Jump to content

Rectifier substitution (aka rolling)


michaelwjones

Recommended Posts

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

Link to comment
Share on other sites

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

  • Like 2
Link to comment
Share on other sites

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

 

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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

  • Like 1
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

  • 4 weeks later...

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?

Link to comment
Share on other sites

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
Link to comment
Share on other sites

3 hours ago, michaelwardjoines said:

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

Hello Mike,

 

The Cary SLI-80 is an integrated amp with KT88 tubes, and all tubes used in it are also indirectly heated - this means that at startup the B+ will rise very fast to levels higher than operational, and drop some 20-30 seconds later gradually to the operational level. It’s strange that a direct heated rectifier tube (actually 2) are applied here, as the circuit would technically benefit from an indirect heated rectifier like the 5AR4/GZ34.

The issue would be that B+ would result at least 15V higher with 5AR4/GZ34 and this might be a problem if anode dissipation is already high for the output tubes.

on the other hand, besides 5U4 types, you could use 5R4 types which would result in lower B+ and possibly slightly lower output power - but would impart a different sound signature that you might like even better.

The russian 5C3S is similar to the 5U4 and if from a good batch (old SSSR production) might be absolutely interesting given the lowish price.

 

On the contrary, the CAD300SE has got 300B direct heated output tubes, thus the tubes will start conducting almost at the same time a direct heated rectifier would.

The CV378 aka GZ37 has a slightly higher voltage drop than the 5AR4/GZ34 but you should be safe with the latter. On the other hand the only issue you might have with 5U4 could be 3A heaters vs 2A for the GZ3x types - which should not be a serious problem because we are talking about 3VA that are certainly not going to tax the power transformer too much.

5U4 should be safe to use here as the B+ will be slightly lower, and the 5R4 is absolutely safe to use (2A heater), but will yield probably 30V less than the GZ34 and you will loose some power - which in your case with the La Scala is definitely not going to be a problem. 
 

Bottom line is that you should be able to use any of the mentioned rectifiers in your 300B amp, while the integrated is slightly pickier - although the same rule might apply. What you should do is “roll” rectifiers and base your choice on the sound you are getting.

 

 I have little experience with current production rectifier tubes, and would advocate either NOS US tubes or NOS Soviet tubes (including the Sovtek jugged edge anode GZ34). I guess you should avoid the Phillips GZ34 as it is too expensive compared to its sound quality - unless you have money to throw away (we only live once) or are a collector.

Link to comment
Share on other sites

On 3/8/2020 at 7:12 PM, 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. 

These MUST be fakes... never heard of Philips 5U4 and the writing is totally wrong font... plus etched (burnt in) codes are nowhere to be seen, and that’s definitely a sign the only Philips on that picture is the writing on the boxes.

The price is exorbitant to say the least - for 5U4Gx (should be GB but these are definitely fishy.

Another thing I don’t understand is why the ad mentions several tube types that have nothing in common besides being popular? 

Link to comment
Share on other sites

On 3/6/2020 at 6:06 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

 
Buy the best tubes you can afford. Vintage rectifier tubes last for a really long time in all the tube amps I’ve owned.

 

Wb

Link to comment
Share on other sites

On 4/4/2020 at 1:24 PM, Alex Kitic said:

Another thing I don’t understand is why the ad mentions several tube types that have nothing in common besides being popular?

It's to take advantage of fLeaBay's search feature. Try typing in RARE and see how much stuff pops up.

Link to comment
Share on other sites

4 hours ago, Davecv41 said:

It's to take advantage of fLeaBay's search feature. Try typing in RARE and see how much stuff pops up.

Thank you for your input. That is exactly what I thought.

In my view, this gives an idea of the kind of seller involved (not serious, just grabbing the money and flying to the next deal).

Also, most sellers do that, so this falls into the “normal” category, I guess.

It’s the ugly side of everyday life.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...