New Tung Sol 6550 Testing

[steve]

Gents,

I have a new finding, but this time it involves the newly
manufactured Tung Sol matched octet of 6550 output tubes (TS for Tung Sol)

I must have 800 hours on the current quad output tubes.
I checked the idle current of each, and against the brand new TS quad
output tubes (10 hours?) today using an old chassis. The 800 hr TS
measured quite similar on average to the boxed new
tubes. And all 8 tubes measure ~4% of each other.

With such similarity between tubes I can only conclude not
much cathode deterioration.

Yet the side getters on the 800 tubes are ~75% used up. And I
ran 6.3 fil voltage for 75% of the time used. Plate/Cathode Voltage
~430 volts. RK = 620 ohms. I recently set the fil voltage to 5.8 volts.

I am really impressed with the longevity..

Measured Idle Current:    Used

A Tube                             52.4 ma
B                                      50.00
C                                      51.8
D                                      50.4
 
                                     New Tubes

A Tube                             51.04 ma.
B                                      50.56
C                                      50.88
D                                      51.28


cheers

steve

[Nick B]

Gents,

I have a new finding, but this time it involves the newly
manufactured Tung Sol matched octet of 6550 output tubes (TS for Tung Sol)

I must have 800 hours on the current quad output tubes.
I checked the idle current of each, and against the brand new TS quad
output tubes (10 hours?) today using an old chassis. The 800 hr TS
measured quite similar on average to the boxed new
tubes. And all 8 tubes measure ~4% of each other.

With such similarity between tubes I can only conclude not
much cathode deterioration.

Yet the side getters on the 800 tubes are ~75% used up. And I
ran 6.3 fil voltage for 75% of the time used. Plate/Cathode Voltage
~430 volts. RK = 620 ohms. I recently set the fil voltage to 5.8 volts.

I am really impressed with the longevity..

Measured Idle Current:    Used

A Tube                            52.4 ma
B                                      50.00
C                                      51.8
D                                      50.4
 
                                    New Tubes

A Tube                            51.04 ma.
B                                      50.56
C                                      50.88
D                                      51.28


cheers

steve

Thanks, Steve. Quite interesting. Any thoughts on why the cathode longevity? Materials...coatings on the metals... gasses within the glass? If I get a tube amp at some point, I would be more inclined to get current tubes rather than going the NOS route.

[steve]

Gents,

I have a new finding, but this time it involves the newly
manufactured Tung Sol matched octet of 6550 output tubes (TS for Tung Sol)

I must have 800 hours on the current quad output tubes.
I checked the idle current of each, and against the brand new TS quad
output tubes (10 hours?) today using an old chassis. The 800 hr TS
measured quite similar on average to the boxed new
tubes. And all 8 tubes measure ~4% of each other.

With such similarity between tubes I can only conclude not
much cathode deterioration.

Yet the side getters on the 800 tubes are ~75% used up. And I
ran 6.3 fil voltage for 75% of the time used. Plate/Cathode Voltage
~430 volts. RK = 620 ohms. I recently set the fil voltage to 5.8 volts.

I am really impressed with the longevity..

Measured Idle Current:    Used

A Tube                            52.4 ma
B                                      50.00
C                                      51.8
D                                      50.4
 
                                    New Tubes

A Tube                            51.04 ma.
B                                      50.56
C                                      50.88
D                                      51.28


cheers

steve

Thanks, Steve. Quite interesting. Any thoughts on why the cathode longevity? Materials...coatings on the metals... gasses within the glass? If I get a tube amp at some point, I would be more inclined to get current tubes rather than going the NOS route.

Good questions Nick. Since the side getters were being used up,

1. either residual gas or gas being produced over time from heat is removed.
(Wish all tubes had side getters as the top getter never seems to be heated
high enough to be that effective.)

2. A second possible reason is very high purity materials were used. Even
small impurities in the cathode sleeve or oxides could also poison the cathode.

3. Over heating the cathode oxides will increase evaporation. My lowering the
filament voltage to the JJ E88cc tubes dramatically increased the life.

4. Related to reason 3, the oxide thickness applied to the cathode sleeve could
be thinner, thus shorter life.

5. A mixture of oxides are often used. The ratio of the mixture may be different
than NOS due to cost or other factors.

I wish I could go more in depth but I do not have the expertise nor necessary equipment
to provide more information.

Hope this helps by listing possibilities.

cheers
steve
 

[Nick B]

Gents,

I have a new finding, but this time it involves the newly
manufactured Tung Sol matched octet of 6550 output tubes (TS for Tung Sol)

I must have 800 hours on the current quad output tubes.
I checked the idle current of each, and against the brand new TS quad
output tubes (10 hours?) today using an old chassis. The 800 hr TS
measured quite similar on average to the boxed new
tubes. And all 8 tubes measure ~4% of each other.

With such similarity between tubes I can only conclude not
much cathode deterioration.

Yet the side getters on the 800 tubes are ~75% used up. And I
ran 6.3 fil voltage for 75% of the time used. Plate/Cathode Voltage
~430 volts. RK = 620 ohms. I recently set the fil voltage to 5.8 volts.

I am really impressed with the longevity..

Measured Idle Current:    Used

A Tube                            52.4 ma
B                                      50.00
C                                      51.8
D                                      50.4
 
                                    New Tubes

A Tube                            51.04 ma.
B                                      50.56
C                                      50.88
D                                      51.28


cheers

steve

Thanks, Steve. Quite interesting. Any thoughts on why the cathode longevity? Materials...coatings on the metals... gasses within the glass? If I get a tube amp at some point, I would be more inclined to get current tubes rather than going the NOS route.

Good questions Nick. Since the side getters were being used up,

1. either residual gas or gas being produced over time from heat is removed.
(Wish all tubes had side getters as the top getter never seems to be heated
high enough to be that effective.)

2. A second possible reason is very high purity materials were used. Even
small impurities in the cathode sleeve or oxides could also poison the cathode.

3. Over heating the cathode oxides will increase evaporation. My lowering the
filament voltage to the JJ E88cc tubes dramatically increased the life.

4. Related to reason 3, the oxide thickness applied to the cathode sleeve could
be thinner, thus shorter life.

5. A mixture of oxides are often used. The ratio of the mixture may be different
than NOS due to cost or other factors.

I wish I could go more in depth but I do not have the expertise nor necessary equipment
to provide more information.

Hope this helps by listing possibilities.

cheers
steve
 

Thanks, Steve. That's quite interesting with enough technical information. There may be a limited revival in tubes with some companies like Western Electric, Apos Ray, JJ, EH etc. I realize that longevity of new tubes is an issue for some. I have not gotten into that as I've only had a tube preamp recently. Over 30 years ago I dabbled briefly with VAC Mono 90s and a Modjeski RM 9.