electronics-forum.com/t35398/ to get some ideas for what ripple to shoot for. Maybe this helps

[Pdavis68]

I feel stupid sometimes. Yeah, of course, you won't see the 9V on the amp. Silly me...

Thanks for the link to the other thread. Based on that, I think two 47uFs and two 10uFs should do the trick.

Mick's comment on that thread, "Ripple needs to be considered in conjunction with the level of amplification and as a percentage of the DC voltage level." makes all kinds of sense to me. I wasn't thinking of it like that, but that really clarified the issue for me.

[Pdavis68]

Got another question:

Because I want to be able to experiment with this amp a bit, is there any harm in having, say an 8 position barrier terminal block running to a couple of the tubes. For example, running all the lines that go to the power tube into one side of a barrier terminal block and then running wires from the tube socket to the barrier terminal block.

This would allow me to do a couple of things: 1 it would let me use two different tube socket sizes (with this amp, the power amp is a 9 pin but the 1st stage preamp is an octal). I may want to try octal power tubes or 9 pin preamp tubes. I could put in sockets for both and then just wire up whichever socket I want to use to the terminal strip. This seems cleaner than desoldering and resoldering. It also makes it easy to reconfigure a given socket for tubes with different pinouts...

I'm just not sure if this is inviting noise issues or what.

[eschertron]

Got another question:

Because I want to be able to experiment with this amp a bit, is there any harm in having, say an 8 position barrier terminal block running to a couple of the tubes. For example, running all the lines that go to the power tube into one side of a barrier terminal block and then running wires from the tube socket to the barrier terminal block.

My only comment is that for power tubes you can have up to 2x the B+ voltage on the plates (for a PP build) so be very careful when selecting the barrier blocks. Some that I've used spec 500vdc, which I thought was very generous. I have no problem using them with preamp stage tube circuits.

[Pdavis68]

Good point. That shouldn't be a problem since it's an SE amp. This is what I'm getting. Surely it can handle 320V.

I have a pretty good collection of sharp cutoff pentodes and I'd like to try a few of them in the 1st stage pre-amp. And I'll almost definitely want to try some different power tubes.