6L6GB vs 6L6GC vs 5881

[cray]

Hello.
I have a newly acquired vintage Harman Kardon A-250 epic that needs new tubes (plus the typical going over with associated cap, resistor etc replacement). The amp was intended to use 6L6GB power tubes but I know that the 6L6GB is no longer in production and I'd like to find a safe/appropriate replacement. Sure, I'll be sending this off to my tech and assume he'll do it right but I've seen so many disagreements regarding the interchangeability of these tubes, ranging from "it'll be fine" to "you'll set your house on fire", that I want to get the straight dope (from those really in the know) to be more informed. I've checked "hifi engine" for technical sheets but there is only an owners manual with a schematic. I've also shopped around for NOS 6L6GB's but find a lot of individual tubes from non matching manufacturers.. It seems much easier to find an ideal equivalent from sovtek, mullard et al, and buy a set of four new ones. As mentioned above, someone will be doing the work for me (I've used a few different techs and all have great knowledge but I really like to be well informed so that I can question any choices made.
Thanks in advance for friendly advice.

 

[gadget73]

6l6gb and 5881 have the same ratings. A 6l6gc is rated for higher voltage but will work perfectly fine in a circuit for a 6l6GB or 5881.

 

[Steve O]

Just adding to gadget73 comments, from a performance perspective, any 6L6 type will work in your amp. This includes metal 6L6 and 1614*, 6L6G, 6L6GA, 6L6GAY, 6L6GB, 6L6GC, 5881, 7581, 5932/6L6WGA as well as Russian 6P3SE & 6P3S. All current mfg 6L6 types should also work although due to conflict in Ukraine, new Russian tubes may be difficult to get and will probably be pricey. Some versions physically larger than others so you'll have to determine for yourself which ones fit your amp

* Metal 6L6 types internally connect pin 1 to the metal shell with intention of pin 1 being grounded at the socket. If you use metal tubes you MUST VERIFY that pin 1 on the socket is not used as a tie point with possible high voltage present which would charge the shell with the same voltage.

Edit: Forgot to mention KT66 and EL37. Although characteristics of these two are similar to 6L6 they're not exact replacements. Both draw significantly more filament power and therefore may not be appropriate for your amp. I mention these two because they frequently get recommended as sonic bliss subs for 6L6 but no mention is made of the higher filament draw. Some amps have no problem. Some amps might become overheated. If in doubt, stay with 6L6 types.

 

[TriodeLuvr]

The least expensive option for your amplifier is the 6P3S-E. It's a drop-in replacement with ratings well above the 6L6GB. Try to find a matched quad if you don't have testing capabilities.

Jack

 

[Palustris]

I've checked "hifi engine" for technical sheets but there is only an owners manual with a schematic.

It is always best to check for technical details yourself since, as you say, the internet is awash in misinformation. There is an amazing resource for tube technical data at Duncan Amplification. Just insert the tube type for which you need details. That will bring up an array of datasheets from different manufacturers. In particular you need to know the maximum ratings:


Compare the maximum ratings of the tube (in this case a 6L6GB) with the schematic of the amplifier in which the tube will be used to ensure none of the max ratings are violated.

 

[nerdorama]

New quads of JJ 5881 and 6L6GC are in stock at Eurotubes and at what seems a reasonable price.

 

[Lavane]

I'm a fan of the Tungsol 5881's. I have some old stock and new manufacture Tungsols and they both sound the same to me. The Russian Reflector 6P3S-E's are n8ce tubes also and won't break the bank. But shipping will take a little time coming from Ukraine. I bought a matched quad of them and they were matched very close. The seller I bought from uses one of those Russian military tube testers.