Disco Volante
Well-known member
Staying in b7g, the ECC91 might replace the 6C8G, seeing as the cathodes are directly connected..
Collins 26C Analysis
- Thread starter DaveP
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Yes you are right, it would do the job, but I was sticking to the same type, mu20 ra10k.
The replacement for the 6J7 was the single ended 6SJ7 and that has the same triode characteristics as the 6J5 and half of a 6SN7, the ECC82 comes into that class as well.
best
DaveP
Disco Volante
Well-known member
Point taken, I need to look at *all* the parameters when looking for subs. I guess in this case Ra is of particular interest since we're driving transformers. ECC82 has mu17, but higher Ra (47k if I read the spec sheet right).
This would be a fun and useable project to recreate! Following with great interest!
Cheers, V!
This would be a fun and useable project to recreate! Following with great interest!
Cheers, V!
The 6C8G tube is rather special, no-one tried to copy it and it looks like it was only made by RCA and TungSol. Each section has this characteristic:-
mu 36, ra 22.5k, gm 1600. It was introduced in 1937. It contains two independent triodes, albeit that one has the top electrode for its grid. Its heater current is the usual 0.3A whereas its closest cousins are the 6A6 and 6N7 which both draw 0.8A, the characteristics of these tubes are mu 35, ra 11k, gm 3200. My guess is that the internal dimensions are similar but the higher heater current increases emission and this increases the gm and reduces the ra. The 6N7 was initially used as the resistance tube in the Collins 26W, but it was replaced by the 5814A which is a special quality ECC82/12AU7.
The successor tube to the 6C8G was the 12AY7, but as the chart below shows, it does not have the same characteristic curve:-
I have plotted two examples of 6N7 and they are very close to each other and pretty close to the 6C8G as well. The 6J6, 6DT8 (ECC81) and 12AY7 are not close at all. I have some research to do on other possible replacements and will post that next.
best
DaveP
mu 36, ra 22.5k, gm 1600. It was introduced in 1937. It contains two independent triodes, albeit that one has the top electrode for its grid. Its heater current is the usual 0.3A whereas its closest cousins are the 6A6 and 6N7 which both draw 0.8A, the characteristics of these tubes are mu 35, ra 11k, gm 3200. My guess is that the internal dimensions are similar but the higher heater current increases emission and this increases the gm and reduces the ra. The 6N7 was initially used as the resistance tube in the Collins 26W, but it was replaced by the 5814A which is a special quality ECC82/12AU7.
The successor tube to the 6C8G was the 12AY7, but as the chart below shows, it does not have the same characteristic curve:-
I have plotted two examples of 6N7 and they are very close to each other and pretty close to the 6C8G as well. The 6J6, 6DT8 (ECC81) and 12AY7 are not close at all. I have some research to do on other possible replacements and will post that next.
best
DaveP
