5F6A Preamp w/ Little Wing Output?

[The New Steve H]

Now that the JTM45 saga is behind me, I want a new project.

I love the 7-watt 6BM8 "Little Wing" idea, but one thing disappoints me. It doesn't have the 5F6A Bassman front end. I like all those inputs, and I like having two channels.

Is there any reason I can't mix and match? I made up a BOM, basically putting the Bassman preamp parts together with the Little Wing OT, PT, and tubes. It looks like all the necessary voltages are there. I may also cram in a PPIMV.

Also, is there any hope this thing will have the Bassman's pick-sensitivity and nice low end? I'm hoping those characteristics have more to do with bypass caps and so on than raw power.

I have been trying to figure out why the Little Wing has such a simple front end, and the only answer I could come up with was that it was considered a practice amp, so some features were just eliminated. I don't want to build a cheap practice amp. I want to build a serious 56FA-based amp with less power.

[The New Steve H]

I should have posted this. I sort of assumed people were familiar with these amps.

[The New Steve H]

Now I'm wondering about setting it up with 4 output tubes so I can shut down two and get 7 watts.

[da Geezer]

I love the 7-watt 6BM8 "Little Wing" idea, but one thing disappoints me. It doesn't have the 5F6A Bassman front end.

The 5F6A Bassman is the very amp this was based on, so all you have to do is add back the inputs & un-parallel the V1 triodes, using them 1 each for each channel.

Now I'm wondering about setting it up with 4 output tubes so I can shut down two and get 7 watts.

sure you can

Also, is there any hope this thing will have the Bassman's pick-sensitivity and nice low end?
I have been trying to figure out why the Little Wing has such a simple front end, and the only answer I could come up with was that it was considered a practice amp, so some features were just eliminated. I don't want to build a cheap practice amp. I want to build a serious 56FA-based amp with less power.

Most folks consider the extra inputs & 2nd channel redundant (as do I) so they were eliminated. As I said, easy to add them back in.
The amp is intended as a recording & quiet(er) stage amp (think church worship groups or small clubs).
A Champ is a cheap practice amp, this is a bit more advanced than a Champ. An amp is also as cheap as you want to build it.
Low power amps are not known for big bottom end lows.....build the 2x or 4x6L6 version & use the volume control for less power.

Sound clips of the amp are posted over @ the Hoffman forum.

DG

[The New Steve H]

Hey, I didn't think the designer himself would respond! Thanks very much for the help. This is a neat amp. I would make it just the way you did, but I can't resist "improving" things.

I have a 5F6A I built, and I like the inputs and channels. I didn't know other people didn't like them.

When I said "cheap," I didn't mean low quality. Just that I thought you took out some features to make it less expensive.

[katopan]

Don't think you could go wrong adding back in the full Bassman front end. Would be a nice amp.

[da Geezer]

Don't think you could go wrong adding back in the full Bassman front end. Would be a nice amp.

Dittos to that

[The New Steve H]

If I go with 4 output tubes, what do I do about an OT? Do I use two in parallel?

It looks like the PT I chose will handle 20 watts, so I guess it's not an issue.

[The New Steve H]

Trying to figure out how to work this.

If I have a switch that shuts down half of the output tubes, I should also have a way of halving the capacitors, right? Won't I lose sag if I have 7-watt output tubes with a power supply for 14 watts?

It's starting to look like a PPIMV with 4 tubes is a better answer.

[The New Steve H]

I keep looking at this thing. Here is where I am.

I think I'll rig it up with 4 tubes. It looks like a single OT will do it, since the size I have to buy will handle anything from 5 to 15 watts. I am GUESSING a PPIMV will be simpler and work just as well as a switch which cuts two tubes out.

[The New Steve H]

Ordered the stuff. We'll see what happens!

[gingertube]

I assume you want to use 4 off 6BM8.
Choose output tranny for 4K Raa instead of 8K and 15Watt rated instead of 7 Watts. Or stick with the 8K and put an 8 Ohm speaker on the 16 Ohm tap. (Or 4 on an 8 tap etc.) to halve the reflected impedance.

That will leave you with 2 unused 6BM8 triode sections. They are very 12AT7, 12AY7 ish so use them in the preamp.

to take 2 tubes out of circuit either use cathode switching or you could switch the screen supplies to the 2nd pair instead.

Cheers,
Ian

[The New Steve H]

Thanks for the help. You posted this shortly AFTER I had ordered the hardware, so I'll have to see what I can do with it when it arrives.

The OT has 4-ohm and 8-ohm taps. No 16.

http://www.classictone.net/40-18045.pdf

[The New Steve H]

Still trying to decide whether a PPIMV or switching out two output tubes is the best way to get good sound at low volume.

Tips appreciated.

Almost all of the parts have arrived.

[Zippy]

Still trying to decide whether a PPIMV or switching out two output tubes is the best way to get good sound at low volume.

Tips appreciated.

Almost all of the parts have arrived.

You'll be able to achieve lower volumes with the PPIMV if that is your goal.

I'd do both - PPIMV and selectable output.