where to get good 5AR4 's

[jlefevre1@me.com]

I am down to my last very old and worn out american made 5AR4's. am also using some old 5U4's I bought about a dozen JJ 5AR4's about two years ago. Am attemping to use them in Dynaco ST70 and Mark III. Had a 5U4 blow out a filament last night. Went through 4 of the new 5AR4. They arced and blew the incoming line fuse as they were warming up for the first time. Found and old RCA 5AR4 and a GE 5U4.. Put them in and they both worked fine. Did I get a bad batch of of the JJ's. Is there a better brand of new 5AR4's At some point I will run out of the old stuff and have to get some good rectifiers somewhere.

[Glowbug]

tubestore.com, tubedepot.com, Jim McShane...all good sources for NOS.

[Eli Duttman]

JJ needs to do something about their Octal production, YESTERDAY. The way things stand now, it's all garbage.

For a while, Chinese 5AR4s were OK. Then the sh*t started to flow again.

Saratov, Russia, made 5AR4s are probably the best of the current production.

Of all current production 5U4s, only the EH 'GB is any good.

5R4s are strictly a NOS proposition.

I 2nd the Jim McShane recommendation. No baloney from Jim.

Given the hassle associated with vacuum rectification, I suggest you switch the ST70 to SS B+ rectification and combination bias. A CL150 inrush current limiter will slow B+ rise down enough to allow the instant on bias supply to protect the "finals" against cathode stripping. A 100 Ω/330 μF. bias network under each O/P tube pair "eats" the extra Volts SS rectification yields, provides the "idle" current test point, and makes the single bias adjustment/channel a non-issue. BTW, EL34 matching requirements are relaxed a bit, when combination bias is employed. Close matching of gm is a must, but cathode current matching need be only reasonably close.

[Bas Horneman]

Another unhappy JJ 5AR4 customer...Mine are ornaments.

[BillEpstein]

tubesandmore.com aka antique eelctric supply. whenever I order nos, they surprise me with delicious brand new sylvanias or mullards or .... Its like a box of chocolates.

[Evenharmonics]

Originally Posted by jlefevre1@me.com

Went through 4 of the new 5AR4. They arced and blew the incoming line fuse as they were warming up for the first time.

Is your ST-70 power supply in good working order? I have one restored with new parts and JJ 5AR4 works fine so far. I did have a problem before the restoration though.
Here is a discussion on remedying the rectifier tube arc issues.

[Geek]

Sovtek 5AR4's are the only ones I know that will survive a Dynaco power amp supply.

Cheers!

[Ty_Bower]

Have you tried installing solid state diodes in series with the plates of the rectifier tube? That seems to help some people. There's a discussion of it here:
Diodes On Rectifier Question - Page 2 - diyAudio

[Geek]

There's an example of that in the top schematic here:
*** t3h GeeK ZonE *** DynaMutt - Page 2

(as well as a SS replacement, but you need to add a STDBY switch or delay)

Cheers!

[DigitalJunkie]

Originally Posted by Geek

Sovtek 5AR4's are the only ones I know that will survive a Dynaco power amp supply.

Cheers!

I had two in a row arc-over,with the stock supply.
I plan on adding the SS diodes on the plates,once I get a new 5AR4.