• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Converting from UL to Triode: Is this correct?

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#44
artosalo said:
By inserting diodes between G2 and UL-tap does nothing but increase THD a bit, which is obvious. Adding non-linear component to NFB-loop does just that.
Click to expand...

That's not what it sounds like..

ultra-linear

Its one of the things you have to try and see if you like it..If I switch between triode and Slipstream its sounds like triode but clearer/louder..YMMV
Triode sounds muddy by comparison..
Triode is nice at low volumes.

Diode enhanced triode is to clean for me sounds like a SS amp no warmth to the sound however it sounds clearer.

Regards
M. Gregg
 
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#48
cogitech said:
Indeed. I am very careful with this stuff.

Thanks again.

[goes off to figure out how to measure and adjust bias]
Click to expand...

The bias should be OK its already set for U/L..

On your diagram its the voltage across RK..
Using Ohms law the voltage across the resistor V/R = current (Voltage divided by resistance)

So as tubes warm up measure the voltage across the cathode resistor it shouldn't go higher than normal in standard configuration..(as it was originally)
Your diagram shows 29V...assuming its correct..🙂

Regards
M. Gregg
 
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#49
So lets work it out,

29V / 250 ohms=0.116...
However that's shared with two tubes so divide by 2
We would expect about 50mA per tube

So what would you have? 🙂

By increasing the resistance in the cathode you reduce the current..Etc.

Hope this helps..so the diagram would show the tubes running 58mA its OK..I prefer about 50mA its not perfect unless you have a CCS..

Regards
M. Gregg
 
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#50
Well, if I am getting this right, the EL34 spec sheet indicates max bias current of 62.5ma (?), so (if my amp is running according to the values on the schematic) my amp is running a "cool" bias?

Is that correct, or complete nonsense?
 
#51
cogitech said:
Well, if I am getting this right, the EL34 spec sheet indicates max bias current of 62.5ma (?), so (if my amp is running according to the values on the schematic) my amp is running a "cool" bias?

Is that correct, or complete nonsense?
Click to expand...

Yes I like to run at about 50-55ma..but its OK..

So normally you can set the U/L and the other connections run less..ie triode etc..pentode would be higher so you would have to watch you don't run to high..

In the end of the day there only set values of resistor so unless you want to start messing with non standard values or use fixed bias setting to adjust.

Regards
M. Gregg
 
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#53
Its something to try,

You might like standard triode or switch etc..

However as long as you have some more ideas and it helps Great!
Always ask no matter how daft it might seem someone on here will help..safe not sorry..

Regards
M. Gregg
 
#56
After moderately thorough reading and thought, I've decided to enjoy my amp in triode mode for quite some time before messing with it any more. I'm enjoying the way it sounds - it is like getting a new amp.

Maybe I'll revisit other topologies in the future, but for now I need to simply be grateful that I accomplished what I did without killing my amp... or myself.

Cheers to all who have contributed - even those who might have been negative. You played your role and I think that is important. You bring a level of control to what otherwide would be a rather reckless approach on my part.
 
#57
I've had a big mix of Astrud Gilberto on for a little while. Throughout dinner I had her at "easy listening SPL" and was almost constantly distracted from dinner-table conversation. I actually had to apologize several times.

I moved my glass of red over to the sweet spot after dinner and brought the volume up to "happy fun SPL" and within less than one minute one of my daughters abandoned her kitchen duties and poked her head over the couch.

"Dad, is this faster than it usually is? It seems like it has been sped up."

"No dear, but the amp is in triode mode now."

"Whatever. I like it."

Note: Persistent effort and time is required to build an appreciation for Astrud Gilberto in your early-teen children.
 
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#60
We skipped like flat stones on water tonight, the family and I. From Neil Young to Enter the Haggis to J-Pop to Mozart violin concertos, to... too many to recall.

We all love the "new" amp. Thanks again, all.

What a fantastic hobby. Especially in the context of what our world has become.
 
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