Brown Eye-ish Amp in Princeton Reverb Chassis

[Ledzepp007]

In my ongoing attempt to design a higher-gain amp to put in a Princeton Reverb chassis, I came up with a variation on that "Dirty Princeton" theme I had posted earlier. This time, it's SS rectified with more filtering and higher gain. The preamp is based on the Friedman BE. Feel free to check out my schematic and make suggestions as you want. Thanks!

[PRR]

You probably do not want 470uFd on the cathode of that cathode-follower.

For any likely guitar input, stage 2 will be grossly overloaded and stage 3 will be OVER-OVER-LOADED before you get to the first gain knob.

[Ledzepp007]

Attached is the schematic that I was inspired by. Did I read it wrong?

[PRR]

That plan has more interstage attenuation than yours.

It still looks wicked.

Build it so you can change things to taste.

[MFowler]

No schematic but Ceriatone's AH50 is based off Friedman BE50 so there is a layout to review if you wish.

[Ledzepp007]

That plan has more interstage attenuation than yours.

It still looks wicked.

Build it so you can change things to taste.

So, I relooked at the original schematic, and it looks like the first triode is actually for a clean channel, so I’ve got one too many gain stages.

[jokn]

The first (input) triode is for both channels. The clean channel adds a tone stack and another triode before the effects loop and PI, while the dirty channel adds four more stages after the input stage. Looks to me that you have the same five-triode string on your plan. I’ve built a similar amp, but mine had the dirty channel gain pot after the channel switch relay, before the second stage.

[Ledzepp007]

Ahhhh. Yes, I see it now. Relays totally scramble my brain when it comes to schematics.

My initial schematic should be close then. It does seem weird not to have a gain pit after the first gain stage.

[SILVERGUN]

You probably do not want 470uFd on the cathode of that cathode-follower.

Attached is the schematic that I was inspired by. Did I read it wrong?

Yes. That cap is 500"P"f in the schematic....just there as a switchable treble dumper. If you don't make it switchable (as it appears in your version of the schematic) then you're just always dumping treble there. Wrong or right is subjective.

[SILVERGUN]

It does seem weird not to have a gain pit after the first gain stage.

Put one in. This is your chance. It's your design.

[purpletele]

No schematic but Ceriatone's AH50 is based off Friedman BE50 so there is a layout to review if you wish.

I wonder what AH stands for.  ceritone certainly has a sense of humor.

[Ledzepp007]

No schematic but Ceriatone's AH50 is based off Friedman BE50 so there is a layout to review if you wish.

I wonder what AH stands for.  ceritone certainly has a sense of humor.

Lol. Didn't even think about that.

I did some more "work." I updated my original schematic with proper attenuation and did a new layout. Those are attached.

I also attempted a two channel version (with a clean channel). I've never done a two channel amp, so it could be a dumpster fire.

[Ledzepp007]

Here is the two channel layout, with an attempt at channel switching. You may LOL.

Also attached is a photo with a proposed layout for the iron.

[Ledzepp007]

Whoops! Forgot to connect V2 P6. New layout attached.

[Ledzepp007]

Would there be too much voltage on the toggle switch?

[jokn]

I think the switch should be fine. Many are rated at 125 VAC and several amps. You seem to be missing a grid reference for V1b, btw.

[Ledzepp007]

Thanks. Would the switch the way I have it wired switch between the two channels?

[SILVERGUN]

Thanks. Would the switch the way I have it wired switch between the two channels?

Your schematic doesn't show a channel switch or 2 channels

[Ledzepp007]

Thanks. Would the switch the way I have it wired switch between the two channels?

Your schematic doesn't show a channel switch or 2 channels

I haven’t made a schematic for the second channel yet

[Ledzepp007]

Sorry to beat a dead horse, but here is a two channel schematic.

[Bantam]

Howdy...not sure what you're going for, but If it's a compact version of BE, Cameron, etc, my thoughts are the high gainers use big iron, high V. , Multiple ohm speaker taps, 4x12 cabs, etc.

Basically, dirty front, tight beefy end.   That said, I still look forward to hearing. Just thinking 6v6's, lower voltage, etc, already gives dirt, but who knows.    What are/is final expectations/use? Studio, grind in a coffee house (oops, sorry for that) heh!

[sluckey]

Concerning the channel switch... Your schematic does not match your layout. Need to move that .0022 and 1M to the plate of V1A on the schematic to match layout. Also, V1B must have a resistor from grid to ground. Other than that, switch should change channels. There should be no dc voltage on the switch.

[SILVERGUN]

You're still gonna want to get rid of that cap on V3 pin 8, or at least change the value and voltage rating.
As it is now, it's a firecracker.

[sluckey]

Yes, get rid of it. There should be no cap on the cathode of a cathode follower.

[Ledzepp007]

Howdy...not sure what you're going for, but If it's a compact version of BE, Cameron, etc, my thoughts are the high gainers use big iron, high V. , Multiple ohm speaker taps, 4x12 cabs, etc.

Basically, dirty front, tight beefy end.   That said, I still look forward to hearing. Just thinking 6v6's, lower voltage, etc, already gives dirt, but who knows.    What are/is final expectations/use? Studio, grind in a coffee house (oops, sorry for that) heh!

Low volume recording amp. I tried to up the tail resistor on the phase inverter to limit power tube distortion, but we shall see.

[Ledzepp007]

Yes, get rid of it. There should be no cap on the cathode of a cathode follower.

Forgive my being a dummy. I thought I saw a cathode bypass cap on the original schematic. I thought it was weird as well.

[SILVERGUN]

Yes, get rid of it. There should be no cap on the cathode of a cathode follower.

Forgive my being a dummy. I thought I saw a cathode bypass cap on the original schematic. I thought it was weird as well.

There is a cap in that position on the "inspired by" schematic you posted, it's just not intended to be a cathode bypass cap.

See reply #8

If you're gonna put it in, make sure it's high voltage handling

[sluckey]

Yes, get rid of it. There should be no cap on the cathode of a cathode follower.

Forgive my being a dummy. I thought I saw a cathode bypass cap on the original schematic. I thought it was weird as well.

There is a 500pF cap that will dump some high freq stuff if you throw the switch. But a 25µF will dump every bit of your guitar signal, leaving you with a quiet amp... until that low voltage cap explodes.   

[Ledzepp007]

Yes, get rid of it. There should be no cap on the cathode of a cathode follower.

Forgive my being a dummy. I thought I saw a cathode bypass cap on the original schematic. I thought it was weird as well.

There is a 500pF cap that will dump some high freq stuff if you throw the switch. But a 25µF will dump every bit of your guitar signal, leaving you with a quiet amp... until that low voltage cap explodes.   

LOL. I can see it now.

BTW, why would I need a resistor from grid to group on V1B?

[shooter]

why would I need a resistor from grid to group on V1B?

The grid and cathode referenced to ground and each other provide bias for the tube, with no reference on the grid it "floats in the wind", causing all manner of odd and weird issues that will drive you down many rabbit holes

[Ledzepp007]

Ahhhh. Thus the reason for R11 (10M ) in the inspired by schematic.

[shooter]

R11 (10M )

that might be a typo for 1M

[Ledzepp007]

OK. Here is another try. Take a gander if you wish.

[sluckey]

10M grid leak resistor for V1B is unbelievable.

[shooter]

is unbelievable.

I have a bumper sticker that says; "honesty is unbelievable " 

[sluckey]

Now that's believable! 

[jokn]

Observations on the schematic (I did not look at the layout yet, as I think it would be best to work out the kinks on the schematic first, and then do the layout): the coupling cap is on the wrong side of the switch, as pointed out by sluckey in post #21. As drawn it puts DC on the switch and/or the top of the clean ch. gain pot.

Were I building this, I’d probably swap the split anode load for a single 330k with the cap across it, since the signal is not being attenuated there, unlike in the “inspired by” schematic.

The voltage divider formed by the 1M series R and the 10M to ground I’d modify with smaller values, say 47k/470k. The 470k will suffice as grid leak, but the series 47k would be less noisy. How big the effect on noise of the series resistor in that position is could be debated, but I’d at least experiment. Also, you may find that you need to dump more than 1/10 of the signal there to keep things under control. YMMV .

And if any of the experts here think I’m way off base, please let me know... gently ;)

[PRR]

.

[Ledzepp007]

OK, OK, I'll move the coupling cap lol.

New schematic attached.

[sluckey]

'Bout time! 

[Ledzepp007]

Anything else look like it will blow up and kill me?

[sluckey]

Probably not lethal to you but certainly gonna kill those 6V6s. Look at the bias circuit.

[Ledzepp007]

Christ the 6V6 cathodes should be grounded and not attached to the bias voltage. Derp

[SILVERGUN]

And one other issue that I've narrowed down to this snip for you to find:

[SILVERGUN]

hint

[davidwpack]

Mustache is causing static electricity?

[shooter]

depression and ropes make strange bedfellows ?   

[davidwpack]

 

[mwelch55]

Looking at the schematic, I noticed that the power transformer is rated at 275-0-275 @ 100ma.  Is that enough current?  I thought 6V6 push-pull at that voltage would be a little higher, like 120ma.

Mike

[Ledzepp007]

Thanks for the feedback. New schem and layout attached. Some small changes. Decided to do a separate bias board and just reverted back to the original Princeton Reverb bias circuit.