Rectifier tube 5AR4 vs. 5U4GB? - Page 2 - diyAudio
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Old 8th September 2008, 03:04 PM   #11
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A while back I thought I remember reading that the CL80 was recommended... which I believe is the part installed in my Simple SE. How does that compare to the others recommended here? I have one in the B+ CT and one in the primary of the power transformer.
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Old 8th September 2008, 09:13 PM   #12
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Tried an RCA 5U4GB out and had no problems. I just assume stay with the 5AR4 which puts the voltage a wee bit over 450v with a 274BX power transformer.
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Old 8th September 2008, 09:43 PM   #13
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Regarding the inrush limiters, here's the GE data sheet: http://www.gesensing.com/products/re...asheets/cl.pdf

I use the CL-80 and CL-70 mostly, with 3A and 4A ratings. The CL-90 is good for 2A, enough for smaller amps and secondary side use.
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Old 9th September 2008, 12:07 AM   #14
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Quote:
I use the CL-80 and CL-70 mostly
So do I. I have the CL-80 in one of my Simple SE's on the primary of the transformer. The 90 gets pretty hot in a Simple SE with fat tubes (EH KT88's) when biased hot (near 100 mA).

I think that these things work best when the average current through them is about half their rating. If operated too cold (not enough current compared to their rating) they never "warm up". Their resistance may remain too high leading to poor power supply regulation. If operated too hot, they may fail. The failure is often ugly involving smoke. It usually takes a lot to blow one, but I did have one explode. The exploding CL80 involved a shorted filter cap and a 20 amp fuse, don't do that!
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Old 9th September 2008, 09:53 AM   #15
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Tom,

Thanks for the GE data sheet! Very much appreciated.
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Old 27th September 2008, 02:19 AM   #16
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I stuck in an old GE 5U4GA. In another thread I've been noting some of the other tubes I've been playing in my Simple SE. Some of them seem to be on the edge of their dissipation limit, notably the Reflektor 6p3s-e and some brown base Shuguang 6L6GC.

I put in the 5U4 to try to drop the voltage a little, and hopefully ease the burden on the output tubes. I think I succeeded here. Measured supply voltage just upstream of the PSU choke is just under 420 volts DC.

I had the voltmeter attached while I powered it up. As expected, the voltage comes up within seconds of hitting the power switch. I wish I had paid closer attention to the peak voltage, but it definitely went way past 420 and came back down again after the output tubes heated up. (edit: saw a peak of 532 volts on the digital meter)

I suppose the initial surge voltage puts a little more abuse on the power supply caps, but overall it reduces the punishment on the output tubes. I'll probably experiment a bit more and see if I feel it affects the sound.
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Old 27th September 2008, 03:09 AM   #17
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It seems that GE 5U4 was weak on one section. I tossed it in favor of an unused Sylvania. Now I see 450 volts just before the choke. I guess I ought to test my tubes before I stick them in...
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Old 28th September 2008, 03:56 AM   #18
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Stupid question... I can add a switch on the 5v filament winding going to the rectifier? Leave it open when I first power up the amp. Give the output tubes twenty seconds or so to warm up, then close the switch. Then the rectifier warms up quickly and starts to conduct.

Or another idea would be to add an IRCL in series with the 5v winding. Might be problematic, since the IRCL should be sized according to the current draw, and that varies from one type of rectifier tube to another...
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Old 28th September 2008, 12:28 PM   #19
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Heating the Outputs before the rectifier filament may make things worse for a directly heated rectifier, since it will face a big current demand during its warmup. 5R4GYs will arc-over very easily in that case.

Check out the RCA 5R4GY data sheet - it suggests warming the rectifier filament for 10 seconds before applying the HT, when higher loads are to be served.

How about a Standby switch in the HT trafo secondary's centre-tap? Power-ON, warm up the filaments & heaters in all the valves, then switch in the HT. If you also use the CL-80, that will be the kindest arrangement for all the components.
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Old 28th September 2008, 09:11 PM   #20
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I am interested in Jeff's observations on the sonic effect of different rectifier tubes. Can anybody enlighten me as to what is causing sonic differenceces? All I can think is the degree of voltage "sag" that each tube has - or have I missed something?

And I also wonder where SS diodes (e.g. the FREDs as optionaly used in the SimpleSE) fit in terms of sonics.

This is of pactical interest to be as I embark on a SimpleSE build.

Cheers
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