6973 VS 6CZ5 substitute

[Bobby Dipole]

The 6CZ5 is supposed to be a good substitute for the 6973 tube. I tried this substitution in an old AMI jukebox amplifier, and the 6CZ5s over heated and turned cherry red. Can any one spot the problem using them in this circuit? (The pin voltages are in the table.)




BTW, I bought a set of Electro-Harmonix 6973s, and they work fine. (Funny, they don't look anything like the RCA 6973s.)

Retired EE who never played with tubes before, that's how long SS has been out!

Bobby Dipole

[leadbelly]

Who told you it was a sub? Lower dissipation & voltage ratings, and different pinout. I can't see what you tried to attach.

[Bobby Dipole]

Originally Posted by Bobby Dipole

The 6CZ5 is supposed to be a good substitute for the 6973 tube. I tried this substitution in an old AMI jukebox amplifier, and the 6CZ5s over heated and turned cherry red. Can any one spot the problem using them in this circuit? (The pin voltages are in the table.)

BTW, I bought a set of Electro-Harmonix 6973s, and they work fine. (Funny, they don't look anything like the RCA 6973s.)

Bobby Dipole

Oh, I forgot to mention that I tied pins 1 & 8 together at the sockets so the 6CZ5 screen grid was taken care of.

Bobby Dipole

[45]

Originally Posted by leadbelly

Who told you it was a sub? Lower dissipation & voltage ratings, and different pinout. I can't see what you tried to attach.

For istance, many sellers try to sell 6CZ5's as substitutes to increase outrageously the selling price.....

45

[smoking-amp]

http://scottbecker.net/tube/sheets/137/6/6CZ5.pdf

http://scottbecker.net/tube/sheets/049/6/6973.pdf

I see the 6CZ5 is rated for 12 Watts for class A1 audio, and 10 Watts Vertical Sweep.

6973 audio rating 12 watts in class AB1, pin 8 is different in base diagram, although 6CZ5 shows an unspecified internal connection for pin 8. Curves virtually identical. Voltage ratings on the 6973 are higher (440V plate, 330V g2), but are specified as design maximum ratings, whereas the 6CZ5 are specified as design center ratings (350V, 285V). 6CZ5 gives a 2200V peak plate voltage rating, so I would guess that the 440V design max plate V of the 6973 can be met OK.

Sure do look like the same tube except possibly pin 8. Maybe you just have a defective tube, a corroded g1 pin maybe.

I suggest checking pin 8 on the 6CZ5 to see if it really does connect to g2 and to pin 1. Easy to check visually and also with an Ohm meter. Tying pins 1 and 8 together will only work if pin 8 really is connected to g2 (or nothing), otherwise "smoke and flames" likely.

[45]

Originally Posted by smoking-amp

so I would guess that the 440V design max plate V of the 6973 can be met OK.

Possibly you can do that and not only with these tubes. For example I can tell you that a 6V6GT can easily take up to 420V anode voltage. However it is "approximately possible".......that sooner or later the tube will fail and when it survives its life is shorter than average.

45

[smoking-amp]

45:
"However it is "approximately possible".......that sooner or later the tube will fail and when it survives its life is shorter than average."

Almost certainly likely, beyond any doubt!

Maybe the original poster could tell us what screen voltage it is actually running at?
I notice that 6CM6 has the same specs too, and the similar base pinout with NC on pin 8. What gives with all these 9 pin 6V6s? Maybe they just sorted them into bins: sloppy, good, excellent.
Let's see: 6CM6 $5, 6CZ5 $7, 6973 $35, Ah Hah!

[smoking-amp]

and 12AB5 for $3. Maybe had to do with how microphonic?

[45]

Originally Posted by smoking-amp

Let's see: 6CM6 $5, 6CZ5 $7, 6973 $35, Ah Hah!

Are these your prices or real prices? I have not been able to find 6cz5's for 7$...

45

[Tom Bavis]

Findatube.com: $5, $9, $21. AES: $6, $10, $50. Vacuumtubesinc: $5.50, $8, "Call". ESRC: $5, $7, $35.