Rod Beauvex
Look at the tiny bunny...
The Article said:
Is this some new definition of "pin out" I was not previously aware of? The 7199 and 6ana8/a are not the same.
7199 vs. 6GH8A
- Thread starter thevic24
- Start date
Is this some new definition of "pin out" I was not previously aware of? The 7199 and 6ana8/a are not the same.
"The 7199 and 6ana8/a are not the same."
I would say it is pretty disconcerting when a text that is supposed to be authoritative turns out to have gross mis-information in the first paragraph. If the first paragraph is wrong, how can one take the rest of the article seriously?
A quick check of the data sheets for the 7199 and the 6GH8A reveals that the triode in the 7199 is similar to a 12AU7 and the triode in the 6GH8A is similar to a 12AY7. The same situation arises with the 6U8. These triodes have very different amplification factors, plate resistances and transconductance compared to the 7199. The 6GH8A or 6U8 could be made to work, but are not ideal for the circuit: the circuit topology is optimized for the operating parameters of the 7199.
With my own ST 70 I replaced the original board with the Triode Electronics board that breaks the two functions of pentode voltage amp and triode phase inverter to two tubes. This is by far the cleanest, most practical, and best sounding solution and allows selecting a variety of pentodes and triodes that are better sounding than the 7199. Converting the ST70 circuit from a 7199 to a different pentode/triode tube requires too many compromises in practicality and sonics.
I would say it is pretty disconcerting when a text that is supposed to be authoritative turns out to have gross mis-information in the first paragraph. If the first paragraph is wrong, how can one take the rest of the article seriously?
A quick check of the data sheets for the 7199 and the 6GH8A reveals that the triode in the 7199 is similar to a 12AU7 and the triode in the 6GH8A is similar to a 12AY7. The same situation arises with the 6U8. These triodes have very different amplification factors, plate resistances and transconductance compared to the 7199. The 6GH8A or 6U8 could be made to work, but are not ideal for the circuit: the circuit topology is optimized for the operating parameters of the 7199.
With my own ST 70 I replaced the original board with the Triode Electronics board that breaks the two functions of pentode voltage amp and triode phase inverter to two tubes. This is by far the cleanest, most practical, and best sounding solution and allows selecting a variety of pentodes and triodes that are better sounding than the 7199. Converting the ST70 circuit from a 7199 to a different pentode/triode tube requires too many compromises in practicality and sonics.
Rod Beauvex
Look at the tiny bunny...
I want to quickly point out that I mean no offense to you, Don P.
Palustris: I assume the extra heater draw is not an issue?
Palustris: I assume the extra heater draw is not an issue?
none taken. i am not a tube expert by no means. i just did a search and found this info and put it up for other to discuss and i would learn from that.
in the heathkit AA-201 se amp the 7199 is used as a high gain preamp. not as a inverter. the 6GH8A works well as a replacment for the 7199 in that capacity
Don P
in the heathkit AA-201 se amp the 7199 is used as a high gain preamp. not as a inverter. the 6GH8A works well as a replacment for the 7199 in that capacity
Don P
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dspth
Member
7199 is used in Dynaco SCA35 also. The link below mention about changing the value of feedback resistor from 32K to 82K and to tack a 150pf capacitor across it, while replacing 7199 with 6GH8, to optimize performance.
http://classicvalve.ca/docs/SCA-35_mainboard_docs.pdf
The feedback resistor value with 7199 in socket in ST-70 is 1K. Tweaking this value may be required, while changing 7199 to 6GH8, to optimize performance.
http://classicvalve.ca/docs/SCA-35_mainboard_docs.pdf
The feedback resistor value with 7199 in socket in ST-70 is 1K. Tweaking this value may be required, while changing 7199 to 6GH8, to optimize performance.
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Destructor
Super Member
My 90's production ST70 Series 2 uses the 6gh8 tube.
Factseeker
New Member
Jcricket, Do you know about the magic Japanese made , unmarked 6GH8A mentioned by thevic24. I would like to know to get them or maybe a photo . Thanks, Factseeker
OK - seems like a topic that needs exploration - I think my Paco sa 40 could benefit from this - that is a Diagram ? Perhaps
Keeping on the original ST-70 topic I'll use a schematic for that, but your Paco is essentially the same circuit.
direct coupled meaning the plate of the pentode (pin 2) is directly connected to the grid of the triode (pin 9). The voltage at the pentode plate is the grid voltage, and thats what will set the current flow through the triode section. The screen resistor you may have seen mentioned in this case is the 1.5K resistor going to pin 3. Changing the value of that resistor will significantly affect the current flow through the pentode, and change the pentode plate voltage, which changes the triode stuff.
the voltages Tom was talking about is percent of voltage that would be measured from terminal 20 on this one. Just for ease of math, lets say its 200 volts. You'd want to see about 50 volts at the cathode (pin 8) of the triode, about 150 at the plate (pin 1). That would be 50v across the cathode resistor, 100 from plate to cathode, and another 50 across the plate resistor.
I think the supply on the ST-70 is closer to 300v but I don't feel like looking it up.
direct coupled meaning the plate of the pentode (pin 2) is directly connected to the grid of the triode (pin 9). The voltage at the pentode plate is the grid voltage, and thats what will set the current flow through the triode section. The screen resistor you may have seen mentioned in this case is the 1.5K resistor going to pin 3. Changing the value of that resistor will significantly affect the current flow through the pentode, and change the pentode plate voltage, which changes the triode stuff.
the voltages Tom was talking about is percent of voltage that would be measured from terminal 20 on this one. Just for ease of math, lets say its 200 volts. You'd want to see about 50 volts at the cathode (pin 8) of the triode, about 150 at the plate (pin 1). That would be 50v across the cathode resistor, 100 from plate to cathode, and another 50 across the plate resistor.
I think the supply on the ST-70 is closer to 300v but I don't feel like looking it up.
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Pio1980
AK Member
I think replacing the screen resistors with something like 1.2 meg may get the average driver splitter closer to the ideal ratio, allowing for variations.
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Possible, I've not had a 7199 thing that i converted and spent any time with to see what values made it happy. The single time i did was a temp adapter for use in an amp going back home to be loaded with good 7199 tubes. The set i got with it were duds and i used some adapters and 6u8 i had on hand to make it work properly enough for testing. I don't remember what the splitter voltage was only that i decided it was close enough