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Old 2nd October 2008, 01:31 AM   #41
tigrine is offline tigrine  Canada
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Default SimpleSe with EL34

What is the best configuration for the SimpleSe with EL34 for the B+ and the cathode resistors ?
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Old 2nd October 2008, 02:01 AM   #42
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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.
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Old 2nd October 2008, 02:26 AM   #43
tigrine is offline tigrine  Canada
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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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Old 3rd October 2008, 01:24 AM   #44
cjkpkg is offline cjkpkg  United States
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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.
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Old 3rd October 2008, 01:58 AM   #45
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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.
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Old 3rd October 2008, 02:11 AM   #46
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Quote:
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.
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Old 3rd October 2008, 02:15 AM   #47
cjkpkg is offline cjkpkg  United States
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Quote:
Originally posted by Ty_Bower
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
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Old 3rd October 2008, 02:23 AM   #48
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You have room under the chassis, so use the ugly but effective Triad C-14X. It is about $15 from Allied Electronics. I use it in my amps. I have noticed a low hum without it. My low hum could be louder with better speakers. Make sure you remove R1 when you add the choke. (www.alliedelec.com)
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Old 3rd October 2008, 02:38 AM   #49
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Quote:
Originally posted by tubelab.com
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.
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Old 3rd October 2008, 02:40 AM   #50
cjkpkg is offline cjkpkg  United States
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OK,

I isolated the RCA inputs and made no difference.

I pulled the 12at7 and the hum actually got worse...and with that it sounded more like a buzz than a hum...
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