Componenet Spacing

[zorro]

Is there any constraint on how close the tubes can be mounted together or how close the tubes can be to the transformers?

[R.G.]

Is there any constraint on how close the tubes can be mounted together or how close the tubes can be to the transformers?

None at all.

Of course, if you want them to survive prolonged operation, not pick up hum, and be replaceable when they wear out, you may want to look a little deeper.

Preamp tubes are relatively low power, so they can be placed fairly closesly. Some power tubes have a recommended minimum spacing for operation based on full power dissipation in natural convection. Putting a tube, especially a preamp tube, next to a transformer is asking for magnetic modulation of the electron flows in the tube, and you can hear that, especially if the transformer is line frequency.

[bob p]

one thing i've always wondered about is why some of the "great" Hifi amps like the Mac 70 and 270, and the Dyna Mk 3 place those 6550/KT88 so darned close together. The spec sheets recommend 4-inch spacing center to center, in addition to orienting certain pins on-axis to orient the hottest parts of the tubes away from one another.

[zorro]

So if I keep the power tubes spaced enough for cooling, which I still might use a small wisper fan, and have the transformers on the same side, I should be able to put the reverb and preamp tubes a little closer than the stock guitar amps do. It just seems to me that most guitar amps space their tubes far apart because they have the space created from all the potentiometers they have in a row.
Thanks for you reply
George

[stokes]

FWIW I put a pair of 6550's in an amp I built for one of my sons,they are almost touching as I was originally going to use 6L6GCs in it,much less than the recomended 4" center to center.He has used the amp three or more times a week for the last 2 years and the tubes are still fine.They may not last as long as they would if they were 4" apart,but 2 years and still going is good enough in a guitar amp.

[Chadwick]

1st stage

Depends on the amount of gain but keep the first stages, preamps away from the power transformer.

[Steve Conner]

As every Zen engineer knows, it's not the components that make an amp sound good, it's the spaces between them If you want an "open", "spacious" tone, you need to leave at least 3ft 6ins between each preamp tube. The resulting 15 foot long combo will sound at its best when played in a forest with nobody to hear it.

But seriously. The only problem I ever found with spacing tubes close is the capacitive coupling between plates of tube stages that are physically close, but electrically near opposite ends of the signal chain. I have one high-gain amp where the preamp tubes are very close to the power tubes. When the gain is cranked up full and the master volume advanced beyond about 10 o'clock, the whole thing goes into an ultrasonic squeal and starts to draw huge plate current. Putting a grounded shield over the first preamp tube cured it.

I'm about to try and squeeze two 6L6s, six 9-pin preamp tubes and a full size reverb tank into a 5E3 cabinet, so I obviously never learnt my lesson from the above ;-) Laying the tubes out in a line that corresponds with the signal path is the first no-brainer thing to do.