Harp amp ideas

[eddie25]

I know this subject has been done a little to death, but I am looking for some input on a harp amp idea I have (attachment included). Essentially a deluxe reverb normal channel with no NFB. I would tweak the values of the pre and tone stack for harp as I go. I'll also probably ad some sag resistors to the power supply.

I've never done a LTP PI fed by a 12ax7 plate, but I like the idea of a single preamp tube which this design would allow, would this work you think?

The reverb circuit isn't on the schematic, but it would either be the typical "rocket w/verb" type, as it is in that schematic (point 1 and 2). Or I would go with the single tube reverb around the 220K and ground the .1uF at the bottom of the PI. Again, the less tubes the better.

Not really sure how this would sound, but I really wanted about 20 watts, two 6v6, LTP phase inverter, SS rectifier, and reverb. I'd like it to get pretty nasty and loud with least amount of feedback.

I didn't draw the inpu on the schem, but you all get the idea.

Any thoughts?

[Firestorm]

I don't think the normal channel of a Deluxe Reverb will ever get "nasty and loud" even w/o feedback. The tone stack is just too lossy. (Well, actually not the one you've drawn; you've left off the ground connection, so it won't do anything at all ). If you really want to go with a single tube, you'll want to kick up the gain of both triodes and try a tone stack with a lower insertion loss. The James stack is a little better, but the tweed stacks are better still. Or maybe just set the floor frequency with coupling caps and adjust treble with a cut control across the PI.

[eddie25]

Thanks! Maybe I'll try a .1uF cap off the first triode plate straight to the grid of the second triode.

I was already considering a cut control at the PI, so I'm glad you mention that. I think a master might be nice as well, maybe some sort of post PI one.

I will attempt another schematic here soon.

Nasty may have been the wrong word... I should have said good and loud, and with some character, but I like these ideas a lot.

[David Root]

For harp you need larger coupling caps, for much mo' bass! Mo' bass be good for harp!. I suggest .22 on the PI output, .1 elsewhere. Also bypass caps could be bigger too. This may require larger gridstoppers, maybe not if your preamp voltages are low enough.

Tweed tonestack is a good idea, +1 on that.

Here's a modified tweed Bandmaster I recently completed, it may help. For example, for a single stage gain, a pentode is a good idea. I used a 5879 as a tonal alternative to 12AU7/5751, so still have the basic Fendery channel too. Note the Fendery channel uses parallel wired tubes (12AU7, 5751)

[KT66]

I agree that the DR normal channel might not get you where you want to be,
so since you want the reverb anyway, just do the trem channel with no trem and then you get the additional reverb recovery stage.

Another way to go which would knock the tube count down by 1 and keep the LTP idea is to do a Brown Deluxe ( 6G3) with a 1 tube reverb. That amp has a nice nasty cranked sound.

[eddie25]

Here's an updated schematic. No tone stack, and a cut control. I've gone back to the one tube reverb idea, around that 220k. That would keep it at 3 nine pin tubes. I forgot to change the one plate resistor on the PI back to 82K. I also kinda want to add a trim pot to balance the PI plate loads, with the hope that it could help with feedback. Then a type 2 PPI Master. I will definitely be experimenting with all the cap values. Any other input is welcome, it would be sweet to get a gigging harp amp outta this.