Draw your load line on the Audiomatica (real, measured) curves posted earlier for the VV30 (300B), and compare to the EL34.
The 300B Ra shifts only slowly, if your load line is 4 - 5x nominal ra, say 4000 or 5000 ohms.
With the EL34, you first have to decide what the ra actually is, since the grid has lost control once the anode voltage is only a short way into its positive swing.
The shifting ra in idhts, and the non-uniform spread of the triode curves are part of the same effect, and both will add distortion that is lower in a DHT.
I'll do the triangle wave test ASAP and will report the results. One question though; What should be the amplitude and frequency of the triangle wave?
Nominally I would suggest starting at 1000 Hz and 1/4 max power output. But changing the test figures around the typical ranges manually allows you to see how distortion varies with freq. and amplitude. Using the Op Amp integrator in addition gives a direct readout of gain change versus signal voltage input with good sensitivity.
https://www.cascadetubes.com/the-6336-set-amp/
The original manufacturer is at the address above. Read the detailed specifications at the address above.
Could we split discussion of the 6336 amp design out to a different thread?
+1 to that. By comparing some anode curves now I completely understand your point. It seems by separating the cathode and building it from a metal shield and making it closer to the grid, the tube manufacturers actually sacrificed linearity in favor of higher transconductance.
He is not a manufacturer and he is a diyer here by the id @Suncalc
Here is the full thread about that amp here:
Hi guys, Yesterday I've finished building the 6336 SET amp based on this website:
https://www.cascadetubes.com/the-6336-set-amp/
After that I did some testing on the amp I found some strange wiggling on 1W output frequency response graph at around 14 - 30 Hz:
What can cause this wiggling? BTW is it even something to get worried about?
Here is some pictures from square wave responses and also power vs. THD if they can help:
Thanks
https://www.cascadetubes.com/the-6336-set-amp/
After that I did some testing on the amp I found some strange wiggling on 1W output frequency response graph at around 14 - 30 Hz:
What can cause this wiggling? BTW is it even something to get worried about?
Here is some pictures from square wave responses and also power vs. THD if they can help:
Thanks
So shall we stop the conversation on the 6336 ??
OOPs!!!
The triangle wave input needs to be differentiated ( not integrated ) to see the Amplifier gain level as a square wave level (versus triangle wave voltage input ). Just reverse positions of the R and C around the Op. Amp. to get a differentiater circuit.
The triangle wave input needs to be differentiated ( not integrated ) to see the Amplifier gain level as a square wave level (versus triangle wave voltage input ). Just reverse positions of the R and C around the Op. Amp. to get a differentiater circuit.
This is KT120 Triode
The curves are not bad. less linear than 300B of course.
And the distance from each other seems to be also good.
For EL34 I have othre curves ( to translate) but less or more are similar.
Unfortunately my loved Sofia is in deep coma; I am working to get more life for it
Walter
The curves are not bad. less linear than 300B of course.
And the distance from each other seems to be also good.
For EL34 I have othre curves ( to translate) but less or more are similar.
Unfortunately my loved Sofia is in deep coma; I am working to get more life for it
Walter
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For 211 I traced something but at max 700 Vdc; I have to look on old pc
Walter
Walter
Thanks for sharing the plots.
Can the tester reach higher anode voltage? The full story can be seen at 2* V.idle - 800V (KT120) for preference.
It goes to 700 Vdc
But now is under heavy maintenance
My Sofia was the scecond or the third sold by Audiomatica; bought in 1996!
It is a long run!!!
Some issue are on boards that I am repairing.
Walter
Can the Sofia also measure G1 grid current at high anode voltage?
Another weakness of IDHTs - the G1 grid easily gets hot (it's too close to the heater, and smaller volume of the cathode concentrates the heat).
Hot grids can become emission sources; certainly not helpful.
If transient grid current can be measured, we could evaluate it.
I suppose I could just put a sniffer resistor in the grid circuit, and use a scope.
Another weakness of IDHTs - the G1 grid easily gets hot (it's too close to the heater, and smaller volume of the cathode concentrates the heat).
Hot grids can become emission sources; certainly not helpful.
If transient grid current can be measured, we could evaluate it.
I suppose I could just put a sniffer resistor in the grid circuit, and use a scope.
I think no, but I have to check.
Regarding the hot grids, honestly I haven't found this problem.
Soon I will re-test one circuit for different config of UL and Schade circuit and I will take a look, I have a good differential probe with very high Zin
Probably it can help with a resistor
Some days ago I test hardly one s.e. circuit; I have a beautiful KIKUSUI HT pwer supply where I can read the total current and it seem to be costant, just very little variation
Walter
Walter
I get the feeling that a lot of people tend to think more favorably of DHTs simply because they're often used in SE, while IDHTs are more commonly found in PP amps. But isn’t that kind of a misconception?
Also, once someone starts using a DHT SE amp, they often end up changing everything—like the volume at which they listen to music, the genres they prefer, and their choice of speakers—in order to bring out the full potential of the DHT and to compensate for its weaknesses.
So when they try out an IDHT PP amp in an environment that’s already been optimized for DHT, I feel like their belief that DHT is better just gets reinforced due to confirmation bias.
And honestly, this isn’t just about DHTs—this kind of tendency exists across the audio hobby in general - "Confirmation Bias".
Also, once someone starts using a DHT SE amp, they often end up changing everything—like the volume at which they listen to music, the genres they prefer, and their choice of speakers—in order to bring out the full potential of the DHT and to compensate for its weaknesses.
So when they try out an IDHT PP amp in an environment that’s already been optimized for DHT, I feel like their belief that DHT is better just gets reinforced due to confirmation bias.
And honestly, this isn’t just about DHTs—this kind of tendency exists across the audio hobby in general - "Confirmation Bias".
Definitely the tangent of curves changing more with voltage rise compared to 300B and 2A3.
If someone could draw a loadline on these and calculate tangent across the grid curves would be helpful too.
Here is a 21HB5A in Schade mode, off the old $1 list. Resistor chosen for best equal spacing.
And here is a 6HJ5 in UnSet mode:
and here is a $0.50 38HE7 just connected as triode:
And here is a 6HJ5 in UnSet mode:
and here is a $0.50 38HE7 just connected as triode:
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