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DHT driver for triode wired SE EL84, 6V6 or EL34
DHT driver for triode wired SE EL84, 6V6 or EL34
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Old 14th May 2021, 06:17 PM   #591
minhaj is offline minhaj  Bangladesh
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I always use 3.3uf film cap for driver tube in my mono block build and I find it better sounding than a 33uf or 47uf or 100uf regular electrolytic. I always keep other Rs and Cs as small as possible.

Regards
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Old 14th May 2021, 06:46 PM   #592
tizman is offline tizman  Canada
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Quote:
Originally Posted by minhaj View Post
I always use 3.3uf film cap for driver tube in my mono block build and I find it better sounding than a 33uf or 47uf or 100uf regular electrolytic. I always keep other Rs and Cs as small as possible.

Regards
I added 33 uF to each of the 2.2 uF caps on the 30s in the 6N1P-EV/KT120 amp, and it didn't seem to make any audible difference. I added capacitance to another amp's driver tube node, in this case a 6N1P-EV/KT120 single ended amp that had the 2.2 uF capacitor on the driver replaced with a 50 uF cap, and it sounded better with the small cap in that case.

It would seem that in the case of the 30/6P15P-EV amp, the concerns about small cap size on the driver tube node are unfounded. If this is the case, I'd rather use a smaller value film cap than a similarly sized higher value electrolytic in the same position. Hopefully someone will give us a definitive answer on the other thread I started on sizing driver tube caps.

With respect to "keep other Rs and Cs as small as possible", I always try to keep series resistance at a minimum in power supplies, but haven't thought about capacitance that way. I usually keep resistance low, and increase capacitance in order to achieve ripple goals.

Last edited by tizman; 14th May 2021 at 06:55 PM.
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Old 14th May 2021, 07:39 PM   #593
FlaCharlie is offline FlaCharlie  United States
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Quote:
Originally Posted by minhaj View Post
I always use 3.3uf film cap for driver tube in my mono block build and I find it better sounding than a 33uf or 47uf or 100uf regular electrolytic. I always keep other Rs and Cs as small as possible.

Regards
It certainly seems like the input / driver tubes can function fine with small values.

Have you compared the sound of a 3.3uf film with something in the 30uf to 50uf range that is also a film cap? I suspect the difference you've found may be simply because the larger values were electrolytics.

I think it's been well established that anytime you can replace an electrolytic with a film cap it's bound to be an improvement.

Can you think of any downside to using a larger film cap? My ears say no but I'm wondering if they might measure differently.

I ordered some 15uf DC Link (film) caps to use for the node that supplies the input tubes. As I mentioned, in my very brief experiment I didn't hear any issues with the 50uf motor run I'm using on the breadboard. In addition to trying the 0.1uf I also tried a 5uf motor run and didn't notice any audible differences.

Last edited by FlaCharlie; 14th May 2021 at 07:43 PM.
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Old 14th May 2021, 07:55 PM   #594
jhstewart9 is offline jhstewart9  Canada
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Default The Enlightenment Part B

IT = CE………………………a very useful relation. So in these examples we can see the change of voltage on the final stage supply cap as program material is run. The supply cap in this case was 100 microF. There are two examples, one playing a CD of Peter Gabriel’s performance of Salisbury Hill, the other a 10 Watt, One KHz burst.
The amplifier in test is another of my brain storms, Class AB2 6V6’s built in 2001. I had a few objectives in mind, try Class AB2 & measure overhead available with a limited PS. Also try a differential cascade front end with output plate NFB to the upper grids of the cascade. The PP loadline is corrected for Class AB2, that is the steeper line.
Peter Gabriels performance results in a 12V drop on peaks (blue trace). Stuffing the numbers into the relation tells us the extra current supplied by the final cap for about 50 ms is ~24 mA.
The 10 watt bursts of One KHz look like only 3.7 mA. Need to check that, looks like the 10X probe was not dialed in.
The Burst Gate was built in about the same time.
Attached Images
File Type: jpg 2013_03_21_001 Peter Gabriel Salsbury Hill.jpg (77.9 KB, 89 views)
File Type: jpg Schema And Burst Example 10W 20C.jpg (90.8 KB, 83 views)
File Type: jpg 6V6GTA 14W 4 PushPull C 7W.jpg (84.1 KB, 84 views)
File Type: jpg PP 6V6 Cascode Front End Burst Results.jpg (82.7 KB, 75 views)
File Type: jpg 026 Cascode Amp A.JPG (898.7 KB, 73 views)
Attached Files
File Type: pdf Amplifier Burst Testing.pdf (589.7 KB, 6 views)
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Old 14th May 2021, 11:01 PM   #595
jhstewart9 is offline jhstewart9  Canada
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Quote:
Originally Posted by minhaj View Post
I always use 3.3uf film cap for driver tube in my mono block build and I find it better sounding than a 33uf or 47uf or 100uf regular electrolytic. I always keep other Rs and Cs as small as possible.

Regards

What is the final tube in those amplifiers? And how does that recommendation apply to a completely different output stage? Where did the use of very small final stage plate supply capacitors originate?
All these questions have importance in discovering why such a change would 'sound better'. And better than what & too who?
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Old 14th May 2021, 11:53 PM   #596
tizman is offline tizman  Canada
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Quote:
Originally Posted by jhstewart9 View Post
What is the final tube in those amplifiers? And how does that recommendation apply to a completely different output stage? Where did the use of very small final stage plate supply capacitors originate?
All these questions have importance in discovering why such a change would 'sound better'. And better than what & too who?
jhstewart9: I asked the question initially to see if I could find a method to work out a capacitance value for a given node. Several folks told me that the value chosen for the capacitor on the 30 tubes in my amp was too low at 2.2 uF. I asked how to work out an appropriate value, and Bill Brown linked the Loesch article. There has been some questioning of that article’s relevance and correctness, but I’m still waiting for someone else to tell me how to do it properly if that article is incorrect. Nothing yet....

Last edited by tizman; 15th May 2021 at 12:18 AM.
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Old 15th May 2021, 12:17 AM   #597
tizman is offline tizman  Canada
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Originally Posted by euro21 View Post
I don't understand this "problem". :-p

At "B+A" point al least 60dB PSRR (relative to B+) due to the PSU C-large R-C-large R-c filtrating.
The #30 anode current alteration is marginal versus output tube current, so "stressing" of PSU mainly due to the output.

The magnitude of "last C" of #30 anode circuit is almost negligible, the 1.5uF as good as 33uF.

If the B+ has 2Vpp hum, on the output only 36mVpp (shorted input), so the 35dB PSRR "thanks to" SE output.
“the 1.5uF as good as 33uF” is the case when listening. In fact the other amp to which I added capacitance to the driver power supply node sounded worse with the extra capacitance.

There was no hum from the B+ once the bias resistor bypass capacitor was added. This of course is a separate issue from the capacitor sizing.
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Old 15th May 2021, 02:56 AM   #598
minhaj is offline minhaj  Bangladesh
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Dear Fla, earlier you wrote:

''It certainly seems like the input / driver tubes can function fine with small values.
Have you compared the sound of a 3.3uf film with something in the 30uf to 50uf range
that is also a film cap? I suspect the difference you've found may be simply because
the larger values were electrolytics.
I think it's been well established that anytime you can replace an electrolytic with a
film cap it's bound to be an improvement.
Can you think of any downside to using a larger film cap? My ears say no but I'm
wondering if they might measure differently.''

If you have a analog multimeter pls check charging and discharging pattern of the capacitors. Usually charging is smooth discharge is not. Yes, in general Film caps are better.

Tizman.....we are growing older in this thread alone, but it is a good exercise. Every design is optimization, my take on PS for 2 stage SE tube amp with tube rectifier where driver draws 5-15 mAmp and output tube draws 35-70 mAmp current is:

CLCRC current tap for 35-70mAmp output tube
and
RCRC for 5-15 mAmp driver tube i.e.

For output tube
C L C R C
1-2uf film 5-10H low dcr 100-200uf 100-200R 50-100uf
and
For driver tube
R C R C
as small possible 33-47uf as small possible 2.2-10uf film

The above is inexpensive and good sounding. IT SEEMS LIKE LOW PASS/HIGH PASS, FREQUENCY RESP not a problem that I can hear in this configuration. Quality of LCR is very important and oversizing resistor is good because heated resistors make noise/distortions.

We can improve the above PS with CLCLCRCRC and all film/oil/motor run caps.

Regards
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Old 15th May 2021, 03:03 AM   #599
minhaj is offline minhaj  Bangladesh
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''Have you compared the sound of a 3.3uf film with something in the 30uf to 50uf range
that is also a film cap? I suspect the difference you've found may be simply because
the larger values were electrolytics.''

Yes and no. Usually charging and discharging time and the smoothness for these
functions are better for smaller caps, be it elec or film.

Regards
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Old 15th May 2021, 03:08 PM   #600
FlaCharlie is offline FlaCharlie  United States
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Quote:
Originally Posted by minhaj View Post
If you have a analog multimeter pls check charging and discharging pattern of the capacitors. Usually charging is smooth discharge is not. Yes, in general Film caps are better.
All I have is a digital meter. When I experimented with the tiny .1uf cap I did connect the meter to the cap and watch it during startup and later with music playing. I was measuring voltage, though, not current, since increases in current draw would lead to a decrease in voltage. And I was measuring the cap that supplies the input tube, not the B+ cap that supplies the outputs.

I saw the same pattern with all the cap sizes I tried (.1uf, 5uf, 50uf) during startup and with music playing regardless of cap size. With music playing the voltage only varied a tiny bit. This variation was in the range of .1v to .2v but it didn't seem to correspond to the music so I figured it was most likely due to small variations in wall voltage. Perhaps an analog meter would be better or some other more sophisticated equipment.

The graph that John Stewart posted seems to be the most accurate and revealing information that's been presented in terms of showing how much charge a music signal is actually drawing from a supply cap. I'm not sure how he measured it or if it's a simulation. But, as with the Loesch article, the graph shows the effect on the B+ node that supplies the power tubes. I would expect the results to be quite different if the input tube supply cap was being measured.

I've never spent much time trying to determine an "optimal" value for any particular PS cap. I've always figured that having a bit more capacitance in reserve is a good idea but just don't go so large that it has a negative effect.

So I just try to strike a vague balance. I doubt I could hear the difference between "ideal" and "close enough".

Calculating the minute details may be an interesting technical exercise for an EE or someone who enjoys that aspect of design, but my brain doesn't work well in that realm.
Quote:
Originally Posted by minhaj View Post
Yes and no. Usually charging and discharging time and the smoothness for these functions are better for smaller caps, be it elec or film.
Of course, smaller caps recharge more quickly than large ones. If you play around with the cap charging calculator I posted, you can see the details.

So I figure the balancing act is to use a cap that recharges relatively quickly but is not so small that it ever runs out of current. Of course, this assumes that the ripple is acceptably low.

That would suggest that the under 5uf caps that you and Tizman are using would be good choices to supply the input tube. But, as I said, I couldn't hear any difference between 5uf and 50uf when both were film caps.
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