5F6A Preamp w/ Little Wing Output?

[The New Steve H]

I want it to sound GOOD at low volume; that's the main thing.

I guess I can stick a switch on two of the cathodes and put a PPIMV in, too.

[The New Steve H]

Here's a new question.

The cathode follower on the 5F6A has a plate voltage of 325. On the Little Wing, it's 263. I'm trying to use the Bassman front end (all the way to the plates of the phase inverter), and that means the cathode follower is taken from the 5F6A, not the Little Wing.

Am I going to have sonic issues if I use the lower voltage? The PT on the Little Wing is spec'd for 630 V between the hot leads, and on the Bassman PT, it's 710.

I assume it's okay, since the same tube (12AX7) is used in both amps.

[10thTx]

The PT on the Little Wing is spec'd for 630 V between the hot leads, and on the Bassman PT, it's 710.

Look at DaGeezer's PT specs on his schematic. 260VAC @ 100ma

He has around 275v on the 6BM8 plates.

With respect, 10thtx

[The New Steve H]

The figure I got comes from his schematic.

[10thTx]

The PT on the Little Wing is spec'd for 630 V between the hot leads, and on the Bassman PT, it's 710.

The figure I got comes from his schematic.

Where on his schematic are you seeing that figure??

If I am misunderstanding something, please accept my apology?

Given the tube data for 6BM8 tubes, what are you planning to use for voltage on the 6BM8 plates?

http://tdsl.duncanamps.com/show.php?des=6BM8

With respect, 10thtx

[The New Steve H]

That's the schematic I just posted. Take a look at the cathode follower. V2. The plate voltage on the right triode is 263.

The PT I'm referring to is the one I bought. I think I made it look like Da Geezer was CALLING for this PT. That's not the case. I picked one I thought would work. He uses a Weber RVBPT, and I chose a Classictone.

Looking at it now, I'm wondering what I was thinking. I'm sure I looked at the Weber specs before finding a Classictone alternative, but the PT I chose is way off. Maybe I made a fatal mouse error when I ordered.

Don't apologize. We're not mud wrestling. I appreciate the help.

[The New Steve H]

It looks like I ordered a somewhat fancier PT than I needed. The schematic calls for 275 V across the primary, but I got a center-tapped PT that has 630 or 550, plus two sets of heater wires (the original PT only has the 6.3V wires).

Is there any reason I can't use half of the primary, to get the required 275? Seems easier than sending the transformer back.

Drawing of the original PT (Weber) attached.

Added: drawing of the PT (Classictone) I bought.

[John_P_WI]

What is 550 / 2?

The transformer that you have will work fine with a full wave rectifier. Since you have a center tap you will NOT use a bridge rectifier as would be required with the weber pictured.

[The New Steve H]

I got one more great question.

My OT is set up for 4-ohm and 8-ohm loads. I am planning to use 4 output tubes instead of the 2 in the schematic. I have been advised to use the 16-ohm tap for an 8-ohm speaker. Obviously, that will not work, when no 16-amp tap is present.

Is there any solution other than getting a second OT or an OT with lower impedance? I guess a second OT would be easy to kill when I only want 7 watts.

[John_P_WI]

I'll get flamed for this, but "one step" off impedance wise, will not be damaging, you may lose some bottom end though and assuming the power transformer is up to it, you will not have the full output power that a impedance matched output transformer would give....

[The New Steve H]

I'm rolling it around in my head. For the thirty bucks or so involved, I'm thinking I might as well go ahead and get two OTs.

I already have a layout; hoping it doesn't explode.

[10thTx]

A 275-0-275 with a 5Y3GT should get you about 305 volts. I think that should work just fine but check the 6BM8 specs to be sure.

I never worry about being "off" with OT impedence. I'll use 16 ohm instead of 8ohm. Or 8 ohm instead of 4ohm & not worry about it.

Kevin O'Connor has some good info about this on his LondonPower website.

With respect, 10thtx

[The New Steve H]

I think I'm going to end up spending about 80 bucks more than I should have, but it doesn't matter. If I have extra junk, I'll use it for something later.

[John_P_WI]

Build it first, leave the leads long on the OT. IF you don't like it then change it or buy a new OT. If it were me, I'd build it with what you have first....

[The New Steve H]

I am trying to figure out how to accommodate 4 output tubes. If I duplicate everything after the coupling caps, the board will be 32 turrets long, and the amp will be huge. The turret bit alone will be 16", so the board will be about 17 1/2".

Is there any reason I can't fork the control-grid leads so each coupling cap feeds the grids on two output tubes? If I can do that, I can get rid of a lot of stuff. I don't know offhand whether significant current leaks through the grids. I would assume that if the current is negligible, you could use one coupling to run more than one grid.

I guess I could save space by removing two of the inputs and putting in a switch that activates the "bright" sound. That would eliminate a bunch of the crap associated with the two channels. I was reluctant to do that, because people have said they like blending the channels.