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Old 6th December 2010, 01:44 PM   #11
Anchan is offline Anchan  United States
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Originally Posted by tubelab.com View Post
I am going to guess that your speakers are less than 8 ohms at 200 Hz. Every speaker system has an impedance VS frequency curve. Sometimes the manufacturer publishes it, sometimes they don't. Google couldn't find the graph for your speakers and it isn't on the Klipsch site either. My Yamahas are "8 ohms nominal" but vary from 6 ohms to 40 ohms across the audio range. You might try your test with a tone closer to 1KHz since that is where most manufacturers rate their speakers.

Your probably right, in that I could probably get lesser distortion at a higher power using a 1KHz tone. I chose a lowish frequency since when listening to music, its often the lower notes that give the peaks- that and I suppose transients from percussion. So I think the 200Hz is a kind of a real world situation- plus the 200Hz tone tends to not cut through by eardrums like a 1K. But I will put some ear muffs on and report back.

This is an important discovery for me. You may buy an amp rated at X watts, but in reality, the full power may not be entirely usuable across the spectrum, especially in the lower frequency where it is needed most. Interesting! I am guessing that this situation is more extreme in a tube amp without feedback, with the other extreme being solid state with feedback. Is this a damping factor issue?
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Old 6th December 2010, 01:53 PM   #12
rknize is offline rknize  United States
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Can you tell us something about your output transformers? Maybe try it with cathode feedback?
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Old 9th December 2010, 11:42 PM   #13
Anchan is offline Anchan  United States
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Originally Posted by rknize View Post
Can you tell us something about your output transformers? Maybe try it with cathode feedback?
I'm using 2 SSE boards together in PP, so I don't think I can use cathode feedback. I am using 10W Edcor PP transformers, but I also used their 25W versions with pretty much the same effect.

I tried running higher frequencies through the amp, including 1K, and yes, I can get a pretty large voltage swing this way- pretty close to 10W with no visual or audible distortion on the wave (at least I don't see any on the scope, and can't detect it with my ears).

I also just popped in some EL34's, and at 200Hz, 5V (10vpp) is pretty much the point that the gross distortion starts. I also tried 40Hz, at which I get less distortion at that voltage.

My final conclusion to all of this, with the help of all of you, is that the impedance curve of the speaker is definitely playing a big part. And I think back emf is at work. At low frequencies, the woofer is moving like mad. If I tap on the woofer with my fingers while looking at the scope a lot of voltage is generated at the outputs. I think the large movement of the woofer, at possibly a slight delay, pushes back on the amp, generating distortion. This seems to be supported by the fact that similar distortion happens at similar voltages with both a 6V6 and EL34 tube, so I do not believe its an issue of overdriving the tube. On top of that, I do no get any distortion on the scope until about 10-12V regardless of frequency while running the amp with a resistive dummy load.

I am thinking the this distortion is related to the physical distance that the woofer is moving, and any delays associated with that physical movement, so the kind of distortion I am getting is proportional to distance and speed of the woofer. So if my speakers were lower sensitivity (say 90db vs 98), I would see a similar distortion, but only at the higher power necessary to drive the woofer the same distance in travel. Anyway, these are all hunches, and not really backed up by much. Feel free to dubunk as necessary.

Having said all this, its not really an issue for me- more of a learning exercise. Musical material, even with peaks much higher than 5V, and not resonating at a single frequency, sound just fine, and I am rarely listening above 2-3W peak anyway.

Last edited by Anchan; 9th December 2010 at 11:48 PM.
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Old 19th January 2011, 02:14 AM   #14
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Originally Posted by Anchan View Post
Can an EL84, possibly an EL84M be used in a Simple SE using a straight pin adapter?
OK, here it is...

Click the image to open in full size.
http://i69.photobucket.com/albums/i4...E/P1150444.jpg

I cut the trace on the board and added an extra choke to the power supply, as described in #6. I haven't checked B+, but I'd expect it is around 335. The plates of the tubes are a nice dull grey color.
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Old 19th January 2011, 12:55 PM   #15
Anchan is offline Anchan  United States
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OK, here it is...

Click the image to open in full size.
http://i69.photobucket.com/albums/i4...E/P1150444.jpg

I cut the trace on the board and added an extra choke to the power supply, as described in #6. I haven't checked B+, but I'd expect it is around 335. The plates of the tubes are a nice dull grey color.
Cool! How do you like the sound?
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Old 20th January 2011, 10:47 AM   #16
Anchan is offline Anchan  United States
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I think I will hold off on trying this at the moment, but I may give it try down the line. What size choke was necessary to drop the B+ by so much? I have a 1.5H, 60 Ohm choke laying around. Will this do it? Typically, my B+ using the newer (higher voltage) 6V6's is around 430V.

You just cut the trace between R2 and C1, and inserted the choke there, right?

Last edited by Anchan; 20th January 2011 at 10:50 AM.
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Old 20th January 2011, 12:26 PM   #17
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What size choke was necessary to drop the B+ by so much? I have a 1.5H, 60 Ohm choke laying around. Will this do it?

You just cut the trace between R2 and C1, and inserted the choke there, right?
Yes, that is the place to make the cut. I made a sketch a long time ago. Ignore where I said "jumper", but the cut is the same. You are also correct in noting where to put the choke. It is easy to do - just use the terminals at L1-O2 and SW1-O1. George described the modifications in post #32.

You need a choke of at least 3H, preferably more. There is some critical inductance value, and if you don't have at least that much the choke doesn't behave properly. It ends up acting like a resistor some of the time, and you get poor filtering and wrong voltages. I would not try it with a little guy like a C354. In my case, I had a good sized 7H choke already in my Simple SE. I just moved it to the first position, and put a tiny 1H choke in the second position. There's a photo in post #113, but you can't really following the wiring under my crowded chassis.

The 6П14ПEВ sound perfectly nice in the Simple SE. They might be a little subdued in the top end, but I need to swap back to some other types for a better comparison. I'm also playing around with a new set of speakers. I had them in my system a while back but took them out of rotation for a while. I admit I have somewhat forgotten how they sound, and I'm still adjusting to them. I'll report back later when I've had a better chance to make fair comparisons.
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Old 20th January 2011, 02:49 PM   #18
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Ty...
Those new speakers look great. I'd love to build something similar, but have absolutely no ability with wood (let alone the required tools).
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Old 20th January 2011, 08:07 PM   #19
chrisb is offline chrisb  Canada
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per post #1 - did anyone mention that when switching from 5AR4 to 5R4 the value of first input cap needs to be revised if you want long life from the rectifier.

of course as Ty and others have probably mentioned, adding a choke after first C also helps considerably

I cut the trace and did that in my Simple P/P, but stuck with the stock 5AR4 as the only 5R4 I had on hand was a Chatham 'tater masher, which wouldn't fit under the mesh safety cover.
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Old 20th January 2011, 11:12 PM   #20
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I cut the trace and did that in my Simple P/P
What choke are you using, if you don't mind me asking. I'm thinking of getting one for my frankenkardon, which will allow me to try a motor-run for C1.
Thanks

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