What circuit's best?

[Diverted]

Hi all,

A friend wants me to build him a 40W reverb amp. One channel, no tremolo. He wants it very clean, as little breakup as possible.
Would something like a Silverface pro reverb aa1069 be a good choice?
Also, if I'm going for cleaner sound what about solid state rectifying the AC and using a transformer with a little bit lower secondary to make up for the higher B+?
Thanks,

Ted

[SILVERGUN]

You should check out sluckey's TDR with 6L6:
http://sluckeyamps.com/tdr/tdr.htm

Scroll to the bottom of the page to see it in it's final form with 6L6s.
Yes, you can use a SS rectifier and shoot for 400-450V B+ and you will have a perfect amp for your friend.
Use a Bassman OT (Mercury Magnetics is not required) and don't worry too much about the details because sluckey has done all of the hard work for us and his documentation is exceptional.

[Diverted]

Thanks Silvergun. I'm checking it out now! He doesn't talk too much about the tone apart from it being a deluxe-ish build.
If that's the case (has anyone played this circuit?) I'm wondering if it mght end up breaking up on him more than he might want. I presume bumping the B+ up to the range you noted should clean it, but how much?

Thanks for the link!

[sluckey]

I would build the Hoffman AB763 One Channel. Just delete the trem circuit.

[SILVERGUN]

I would build the Hoffman AB763 One Channel. Just delete the trem circuit.

You did! 

Thanks Silvergun. I'm checking it out now! He doesn't talk too much about the tone apart from it being a deluxe-ish build.
If that's the case (has anyone played this circuit?) I'm wondering if it mght end up breaking up on him more than he might want. I presume bumping the B+ up to the range you noted should clean it, but how much?

Thanks for the link!

I had this laid out on my breadboard for a while and then built a version for someone else.
The version I built was so much fun to play that I didn't want to sell it. While it was on my breadboard I experimented with 6V6 and 6L6 and I agree with Sluckey that it just sounded 'better' with the 6L6s and a B+ up above 400VDC.

It won't break up much, but if it turns out to be too much for the player it will be easy to modify it to breakup less.

One mod that I liked was to put a switch on the first stage bypass cap so that if I was using humbuckers I would remove that cap from the first stage and in turn lower input sensitivity and reduce gain. If I'm using single coils I would switch the cap back in.

One other move I wouldn't hesitate to make would be to reduce the value of the dropping resistor between the screen supply and the PI supply which will raise the voltage on the PI and give you some increased headroom there.

If you build it (or anything else) we can help you get it where it needs to be. The AA1069 is not very much different by design, and neither are any of the blackface era designs. The AB763 label is used across a lot of amp names from the time period and everyone seems to agree that this was a great time for the Fender cleans that we all know and love.

[Willabe]

use a SS rectifier and shoot for 400-450V B+ and you will have a perfect amp for your friend.
Use a Bassman OT

Agree, keep the B+ up, black face Super Reverbs (BFSR/AB763) were ~470dcv on the 6L6's and ~270dcv on the 1st preamp tube plate!

A SS rectifier will help keep the B+ up, but it will also have a stiffer feel. For me, I really don't like that at all, to unforgiving, but some guys love it. 

The BFSR's had a little bit larger output transformer (OT) than Bassmans.

BFSR's, AB763 circuit, are pretty clean, cleaner than all the other 2x6L6 Fender BF amps. Mainly because of the higher B+ on the power tubes and the preamp tubes and the beefier OT.

If your friend installs higher wattage, higher Db speakers that will also help keep it cleaner.   
 

[Diverted]

Excellent! Thanks for the great responses. I think this sounds like a great way to go. This should be a fun build! Will post a thread once I start, and could definitely use some more great insight as I go through it.

Ted

[92Volts]

If I wanted a 40 watt amp that was as clean as possible... I'd build an 80 watt amp! 

Did weight, cost, or size constraints lead to the choice of 2x6L6s for the poweramp? The Twin Reverb seems to fit his needs (from what I've heard about them, never played one). The downsides being cost, weight, size.

Of course, the design is very similar to a Pro Reverb or Super Reverb (depending on year) with voltages, output tubes, and OPT being the main differences. So you're on the right track in terms of the circuit, but you could "tweak" for higher power.

[Diverted]

For the space he's going to be using it in, he wants about 40w or so, so two 6L6GCs it is. He also wants me to build a 2x12 cabinet.

[92Volts]

For the space he's going to be using it in, he wants about 40w or so, so two 6L6GCs it is. He also wants me to build a 2x12 cabinet.

If he wants it clean, as little breakup as possible, I'm not sure there's a "right" amount of power for a space... you can always turn down the volume if it's too much.

Just playing the devil's advocate, since overkill amps can be fun to design and build. Realistically, 40w is perceived as very close to 80w. Especially with a 2x12 cab like a Twin, this should be plenty loud (very close to a Twin)!

I'd be tempted to give the option to use 2x or 4x 6L6GC, depending on the cost and availability of transformers. Of course, if 80w really won't be used, it isn't worth spending anything on that "upgrade".

[Ed_Chambley]

Build a 64 bassman. Add reverb. No master. TMB plate driven stack. Build a single 12 cab and use a JBL or altec 417 or an EV. Get a  fat stack Output trans from Mercury Magnetics.


Build it in a blackface deluxe cab, except order the back with the ability to add half inch birch in 2 additional sections to partially close or fully  close. Whatever covering preferred provided it is fender black.


Use both sections of V1 as input with different bypass and bias to add complexity. You will have to tweak this while he plays to get it in his preferred wheelhouse clean tone. This will remove the HIFI tone from the speaker which will not break up.


Shoot for 450 plate voltes.  It will rise sometimes. Ss rectification is fine. If he likes some give or sag, increase the screen resistor values. This will make the amp more forgiving if that is preferred.


IMO, I would use a Gibson style bias vary tremolo. A lot of people don't like tremolo simply because they run the intensity too high. A low intensity like George Benson uses adds character and improves the hand vibrato since the intensity is low enough that amplitude modulation is not noticed.


When building for someone I always consider they will want to sell the amp at some point and a LOT of music has tremolo.


You can also increase the amount of negative feedback to tighten up the power section and not get sterile due to v1.


If it sounds like I have done this, you would be correct. The most difficult part of clean is most players consider clean as being dimensional. From the bassman circuit you will see an additional tube. This is the tremolo.


Use orange drop 225 at v1 coupling cap and 715 for the rest. No Carbon resistors. Metal film. Most prefer the silver mica caps in small values, I use either ceramic or the clear poly caps  that are no longer made, but still easy to get. If you use mica caps do not get cheap ones. Doug sells good ones and Cornell from Mouser are great. They do not like heat. Solder fast.


Henge the back panels to fold down so they stay with the cab. Got to hence and hook tight so no rattle. Easily done with thin rubber wetherstrip. The reason to close the back is 2 fold. One is a way to turn down and make it directional. The other is for even more solid bass.


Have the cab built with angled up baffle so no kickstands are needed. The player can hear it more and the highs go above the listeners ears so no ice pick since the highs will hit the players ears.


Of course use what knobs you want or is wanted. The black fender skirts which are numbered comes to mind.


This amp will punch your lights out, stay swirly clean. Or you can build an AB763 like Sluckeys amp but get a real chassis.


To me it is just easier to use a blackface style for a combo and the Deluxe chassis has plenty of room so it is easier even tho I prefer heads for myself.


Sometimes we have to define clean. A Fender amp is not that clean. A Standel is.


Mostly, have fun.

[shooter]

Sometimes we have to define clean.

+1
coming from the other side of the tracks with a HIFI type amp, I try real hard to make the input and output look exact, well except bigger at the out.  Musicians I've found have a totally different idea 

[plumcrazyfx]

Or do what I did, buy a MM RD50 for the clean. Then build the dirty.