SUNN SONIC 1 BASS head

[Coolio13]

I just purchased a SUNN SONIC 1 bass head and was hoping to get some info on tubes. It is rated at 40 Watts but SUNN usually rates their watts conservatively so I'm hoping that a change in tubes and re-biasing will had some head room (I am using this head and matching 15" cab for bass not guitar). It comes with stock EL34's. Can this head handle KT88's. I would appreciate any advice on Power and pre-amp tubes to give it more head room if possible.

Thanks for you time,
Ted

[loudthud]

Many people judge headroom by how far they can turn the volume control up before they hear distortion. That's not headroom, it's gain. Headroom is how loud it will get (watts) before you hear distortion. You can put KT88s in a Sonic 1 but the amp won't get appreciably louder than it will with fresh EL34s. You can change the 12AX7 to a 12AU7, 12AY7 or 12AT7 and you will have to turn the volume control up higher but the amp won't get any louder. If you want more headroom, sell the amp to someone on this board and get something with more watts.

[Coolio13]

ThanX. I have been a big fan of SUNN amps for years and my main bass amp (until the transformer blew) was a Sunn Sceptre. I'm not trying to make this amp into something that its not but I would like to get a bit more volume out of the amp before it starts breaking-up/farting out so I can play it out more. When I put KT88s in the Sceptre it made the head sound more subtle for bass so I was hoping I could get some suggestions from SUNN experts on this message board on Power Tubes and preamp tubes to put in it.

ThanX,
Ted

[Johnny]

IMO, the best preamp tube for bass is the JJ ECC83S. For EL34s I like Winged C, but you might also like JJ's there.

[Soundmasterg]

Some of the Sonic 1's (mostly the later ones) came with 6550/KT88's instead of the EL34's. I have one from 1970 that is identical to a 200S except for the name and came with 6550's. It also has the Schumacher transformers instead of the Dynacos and higher voltages.

You should be able to run 6550's or KT88's without any issues. The filament current is about the same. The OT may be smaller on your amp than the 6550/KT88 amps, in which case, at extreme volumes you may run the risk of vlowing the OT. It may also have a different impedance but it will work regardless. You won't get any more power, though the EL34's are a soft vacuum tube that tends to overdrive early, so going with 6550's or KT88's may give you a bit more useable headroom.

Greg

[Coolio13]

ThanX Greg! I think I'm gonna' put some JJ KT88s in it. Not the best tubes but they sounded great in my SEPTRE and can be got for decent price. Would you go with 88s or 6L6s? If so what brand do you like?

ThanX,
Ted

[pickinatit]

Some of the Sonic 1's (mostly the later ones) came with 6550/KT88's instead of the EL34's. I have one from 1970 that is identical to a 200S except for the name and came with 6550's. It also has the Schumacher transformers instead of the Dynacos and higher voltages.

You should be able to run 6550's or KT88's without any issues. The filament current is about the same. The OT may be smaller on your amp than the 6550/KT88 amps, in which case, at extreme volumes you may run the risk of vlowing the OT. It may also have a different impedance but it will work regardless. You won't get any more power, though the EL34's are a soft vacuum tube that tends to overdrive early, so going with 6550's or KT88's may give you a bit more useable headroom.

Greg

Greg,
I take it then that the amps with KT88's or 6550's are 60+ watts instead of 40 watts (EL34's) because of a different OP,  NOT because of the tubes ?   Am I reading that right ?
Michael

[Soundmasterg]

Ted, I like the JJ KT88's a lot in Sunns. The EH KT88's, and the Winged C KT88's are also very good.


Michael, the tubes play a part, but the limiting factor given that the plate voltage remains the same is usually the output transformer. My Sonic 1 actually came with EL34's but it had the larger output transformer in it so I knew it was meant for the 6550/KT88. I think the EL34 amps also had a lower plate voltage but I'd have to check the schematic or talk to Conrad to get a definitive answer on that score.

Greg

[Coolio13]

Greg,

I'm pretty sure my SUNN SONIC 1 is the early '67 model. Is there an easy way to tell if the output transformer can handle KT88s at loud volumes?

Thanks for your time,
Ted

[Soundmasterg]

Post a pic of the amp head or email me a picture and I could tell you for sure which one it is. PM me for my email address if you want.

Aside from that, I think I would try it and see. KT88's won't make a whole lot more power than EL34's in that circuit because the voltage isn't changing, and the output transformer's impedance ratio isn't changing, so the only difference is the tubes themselves. I would say you are probably ok.....if a Silvertone 1484 output transformer can handle it's operating environment then the Sunn transformer cna handle it with KT88's. The Silvertone 1484 uses two 6L6GC's with 475v on the plates and 340v on the screens and an output transformer the size of a champ, where it should be the size of a Bassman. Now those transformers do blow, but they also work for many years. The Sunn 40W OT is bigger proportionally so I don't think it will be a problem. Remember that these Sunns were basically Dynaco hi-fi copies with a different preamp, and hi-fi transformers are larger than they need to be for guitar amp duties. Bass amps benefit from hi-fi transformers but its not common to use them, and Sunn was the main one that did. So bottom line is that they are oversized comparably already so it should be fine.

Greg

[Isaac]

Coolio, consider that even if you were to get twice the power out, that would be only a 3dB difference. You might notice a difference, but you might not. Using a second speaker cabinet will get you at least that much, and probably more.

[Coolio13]

Thanx for all of the replies. I will try and post a pic sometime this week. The reason I was going to re-tube the amp in the first place was the gentleman that I purchased the amp from said it had been serviced a few years back and Sovtek tubes were installed and I'm not a big fan of Sovtek tubes. Tunes out that the Sovtek tubes were put into another amp that he had owned and I was stoked to find that the amp has late '60s Mullards in it. It also has a tube that I had not heard of so I looked it up and found it to be a International Servicemaster GZ34/5AR4 tube, Made in Japan (by Matsushita). It looks like I made out well on the tube front!

BTW. . . this was the 40WATT and not the 30 WATT model and it sounds stellar. It is louder than I though and has a sweet-spot when it is on a little above 6. The standard Bass and Treble are pretty versatile and can dial in a good variety of tones for such a simplistic configuration. I think the Treble and bass boost switches sound pretty bad. . . maybe someone can suggest a setting for these? I will be using this amp with a band tomorrow night and very much looking forward to it!

Ted

[Coolio13]

Here 'Tis my new toy!

Ted
www.myspace.com/breakupsdc

[Coolio13]

Another pic of my amp!

I'm really liking the amp. . . I think the only thing I would rather have right now if the 60watt version.

Ted