5AU4GB into 5Y3GT

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Philip A

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5AU4GB into 5Y3GT
« on: 13 Oct 2014, 05:27 pm »
Hello all.

After just finishing my Cornet 2, I have already started to look at making it better.  I have ordered a phono stage burn in CD from Granite Audio.  I hope to start cooking in the C2 next week.  I have also tried a number of tubes.  EH 12ax7 sounded too harsh and grainy for me.  TAD 12ax7 were better, although the gain did not seem to be as good. Tong Sol 12ax7 seem to be the smoothest...to my ears anyway.  I have a also swapped in briefly a 5AU4GB for the 5Y3GT.  My LED turned from RED to GREEN...or in my case, GREEN TO RED in about 2 seconds.  I still have my LED wired in backwards.  I have to say that I do not mind it being RED and will most likely leave it this way.  I only ran the C2 with the 5AU4GB for a few minutes.  What I did notice was allot more detail.  Bass was also much deeper with less bloom.  Gain was the biggest plus.  I am only turning the volume knob to about the 9 o'clock position instead of the 1 o'clock position with the 5Y3.  Hiss and hum are much less noticeable at this volume position.  After doing some on line research I am a bit confused.  Most agree that the 5AU4 can be swapped for the 5Y3 but not the other way around.  The 5AU runs 225ma vs 125ma for the 5Y3.  Current is 3A (15w) for the 5AU vs 2A (10w) for the 5Y3.  My question is will this work long term with the 370B tranny, or am I going to burn something up?  Thank you to everyone that reads and offers their opinion on this forum.

Regards.

Philip


tubesurf

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Re: 5AU4GB into 5Y3GT
« Reply #1 on: 15 Oct 2014, 08:02 am »
Did you mean 5U4?

Philip A

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Re: 5AU4GB into 5Y3GT
« Reply #2 on: 15 Oct 2014, 12:35 pm »
Hello tubesurf.  Yes, sorry I did mean 5U4GB.  I apologise for any confusion.

galyons

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Re: 5AU4GB into 5Y3GT
« Reply #3 on: 15 Oct 2014, 11:44 pm »
snip...I have a also swapped in briefly a 5AU4GB for the 5Y3GT.  ...snip... I only ran the C2 with the 5AU4GB for a few minutes.  What I did notice was allot more detail.  Bass was also much deeper with less bloom.  Gain was the biggest plus.  I am only turning the volume knob to about the 9 o'clock position instead of the 1 o'clock position with the 5Y3.  Hiss and hum are much less noticeable at this volume position.  After doing some on line research I am a bit confused.  Most agree that the 5AU4 can be swapped for the 5Y3 but not the other way around.  The 5AU runs 225ma vs 125ma for the 5Y3.  Current is 3A (15w) for the 5AU vs 2A (10w) for the 5Y3.  My question is will this work long term with the 370B tranny, or am I going to burn something up?  Thank you to everyone that reads and offers their opinion on this forum.

Regards.

Philip


This makes no sense to me.  First the 5U4 draws 3 amps filament current. The 370BX is rated for 2 amps.  You are asking the PT to output 50% more current than it's rating. Not good. That is why the 5Y3 is spec'd by the Jim. 

The rectifier swap could not possible give you that much more gain.  The two rectifiers have different voltage drops, maybe the 5URGB drops 10-15 fewer volts than the 5Y3, depending on the circuit. That will not noticeably impact the gain. From 1 0'clock to 9 o'clock is really a huge gain difference on a typical audio log potentiometer. Not sure what you are hearing. 

Have you given the C2 time to burn in? If not, put away all of the "improvements" until you have at least 40 hours on the unit. For now just burning in the unit will give you more benefit than anything else.  After burn in change one thing at a time, and give that "thing" time to burn in as well. 

BTW,  Do all of you test point voltages meet spec? Still pondering the perceived gain difference.

Cheers,
Geary


Philip A

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Re: 5AU4GB into 5Y3GT
« Reply #4 on: 16 Oct 2014, 12:58 am »
Hello Geary.  Thank you very much for your thoughts.  I have not burned in the C2 yet.  My phono stage "burn in CD" in in the post.  I probably have 3 hours on it now.  Not sure why the gain is so much with the 5U4GB either.  Just had the tube swapped for a few minutes, but the difference was huge!  As I had stated, the volume knob went from the 1 o'clock position with the 5Y3 tube to the 9 o'clock position with the 5U4. I have not checked my voltages since sorting out the heater circuit resistor.  I mistakenly installed a 1.8K resistor in place of what should have been a 1R8 resistor.  The 1R8 resistor actually measured 1.5 ohms.  Not sure if this is too low.  Would appreciate your thoughts.  Thank you again.

Best regards.

Philip

hagtech

Re: 5AU4GB into 5Y3GT
« Reply #5 on: 16 Oct 2014, 06:00 am »
Hard to guess what the long term effects of pulling 3 amps on the 5V winding.  Tranny will definitely run hot.  I can't recommend it.  Try the 5AR4.

jh

Philip A

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Re: 5AU4GB into 5Y3GT
« Reply #6 on: 16 Oct 2014, 01:15 pm »
Hello Jim.  Thank you for the comments.  I will look into purchasing a 5AR4 tube.  Just curious if you would know off hand if there is a transformer that would make the 5U4 tube work, and if I would need to change anything else.  Thank you again.

Philip A

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  • Posts: 17
Re: 5AU4GB into 5Y3GT
« Reply #7 on: 16 Oct 2014, 03:15 pm »
Hello All.  After checking specs online, I have found a Hammond Transformer that matches the specs of the 370BX except the secondary output amperage is higher.  Here are the results.

                                             370BX                                                               370EX
 
Total Power (VA)                     55VA                                                                 119VA
AC Secondary RMS                  550V C.T.@ 58ma                                              550V C.T. @ 144ma
Filament #1                            5V C.T. @ 2A                                                     5V C.T. @ 3A
Filament #2                            6.3V C.T. @ 2A                                                  6.3V C.T. @ 3A

I look forward to everyones thoughts on using this transformer.  Thank you again.

tubesurf

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Re: 5AU4GB into 5Y3GT
« Reply #8 on: 17 Oct 2014, 12:06 am »
Not sure what you are trying to accomplish by modifying the C2 to use the 5U4.   Jim recommended the 5AR4 and there are other rectifier tubes you can use with the existing transformer.  If you search the forum, there are quite a few threads discussing different rectifier tubes compatible with the C2 as designed.   I don't think volume pot position should drive your proposed redesign of the C2.

Philip A

  • Jr. Member
  • Posts: 17
Re: 5AU4GB into 5Y3GT
« Reply #9 on: 17 Oct 2014, 03:16 am »
Hello tubestuf.  Thank you for your comments.  First let me say I am not trying to reinvent the wheel here.  I also defer to Jim on this, however what I am trying to accomplish is getting the best sound, (to my ears) out of my system.  I listened today for an hour with the 5U4.  I kept checking the transformer, and it did not seem to be getting too hot.  I will machine my C2's transformer cover to hopefully vent away excess heat.  I was also a bit off in my initial statement regarding volume pot position.  It's around 11 o'clock vs 1 o'clock for the 5Y3 tube at the volume I normally listen too.  This seems to be in the "sweet spot" for my tube amp.  I have also read the posts relating to other rectifier tubes that work in the C2.  Unfortunately I do not have any of these on hand.  I stand by my previous post that the 5U4 tube sounds better.  More bass.  Cleaner fuller sound, and less hiss and hum.  Most likely due to my amp not being close to its clipping point.

Today I received the Granite Audio Phono Stage burn in CD.  My C2 is cooking as I write this, (with the 5Y3 installed).  I have also reinstalled the removable ground pin on the power cable feeding my C2.  After rerouting and twisting wires the hum is gone...for the most part.  I agree that there may be a ground loop elsewhere in my system as Jim has suggested.  There is definitely some transformer hum from another unit.  I have ordered a R-Core transformer to correct this.  Let me also say the "hum" I am trying to remove is very, very small.  It is just higher than I am used to hearing in my system. 

I have also ordered the 370EX transformer, and will post my findings here.  For me, the great thing about this hobby is that there are no absolutes!  What sounds good to you may not sound good to me.  I believe that is why we are all here.  To build and modify our equipment to be the best they can be, and this forum allows everyone to exchange ideas.  That said, every component in my system is highly modified.  From my Altec Lansing 604E's to my Emotiva ERS-1CD player, to my point to point tube buffer stage and Xindak tube amp.  I also have two highly modified phono stages.  A Jolida JD9 with two separate power supplies and a 36db/Octive Subsonic Filter and a Pro-ject PhonoII that is also modded.   

If you have looked at my other post you will see that I spared no expense (within my budget) building my C2.  A rough total is $1527.19 + the power cord and the new transformer.  I tried building it for "around" $600, but I exceeded that on my first parts order.  I will also be purchasing a really good fuse.  I have Hi-Fi Tuning fuses in the rest of my system and they "sound great".  I will be installing it after all the mods are done.

I also feel that things posted here should be on a positive note.  I always try to be respectful and polite on these forums.  I also do not offer an opinion on something I have not personally tried.  There is something to be said regarding thinking outside the box.  I hope that is what I am doing here. 

Respectfully

Philip