6550 Diameter

[you_never_know]

I'm punching a chassis for an amp that uses a pair of 6550's. What would you say is a safe diameter to assume for a 6550? I don't have any lying around at the moment. Thanks.

[defaced]

I don't have any either but the data sheet usually has max dimensions.

[you_never_know]

True, but they vary across manufacturers, according to bottle style. I was hoping to get a safe max diameter for just about anything I'd run into.

[crisisat22]

I measured a Svetlana winged C and got 1.9", I would guess that somewhere in the range of 2" is probably the average although I think some are definitely a bit wider.

If your real estate allows, space it for the wider KT88's and then you should be safe with any 6550?

[andrew_k]

~2.05"
That's for Winged =C= 6550 or the original Genelex KT88.
The KT88 datasheet recommends 4" between the center of each valve socket for adequate airflow. You won't need that much in a guitar amp running at ~70% dissipation and with vents behind and above the valves, but be aware that these things generate some heat and should not be crammed up against each other.

[Jag]

You want a hole for the tube or do you mean the socket into which the tube will be inserted? Or are you trying do decide how far apart the tubes will need to be, as Andrew refered to.

I assume you are wanting to punch holes for the socket. In that case, it will vary depending on the socket you use. The diameter of the socket should be listed as part of the spec for the socket you are using. Common socket hole diameters vary from 1 1/16" to 1 1/4" IME.

If you are mounting the tube on a card inside the chassis, then I'd probably go a little larger than the 2.05" Andrew mentioned. Likewise, I'd go with his rec's for spacing and air flow.

[you_never_know]

I'm looking for a safe distance between centers to accommodate different bottle styles.

4" between centers! Wow, I don't think there's an amp on the planet that adheres to that. My 6L6 amp has 2 3/8" between centers. I was thinking of bumping that to 2 3/4" or 3", at the most. Maybe I'll stick a fan in there if things get warm.

[defaced]

4" is just for KT-88s. I've never seen them spaced that far before either. On my build I'll be spacing them 3" on center.

[andrew_k]

Originally Posted by you_never_know

4" between centers! Wow, I don't think there's an amp on the planet that adheres to that.

Probably one made by GEC as a demonstration of KT88, but other than that you might just be right!

I spaced the centers at 3" on my KT88/6550 amp. So far there's been no indication of hot spots at the closest points between valves, including last summer's 40+ celsius days. That was using Winged C 6550 and EH KT88.

[Steve Conner]

When you're installing beam power tubes like 6550s, bear in mind that the hottest parts of the plate are at the seams where the two plate halves fit together. That's where the electron beams hit.

So if you're going to crowd them close together, rotate the tubes so that the seams point outwards rather than facing each other, this helps to radiate the heat away. I think the KT88 datasheet mentions something like this.

[you_never_know]

I saw orientation information in one of the data sheets. I assumed it was for alignment of the heaters so the magnetic interference from them would cancel each other out.