Quote:
Originally Posted by IceClass /img/forum/go_quote.gif
Cool! Thanks.
Any ideas on how they sound?
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The 7N7 is essentially a 6SN7GT with the special locktal base. The 7N7 dates back to the 1940s. All 7N7s were made by Sylvania except the very rare Nation Union 7N7 .... which is also extremely good sounding. Unfortunately, NU went out of business around 1950 and there just are not many around. The earlier 7N7 sounds great but there are several variations.
The original tall bottle version is the equivalent of the wonderful sounding Sylvania VT-231 and clearly the best, IMO. The tube was changed to a short bottle type in the early 1950s and maintained a similar plate structure. This 2nd version was like the standard short bottle Sylvania 6SN7GT from the same era and this is another excellent tube. But, this version is hard to find; probably because this second version only existed in this form for a few years. I have far more luck finding the older tall bottle 7N7s .... probably because there was a lot of military stock.
The final version was the short bottle tringular plate 7N7. This version is equivalent to the later 6SN7GTA/B and is the most available = easiest to find. This triangular plate tube has different specs and can handle far higher plate voltages. But, the changes made to allow the tube handle more voltage seems to have compromised the sound quality. This tube doesnt have the treble extension or detail of the older 7N7s. Moreover, the bass is much more present in this tube. In some amps this tube sounds very good .... certainly better than any of the new production 6SN7s. But, this 7N7 version is not as universally good across the board as the older versions.
Lastly, the is another locktal tube you can use with this adapter called the 7AF7. This tube is listed as another 6SN7GT sub. The 7AF7 is once again a Sylvania made short bottle tube .... but this version has round plates. I find this tube very good sounding but not quite as good as the tall bottle 7N7. This tube is easy to find and generally runs around $10 each. The 7AF7 is a good choice if you cant find the tall bottle 7N7.
One final note .... notice the rust on the tubes metal base in the pic. The base and tube pins on these metal base tubes tend to corrode. So, you will often have to clean the tube pins or you will get noise from having a poor contact surface. A wire brush and some deoxit is what I use. Once cleaned these tubes are very quiet .... and these are tough tubes that last a long time. Dont worry about rust on the base itself unless you just want to improve the tubes appearance.
Here is the tall bottle 7N7 up close ....
Here is the 7N7 tall bottle in a PPX3 SLAM .... the center amp in the pic.
