Hello to the Brain Trust,
I looked about the shop and saw many posts about TV sweep tubes. Today I bought several 6BQ6GTB’s to play with. I want to construct a SET headphone amplifier. I have a pair of 5K : 300 ohm 3 watt Edcor output transformers that work nice with 1625’s and EL34’s. (The setup.)
Here is the request! Does anyone have 6BQ6 triode plate curves to share?
Thank You
DT
I looked about the shop and saw many posts about TV sweep tubes. Today I bought several 6BQ6GTB’s to play with. I want to construct a SET headphone amplifier. I have a pair of 5K : 300 ohm 3 watt Edcor output transformers that work nice with 1625’s and EL34’s. (The setup.)
Here is the request! Does anyone have 6BQ6 triode plate curves to share?
Thank You
DT
Thank You Enzo and Geek,
The data sheets do help, the triode amplification factor is given. I do not know how to derive triode plate curves, rp, output impedance, and cathode reistor values from the pentode data. I am not oposed to trial and error. I will go eazy to avoid letting the smoke out.
The headphones are Sennheiser HD-600's. My guess is that 0.03 watts will blow the ears off. In terms of watts not much load on a tube that will idle arount 6 + watts. I want to test the idea that a relitivily light load will not drag down the bottom end of the load line. Not the typical way to load a Single End Triode?
Thanks
DT
The data sheets do help, the triode amplification factor is given. I do not know how to derive triode plate curves, rp, output impedance, and cathode reistor values from the pentode data. I am not oposed to trial and error. I will go eazy to avoid letting the smoke out.
The headphones are Sennheiser HD-600's. My guess is that 0.03 watts will blow the ears off. In terms of watts not much load on a tube that will idle arount 6 + watts. I want to test the idea that a relitivily light load will not drag down the bottom end of the load line. Not the typical way to load a Single End Triode?
Thanks
DT
The attached photo is what you want. The graph was figured by TINA
simulator based on Ayumi's Tube Model of 6BQ6(T). He generated
the 6BQ6(T) model from GE's datasheet.
Attachments
Hello,
This 6BQ6 is a interesting tube. Several fellow DIYers have praised its audio capabilities and noted that it can operate above it name plate horse power. Thank You to jacdhc for the plate curves. I knocked about more on google and also found this link to more data.
homepage2.nifty.com/the-tube/drawin/No148-6BQ6GTB.doc
I also found a reference that called the 6BQ6 a Remote Cutoff tube, also called a variable mu tube. The typical remote cutoff has it grid wound with varying pitch (uneven spacing between the grid wires). An example is the 6ES8. The plate curves really do stack up or have an extended knee. It looks like this tube, 6BQ6 needs to run with plate currents above the knee of the plate curves to avoid exaggerated nonlinear distortion. This might be why the reports that say this tube sounds good also have the tube operating above the manufacturer recommended 11 watts at idle.
Does anyone have thoughts to add?
DT
This 6BQ6 is a interesting tube. Several fellow DIYers have praised its audio capabilities and noted that it can operate above it name plate horse power. Thank You to jacdhc for the plate curves. I knocked about more on google and also found this link to more data.
homepage2.nifty.com/the-tube/drawin/No148-6BQ6GTB.doc
I also found a reference that called the 6BQ6 a Remote Cutoff tube, also called a variable mu tube. The typical remote cutoff has it grid wound with varying pitch (uneven spacing between the grid wires). An example is the 6ES8. The plate curves really do stack up or have an extended knee. It looks like this tube, 6BQ6 needs to run with plate currents above the knee of the plate curves to avoid exaggerated nonlinear distortion. This might be why the reports that say this tube sounds good also have the tube operating above the manufacturer recommended 11 watts at idle.
Does anyone have thoughts to add?
DT
Hello, The URL is in Mr.Mito's Web page. He is very expert in tubes and
tube circuitry.
I could not find "Remote Cutoff" in the datasheets in the Frank's Web.
Hello,
Mr. Mito’s web page has lots of data and technical information, it appears to be the product of much thoughtful work. Unfortunately I can read very little.
The other reference that I found that calls the 6BQ6 a remote Cutoff is the electronic Tube Manual I purchased from TubeCad.com.
I will open a 6BQ6GTB tube carefully with a hammer, take some photos and report back regarding the variable pitch, or not, grid winding.
DT
Mr. Mito’s web page has lots of data and technical information, it appears to be the product of much thoughtful work. Unfortunately I can read very little.
The other reference that I found that calls the 6BQ6 a remote Cutoff is the electronic Tube Manual I purchased from TubeCad.com.
I will open a 6BQ6GTB tube carefully with a hammer, take some photos and report back regarding the variable pitch, or not, grid winding.
DT
If you need some points from his Web, I can translate it into English.
Please limit the volume less than 10 lines or so.
Wrong tube. The 6BQ6 is a TV sweep (line output) tube. They must be linear in order for round things to appear round on the TV screen
The 6BQ7 is a dual triode TV tuner tube and indeed it has a remote cutoff characteristic so that the RF amplifiers gain could be controlled by the AGC circuits in the TV set. The 6BQ7 will make a good low level audio amp and can even be used at higher levels in an LTP configuration where the second harmonics cancel.
I have already been inside one (after I blew it up). The grids are equal spaced.
The 6BQ6 can be used in a SE amp but it isn't really happy there. You may be able to get enough power for your applications at reasonable bias currents, but the 6BQ6 and many sweep tubes exhibit better linearity at currents that violate the plate dissipation ratings. The first picture shows a pair of 6BQ6's operating a wee bit above the published ratings. They sounded nice but I bet that tube life can be measured in minutes!
The second picture shows a pair of 6BQ6's in a dark room happily cranking out about 60 watts in a screen driven P-P amp. These tubes will last forever at this level. Increasing the drive to obtain 90 watts did not cause plate glow but caused excessive screen grid dissipation. I then cranked it up more and at about 110 watts a large lighning bolt shot through the tube causing it and the screen drive mosfet to die. Hence the hammer autopsy. Death was caused by severe cathode stripping, and s few fried grid wires.
Attachments
Hello,
After looking at the 6BQ6GTB plate curves. The curves do look like they straighten out at higher currents. I drew a straight line tangent to the -15 volt grid/plate curve at the 60 ma and 122 volt point. I know this is not as much fun as cranking it up until it smokes. At this point the plate resistance is 665 ohms, mu is 4.8 and gm is 7.26 ma/Vg. I started this look into SET headphone amplifiers trying to sort out what effect varying output impedance has on the frequency response of HD600 300 ohm headphones. High output impedance = flabby bass? Damping Factor? Critical damping? I have not seen Thiele Small parameters on a set of headphones.
With the 6BQ6GTB rp at 665 ohms operating into the Edcor 5K : 300 ohm transformers the Zo calculates out to ~ 35 ohms.
First I am going to carefully break a tube with a 4 oz ball peen hammer and take a look inside. Never done that!
Then build the amplifier at the above operating point (just a starting point).
DT
All just for fun!
After looking at the 6BQ6GTB plate curves. The curves do look like they straighten out at higher currents. I drew a straight line tangent to the -15 volt grid/plate curve at the 60 ma and 122 volt point. I know this is not as much fun as cranking it up until it smokes. At this point the plate resistance is 665 ohms, mu is 4.8 and gm is 7.26 ma/Vg. I started this look into SET headphone amplifiers trying to sort out what effect varying output impedance has on the frequency response of HD600 300 ohm headphones. High output impedance = flabby bass? Damping Factor? Critical damping? I have not seen Thiele Small parameters on a set of headphones.
With the 6BQ6GTB rp at 665 ohms operating into the Edcor 5K : 300 ohm transformers the Zo calculates out to ~ 35 ohms.
First I am going to carefully break a tube with a 4 oz ball peen hammer and take a look inside. Never done that!
Then build the amplifier at the above operating point (just a starting point).
DT
All just for fun!
Hello,
I recieved a box full of mixed brand 6BQ6GTB tubes from the big brown UPS truck. Here are the results of the 4 OZ ball peen hammer test. The screen and grid are of equal and non tapered pitch. No varriable pitch as in the remote cutoff tubes. I will wire up a prototype amplifier after burning amp this weekend.
DT
All just for fun!
I recieved a box full of mixed brand 6BQ6GTB tubes from the big brown UPS truck. Here are the results of the 4 OZ ball peen hammer test. The screen and grid are of equal and non tapered pitch. No varriable pitch as in the remote cutoff tubes. I will wire up a prototype amplifier after burning amp this weekend.
DT
All just for fun!
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