12AX7/ECC83 Suffixes ?

[jefrs]

Hi, it's a bit of a nightmare choosing replacement ECC83...

Please would someone explain what the various suffixes mean. As in -STR, -C e.g. ECC83-STR, ECC83-C, 12AX7A-C, 7025-STR.

What makes these different to bog-standard ECC83? Because there is no bog-standard 12AX7/ECC83/7025 etc.

These suffixes do not exist on valve data sheets. It seems to me that all ECC83 types have much the same published spec, if you can find it, and no, the valves are not the same are they.

[sjhusting]

'STR' is 'Special Tube Request' or something similar.

In the old days, the suffixes had meaning. These aren't the old days anymore, and the suffixes don't mean much.

Even when they did mean something, it had little to do with tone. Some of the suffixes had constant meaning (like 'G' in 6L6G = glass, as versus 6L6 = metal) or the 'Y' in 6V6GTY = meant a base of a particular composition. There's a list of all the standard suffixes somewhere on the net. Others just meant a characteristic change - 12ax7, 12ax7a, 6L6GA, GB, GC - might have been plate dissipation, whatever.

Nowadays the suffixes dont mean much of anything.

Different tubes of the same type are constructed differently, and will sound different. You either have to try them all out yourself or get advice. Here's one view of it for current tubes:

http://www.tube-town.net/info/doc/tt...tubes-engl.pdf

steven

[jefrs]

Originally Posted by sjhusting

Different tubes of the same type are constructed differently, and will sound different. You either have to try them all out yourself or get advice.
steven

Thanks Steven.

I've been playing the swap the valve game, it can be an expensive hobby.

Watford Valves have a similar review at http://www.watfordvalves.com/cgi-bin...streport_2.pdf, which muddies the water even more.

I read glowing praise of the latest cryogenic what-ever tube, buy one and it's a wimp, or it sounds like an angry wasp in a jam-jar. Only to be told by knowledgeable type that cryo is added bs, avoid and only use NOS.

I find some NOS Mullards ECL82 for odd-ball Wem Westminster type, wow! But they were in white boxes, er - Mullards were all tested and only got sold in Mullard boxes, only rejects get re-boxed. They immediately went red plate and fried amp. Fixed that and Telefunken came to the rescue.

So how do I select preamp valves? Same with power valves, only there are less options. What's good in what position? Laney were good enough to email advice for the L5T :-
V1 = TAD RT030 7025/E83CC HIGHGRADE Premium Selected
V2 = TAD NN001 12AX7A/ECC83-C SINO
V3 = TAD NN003 ECC83S JJ Red Label (former Tesla)
V4 = TAD NN871 EL84-STR (-6BQ5)
Like the amp was not exacly fitted with these:- V1 = V3 = RT030, V4 = NN871 but V2 was a no-name, and V2 went belly up. Now I've got a box of old bottles, so an old Mazda is riding in V2 and a Harma 7025-STR, which I gather is a selected, re-badged JJ ECC83S riding V3.

It's a lottery.

[Dacious]

Back in 'the day' the nomenclature indicated different specs - for instance, first stage preamp tubes were 7025 meaning low-noise, whereas your tremolo driver or phase inverter could be a 12AX7. Tubes were sorted for low-noise ones which were marked accordingly. (Did you know missiles and bombers used to have tubes?). Now that 99.9% of tubes are used in audio, all of them are made to be low-noise designs.

ECC83 is just the European standard designation for 12AX7, ECC82 is 12AU7, ECC81 is 12AT7. Like EL34 (Euro) is 6CA7 (US) and EL84 is 6BQ5 in America. JAN tubes were usually ruggedised standard tubes for Joint Army-Navy. Often just standard tubes put through a selection processs.

STR= Special Tube Requirement, usually indicated by Fender for amps with high plate volts like late Silverface. Never seen anything about STR 12AX7s, usually because the preamps were kept at within-spec volts.

Today you can safely plug in any 12AX7 where a ECC83, 7025 is called for. There will be differences in sound - always were.

[jefrs]

Thanks Dacious,
you have answered the STR question.
I was not asking about the official designations but about the added suffixes we see as in ECC83-C, wot's with the -C bit, it's not an E83CC and it's not a ProElectron designation.
I was not actually asking about the naming system as in a 12AX7 is an ECC83 but a 7025 is not because it has a different type heater, but it does beggar the (rhetorical) question, what on earth is a 7025/E83CC.
So if the STR designation is redundant on a preamp tube how does a JJ/Tesla ECC83S get re-badged as "ECC83/7025 HARMA DR250-CRYO (HARMA Cryo valves)" [phew!] and marked "Harma Drive Tested STR-7025". This what a colleague knowingly called added bs. It's a nice tube in the drive position, but sometimes I feel I'd be best served by a ouija board for picking valves.

[Scott S]

Those are good questions for whatever store is relabelling these tubes. I just make things easy for myself by ignoring any suffix that wasn't used in the 1960s.

- Scott

[jefrs]

Actually Watford Valves (Harma) are good at supplying valves, and provide information, and more if asked. But with 24 pages of valves listed... :-(

[Dacious]

The suffix usually indicated a revised rating - i.e. and going on memory, 6L6G or 6V6G indicated a later than 1940/50's version glass envelope, important for those tubes like them that were previously available in metal.

6L6GAs were usually about 400 plate volts
6L6GBs were usually about 450 plate volts
6L6GCs were the same volt rating but more current for higher dissipation.

Sometimes the same tube was re-rated - for instance RCA 7027As which were rated for a much higher voltage than 6L6GCs were identical except for the extra parallel internal pins used in them. 5881s were rated only 350 volts, but many examples will exceed that rating and are more indistructible than some later tubes.

You really need a tube manual, or there are several tube data sites online with the info like Tube Data Search Locator or NJ7P search engines.

NJ7P tube data search

The important thing to remember is: more isn't necessarily better -like the Sovtek EL84M which is a rugged Russian millitary tube. Sounds OK, lives a long time but is probbly sonically inferior to other current production EL84s for audio.

Some of the siffixes indicated same characteristics in a different envelope = 6V6GA (IIRC) coke bottle glass, GT = commonplace conventional octal envelope with a wide 6L6-type base, GTY = later tall slim envelope on a smaller octal base with the same pinout and config so interchangable.

Good to have a manual - I have a 1976 RCA manual. Even then it doesn't list some types for which RCA seemingly sold no equivalent. Same with the 1950's Phillips Miniwatt manual.

[Scott S]

You sure about those ratings for 6L6GA and 6L6GB, Dacious? Everything I've read gives the same specs as the 6L6 (19W, 360V plate, 270V screen).

[Dacious]

Actually the jump is in C's - shows you shouldn't rely on memory.

Metal 6L6
Maximum Ratings (Design Center Values)
PentodePlate Voltage ................................. 375 VGrid No. 2 Voltage ............................ 250 VPlate Dissipation ............................. 20.5 W
Grid No. 2 Dissipation ........................ 3.5 W

6L6GA-GB

PentodePlate Voltage ................................. 360 VGrid No. 2 Voltage ............................ 270 VPlate Dissipation ............................. 19 W
Grid No. 2 Dissipation ........................ 2.5 W


6L6GC
Maximum Ratings (Design Center Values)
PentodePlate Voltage ................................. 500 VGrid No. 2 Voltage ............................ 450 VPlate Dissipation ............................. 30 W
Grid No. 2 Dissipation ........................ 5 W

7027A
PentodePlate Voltage ................................. 600 VGrid No. 2 Voltage ............................ 500 VPlate Dissipation ............................. 35 W
Grid No. 2 Dissipation ........................ 5 W

That's why a manual can be important. I wouldn't run 6L6GA-Bs at anything above rating - and especially not coke-bottle shaped tubes. But Bs-up are probably OK on 400+ volts, despite the conservative rating, especially in Fenders which are biased coolish A/B. Key is, as volts go up, current must come down.

Triode Electronics has an article on running 6L6s as a replacement for 7027As in Ampegs, which put humungous (550) plate volts on them, as long as current draw is kept in the mid-teens they run fine. It was them that discovered the dissipation curve printed in the RCA manual for both is identical, and inside the only difference is the extra pin connections along with gold-plated contacts.

On a hot quad tube stereo setup running close to class A pushpull, maybe not so good.