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michaelwardjoines

Rectifier substitution (aka rolling)

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I have one amp which came with (and is specified to use)  a CV378 rectifier. I have another amp which came with (and is specified to use)  a 5UG4 rectifier. Neither instruction manual discusses or says not to use a different rectifier, but as noted, specifies the respective tube. It’s time to retube.

 

Depending upon what you read (God bless the internet), these tubes are interchangeable or cannot interchange or are bested by a 5R4GYS.

 

It’s time to retube. May I please have some advice and thoughts from our tube experts ?

 

Thanks in advance.

 

Mike

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43 minutes ago, michaelwardjoines said:

I have one amp which came with (and is specified to use)  a CV378 rectifier. I have another amp which came with (and is specified to use)  a 5UG4 rectifier. Neither instruction manual discusses or says not to use a different rectifier, but as noted, specifies the respective tube. It’s time to retube.

 

Depending upon what you read (God bless the internet), these tubes are interchangeable or cannot interchange or are bested by a 5R4GYS.

 

It’s time to retube. May I please have some advice and thoughts from our tube experts ?

 

Thanks in advance.

 

Mike

 

 

I would suggest you buy a Electro Harmonix 5U4GB from Antique Electronic Supply, for only $15.40, and use that.  Compared to your " CV " tube, which is a GZ37 :

 

1)The GZ37 has a maximum current per plate of 750 mA.

 

2) The EH 5U4GB has a maximum current per plate rating of 1,000 mA.  It is rated to do 4.7 AMPERES on a peak instantaneous basis.

 

3) The GZ37 has a cathode, whereas the 5U4GB is a DIRECTLY HEATED rectifier, has no cathode.

 

( some would say the directly heated rectifier tubes are nicer sounding, more IMMEDIATE sounding, because they do not have a cathode to get in the way.  Its sort of like a 2A3 VS a 6L6. )

 

The directly heated rectifier ( 5U4GB ) will have a slightly higher noise level, than a rectifier with a cathode, but in an amp ( and not a preamp ) your signal levels are higher, and this should not be a factor.

 

One word of advice, IME, it takes an EH 5U4GB a full 75 hours to break in, and sound its best.  In really good circuits, the tube displays a " snappy" instantaneous music presentation, such that it is all I use in amps.  I use TWO EH's in my KT88 SE DC amp.

 

Jeff Medwin

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NEVER substitute a filament type rectifier for a cathode type without checking the working voltage rating of the power supply electrolytic capacitors!   This needs to be significantly higher for the former type of rectifier due to the peak voltage the caps will "see" at initial turn-on.  Cathode type rectifiers allow power supply caps to be used with a much lower working voltage. 

 

Manufacturers typically select tubes for a specific reason.  Indiscriminately changing to something else isn't always a wonderful idea.

 

As to the "sound" of rectifier tubes, I can only say that if the tube delivers the correct voltage to the circuit as designed, all is well.

 

I urge you to call the manufacturers of your amps to discuss any changes you contemplate.

 

 

Maynard

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The 5R4 you mention is also a filamentary rectifier, so it has no separate cathode.  However, it only has a 650 mA. rating per plate, VS a 1,000 mA. rating of a 5U4GB.

 

Attend to Maynard's proper concerns, but my vote is still the same, an EH 5U4GB after 75 hours break in.

 

Jeff Medwin

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I have found vintage rectifier tubes last longer than new production tubes. I prefer Mullard.

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2 hours ago, kevinmi said:

I have found vintage rectifier tubes last longer than new production tubes. I prefer Mullard.

  

 

Mullard.thumb.JPG.f08df3df2922ecf7b3589865c30d3eac.JPG

 

1839017289_E.H.5U4GB15_40.thumb.JPG.ae92292ea89b690088a4d692978ec112.JPG

 

 

 

Mullard ( eBay ) at $325 a tube       VS          $15.40 ( Antique Electronic Supply ) a tube. 

 

21.10  times   cost difference. 

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15 hours ago, Jeffrey D. Medwin said:

  

 

Mullard.thumb.JPG.f08df3df2922ecf7b3589865c30d3eac.JPG

 

1839017289_E.H.5U4GB15_40.thumb.JPG.ae92292ea89b690088a4d692978ec112.JPG

 

 

 

Mullard ( eBay ) at $325 a tube       VS          $15.40 ( Antique Electronic Supply ) a tube. 

 

21.10  times   cost difference. 

 The Philips are priced on rarity. 

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On 3/6/2020 at 8:06 AM, michaelwardjoines said:

I have one amp which came with (and is specified to use)  a CV378 rectifier. I have another amp which came with (and is specified to use)  a 5UG4 rectifier. Neither instruction manual discusses or says not to use a different rectifier, but as noted, specifies the respective tube. It’s time to retube.

 

Depending upon what you read (God bless the internet), these tubes are interchangeable or cannot interchange or are bested by a 5R4GYS.

 

It’s time to retube. May I please have some advice and thoughts from our tube experts ?

 

Thanks in advance.

 

Mike

Here is a link to the Tube Substitution Handbook  http://www.smcelectronics.com/DOWNLOADS/TUBE SUB 1980.PDF

 

You could use a 5R4GYS instead of a 5U4G. The CV378 in an indirectly heated tube. You should check with the manufacturer before using something else. It's a very long life tube and if you could have it tested it may be fine. If you have to buy one Upscale is a trusted seller. https://upscaleaudio.com/products/mullard-gz37-cv378

 

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1 hour ago, Les Lammers said:

Here is a link to the Tube Substitution Handbook  http://www.smcelectronics.com/DOWNLOADS/TUBE SUB 1980.PDF

 

You could use a 5R4GYS instead of a 5U4G. The CV378 in an indirectly heated tube. You should check with the manufacturer before using something else. It's a very long life tube and if you could have it tested it may be fine. If you have to buy one Upscale is a trusted seller. https://upscaleaudio.com/products/mullard-gz37-cv378

 

 

Hi Les, 

 

One should consider this

 

The 5R4 you mention is also a filamentary rectifier, so it has no separate cathode.  However, it only has a 650 mA. rating per plate, VS a 1,000 mA. rating of a 5U4GB. "

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21 hours ago, Jeffrey D. Medwin said:

Mullard ( eBay ) at $325 a tube       VS          $15.40 ( Antique Electronic Supply ) a tube. 

 

21.10  times   cost difference. 

I've gotten Mullard 5ar4 and GZ-33 rectifier tubes for $100 each. I guess it pays to shop around.

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10 minutes ago, kevinmi said:

I've gotten Mullard 5ar4 and GZ-33 rectifier tubes for $100 each. I guess it pays to shop around.

 

 

True, but should one use them in a really well-designed amp? 

 

The $100 Mullard 5AR4 does 825 mA. per plate continuous, and 3.7 A. peaks, whereas the under $16 .00 Russian E.H 5U4GB does 1,000 mA,. per plate, and 4.6 A. peak.   Download both data sheets and see.  75 hours to break-in an E.H.

 

Jeff 

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3 minutes ago, Jeffrey D. Medwin said:

True, but should one use them in a really well-designed amp? 

The better question might be: should you trust a $16.00 rectifier tube in an expensive amp? I've had no luck with EH tubes

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12 hours ago, kevinmi said:

The better question might be: should you trust a $16.00 rectifier tube in an expensive amp? I've had no luck with EH tubes

 

 

Depends upon :

 

  (1) what you call an "expensive amp," and

 

  (2) what are the circuit ramifications if a 5U4GB were to fail, and

 

  (3) how WELL the amp is designed and made, and...

]

  (4) how many EHs  have you had experience with. 

 

I have a manufacturer friend who regularly uses EH 5U4GBs, which is a Russian military tube, as a rectifier tube-of-choice, in supremely well designed directly coupled SE DHT tube amps.  The amps retail for about $19.000 a pair.  He tells me, out of 50 EH 5U4GB tubes, 3 may fail. 

 

I take it, as a private party, you have not equal direct-experience in judging EH 5U4GBs, as does my manufacturer friend.

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18 hours ago, Jeffrey D. Medwin said:

I take it, as a private party, you have not equal direct-experience in judging EH 5U4GBs, as does my manufacturer friend.

I haven't used EH 5U4GB's, only 5AR4/GZ34, and KT-88 power tubes. A 6% failure rate isn't anything to brag about.

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30 minutes ago, kevinmi said:

I haven't used EH 5U4GB's, only 5AR4/GZ34, and KT-88 power tubes. A 6% failure rate isn't anything to brag about.

 

 

Agree with you, but I was not bragging about that !!    $15.40 VS $100.00,  is a 649% cost difference.   But you can take the last word on this !!

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Posted (edited)

Great advice; it's just what I was hoping to read!

 

Thanks and see you in Hope next time.

 

Mike

Edited by michaelwardjoines

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On 3/6/2020 at 12:33 PM, tube fanatic said:

NEVER substitute a filament type rectifier for a cathode type without checking the working voltage rating of the power supply electrolytic capacitors!   This needs to be significantly higher for the former type of rectifier due to the peak voltage the caps will "see" at initial turn-on.  Cathode type rectifiers allow power supply caps to be used with a much lower working voltage. 

 

Manufacturers typically select tubes for a specific reason.  Indiscriminately changing to something else isn't always a wonderful idea.

 

As to the "sound" of rectifier tubes, I can only say that if the tube delivers the correct voltage to the circuit as designed, all is well.

 

I urge you to call the manufacturers of your amps to discuss any changes you contemplate.

 

 

Maynard

 

Hello Maynard, 

 

According to the Original Poster, he wrote his amp is specified to be able to use a " 5UG4 "........... and,.. he really meant to say ....a" 5U4G " . 

 

The thread's suggested $15.40 5U4GB by Electro Harmonix, and any usual 5U4G are each directly heated dual plate rectifier tubes.  They use a beefy 3 Ampere filament. 

 

Since the Manufacturer actually specifies a 5U4G , there should be minor concern with the good advice you posted above, as far as using a rectifier with a cathode, VS. a directly-heated 5U4G or 5U4GB. Tube socket pin-outs are exactly the same.  Correct me please, if I am in error.

 

Jeff 

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Jeffrey, you recommended  a 5U4 as a substitute for the GZ37.  That is not appropriate unless one knows the working voltage of the power supply caps which may be exceeded at initial turn on with the former.

 

 

Maynard 

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I find it amazing that after so many posts a lot of advice was given without asking a very important question - what amps are those?

I mean manufacturer, model...

Another interesting fact is that the discussion was about the technical characteristics of the rectifiers (some of which are current production, therefore quite approximate in their ratings - if I may). The accent was not given on the sound said rectifiers will impart on the amps.

Once I know the application, I can give advise - which of course doesn’t seem be needed in this thread - as the OP has already procured some replacement rectifiers?

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Posted (edited)

Sorry for the typo; my Cary SLI-80 specifies the CV729/5U4 rectifier. My Cary CAD-300SE specifies the CV378.  I listen through a pair of La Scalas primarily to jazz & vocals (although I played U2's Joshua Tree at appropriate levels yesterday...) 

 

Thanks to all.

 

Mike

Edited by michaelwardjoines
add'l info

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