I mostly leave it on UL.
But, when it's late in the evening I sometimes throw it into triode mode, which about halves the power and sounds nicer during those times.
I posted my thoughts and conclusions on post #1290 on the previous page. I tried to tag you but misspellt your handle, sorry. Have you seen my pictures in #1291?
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Just to reiterate, these are the OPTs I installed.
They're specced at 3K5,10W, single-ended with a screentap and 8ohm secondary with 4 ohm tap. I measured the DC resistance to be 100 ohms more than the stock OPTs but I can't remember the exact value.
They can be attached to the chassis without having to drill additional holes and with the M4 bolts used by the stock OPTs - just get M4 nuts. There's a definite improvement in bass response if not overall power. On the test bench, my scope showed no low frequency distortion at 30mhz!
And they're not expensive at all!
I highly recommend!
￡14.93 10%OFF | 10w Single-ended 6P6P EL34 FU50 FU7 tube amp output audio transformers 3.5k output of 0-4-8 Ohm 1pcs
10w Single ended 6P6P EL34 FU50 FU7 tube amp output audio transformers 3.5k output of 0 4 8 Ohm 1pcs|tube amp|audio ampel34 amp - AliExpress
They're specced at 3K5,10W, single-ended with a screentap and 8ohm secondary with 4 ohm tap. I measured the DC resistance to be 100 ohms more than the stock OPTs but I can't remember the exact value.
They can be attached to the chassis without having to drill additional holes and with the M4 bolts used by the stock OPTs - just get M4 nuts. There's a definite improvement in bass response if not overall power. On the test bench, my scope showed no low frequency distortion at 30mhz!
And they're not expensive at all!
I highly recommend!
￡14.93 10%OFF | 10w Single-ended 6P6P EL34 FU50 FU7 tube amp output audio transformers 3.5k output of 0-4-8 Ohm 1pcs
10w Single ended 6P6P EL34 FU50 FU7 tube amp output audio transformers 3.5k output of 0 4 8 Ohm 1pcs|tube amp|audio ampel34 amp - AliExpress
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It's a connection per channel, in my case from the 6CA7 back to the 6SL7.
It's been mentioned once before in this thread and I've read about it in varous places.
https://www.diyaudio.com/forums/tubes-valves/268969-boyuu-el34-a9-tube-amp-116.html#post6263328
I like the way it sounds on my setup. Seems to bring the bass up a bit and opens up the sound in general.
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Ah, that!
Yes I have that too - negative feedback.
I'm using 1 Meg resistors, though.
The reason I installed then was because I added bypass caps to my 6SL7GT cathodes which nulled the NFB they previously had.
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Sorry - strange question. If I used a different Triode/Pentode switch per channel I could see how the different channels sounded. Is there an issue with doing this? Does this introduce problems through the power supply?
Thanks
Thanks
You could do, sure.
The way I describe how triode mode sounds is... well, it sounds more vintage, like an old tube stereo.
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It already sounds like an old bass valve amp I had, so cant wait to hear how much older the triode setting sounds. And you said earlier that it was quieter in triode setting, but I am only ever at 3 on the volume anyway so hopefully it should still be fine.
And i was trying to find a switch that would work with existing holes in the chassis. Do you think that two 5A 125V / 2A 250V switches would be up to the job assuming I allow plenty of time to discharge before switching etc etc?
Thanks for all your help in this.
Well, triode mode would make it sound older still! Haha.
From what I understand, triodes amplify the mid range frequencies most efficiently and roll off both the lower and higher ends. This is what gives them their vintage/warm sound.
Pentodes strapped in UL flatten the frequency response and so raises the fidelity.
But during quiet evenings on low volumes triode mode just sounds sweeter/warmer to my non-golden ears, similar to my dad's old Blaupunkt console stereo..
Regarding the switches, depends on where you want to install them. I used one of the holes for the hollow aluminium bolts that hold the sub chassis. I had to enlarge the hole for the switch to fit and it now doubles as one of the fixing bolts.
Personally, I don't see the merit of installing a switch for either channel - it plays with my OCD..
But if you do, then go for it.
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Tubby23,
Generalization:
Without Global Negative Feedback:
I. Triode mode has the highest damping factor.
The frequency response to the loudspeaker, tends to be Less dependent on the variations of loudspeaker impedance versus frequency.
II. Pentode mode has the lowest damping factor.
The frequency response to the loudspeaker, tends to be More dependent on the variations of loudspeaker impedance versus frequency.
A. It will raise the sound level of the bass frequencies at the bass resonance(s):
1. For a closed box/acoustic suspension, and for an open box, there is 1 bass resonance.
2. For a bass reflex/tuned port, there are 2 bass resonances. And between the 2 bass resonances, there will be a sound amplitude "suckout" of those bass frequencies.
B. At the crossover frequency of a typical 2 way loudspeaker, the impedance is relatively high, so the sound level of the mid frequencies will be increased there.
C. High frequency
1. At higher frequencies, if the loudspeaker impedance is high, the sound level will be increased there.
2. The leakage reactance of the output transformer may cause a rising amplitude at higher frequencies, due to the higher impedance load on the Pentode (its plate signal will increase). This is especially true if the loudspeaker impedance is high at those frequencies.
III. Ultra Linear modes characteristics are in the middle, in-between the Triode mode and the Pentode mode effects listed above.
IV. Beam Power mode acts the same as the Pentode mode above.
V. Now, apply Global Negative Feedback, and the results of the above will change, depending on the amount of negative feedback, and whether it is
Triode Mode, Ultra Linear, or Pentode mode (and of course the impedance versus frequency of the loudspeakers that are connected to the amplifier).
Your Mileage May Vary . . .
It Will
Generalization:
Without Global Negative Feedback:
I. Triode mode has the highest damping factor.
The frequency response to the loudspeaker, tends to be Less dependent on the variations of loudspeaker impedance versus frequency.
II. Pentode mode has the lowest damping factor.
The frequency response to the loudspeaker, tends to be More dependent on the variations of loudspeaker impedance versus frequency.
A. It will raise the sound level of the bass frequencies at the bass resonance(s):
1. For a closed box/acoustic suspension, and for an open box, there is 1 bass resonance.
2. For a bass reflex/tuned port, there are 2 bass resonances. And between the 2 bass resonances, there will be a sound amplitude "suckout" of those bass frequencies.
B. At the crossover frequency of a typical 2 way loudspeaker, the impedance is relatively high, so the sound level of the mid frequencies will be increased there.
C. High frequency
1. At higher frequencies, if the loudspeaker impedance is high, the sound level will be increased there.
2. The leakage reactance of the output transformer may cause a rising amplitude at higher frequencies, due to the higher impedance load on the Pentode (its plate signal will increase). This is especially true if the loudspeaker impedance is high at those frequencies.
III. Ultra Linear modes characteristics are in the middle, in-between the Triode mode and the Pentode mode effects listed above.
IV. Beam Power mode acts the same as the Pentode mode above.
V. Now, apply Global Negative Feedback, and the results of the above will change, depending on the amount of negative feedback, and whether it is
Triode Mode, Ultra Linear, or Pentode mode (and of course the impedance versus frequency of the loudspeakers that are connected to the amplifier).
Your Mileage May Vary . . .
It Will
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I have a guitar amp with pentode/triode switch on a PP EL84 end stage. In triode mode, it adds compression and harmonics compared to pentode mode. It can be heard especially with high gain sounds. My A9 sounds pretty good stock, only with grid stoppers and heater balance resistors added and on the tube HiFi amps I had in the past, I preferred the ones with ultralinear output, both single ended and PP. On the other hand, SET + Lowther in a backloaded horn is not really HiFi, but there is some enjoyable "magic" in the sound. There was slightly less magic with the A9🙂
pelanj,
A PP EL84 amplifier that has a switch to change from Triode mode to Pentode mode,
and no other circuit differences . . .
The Triode mode will have less maximum output power before hard clipping.
The Pentode mode will have more maximum output power before hard clipping.
That might be the difference in sound you observed.
A PP EL84 amplifier that has a switch to change from Triode mode to Pentode mode,
and no other circuit differences . . .
The Triode mode will have less maximum output power before hard clipping.
The Pentode mode will have more maximum output power before hard clipping.
That might be the difference in sound you observed.
Me?
I answered you in post #1311.
If you insist on installing two separate switches, I'd go for the 250v ones for the damage mitigation in case you forget to switch off the amp first.
If you're careful never to do that then go for the 125v ones if they're smaller or easier to install, etc.
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6A3sUMMER: This was well below the clipping of the end stage. I think it is also related to the way it interacts with the phase splitter.
pelanj,
In that case, without a complete schematic of the amplifier, it is impossible to even guess the reason for the difference of the way it sounded in pentode mode versus triode wired mode.
How about the fact that there might have been very little negative feedback, or no negative feedback at all.
With no negative feedback . . .
A pair of EL84/6BQ5 in triode mode, versus a pair of EL84/6BQ5 in Pentode mode
Will sound Completely different even at low volume and mid volume.
And those sounds will also be very dependent on the loudspeaker they are driving.
That is true for Push Pull, and true for Parallel Single Ended too.
Also with no negative feedback, the Pentode mode and Triode mode will have completely different gain.
You would have to change the setting of the volume control to get the same sound level.
And depending on where the volume control circuit is, and the other parts there, and the tube types there, the
high frequency response of the amplifier can vary widely, versus the volume control setting.
Just sayin'
And what did you mean by "High Gain Sounds".
I am not a Guitar Amplifier person, and I am not familiar with that term.
Thanks!
In that case, without a complete schematic of the amplifier, it is impossible to even guess the reason for the difference of the way it sounded in pentode mode versus triode wired mode.
How about the fact that there might have been very little negative feedback, or no negative feedback at all.
With no negative feedback . . .
A pair of EL84/6BQ5 in triode mode, versus a pair of EL84/6BQ5 in Pentode mode
Will sound Completely different even at low volume and mid volume.
And those sounds will also be very dependent on the loudspeaker they are driving.
That is true for Push Pull, and true for Parallel Single Ended too.
Also with no negative feedback, the Pentode mode and Triode mode will have completely different gain.
You would have to change the setting of the volume control to get the same sound level.
And depending on where the volume control circuit is, and the other parts there, and the tube types there, the
high frequency response of the amplifier can vary widely, versus the volume control setting.
Just sayin'
And what did you mean by "High Gain Sounds".
I am not a Guitar Amplifier person, and I am not familiar with that term.
Thanks!
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@6a3summer
If I may pick your brains Sir,
I'm currently running my power stage at 70% dissipation.
On the bench, my scope shows symmetric sine waves with equidistant clipping as far as I can see.
It plays nicely to my untrained ears.
Was wondering what the improvement would be if I increased the biasing even more. I know cathode biased class A are meant to run at 100% but I'm also concerned about tube longevity and if that will tax my power transformer.
If I may pick your brains Sir,
I'm currently running my power stage at 70% dissipation.
On the bench, my scope shows symmetric sine waves with equidistant clipping as far as I can see.
It plays nicely to my untrained ears.
Was wondering what the improvement would be if I increased the biasing even more. I know cathode biased class A are meant to run at 100% but I'm also concerned about tube longevity and if that will tax my power transformer.