The sunn Forum

Looks like a reasonable substitute for my '68 Sentura I, but its sure hard to justify the price minimum size when all I need is enough to cover the grill panel of the front of the amp.

Dumb-O me decided to paint it black back in the day..

So you suppose he might sell smaller cut off pieces in that size ?

Here are two more pics for a clearer look...

https://ibb.co/cTG6ga

https://ibb.co/jKqMEv

So, with that in mind, here's my question...Is there a lower gain pre-amp tube that I can install to lower the output and make it break up sooner? Something (without using a power soak) to make her sing without turning up to 8? Yes, I use peddles but, the clean is also kind of brittle sounding and could use some softening up. Any suggestions? Thanks!
   

Sunn amps are ultralinear (UL) amps, and they also have a lot of negative feedback. That results in an amp that is very clean and detailed, until it breaks up. Once it breaks up, then the character of the overdrive/distortion is somewhat harsh. If you disconnect the negative feedback loop, then the gain of the amp will go up and it will distort at a lower volume, but the noise and hum go up also. It is usable this way however, but it will still be bloody loud and have a harsh character to the distortion.

The output power is determined by the power tubes used, the size and capabilities of the output transformer, and the B+ voltage that the tubes are seeing. The output transformer on a Sunn is large with a wide frequency response; the B+ voltage is on the high side; and the power tubes usually used in a Sunn (6550) are not a great tube for guitar. Your amp is using EL34's, which some of the Sunn's used, but I suspect that your Sunn might be meant for the 6550's given it's vintage. Could tell more from a pic, or identifying the numbers stamped on the end bells of the transformers, and also the B+ voltages, but it will function with those tubes without issue.  The high voltages and the circuit design are what result in the brittleness and harshness of the amp. That is one reason why I personally don't like any Sunn I've ever heard/played for guitar. I love them for bass however. Anyway, the point is that trying to sub in a preamp tube wont get you where you want to go. Adjusting the circuit might get you in the direction you want to go, but it might not also, and since you aren't a tech, you would spend a lot of money to find out. It is possible to add power scaling and a master volume to it and it might become more usable to you. Power scaling allows you to turn the output power down, and you adjust the volume and the master volume to get the same (mostly) loud tone at lower volumes. It works pretty well but it does require a master volume, and it does require some tweaking to get it to work the way you want it to, which again would cost you a fair amount of money to achieve. I would advise you to sell it and get an amp that is more suited to the sounds you want to achieve at the volumes you want to achieve them.

On another note, are you interested in selling your HiWatt?

Greg

I would think that the power amp section of the Sunn would not lend itself to making it sound like another amp, being an ultralinear amp. But why would you want to make it sound like another amp? Other amps already sound like other amps.

One thing you might think about, though, is converting the ultralinear power section to a triode power section. That would, of course, greatly reduce the power output, but low power amps are popular these days. It might sound really good when driven into distortion, and should be easily reversible.

I'm with Isaac....other amps already sound like other amps. You could leave the amp UL and disconnect the NFB and get some more grit out of the amp, but with the 6550/KT88 output section and general design of the amp, it generates a hard distortion that isn't particularly pleasant for a guitarist unless you are trying to be the doom and gloom bands that like that sound. There are many ways you could redesign the circuit or add tubes, etc., but at the end of the day with the high voltages, the choice of output tubes, and the large output transformer, the amp will have a certain type of sound that many guitarists just don't like, and you probably won't like, and then you'll end up trying to sell a modded amp that people won't like.

Greg

I'm with Ryan on this one.