Finally have my Splawn but an issue

[speedemon]

Fortunately, the 6550 is an easy sub with EL34/KT88. You might find the 6550 to be more bass-y than an EL34 or KT88.

To get back to your original problem. In owning a bunch of Marshalls, a Splawn and Randall RM100, and playing on a 5150II and I found a few things consistently,

1. the JJ preamp tube could cause muddy response in the V1, 2
2. The Celestion G12T and chinese pre tubes are very trebly in a high gain amp.
3. "NOS" pre tubes produce superior clarity and more "classic" midrange over other preamp tube types, esp in high gain amps. (what they did for the RM100 was astonishing, effect on the Splawn is subtle)
4. a rebranded tube can be anything.

I am certain if you called Splawn they would be happy to help you with your situation. Your problem sounds "complicated" so it makes sense to speak with Splawn, and have the amp guy check it out, before you buy anything.

Good luck!

[1960lespaul]

So I have 2 multi meters and the one I am more comfortable with I cant find so I try to figure out whats going on the Splawn. So I put my weber bias right on each tube. The outside tubes pull 40mA and the insides pull 39mA so that appeares to be a matched set to me. I get my plate voltage by tapping off on the third socket pin from the underside one of the tubes. Here is where my inexperience with my other multi metter comes in but I believe it is running 480 plate volts. A guy on Splawns site said his EL34s were 475 so I feel thats right.

Since it is a 120 watt amp I say 30 watts divided by 480 plate volts = 62 and I x that by 60% tube dissapation since Splawn's run better cold like 5150 which gives me a bias of 37.2 and thats what I do. It was @ 41.2 so this did tighten the amp up but I still feel something isn't right as it is still a little muddy. Even though the tubes test out as matched I am assuming they are just tired or possibly damaged.

Why damaged? Well with the head out of the chassis I can see that it looks like something was spilled and the Far right transformer brackets on one side appear to be bent like it was pryed up or as if the amp was dropped. I was also told this head was a 2010 and based on the condition not taken care of very well. And now it has developed some sort of microphonic feedback.

[rocknrolla]

Power tubes sound like there good. I'd bias it a little hotter. My EL34 Nitro is just right at 35 but I had 500 plate volts.
You need to try new preamp tubes.

[1960lespaul]

The previous owner said when he tested it he thought it came out to be 480 plate volts too. It originally came to me with Mesa preamp tubes in v1 and v2 and JJ in v3 and v4. I have swapped around so many times with some JJs I had I dont know which were mine or his.

[1960lespaul]

Sending the amp back to Scott to give it a clean bill of health and make a few changes. Upgrade to 2010 specs and retube to EL34s. I tried a KT88 nitro at guitar center today and I didn't like that one either. I think most of the clips I have heard online were QRs and EL34 Nitros. I may have a transformer issue so I would rather Scott be the one to look at it.