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Old 25th March 2012, 12:51 AM   #11
kkcinc is offline kkcinc  United States
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PRI:110-120V, 50/60HZ, 750VCT @150DCMA, 5V @3A, 6.3A @ 5.0A, LEADS

Mfr. Part#: 6K7VG Allied
That's the power xfmr. The opt's are 3k.
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Old 25th March 2012, 01:34 AM   #12
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I wish George would chime in. I would love to hear his advice on setting up the amp for 6l6's other than gc's......Mfr. Part#: 6K7VG Allied That's the power xfmr.
OK, but you might not like what I have to say. My SSE has the same Allied 6K7VG. The B+ is 430 volts with KT88's biased up to 100 mA each! It goes over 440 volts when I drop the current back to 65 mA each. Granted my wall outlet never goes below 120 volts and has been seen over 126 volts, but this is too hot for even some 6L6GC's.

The inrush surge with this transformer is tough on rectifier tubes. Some 5Y3's and 5R4's will spark out. Some poorly built new production 5AR4's will spark out on initial power up. Putting a 1N4007 in series with each red transformer lead will help prevent this. It will be implemented in the next PC board revision. Tube purists can always install a jumper or a resistor.

To run 6L6GC's in my amp I need a cathode resistor in the 620 to 680 ohm range. Even with a 5Y3 rectifier and a 750 ohm cathode resistor the voltage across the tube will be over 360 volts which is the screen grid maximum for a 6L6GA. Did that stop me from stuffing them into the amp? NO! Did any blow up? YES! Were they already bad? Maybe.

I found a box full of used and dirty 6L6GA's in my warehouse. I plugged in a 5Y3 and ran several of these tubes through the amp. Some worked, some didn't and two sparked out. the second sparking 6L6GA took out the 5Y3, which was also rather old and crusty looking. That was two weeks ago and I haven't even replaced the blown fuse yet. If I have some time tomorrow I might get over to the warehouse to grab all the tubes. I plan to test them and sell some of the good ones on Ebay. Most are smokey glass RCA's.

I believe that the dissipation was too high since I could see a faint glow through the smoked galss on some tubes. Maybe an 820 ohm cathode resistor would be needed. I have 750 ohms in my amp and I have a collection of resistors with small alligator clips that I use for boosting the current by clipping them across the 750 ohm. Some users have a switch.

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The opt's are 3k.
A 3K ohm load is a bit low for a 6L6GC running at over 400 volts. It will make more power but the distortion will be higher and the damping factor will be lower. I have Transcendar 3K OPT's in that amp. It all depends on your speakers, but I get better sound with my "8 ohm" speakers plugged into the 4 ohm jacks. This puts a 6K load on the tubes. It's not quite as loud, but the bass is cleaner and the vocals are much more detailed. The only time I use the 8 ohm taps is with KT88's in UL with cathode feedback, the 15 inch speakers and something loud (Pink Floyd...) in the player.
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Old 25th March 2012, 02:24 AM   #13
kkcinc is offline kkcinc  United States
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How did you wire the transcendar's for nfb? Straight or reverse like on your site? I'm getting good bass out of 6l6gc's in triode, 3k, 4ohm tap, and 4ohm rated 15inch efficient woofers. Tight and clean. Loud as heck. I can't listen past 1/3 of volume knob with cd's. Too loud. With my low gain phono stage I can get it to clip, but I am way up on the volume. I am VERY happy as is, but I constantly tube role that's why I asked about the other 6l6 types. Did I make a huge mistake using the 3k opt's? I think I might have limited myself a bit, but not a huge mistake.
I have the inrush limiters in place and watched the thing power up slow and steady with a voltmeter. I even switch the 5ar4 to a 5u4 and no inrush problems as long as I start when cool.
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Old 25th March 2012, 05:43 AM   #14
w5jag is offline w5jag  United States
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Originally Posted by kkcinc View Post
So by changing the rectifier tube I can use regular 6l6's and g's. And not be stuck with gc's only?
Can anyone tell me roughly where I stand for voltage across the tube with 5ar4 , B+ at 440v, using a 680
Cathode resistor in the standard sse layout? If not, I'll pull it out of the cabinet and take measurements.
Possibly, but, as George has noted, the plate and screen rating for all of the lesser 6L6 variants is 360 volts, and you will wind up around 385-375 volts, maybe a bit more, across the tube with a 5Y3 or 5W4. It will also be right at, or over, the output current rating for the rectifier tube. The cathode resistance for the power tubes will likely need to be increased.

The late production 6L6WGB's should easily handle these voltages, they have the guts of a late production 6L6GC in them.

Personally, I have run RCA 6L6G's, ( real ) Tung Sol 5881's, older 6L6WGB's, 5932's, and even 807's at 375-380 volts across the tube and have not lost one, but I accept the risk that it can happen and that expensive amplifier damage can also occur when going outside the ratings.

I have some real nice 6L6GA's and 6L6GAY's, but I have not run them past the ratings because I am unwilling to risk frying them.

There are also a few threads on using a choke input power supply. IIRC, Ty Bower used an LCLC setup to run 6L6GA's in his SSE. That requires a destructive modification to the pcb, however.

Win W5JAG
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Old 26th March 2012, 02:19 AM   #15
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Originally Posted by w5jag View Post
There are also a few threads on using a choke input power supply. IIRC, Ty Bower used an LCLC setup to run 6L6GA's in his SSE. That requires a destructive modification to the pcb, however.
The mod to the circuit board wasn't so bad. It only involves cutting one trace, which can be jumpered back together without too much trouble. Here's my post where I showed the results:
Another Simple SE builder
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Old 26th March 2012, 06:59 PM   #16
kkcinc is offline kkcinc  United States
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Default 6l6

I like the lclc idea. I'm told that makes a better supply. For now I'll try messing around with 6l6gc's and tubes that are close like 350b. BTW I took measurements today. 440v B+, 435v plate voltage, 33v across cathode resistor. Measurements were taken with 5ar4, 6201, and two el34 after warm-up. 680 ohm cathode resistor. Don't forget 3k opt. Based on these measurements, I think I can drop the resistor to 560 ohm.
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Old 26th March 2012, 09:26 PM   #17
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kkcinc: What are you presently running for PS filtering? CRC or CLC? what values?
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Old 26th March 2012, 10:43 PM   #18
kkcinc is offline kkcinc  United States
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Clc with the auxiliary motor run cap.
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Old 26th March 2012, 10:56 PM   #19
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Originally Posted by boywonder View Post
kkcinc: what values?
C1=? C2=? L=?....
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Old 26th March 2012, 11:30 PM   #20
kkcinc is offline kkcinc  United States
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47,100,5h,100 for the aux.
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