sugestions for next build - super clean amp

[yalesmith]

I have finished a bunch of amps this past year and I build just to build and learn. I want to build a clean amp amp that works well with pedals. Any sugestions would be appreaciated. I built a rocket and that was way too dirty for what I am looking for. I also looked at a steel string singer and it is way too much power and I could not find a layout. Any suggestio will be awesome.

Thanks!

[Phil_S]

I think the keys to lots of clean headroom include the following:
Keep plate voltage on the preamp tubes reasonably high, in the 200's. This reduces distortion.
Use a split load (cathodyne, concertina) PI, as it has 0 gain and adds no distortion. Try using a 12AU7 or 6SN7 for the PI. These tubes are all about current as opposed to voltage and make a good pick for split load. 12AT7 is also a good choice.
Use big output iron and good quality.
Go for a pair of 6L6 tubes in PP at about 30-40W.
Try a low loss tonestack like the Roy Bean tone stack http://www.freewebs.com/balijukka/roybeanstack.htm

[Bear]

How loud do you need the clean? I had a Bandmaster Reverb that was clean as all get out until it wasn't. The volumes that it wasn't would probably be something above a small club unless for a loud band. That's about a 35-40 watt amp.

[Roe]

I'd consider something like a silverface twin

[yalesmith]

I was thinking about the band master or showman.

[Roe]

try showman then

[rdjones]

If clean with high headroom is what you want, don't be afraid of an Ultralinear design.
Look at the Sunn type UL circuit with Dynaco iron.
The Fender ULs can be tweaked a bit, even stock they are good pedal platforms.
That said, I think "works well with pedals" can span a wide range.
It's hard to go wrong with a 50W Blackface/Silverface Bassman.

rd

[M Fowler]

I built a clean head room amp for a Nashville guy using a Rocket preamp into 6L6s power section using MC Bassman iron and subtle reverb.

Trick for Rocket clean is toss the 220k plate for 100k to 120k. I kept the voltage lower to the preamp on this build. The guy loves the amp and wanted a clean amp which he says it is.

I want to build another one of these soon.

Mark

[selloutrr]

Roland jc-120. As clean as they get takes pedals like a champ.

Tube amps. Hiwatt or a bass amp not pushed will be lean and take pedals.

[brewdude]

I think the keys to lots of clean headroom include the following:
Keep plate voltage on the preamp tubes reasonably high, in the 200's. This reduces distortion.
Use a split load (cathodyne, concertina) PI, as it has 0 gain and adds no distortion. Try using a 12AU7 or 6SN7 for the PI. These tubes are all about current as opposed to voltage and make a good pick for split load. 12AT7 is also a good choice.
Use big output iron and good quality.
Go for a pair of 6L6 tubes in PP at about 30-40W.
Try a low loss tonestack like the Roy Bean tone stack http://www.freewebs.com/balijukka/roybeanstack.htm

I just built an amp with a 12AU7 cathodyne PI. It's a little unorthodox, in that I actually used both triodes in parallel for the PI. I used 6V6's so it's not super clean or super loud.

[gingertube]

brewdude,
Thanks for posting your design. A critism if you allow. Unless the VVR circuit includes a current limit function you are asking for reliablity problems with the standby switch.
See what I posted here:
https://tubeamparchive.com/viewtopic.php?t=17980

Standby switches are a BAD idea if using either cathode biased output tubes or a cathodyne splitter (as explained in that post). You have both!!!!

Also the 330K resistor for cathode bias I'm sure was intended to be 330R.

Cheers,
Ian

[brewdude]

gingertube, thanks for the info. I appreciate all the constructive criticism that is offered... uuhmm.... constructively.

You''re right, the cathode resistor is supposed to be 330R.

I am not really all that attached to the stand by switch. In fact, I generally don't even use it. It already existed on the chassis that I used as a donor for this project.

I believe that the VVR circuit does indeed include a current limiting feature--forgive me but I don't really understand how it works.

[Colossal]

gingertube, thanks for the info. I appreciate all the constructive criticism that is offered... uuhmm.... constructively.

You''re right, the cathode resistor is supposed to be 330R.

I am not really all that attached to the stand by switch. In fact, I generally don't even use it. It already existed on the chassis that I used as a donor for this project.

I believe that the VVR circuit does indeed include a current limiting feature--forgive me but I don't really understand how it works.

If you wanted to keep the switch (because the hole is already there...), it's a simple matter to put 100-220k (2-3W is more than enough) across it. This will serve as a soft start that will limit inrush current and let the amp warm up below audible levels. I don't bother with a standby either on cathode biased amps, but if I must have one, then I'll add the resistor. It works very well. Merlin Blencowe shows a novel method of limiting heater current concurrently with a high-current diode on one leg of the heater filament supply so the standby can be double-pole to include this feature.

The current limiting resistor on the VVR is usually a 5W cement type, typically on the order of 10-47R and is placed just after the mosfet, on the Source. The zener then is placed between the output of the resistor and the Gate. Ohm's Law regulates I, putting the brakes on the mosfet.

The resistor value is found by:

Imax - whatever current is desired as a max in the amp
Vgs (Gate to Source) - 4-5V typical of Mosfets suitable for VVR use
Vzener - 6-12V

Solving for current if you already know Rsource:
Imax = (Vgs - Vzener)/Rsource

Finding the resistor's value if you already know the current:
Rsource = (Vgs - Vzener)/Imax

[Darkbluemurder]

Check out Dr. Z's Stang Ray - one of the most beautiful clean tones I have ever experienced - very Brad Paisley like. I built one with 6V6 power tubes. Not very loud but what clean tone.

Couple this with a pair of KT88 tubes and a paraphase drive stage and you should have one loud clean tone monster.

Cheers Stephan

[M Fowler]

I have a Dr Z Stangray in red of course.

It is a great amp, very loud, clean and has that great EL84 chime matched with blue/gold open back 212 cab.

Doesn't get much cleaner.

Mark