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Long time lurker - first build a tubelab Simple SE

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I'm a big fan of the Hammond 374BX, though it is more expensive than some of the other options. It'll give you a B+ of about 450 volts. You could also use the less expensive Hammond 274BX or the downright frugal Allied 6K7VG. They should result in similar B+ voltages.

With 560 ohm cathode bias resistors, you'll probably end up just a bit over 60 mA idle current per tube. Overall dissipation would be somewhere over 20 watts, but under 24. If your tubes will handle that without overheating the plates, then go for it. The big Electroharmonix 6CA7EH are perfectly happy running here. I've also tried some Reflektor 6p3s-e and some Shuguang 6L6GC and the wattage is just a bit too much for them. They'd probably be happier with a 620 or 680 ohm cathode resistor instead.
 
I have already built a SimpleSe with KT88.

I use for power transformer the Hammond 374BX
For OPT's the Tango U-808
output tube KTt88-98 Shuguang
driver tube 12AT7 Siemens
rectifier tube 5AR4 Telefunken
My B+ 450 volts With 560 ohm cathode bias resistors.

In this condition I think the setting is perfect but the B+ a bit high for the EL34. I would like to use it with a conservative setting.

I have in stock for the OPT James 6123HS and for the power transformer the James JS9611.
 

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Well.

I started turning my top plate into swiss cheese tonight to rotate my PT...as I did discover that I had a hum issue.

I rotated the PT and the hum is still there. I left the PT sort of loose and was able to move it around 1-2 inches and the hum did not fade in or out, it is just there...

If I plug in or unplug the RCA's it makes no difference.

Another question. I bought a capacitor off ebay a while back when I was still at the beginning of my learing curve (believe me I am not much farther up the curve yet, but I'm getting there). It is a 90uF 375VAC as labeled. The DC voltage I read where it would be installed is about 500VDC. I think I can safely assume I should NOT use this cap. Not sure what, if any, the rating difference between DC and AC may be.
 
A film or oil cap rated for a particular volts AC is suitable for use at much higher DC voltages. I can't recall the exact conversion factor, but I think it's somewhere between 1.4x and 1.6x. In other words, your 375VAC cap ought to be safe to use at 500 volts DC.

My Simple SE had a noticeable 60 Hz hum when I first assembled it. It seemed to be a ground loop passing through the chassis ground and over the RCA jack grounds. When I built it, I failed to use isolated RCA input jacks. Lifting the chassis ground eliminated the hum. I think the permanent fix is to use plastic washers to lift the RCA inputs off the chassis plate.

I also notice you have no power supply choke on the top deck. Is there one under the chassis? From the simulations, it seems even a small choke (1.5H, like a Dynaco C354) should cut the residual 120 Hz hum on the B+ supply by a factor of four. A decent sized choke, say 5~10 H ought to reduce it by a factor of ten.
 
It is a 90uF 375VAC as labeled. The DC voltage I read where it would be installed is about 500VDC. I think I can safely assume I should NOT use this cap. Not sure what, if any, the rating difference between DC and AC may be.

You CAN safely use this cap. The cap in my Simple SE is rated for 370 VAC. There have been several different opinions on the actual DC rating of a cap that was meant for (and rated for) use on AC only. The safest and most conservative value is to multiply the AC rating by 1.414 to get the DC rating. This lets your cap handle at least 525 volts of DC. This is safe because the peak voltage of an AC sine wave is 1.414 times the RMS value, so a 370 volt AC sine wave hits 523 volts peak at the crest of the sine wave, and the cap will see at least 523 volts.

I have seen published multiplication factors as high as 2X. The normal application for these caps is to shift the phase in a motor winding which is an inductor. This means that the voltage seen by the capacitor may be higher than 1.414 times the RMS value. I wouldn't go that far since one of these things could be ugly if it ever blew up. I have applied about 600 volts to my cap for short periods of time during some experiments.

The hum in your amp could be 120 Hz from the power supply. This usually sounds more like a buzz than a hum. It could also be a 60 Hz hum from a grounding issue. It is not always easy to chase this down. Try this test. Remove the 12AT7. Turn the amp on and see if the hum is still there. If it is, it is not coming from the input wiring. Do you have a choke in your power supply? If not, it might be a good idea. The motor run cap will help too. If the hum goes away it was likely due to the grounding associated with the input wiring.
 
Ty_Bower said:
A film or oil cap rated for a particular volts AC is suitable for use at much higher DC voltages. I can't recall the exact conversion factor, but I think it's somewhere between 1.4x and 1.6x. In other words, your 375VAC cap ought to be safe to use at 500 volts DC.

My Simple SE had a noticeable 60 Hz hum when I first assembled it. It seemed to be a ground loop passing through the chassis ground and over the RCA jack grounds. When I built it, I failed to use isolated RCA input jacks. Lifting the chassis ground eliminated the hum. I think the permanent fix is to use plastic washers to lift the RCA inputs off the chassis plate.

I also notice you have no power supply choke on the top deck. Is there one under the chassis? From the simulations, it seems even a small choke (1.5H, like a Dynaco C354) should cut the residual 120 Hz hum on the B+ supply by a factor of four. A decent sized choke, say 5~10 H ought to reduce it by a factor of ten.

WOW 2 replys in short order...

I will try out the cap.

I will play around with the RCA's.

I will try the 12AT7 test and let you know...

Thanks!
Carl
 
tubelab.com said:
Do you have a choke in your power supply? If not, it might be a good idea. The motor run cap will help too. If the hum goes away it was likely due to the grounding associated with the input wiring.

What does the peanut gallery have to say about the choke and the supplemental capacitor? If a person had $15 (or enough chassis real estate) to spend on one or the other (but not both), which offers the greatest improvement?

For what it's worth, I placed my bet on the choke. I sometimes wonder if I'm missing out because I didn't add the motor run cap.
 
Go buy a filter choke, like the Triad C-14X or a Hammond P-T159Q.

I used the 159Q in my Simple SE. My speakers are Paradigm 7se Mk3. If I recall correctly, they are 92 dB efficient. If you want to hear my Simple SE humming, you need to have your ear within an inch of the woofer and hold your breath.

Oh, I went and checked the PSU simulation again. With a 150 ohm resistor expect 1.03 volt ripple on the B+. Adding an extra 90uF to the second cap shows 0.74 ripple. Using a 7H, 100 ohm choke (without the extra cap) reduces the ripple to 0.03 volts.
 
What does the peanut gallery have to say about the choke and the supplemental capacitor? ..... For what it's worth, I placed my bet on the choke.

My peanuts go toward the choke also. And I have found that a choke can clean up a power supply better than all of the caps in the world wired together. A choke will reduce the peak circulating AC current. Raising the total capacitance can raise the peak AC currents, and shorten their duration leading to more harmonics.

The $7.74 C-24X choke is better than no choke. I use one in my industrial amp since that is all I could fit under the chassis.
 
I hooked up the run cap and I think that I did notice a slight improvement. I also went ahead and ordered a C-14X choke - I had a 10% off my next allied order...

I also ordered a new top plate since I pretty much destroyed it moving the PS around. Acutally I think it will work out better since I ordered the 10X14 plate instead of the 10X12 one to give me a little more room with everything. I've got some more poplar kicking around too to replace the length pieces.

Measure once, cut twice...thats my motto...

Thanks again guys.
Carl
 
OK update 10/22

1. New top plate - reconfigured pretty much how everything is mounted...see pics
2. Upgraded to some 715P orange drop coupling caps
3. Installed C-14X choke
4. Removed FREDs - they blew again I think because I they got fubar'd upon trying to desolder the old ones and reinstall the new ones...the 5AR4 is doing a wonderful job
5. Ty was nice enough to hook me up with a couple resistors for R17 and R27 for increased resistance - works great - no more glowing plates on the 6L6GC's.

That is about it...I must say with the choke and the run cap the amp is now DEAD SILENT...

I am now going to take on an Aikido preamp to free up my Yamaha CA-810 for another purpose...

And no, the amp is not plugged into that outlet :D And I need to make a new chassis back board from moving the outlet.

IMG_1717.jpg

IMG_1715.jpg

IMG_1720.jpg
 
Carl,

Nice looking amp. FYI I dropped a Chinese 6L6GC (coke-bottle style) and decided to take it apart for fun. Other than having a somewhat thin glass envelope this tube appears to be solidly constructed. Mica spacers are tightly fitted, welds are clean, and the kicker- gold control grid wire. Now I'm going to make a run on the small-ST shape with brown base on sale at AES.
Thanks for the inspiration.

Probe
 
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