Another G*S*G done...but with some questions

[pgeejr]

So I finally got around and finished my first GSG. Sounds really good, but when I used the 6B4G JAN NOS, they had a slight hum. Then when I switched to NOS 6C4C, it had no hum. The sound is very nice from both set of tubes. I am planning to get another set of JAN NOS 6B4G to test them out. So my question is on the 6C4C. I read from another thread that it takes a while for the tubes to become visible, is that true? Because when I had them in, the glow was so low that it was hardly noticeable, but I still had sound. The tubes were warm when I gently glided my hands over them, so I know they are working, or do I have a defective pair?

[Shannon Parks]

Congrats on your finished GSG! Tell me more about the NOS JAN tubes - maybe a pic? I seem to recall rewired bases (ie originally another tube) in the past for some JAN 6B4Gs, but my memory fails me.

Shannon

[pgeejr]

photo (1).jpg (164.14 KiB) Viewed 3464 times

well here is an image of the NOS JAN 6B4G. I think I know what you are talking about, how there is a NOS JAN 6B4G that was supposed to be pentode mode but rewired as triode. I do not know if there are it though, hopefully the image might give some clue.

[Shannon Parks]

Ah yes - that's a re-pinned 6AV5. It's a cheap tube that can easily trioded and has a nice sound but it isn't a true 6B4G. My SWAG is that the cathode is tied internally to one side or the other of the filament, while the hum nulling circuit in the GSG counts on the cathode to be center tapped like a normal 6B4G.

George talks about it:
http://www.tubelab.com/6AV5.htm

Shannon

[EWBrown]

I found from experience and experimenting, that a triode strapped 6AV5GA behaves more like a 300B than a 6B4G,
and modeling it on John Broskie's SE AmpCAD verifies this.

It does not have the 300B's full B+ and PD ratings, I keep the PD to 20 Watts or lower, and B+ 380V or lower.

The best and beefiest 6AV5GAs are the larger-bulbed Sylvanias, or DuMonts (which are re-branded Sylvanias).

Tube Lab George puts 6AV5GAs through the "torture" test:

http://www.tubelab.com/6AV5.htm

/ed B

[HighCtenor]

Hello Ed,

What are your impressions about the linearity of 6av5gas as compared to a Solvtec or other 300B? Sonically is the picture more lean in the middle like a 2a3 or more like the 300b? Your point to point looks delightfully free of unneeded stuff, congrats. Have you tried out using the 6FW5 for the 6av5ags. I believe they have the same pin configuration but are much higher rated: 550v/5500max to 770V/6500max. That could allow higher dissipation, but my interest is in how it would sound compared to the others.

[EWBrown]

My hearing isn't the of best, but I have "golden ear" friends who tell me that the 6AV5GA amp sounds very good, as good or even better than 6B4G or 2A3, with the higher plate voltage and current, and hefty PSU filter caps, it delivers a noticeably stronger bass response. I used 3K 10 Watt Transcendar OPTs.

6FW5 has different transconductance and internal plate resistance, and in triode strapped it acts like a "super" 6B4G, same basic operating characteristics, but with higher plate dissipation capability. 6GE5 and 6GV5 are internally same as 6FW5, but in duodecar (12 pin) compactron package. 6GV5 has a plate cap, 6GE5 does not.

For cheaper tube expenses, use 12AV5GAs, Dumont or Sylvania, they cost "chump change" compared o 6AV5GAs (which used to o for "chump change).

I use 12AT7 SRPP driver stages, so the filament can be fed with either 6.3 or 12.6VAC, as needed. 6DT8 and 12DT* are the "cheapskate" equivalents of 12AT7,
with filament connected to pins 4 and 5, no center tap on pin 9.

/ed B