Re: 7189 = 7189a
Originally posted by MikE
7189A has screen connections on pins 6 & 9, whereas the EL84 and 7189 only have screen connections on pin 9. This is a consideration if one wishes to replace 7189A with EL84 or 7189, one might have to move screen connections to pin 9. A 7189 can always be substituted for an EL84. The other way around is a "NO-NO". The 7189 is rated for higher B+ voltage than the EL84. Regarding the 7189 and EL84, there are no electrical or physical difference between them.
MikE
EXCUSE ME... but I kinda think that is
All Wrong... now most tube experts think they know it all, but well, this is a technology from when when our parents were young, and all of the nuances might not be readily apparent 40 or 50 years later.. so here goes !~~!
First of all. as far as I know 6BQ5, 8BQ5, 10BQ5, and EL84, 7189, with pinout as type 9CV and the 7189A as pinout 9LE are all pretty much interchangeable, and perhaps are functionally identical. Its also possible that the "higher voltage" rated tubes were just
tested to a higher voltage level, but are not actually mechanically or electrically different ( a statement which maybe conflicts with some of what is quoted above ).
Now I'm not stating
for sure that all six tube types are identical, there could be true differences between 6BQ5 / 7189 / 7189A, but this possibility has never come up in any prior discussion that I can recall.
IF one looks carefully, among the RCA and Sylvania and other tube manuals from ancient days, one sees that these books show pin #6 on the various six tubes mentioned above, either as G2 or IC. Now to me, IC means
"Internal Connection" which could be considered a bit ambiguous. I'm afraid that "IC" might mean pin 6 is connected to a shield, or G2, or basically anything they wanted to connect it to, even nothing! So does it also mean the same thing as connected to G2 - but is just denoted differently by RCA on the 6BQ5, EL84, and 7189 as compared to Sylvania on the 7189A which shows pin 6 connected to G2 ? Well, I don't know. There are different pinouts 9CV and 9LE which does show a difference on pin 6.
So - has anyone taken a whole bunch of these aforementioned vintage and modern tubes and run meter tests between pin 6 and pin 9 ( and perhaps pin 6 and the others ) to get the true lowdown ???
I'm sure gonna pull some tubes from boxes and run some tests this weekend...
-Steve
:smsex: