Tung Sol 6550's... they look like KT88's. Will they fit in a SVT Classic?

These days manufacturers are shoving tube structures into any shaped glass envelopes they have handy. You'll need to carefully measure the socket to socket spacing within your amplifier to see if they will physically fit. What you need to watch for is that if the shoulders of the tube bottle are too close to it's neighbour" hot spots" can develop leading to possible physical tube failure. Somewhere in the selected tube's specification should be a minimum safe operating distance to the next tube.

 

Another thing is that the KT88's and 6550's have different bias parameters. In general, even if the physical location isn't an issue, they won't sound optimal without re-biasing.

 

Well the Tung Sols he wants aren't KT-88's but 6550's in the large bottles. Looking at this pic of my Heritage out of the headbox makes me think they would fit but might be a shade tight.

 

I may be totally wrong, but I thought I remember the power tubes in the 70s SVTs were 6550s.

 

They were, except for the first year and a half where they used 6146b's. But the guy's looking at 6550's, not KT-88's.

 

Oh, I misread his post, then. I thought he was wanting to replace KT-88s with 6550s.

 

I never get tired of seeing that Jimmy

 

I've got Coke bottle JJ KT88's in my SVT-CL. Not an issue. And while we're on the subject, these are the best sounding output tubes I've ever had in this amp. I highly recommend them.

Edit: and the only time I tried Tung-Sol 6550's, two of the sextet went gassy immediately and one more within a few weeks and I had to get a whole new set of tubes. Maybe this was a fluke but I'll never buy current production Tung-Sol anything again.

 

I've had much the same experience: Tung-Sol reissue 6550s that went gassy, not right away, but two went within a year. One of them took out a screen resistor. Replaced them with JJ KT88s and agree, they sound great, and I now know the true meaning of the phrase "stupid loud!"

 

Me neither. Looks even cooler live

I've never tried the Tung Sol power tubes before, but I've had the JJ's in my Heritage since I got it in May 2013, and I'm completely happy with their performance. I cannot tell the sonic difference between it and my 69 SVT with GE 6146b's.

 

I'm confused. Can you put KT88s in an SVT CL?

 

With a rebiasing, yes.

 

+1 for JJ's I don't know what they did with quality control but I can't recommend these tubes enough I think they are the best current production tube out there.

 

Right, the bias lights are fine. Might get a little more pinpointed with going in there with a meter, but it's certainly close enough for rock and roll. But I've never done the switch so I can't tell you much about it firsthand. Reading comments, it seems that they are tighter and brighter and have slightly improved clean headroom and a different breakup characteristic.

 

Just try to make sure whatever power tubes you buy they have been screened for at least 24 hours at real amp plate volts....as in at least 400 to 450 plate volts.

The tubes current draw should be measured at full operating plate volts as well.......current draw can drift while burning in....but runaway current draw is something that can happen occasionally and will be caught during a 24 hour burn in....usually fairly quickly in a matter of 10 or so minutes.

Know your vendors test & screening methods!

 

Go with the JJ KT88'S

 

Unless you don't want tighter and brighter with different breakup characteristics (like me)

 

Here's a place that will actually test tubes at the required voltages in an SVT, I purchased a set of Sovtek 6550's and had no issues, they carry the Genalex Gold Lion KT88
tctubes.com vintage vacuum tubes