5F6A-M Bassman Micro

[dorrisant]

Deleted this portion - Rob fixed it.

Love the idea. I have some parts on the way.

Tony

[robrob]

Yea, it's hard to read volts with the meter set for ohms.

[The Ballzz]

robrob,
Have you ever experimented, or seen anyone else experiment with the use of two 12AU7's or 12BH7's in push/pull to get the wattage to a point that is somewhere between that of a single 12BH7 and either a pair of 6V6 or EL84? I wonder at the tonal characteristics. What is the general difference of tonality and dynamic response of the power section between your "parallel" single ended Deluxe Micro and the push/pull Bassman Micro?

While I realize you have not yet built/finished the Bassman, I'm kind of assuming you have already proven the concept?
Thanks,
Gene

[robrob]

Have you ever experimented, or seen anyone else experiment with the use of two 12AU7's or 12BH7's in push/pull to get the wattage to a point that is somewhere between that of a single 12BH7 and either a pair of 6V6 or EL84? I wonder at the tonal characteristics. What is the general difference of tonality and dynamic response of the power section between your "parallel" single ended Deluxe Micro and the push/pull Bassman Micro?

Since the 12AU7 and 12BH7 are twin triodes you can do true push-pull with one tube. You could run two of them in a two parallel push-pull quad triode setup but I've never seen that done, probably because it would be easier to use two 6v6's and get pentode tone.

The main difference between triode and pentode power amps is the overdrive tone. The Deluxe Micro's clean tone sounds very much like a full sized Deluxe but there is a difference in overdrive tone. Having said that I really think most players will be very happy with the tone and dynamic response of the Deluxe, Champ and Bassman Micro's.

I haven't built the Bassman Micro prototype yet but the preamp is the 5F6A bright hi channel, the phase inverter is a standard Fender cathodyne and the power amp is a standard triode push-pull design. Using a pre-cathodyne phase inverter master volume makes the preamp to power amp interface pretty straightforward. The success of the Deluxe Micro leads me to believe very little tweaking will need to be done to the Bassman Micro's design.

[Thomas_H]

Hi,
nice design,

which impedance are you using for the OT primary?

Could you make some samples with the prototype?

Thomas

[robrob]

which impedance are you using for the OT primary?

Using a Hammond 125B output transformer I'm going 8 ohm speaker to secondary wires 2 and 4 for 22500 to 8.

[robrob]

We finally have our first clip of the Deluxe Micro (hopefully more to follow). Keep in mind it was recorded using an iPhone but it still sounds really good. This is from Deluxe Micro #3's builder:

https://www.youtube.com/watch?v=aD42Z26 ... e=youtu.be

[dorrisant]

Nice sounding clip! Tele? Details?

[robrob]

Tele neck pickup playing through a Tester 8 inch speaker in a completely open back cab.

[davidjon_99]

Rob,

Sent you the below in an email because I couldn't remember which forum I saw this post of yours. Since I found it, I thought I'd ask my questions here. Maybe, if the questions aren't too simplistic, others might also benefit from the answers.

I'm starting to order parts to build your Bassman Micro and have a couple of questions. This will be my third amp build and the first where I'm not building from a kit.

I'm going to use a tube rectifier, but have never used the EZ81. Is there any pro/con to using the EZ81 versus a 5Y3? The power transformer I plan to use has a 5v 2a tap for filament voltage for the 5Y3.

Also, what is your opinion about the sound difference in this amp when using the 4H choke versus the 1.5K 2W resistor?

And lastly, since I am going to use tube rectification I plan on using a higher voltage power transformer as you suggest. I like the Hammond style since it stands up rather than having to cut a large hole in the chassis for the lay down style of the ClassicTone. The transformer I'm thinking of using is the Hammond 270DX. It has 550v 104ma ct, 5v 2a and 6.3v 3a. It does not have a center tap on the 6.3v output so I'll have to add the 100 ohm resistors, but other than that I'm thinking it should work fine. Your thoughts?

Thanks and I really enjoy your site and your posts on the various forums. It really helps guys like me who are just getting started.

[robrob]

I'm going to use a tube rectifier, but have never used the EZ81. Is there any pro/con to using the EZ81 versus a 5Y3? The power transformer I plan to use has a 5v 2a tap for filament voltage for the 5Y3.

Also, what is your opinion about the sound difference in this amp when using the 4H choke versus the 1.5K 2W resistor?

And lastly, since I am going to use tube rectification I plan on using a higher voltage power transformer as you suggest. I like the Hammond style since it stands up rather than having to cut a large hole in the chassis for the lay down style of the ClassicTone. The transformer I'm thinking of using is the Hammond 270DX. It has 550v 104ma ct, 5v 2a and 6.3v 3a. It does not have a center tap on the 6.3v output so I'll have to add the 100 ohm resistors, but other than that I'm thinking it should work fine. Your thoughts?

Thanks and I really enjoy your site and your posts on the various forums. It really helps guys like me who are just getting started.

The EZ81 will give more authentic voltage sag because of it's low current rating. That's really the only benefit.

The choke is cheap so I recommend it for a more authentic Bassman tone. The choke will stiffen up the power supply a little and reduce hum compared to a resistor.

For EZ81 rectification I recommend the Hammond 270DX.

A 5Y3 rectifier probably won't drop as much voltage so I'd recommend a 500v 270CAX.

Feel free to ask anything during the build.

Rob

[martin manning]

Rob have you or anyone else built one of these yet?

[davidjon_99]

The EZ81 will give more authentic voltage sag because of it's low current rating. That's really the only benefit.

The choke is cheap so I recommend it for a more authentic Bassman tone. The choke will stiffen up the power supply a little and reduce hum compared to a resistor.

For EZ81 rectification I recommend the Hammond 270DX.

A 5Y3 rectifier probably won't drop as much voltage so I'd recommend a 500v 270CAX.

Feel free to ask anything during the build.

Rob

Thanks Rob. I think I'll go with the 5Y3 since I have a couple laying around and plenty of octal sockets. I think I'll also go with the choke vs the resistor.

I plan to order most of the parts tomorrow, but will have to wait until I finish the 5e3 kit I'm working on now. Hopefully I'll have most of it finished this weekend and I can clear my bench (aka kitchen counter) to start the Bassman micro. I'm really looking forward to this build and the end results.

[robrob]

Rob have you or anyone else built one of these yet?

No, not yet. I have all the parts on hand and need to drill turret board as my next step. I did get my 5F6A head amp completed and it sounds unbelievably sweet. The Bassman Micro is next but I'm pretty busy this time of year so not sure when I'll actually get it built, tested and tweaked.

[davidjon_99]

Ordered all the parts needed from AES and Mouser. I'm going with the 5Y3 rectifier and will use a choke rather than the resistor.

I'm using Visio to draw the hole patterns for the front, back and what will be the top of my amp chassis.

Not sure what I'll do for a face plate, but it'll be a while before I get to that.

I hope to finish the 5e3 I have in the works this weekend. Then hopefully I can start building this amp next weekend.