I've got to the power up stage of the Filmosound projector amp conversion? and seem to have an issue with the 6sj7.
I've wired it up according to the following:
(Note: the scheme is for a 6j7 which I have substituted with 6sj7 - the red numbers are the new pin numbers. The scheme seems to suggest pin 8,4,5 are connected which I believe is wrong. I connected the suppressor grid 3 to cathode 5.
Bringing the amp up on a Variac, I see the B+ raise normally and settle.
But I measure the full 275v (or whatever is dialled in) at the plate side of the 270k resistor.
The 6sj7 is metal can.
*Does pin 1 need to be grounded for this to work?
*Is the tube likely to be faulty?
Thanks!!
*This might need to be moved to Instrument amps.. oops
I've wired it up according to the following:
(Note: the scheme is for a 6j7 which I have substituted with 6sj7 - the red numbers are the new pin numbers. The scheme seems to suggest pin 8,4,5 are connected which I believe is wrong. I connected the suppressor grid 3 to cathode 5.
Bringing the amp up on a Variac, I see the B+ raise normally and settle.
But I measure the full 275v (or whatever is dialled in) at the plate side of the 270k resistor.
The 6sj7 is metal can.
*Does pin 1 need to be grounded for this to work?
*Is the tube likely to be faulty?
Thanks!!
*This might need to be moved to Instrument amps.. oops
Then the tube is not conducting.
How about your ACTUAL volts, not a scan of "factory" volts.
FWIW: I have seen a 6J7 with a cracked heater. It conducted fine cold, cut-out when hot. Because of the metal shell, it took way too long to figure this out.
I'm on a plane at the mo so the schematic excerpt was the best I could muster without the PC.
I measured 270v between pin 8 and ground (or whatever I set the Variac to be at D).
0v plate to cathode (8-5).
0v at pin 4.
0v at pin 5.
Does pin 1 need to be grounded?
The tube was a 'tested NOS' but that doesn't really mean anything if it isn't working. I don't have a tube tester or access to such a thing.
Is there a simple test I can do to check the tube out?
I measured 270v between pin 8 and ground (or whatever I set the Variac to be at D).
0v plate to cathode (8-5).
0v at pin 4.
0v at pin 5.
Does pin 1 need to be grounded?
The tube was a 'tested NOS' but that doesn't really mean anything if it isn't working. I don't have a tube tester or access to such a thing.
Is there a simple test I can do to check the tube out?
It can't smoke with full B+ on the plate. All the resistors are at dead ZERO volts and watts. The tube is fine for more than 300V (330V operating, >500V sitting there no-current). Anyway smoke can't get out of a metal bottle.
Be sure that G2 has some voltage on it. Be sure the heater is heating (not just the tube absorbing heat from other hot parts). Re-re-re-check your connections... a bad solder joint is the #1 most popular problem.
Be sure that G2 has some voltage on it. Be sure the heater is heating (not just the tube absorbing heat from other hot parts). Re-re-re-check your connections... a bad solder joint is the #1 most popular problem.
Pin 1 should be grounded. It is connected to the metal shell. With no connection at all enough stray electrons can find their way to the shell causing a voltage to build up. This can cause a shocking experience and noise, snaps or crackle in the speaker as it tries to find a discharge path.
Note: some amps that were never intended for metal tubes may use pin 1 for a tie point or other use. Care should be used when putting metal tubes into any amp that was not intended for them. We had a bunch of old Stromberg Carlson PA amps intended for 6L6GB's in high school electronics class. We also had hundreds of NIB RCA metal 6L6's, so naturally, they wound up in the amps.
One day while blasting the classroom with some 60's rock I made 3 simultaneous discoveries.
1) Stromberg had used pin 1 on one of the 4 6L6GB sockets as a tie point for the screen dropping resistor, pitting a couple hundred volts on the tube's shell.
2) The foil album cover on Stepenwolf's second album conducts electricity.
3) It flies like a Frisbee when the dumb blonde one accidentally touches it to a metal 6L6 while leaning against a grounded metal bench in the classroom.
The old (1956) GE data sheet for the 6SJ7 states that pin 1 is a shield on the glass version, and pin 1 is a shield and the metal shell. A note states that the capacitance data was taken with pin 1 connected to the cathode.
The "tube installation - shielding" section (page 58-59) of the 1956 RCA tube manual (RC18) states that "When metal tubes, and in particular the single ended types, are used, complete shielding of each tube is provided by the metal shell which is grounded through it's grounding pin as (at?) the socket terminal. The grounding connection should be short and sturdy."
The "tube installation - shielding" section (page 58-59) of the 1956 RCA tube manual (RC18) states that "When metal tubes, and in particular the single ended types, are used, complete shielding of each tube is provided by the metal shell which is grounded through it's grounding pin as (at?) the socket terminal. The grounding connection should be short and sturdy."
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