- You must be logged in to reply to this topic.
When looking at schematics for specific tubes there are letters beside the pins that indicate what the connection is. For example heaters are sometimes shown as h and other times as f. Cathodes seem to usually be k but there are some that I just can’t figure out.
In the attached images
Maybe it means metal but not sure.
In a 6J5 with no letters , the pin marked “m” is connected to the metal case. (check it with an ohmmeter if you have a metal 6J5. In some tubes S or IS is a connection to an internal shield.
A 6SQ7 has in effect, 3 plates. 2 act as diodes and are labelled PD1 and PD2. The other P is the plate for the triode and is labelled PT.
I can’t help you with “GT” other than to suggest it is leftover from something else.
In a tube with a triode and a pentode such as a 6AU8, the grid of the triode is labelled GT and the grids of the pentode as g#P.
There is no real requirement for it to be labelled GT as opposed to just G. in a single triode tube such as a 6SQ7.
Just my 2 cents. Perhaps there is a better reason out there .
John G. VO1 CAT
gt= grid triode
pd1=plate diode 1
pd2 =plate diode 2
pt= plate triode
hope this helps. Gord
Thanks to Gordon Dann, John Greenland and Sterling Spurrell for the advise on the pin designations. Much appreciated.
From the book Tube Lore:
G suffix means large , spherical tubular (ST) bulb
GT suffix means small tubular (T9) bulb
GT/G is a GT size bulb which is a replacement for either G or GT bulbs.
The is no definition for 6J5M, however M/G is listed as metal-glass construction.
Hope that helps.
Click on the different category headings to find out more. You can also change some of your preferences. Note that blocking some types of cookies may impact your experience on our websites and the services we are able to offer.
These cookies are strictly necessary to provide you with services available through our website and to use some of its features.
We provide you with a list of stored cookies on your computer in our domain so you can check what we stored. Due to security reasons we are not able to show or modify cookies from other domains. You can check these in your browser security settings.
We also use different external services like Google Webfonts, Google Maps, and external Video providers. Since these providers may collect personal data like your IP address we allow you to block them here. Please be aware that this might heavily reduce the functionality and appearance of our site. Changes will take effect once you reload the page.
Google Webfont Settings:
Google Map Settings:
Google reCaptcha Settings:
Vimeo and Youtube video embeds: