First build. Little Wing amp (B68M). Transformers

[nonost]

 Hi. I'm kind of new here. I've been building guitar pedals for years and now I want to build a small amp. I have some experience with the basics since I've build some starve plate guitar overdrives and, lately, a mini amp using a 12ax7 + 12au7 at 250v with a nixie power supply and a reverb transformer as the output transformer.

I want to build the Little Wing: https://el34world.com/Forum/index.php?topic=562.0

I have some questions regarding transformers.

I can get this PT (Hammond 291AEX): https://www.hammfg.com/files/parts/pdf/291AEX.pdf

I'm in Europe, so 230vac here. Can I wire this thing for 230vac primary? With BRN & BLK tied together,  I would use WHT & BLU as neutral & hot. Is it ok? If so, which one is neutral/hot?

It delivers 3A at 5v, so no problem for tube rectifiers. But it only puts 2250mA at 6.3v

In this amp there are 2 x 12ax7 and 2 x 6bm8:

300mA + 300mA + 780mA + 780mA = 2160mA

It's within specs, but really tight. Is that a problem? I'd like to use this trafo because it's lighter than others that I've found. The others are like 2kg and more, whereas the 291AEX is 1.3kg.

About the output transformer, I'd like to have both 8ohms & 16ohms outputs, so I found these:

A 18w one: https://www.tube-town.net/info/datenblaetter/transformatoren/tt-ma18-ot.pdf

And a 25w one: https://www.tube-town.net/info/datenblaetter/transformatoren/tt-5e3-ot.pdf

Both have a 8k primary, CT and cost about the same.

The schematic asks for a Deluxe Reverb OT, and next one it's a supposed replacement:

http://www.banzaimusic.com/25-Watt-Output-Transformer.html

but this one only has 8ohms output...

Which one do you think is a best choice?

Cheers!

[WiderGates]

Hello nonost,
should be no problem.

as alternative look at these PTs from Tube-Town:

TT Netztransformator 18Watt, universal
Prim: 0-120-230-240V @ 50/60 Hz
Sek. 1: 600 V C.T. @ 100 mA
Sek. 2: 6,3 V C.T. @ 3,2 A
Sek. 3: 0V / 5V (@2,5A / 6,3V @1,8A
Made in Europe.
Marshall 18 Watt Style
2,25 kg

Ringkern Netztrafo 80VA
Pri: 0-230 V (gelb)
Sec1: 260 - 0 - 260 V @ 0,1 A (rot - grün / weiß - blau)
Sec2: 3,15 - 0 - 3,15 V @ 3 A (orange - braun - lila)
Sec3: 5 V @ 2 A (schwarz)
freie Enden ca. 200 mm
d = 92 mm h = 45 mm
1,2 kg

But be aware you have to change the rectifier like in the LWR.sch file.
Even with the Hammond.


I would take the TT-MA18 & TT-T80 & 5Y3.
GZ34 is overkill for this little amp and you need 5V 3A.

[tubeswell]

It delivers 3A at 5v, so no problem for tube rectifiers. But it only puts 2250mA at 6.3v

In this amp there are 2 x 12ax7 and 2 x 6bm8:

300mA + 300mA + 780mA + 780mA = 2160mA

It's within specs, but really tight. Is that a problem?

If you’re going to run a Type 47 6V lamp, you’ll want the LED substitute. ( the real thing is 150mA or 300mA depending on who made it).

[tubenit]

I am certainly NOT trying to talk you out of building the Little Wing amp.  It's a fantastic amp! 

I will offer you something to consider along the same lines ................

This amp "the Minimalist" has some similar features but has a 5879 pentode in V1 and then uses a mosfet cathode follower which allows the V2b triode to be used as a recovery stage for an active FX loop.  I play this amp more than my other two & when I play out at an open mic locally, this is the one I bring.  I do have a layout for this.  (The Minimalist is the nickname for the HoSo56 6BM8 & FX amp)


  https://soundclick.com/share.cfm?id=14391017           (lead only)
  https://soundclick.com/share.cfm?id=13741608           (all guitar rhythm, fills and solo)

Just offering another thought and not pushing the idea at all to change your direction. Just thought you may have not known about this approach IF you're new to building amps.  You might consider at least studying this idea.

With respect, Tubenit

[tubenit]

Little Wing sound clips here:   jallenshaw's MP3 Website at MusicWebTown.com


It's truly a fantastic amp and the playing on these soundclips is excellent.


With respect,  Tubenit

[nonost]

Hi WiderGates. Both transformers look good. Although the first one is too heavy: 1kg more than the Hammond. The toroidal is light and cheap, it's great!

Oh, I didn't take into account the lamp! Thanks tubeswell. I guess could use a 8mm led: a diode and a resistor should do the trick. Thanks.

Regarding the choke, is it necessary? I've found a couple 4H that I think they could work:

https://www.hammfg.com/files/parts/pdf/194A.pdf

https://www.hammfg.com/files/parts/pdf/194B.pdf

I wish the smaller one would work.

Ey tubenit! Thanks for your recommendation. I've come across a lot of your of schematics and comments in these last days. I want to stick to the LW because its kind of based in the Fender Bassman and I think it's a good start. I can compare schematics and draw load lines and all that stuff, trying to figure it out how to adapt the big amp to this small amp.

I will definitely build the HoSo in the future ;)

[nonost]

Current draw from 6B8m screen is 8mA. So with the 50mA choke it's more than enough I think. Two 6B8M screens + three dual triodes would around 25mA.

I'm studying tubes and schemas and all that stuff, and the screen grid resistors look quite big at 4k7. Highest values I've seen out there are 2k2, and they are a bit rare. From 470r to 1k5 is the common range. Are there any reasons for that? Maybe these low power pentodes are different from the big ones in that regard?

Cheers!

[AmberB]

What Tubeswell said about the #47 lamp for the indicator light, you can buy an LED direct replacement for the #47 light bulb, fits right into the standard socket and works without having to add anything else.  Just for your info...