5R4 Test

[stokes]

I saw a thread,I believe it was on this board,concerning the 5R4 rectifier.It seemed there was a question as to this tubes reliability in guitar amps,because the tube data recomends a 4uf input capacitor.As we all know the tube data usually gives conservative ratings.I picked up 6 NOS JAN 5R4's,and ran some tests.I started with a 47uf input cap,went to 100uf,150uf and finally 220uf.In each case I got no arcing at start up or when playing full out for 10-15 minutes,leading me to believe the tube is safe to use.Just to be sure I wasnt missing something,I ran my findings past a well known amp builder and author,who I wont name,and although he had never tried it himself,he agreed that it would be safe to use.So if you have these tubes dont be afraid to use them,they dropped a couple more volts than the 5U4 but I could not hear any significant difference.I cant say for sure if other brands would perform the same but these were JAN Phillips,and were a lot cheaper than the 5U4 or 5V4's.

[Enzo]

My RCA shows 20uf filter input for 5R4.

[Bruce / Mission Amps]

I saw a thread,I believe it was on this board,concerning the 5R4 rectifier.It seemed there was a question as to this tubes reliability in guitar amps,because the tube data recomends a 4uf input capacitor.As we all know the tube data usually gives conservative ratings.I picked up 6 NOS JAN 5R4's,and ran some tests.I started with a 47uf input cap,went to 100uf,150uf and finally 220uf.In each case I got no arcing at start up or when playing full out for 10-15 minutes,leading me to believe the tube is safe to use....

I've used MANY of these with 16uF through 33uF caps and so far have had no failures from high capacitance filter caps.

Bruce

[stokes]

The 2 RCA manuals I have dont list the 5R4,but any data I've seen show 4uf as the recomended input.Mine are from '54 and '60.I went to Duncans tube search and there is various links to the data and they all show 4uf.Anyway I am not sure if the thread was on this board,could have been elsewhere,it was a while ago.http://www.mif.pg.gda.pl/homepages/f...49/5/5R4GY.pdf This is a link to RCA data showing 4uf.But 4 or 20 it will still take a lot more.

[Enzo]

That is from 1948. It says also typical application 4uf, not max input capacitance. In 1948 4uf was a bigger deal than it would be 60 years later. How old are the tubes you have.

I see two RCA reprints on the market - RC10 and RC30. The older RC10 is a cool book, but it lacks many later tubes we commonly use, plus i,[rpved versions are not in it for many tubes. The RC30 is from like 1973 or thereabouts. You really ought to have the newer one on the shelf along with the old.

I find it interesting the altitude specs for the tube. Both in the 1948 sheets and the later books. Apparently made for avionics. I think military stuff was running at 400Hz, so filters could be a lot smaller than for 60Hz. That might be part of the deal.

Not sure if I have some of those or not.

[stokes]

They are JAN Phillips 5R4GA with the brown base, have the code 8726 on the tube and the boxes are marked 4/87.The 2 RCA manuals are,like I said,'54 and '60.I'm surprised they dont have this tube,since it was in the '48 book and in your newer one.Like I said earlier I did this because I saw a discussion about the 4uf capacitor issue.It may have been on a different board but the argument was that the tube wasnt suited for guitar amps,I got these for $18 on ebay,for six tubes in clean original boxes,nice looking ,definately unused.I really thought the 220uf would blow one,was very surprised it stood up.I read in a book that it could be subbed for 5V4 or 5U4 and wanted to see for myself.The author was surprised it held up to the 220 also.I was wondering what the elevation data was about too.That makes sense,the 4uf recomendation also.Just goes to show,dont always believe what you read.I'm going to put them in a couple of amps and see how long they hold up,should do okay.

[Bruce / Mission Amps]

The bigass ones are the mil spec tubes:
http://hififorum.knaak.dk/niro/IMGP0333.JPG
http://home4.highway.ne.jp/atg/image/5R4G.jpg
I like the 5R4GA tubes in the twed 6L6 amps and have amased a decent selection of these and the standard base tubes.

Bruce

[stokes]

I've seen that big one on ebay before.The ones I got are the straight glass with the brown base,like the GE 5U4 but taller-5".That big sucker you got looks like it would be tough to fit in some amps.I'd post a pic of one but that is beyond what I even want to know about computers.Tech wise I'm still in the '50's!Okay,maybe the '60's.

[Wild Bill]

Merry Christmas, y'all!

Not to disagree with what has been posted but Mr. Stokes started off by saying he did a test relating to voltage, in that he saw no evidence of arcing.

Is that really the issue? I thought the limit on the size of the 1st filter had more to do with the initial inrush CURRENT when the cap is first charged up!

If so, that would mean the caution is all about stressing the 5R4 with charging current pulses. The cap would work just fine until it failed months or years prematurely.

As a sidebar, it's 40 deg F and rainy up here in Ontario, Canada. The greenhouse effect doesn't seem so bad to us Canucks...

Wild Bill

[Bruce / Mission Amps]

Not to disagree with what has been posted but Mr. Stokes started off by saying he did a test relating to voltage, in that he saw no evidence of arcing.

Is that really the issue? I thought the limit on the size of the 1st filter had more to do with the initial inrush CURRENT when the cap is first charged up!

If so, that would mean the caution is all about stressing the 5R4 with charging current pulses. The cap would work just fine until it failed months or years prematurely.

Wild Bill

Right and as you probaly know, but other might not, a simple way to limit damaging inrush current is to install a 2 to 5 watt power resistor with a fairly low value, like 33-47 ohms, right after the cathode of the recitifer and before the first filter cap.

[Wild Bill]

Yep! What he said!

Right and as you probaly know, but other might not, a simple way to limit damaging inrush current is to install a 2 to 5 watt power resistor with a fairly low value, like 33-47 ohms, right after the cathode of the recitifer and before the first filter cap.

Yeah, and if you have a 5R4 it's cheaper to use the resistor than to buy a different rectifier tube.

BTW, before I learned about the filter value limit I cheerfully used 5R4s in a bunch of 50 watt projects and never had a problem. Then again, tube rectifiers seem to last for years and years anyway so maybe a reduction in LOOOOONG life is merely LOOONG life!

Hope you had a merry and fine Christmas, Bruce! I expect you've had your share of snow...

[stokes]

If there is going to be any damage caused by the initial inrush current,you will see arcing in the tube.As for long term problems,that is how a rectifier wears out eventually anyway,so the real test is to see how long it lasts.The amp I have it in gets a lot of use on a daily basis,and so far after about a month there is no problem,I even took the tube out and tested it,after reading Wild Bills concern, and it still reads as strong as it did when I first installed it.This amp gets used 2 or 3 times a day between myself and my sons and their friends who are always in my basement jamming,from the amount of use it has had over the last month,I would have to say it is going to hold up just fine.As for the extra power resistor between the rect.and first filter cap,this will also cause more sag,which may or may not be desireable.That is an old trick to induce a little sag into a solid state rectifier.