Ultimate small home amplifier

[luthierwnc]

Hi Everyone.  After a few years off, I've been rebuilding some of my DIY (well, they are all DIY) amps to higher build standards than I did back in the day, mostly because I used donor chassis and adapted to the available layouts.  Now that I'm almost done, I realized they are almost all pretty loud and I don't get out enough to air them out.  A few will be given to friends or to a local music school that encourages youngsters to damage their parents' hearing but I got to thinking that I really don't have a 5-7 watt beastie for the house.  I do have a one- power-tube 7868 former Bogen PA done as a Champ but I lose clean at about 1 out of 10.
So ... I am casting about for a project that will give me a range of tones at low-wattage.  This will be a head, probably over a single 8-ohm 12 (since I have lots of 1x12's).  If possible I'll use transformers, boards and other parts in the bin but only if they are exactly what I need.  Chassis' I get laser-cut at a local CNC shop.

I am an experienced amp builder and know tubes well but have worse than fair skills with solid-state.  When I stopped last time I was doing Dumble variants.  For pure fun, I'd love to hear what you have done that might work.  It can be a louder than living-room too but should be clean and versatile without making the dog howl.  I figure 4-5-watts for fun.  Oddball tubes are fine.  Complex is fine. 

Thanks, for looking, Skip
PS  Tubenit, this is right up your alley!  sh

[turtle441]

I don't have a huge stable of amps, but I did a plexi SE conversion on a Valve Junior and it's super versatile with a lot of clean headroom.  (More so than I was expecting.)  I cheated and used the pcb from gapcb.com, but it'd be very easy to do that as a point-to-point build as well. I ended up using an upgraded OT as I felt the Valve Junior OT was limiting things a bit, but I'm super happy with the end product.   

Apparently, the extra headroom is related to the lack of a PI.  I've also seen a version (I've got the schematic floating around somewhere) that added in a "dummy PI" to get the amp into that medium-gain territory.  Depending on what you're looking for, that might not be a bad option either.  If I was doing a scratch build, that's probably the direction I would have gone.

[66Strat]

For a flexible platform, it would be hard to beat the AA764 Champ or Vibrochamp circuits, very satisfying clean sounds and very pedal friendly. For something a little dirtier, the 5F1 Champ, 5F2A Princeton, or Supro S6606 are good candidates. For something more eclectic, one of the Garnet circuits could be of interest. A BTO overdrive circuit in front of a Banshee could be lots of 5 watt fun.

[yorgle]

I recently built a valve jr with a trem for my living room amp and love it.  A 10" speaker and a 12AT7 in V1 yields "living room loud" clean all the way to 10.  With a 12AX7, it breaks at 4-5 but at 10 may upset the neighbors. 

[sluckey]

Take a look...

     http://sluckeyamps.com/index.htm

L'il Smokey or the RCA Victor conversion may interest you.

[1blueheron]

I'm a true novice but if this were my pursuit, I would likely experiment with the 12BH7.  I put one in the little SE amp I have to play around with and it sounds great compared to the 12Ax7 etc.

Blackstar used it as a single PP power tube in the HT5 I think so apparently it can be used as Pre, Power or in between.  Has a lot of history on the Hi-Fi side most notably probably McIntosh using it in the 225.  Trinity used it in the TriFly as self split push pull...  Interesting tube good for about 3 Watts per side or so. 

[luthierwnc]

That was fast!  Thanks everyone.  I've got several 6AQ5's in the box and fiddled with this design watching it rain today.  It is based on Alessandro amp pictures I ransacked from the net 20 years ago; very simple with high-end components.  I might sneak an FX loop in there for a Wet reverb pedal.  The resistor values for the screens and power tube grids are left blank to give me time to research the characteristics of that tube.  I've got some NOS 6SL7s too.  I won't make this out of platinum but I do have a few Riken resistors.  Generally I use Takman's these days. 

Slucky, love the Lil Smokey!  I poked through old projects I found pictures of two Ampeg V2 rebuilds in my checkered past.  Looks like you have a few of about the same weight.  sh

[shooter]

might want to look at the TS switch, while it's fun flipping them, usually they have purpose 

[luthierwnc]

oops.  it's fixed

[PRR]

> 7868 former Bogen PA done as a Champ but I lose clean at about 1 out of 10.

Why?? Might just be too much gain.

[tubenit]

I like my HoSo56 "the Minimalist" with just 4 tubes. I probably play it more then any of my other amps.
Original thread on this is here:  http://el34world.com/Forum/index.php?topic=23013.msg246671;topicseen#msg246671

sound clips here:   https://www.soundclick.com/music/songInfo.cfm?songid=13741593
                            https://www.soundclick.com/music/songInfo.cfm?songid=13741608

With respect, Tubenit

[Glenn]

Tubenit. What’s the purpose of the mosfet ion the schematic?
I’d like to build this.... thanks

[tubenit]

Using the mosfet  as a cathode follower (instead of V2b) allows me to use V2b as a return from an active FX loop.   Using a mosfet as a cathode follower has zero negative impact on tube tone from what I can tell.   

http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm

The cathode follower and tone stack act as a sorta pseudo FX send and V2b works well as an active FX return, IMO.

I think this is really a nice sounding amp.  I am amazed at how "big" the 6BM8 tubes sound & how good the bass is with that small tube.  I prefer them way over EL84's which I don't care for.  The amp has a really decent clean tone to it.  However, with the switches, one can get it to dial in some breakup also.

The idea of this amp was to have a small amp with a warm big tone and only 4 tubes.  This is likely to continue to prove being my favorite of the HoSo56 amps I've done based on DaGeezer great design.

With respect, Tubenit

[Glenn]

Thanks for all of that...

I have an Edcor PT that is 120 0 120 - if I make it a full wave bridge, this should get me in the mid 300 plate volts ish range.
Thanks again... sorry didn’t mean to derail this thread a bit

[tubenit]

120 X 1.4 = 168v on plates guesstimate

Did you mean to say 120-0-120 or 220-0-220?

With respect, Tubenit

[PRR]

> Did you mean to say

A 120-0-120VAC (240VAC CT) through a FWB (4 diodes) makes 336VDC.

That plan is not on your cheat sheet but is very common in non-tube-world.

[Glenn]

> Did you mean to say

A 120-0-120VAC (240VAC CT) through a FWB (4 diodes) makes 336VDC.

That plan is not on your cheat sheet but is very common in non-tube-world.

Yes what PRR said, sorry if I was confusing....
Thanks guys

[Jennings]

I've had a Torres Tiny Tone for about 12 years, and it's the amp I play almost exclusively at home.  It's only 1 watt, and has two 12AX7 preamp tubes coupled with a 6AQ5 power tube.  Solid state rectification.  I max the tone controls, and just use the volume.  It does some great clean tones, breakup tones, and full on 70s rock when dialled.  That's why I love it...there's plenty of home-use clean fun to be had before the overdrive kicks in.  I have mine in a combo with a 10" Jensen alnico speaker.  I'd advise at least taking a look and thinking about it.  I don't have a schematic though off hand, sadly.

[tubenit]

A 120-0-120VAC (240VAC CT) through a FWB (4 diodes) makes 336VDC.

I apologize then for providing incorrect information.  I understood a 120-0-120  to have a center tap as opposed to 240-240 (without a center tap)?    I thought the full wave bridge rectifier was for a PT without a center tap?  Maybe that is not a correct understanding?

Perhaps I am not reading and understanding the 120-0-120 correctly?  I have used all of the illustrations in Hoffman's Library of Info on rectifiers at one time or another.

With respect, Tubenit

[Glenn]

Hey Tubenit... no need to apologize. You give us great schematics and designs and are very helpful
I didn't make myself clear enough. My PT has a center tap, but I would just tape that off (or the PT would blow up eventually..lol)
and follow the Full wave diagram like the one you provided. I have done this on a 6aq5 plexi type amp I built awhile ago

alas I looked and I don't think I have a Mosfet. will have to wait, until I have enough need to order more stuff...
thanks again

[PRR]

> I understood a 120-0-120  to have a center tap as opposed to 240-240 (without a center tap)?    I thought the full wave bridge rectifier was for a PT without a center tap?  Maybe that is not a correct understanding?

Yes to all. You can have a CT and not use it. You can instead use it if you need a solid half-voltage supply. While Glenn may have no use for solid raw 160VDC, a bunch of big amps ran 600V on plates and 300V on screens using the CT of the 600V supply as a 300V source. And in another world they ground the CT to make +/-30V for sand-state loudspeaker amps.

When a rope has three ends it gets confusing.

[luthierwnc]

Thanks PRR, I may have overstated the rawk but I should probably reduce the gain.
Tubenit; thanks for the schematic.  I'm currently rebuilding my t-lite reverb in a purpose-built chassis.  It uses 7591s and is a great little amp.  I get the aluminum cut at a local laser-shop and they get it to very fine tolerances.  Cheers, sh