[mikeg]

While listening to an SACD of Vivaldi's "The Four Seasons", I felt that the sound was too "hard" when using Sylvania 6BL7GT output tubes, and a 5687 power tube (with adapter), and with the SDS voltage switch in the high votage setting. But,the sound was much improved when I substituted Sylvania VT-231 tubes as output tubes, in place of the 6BL7GT tubes, while retaining the high voltage setting. Listening was done with a late production R10 headphone, which is thought to have stronger bass than early production R10s.

Following this, I changed the voltage switch to the low voltage setting, while still using the VT-231 output tubes. This resulted in a noticeable loss in sound quality; i.e., the sound stage became more flat, and the resolution diminished.

Returning the voltage switch to the high voltage setting, I substituted a Ken Rad VT-231 tube in place of the 5687 tube, as the power tube. The result, once again, was a noticeable loss in sound quality.

Thus the best tube and voltage combination that I found was as follows: voltage selector in the high voltage setting; 5687 tube (with adapter) as power tube; and Sylvania VT-231 tubes as output tubes.

Finally, using these optimal tube and voltage settings, I briefly listened to a regular (i.e., Redbook) CD recording of J.N. Hummel's "Mandolin Concerto". The layering of sound of the various string sections of the orchestra was amazing, as well as the spaciousness of the sound stage. The resolution and clarity of everything was truly outstanding.

Thus, my little tube rolling experiment suggests that this may be the optimal tube and voltage combination for my Supra SDS/R10 setup.

 

[luvdunhill]

mikeg:

thanks for the report! Which 5687 output tubes were you using? Perhaps there are a few more varations worth trying? I'm really enjoying the steel-pin Sylvania GB-5687 tubes these days as well as the Raytheon 5687 square-getters!

 

[Jahn]

you could probably put christmas tree lightbulbs in that rig and it would still sound gorgeous. congrats on having such a nice rig to roll!

 

[mikeg]

It's a Tung-Sol 5687.

Quote:

Originally Posted by luvdunhill mikeg: thanks for the report! Which 5687 output tubes were you using? Perhaps there are a few more varations worth trying? I'm really enjoying the steel-pin Sylvania GB-5687 tubes these days as well as the Raytheon 5687 square-getters!

 

[KenW]

Thanks for the thoughts. My Supra XLR with the voltage control is due to ship Monday...I hope and this was a welcome post. Granted, it's not apples to apples here but in my MPX3 slam, I found my favorite combo was either a VT-231/7n7 tall bottle for the drive and 5687's in the output positions. Keep the thoughts coming.

 

[mikeg]

At the high voltage setting, the tubes glow a bit brighter than Christmas tree lights.

Quote:

Originally Posted by Jahn you could probably put christmas tree lightbulbs in that rig and it would still sound gorgeous. congrats on having such a nice rig to roll!

 

[mateo05]

Interesting...I thought the main point of the different tube type (6BL7) was the fact that it could handle the higher voltages. I would think doing this long-term to a 6SN7 would be rather harmful, but correct me if I'm wrong...

 

[PFKMan23]

the 6sn7GT can only handle 300V at the plats (the GTA/GTBs can handle up to 425V IIRC), so if you run it at a higher voltage (375, etc..) you're going to blow up the tube. That said the higher voltage does make it glow brighter...

 

[mikeg]

I inquired about this, and was told that it would only slightly reduce the life of the VT231 tubes. Since I only use them for a couple of hours a day, I'm not really concerned about it.

Quote:

Originally Posted by mateo05 Interesting...I thought the main point of the different tube type (6BL7) was the fact that it could handle the higher voltages. I would think doing this long-term to a 6SN7 would be rather harmful, but correct me if I'm wrong...

 

[mikeg]

So far the VT231s perform perfectly, and I've gotten Mikhail's blessing to use them in this manner. I thus continue to enjoy their lovely glow and lovely sound.

Quote:

Originally Posted by PFKMan23 the 6sn7GT can only handle 300V at the plats (the GTA/GTBs can handle up to 425V IIRC), so if you run it at a higher voltage (375, etc..) you're going to blow up the tube. That said the higher voltage does make it glow brighter...

 

[Hirsch]

The life of the tube is not determined by voltage alone, but by plate dissipation, which is a function of both voltage and current. While the 6SN7GT is rated at around 300v and the GTA and GTB variants are rated at 450 v, something like a MicroZOTL pushes 800 v up the plates and does not hurt the tubes. Although voltage is high, current is low, so everything balances out. You need high voltage AND high current to start blowing things up.

Mateo05,
The point of the 6BL7 is not that it can handle higher voltage, but rather that it can output higher voltage (or current). The tradeoff is that it simply does not have the microdetail of a great 6SN7. However, the sound is very good, and sometimes you just need the extra power.

PFKMan23,
Plate voltage does not make tubes glow (unless you really are about to blow them up). Filament voltage causes the tubes to glow. That's about 6.3 v for either the 6SN7 or 6BL7. Increasing the plate voltage will not normally affect the glow of the tubes.

 

[mikeg]

Hirsch - Thank you very much for the clarifications. I know virtually nothing about the technical aspects of tubes, but only enjoy their sound.

 

[Vic]

Quote:

Originally Posted by mikeg So far the VT231s perform perfectly, and I've gotten Mikhail's blessing to use them in this manner. I thus continue to enjoy their lovely glow and lovely sound.

Mike,
this is an extremely interesting post for me: so far in my Supra XLR I have only used 6bl7 in high voltage as output (while I have rolled several 6SN7 as gain). I was thinking 6SN7 could not take the high voltage.
Now a lot of new tube rolling possibility are open

 

[PFKMan23]

Quote:

Originally Posted by Hirsch PFKMan23, Plate voltage does not make tubes glow (unless you really are about to blow them up). Filament voltage causes the tubes to glow. That's about 6.3 v for either the 6SN7 or 6BL7. Increasing the plate voltage will not normally affect the glow of the tubes.

That is interesting becasue atleast when I have run some tubes at a higher voltage (and current) then the glow has been affected. Whether it's the plates or the filament I don't quite remember, but for me, one of the tell tail signs was in some cases the glow of the tube. And heh, while I would agree that the tube is a function of both voltage and current, with the current that the SPs run at I wouldn't risk running a 6sn7GT at a higher bias or voltage. IME if you're running the tube at a higher voltage like 425, you're also goigto be running at a higher bias as well. Of course, if the amp auto biases then... IMO running something like a 6sn7 GT at 400V is just running the tube alot harder than it needs to be run.

 

[mikeg]

I'm glad that I got the info out.

Quote:

Originally Posted by Vic Mike, this is an extremely interesting post for me: so far in my Supra XLR I have only used 6bl7 in high voltage as output (while I have rolled several 6SN7 as gain). I was thinking 6SN7 could not take the high voltage. Now a lot of new tube rolling possibility are open