7189 A replace an EL 84?

[Strat N My Stuff]

I bought a quad of Tungsram EL84's that when I tried them in my LSS the outside two looked like they were "neon", so I shut down and pulled them. Seems I'm in for a rebiasing, either cap replaced or pot. ANYWAY......

I was looking online and found a quad of 7189 a's. The specs have 13.2 wt. max plate dissip. vs. the 12 wt. of EL 84; and 440v max plate v compared to 300v max plate volts with the EL 84.

Would such a tube work as a temp replacement, as it seems my plate voltage is too hot for the Tungsrams???

My logic may not be correct in this area? If this is stupid, sorry. Jeff

 

[212Mavguy]

There is a very slight pinout difference between 7189a and el84. You want 7189, not 7189a.

 

[Strat N My Stuff]

Thanks

 

[Strat N My Stuff]

Can you tell me if, as I suspect, due to the 400 max plate volts of the 7189 compared to 300v with the el-84 that the relationship is such that the tube "should" be less likely to overheat? Jeff

 

[212Mavguy]

Most likely. Check out 6p14p-ev on ebay. el84 pin compatible, 5000 hour rated, 7189 voltage rated. Inexpensive and very fat tone. Rich and full when distorted. I run them in my Maverick. Highest quality Russky el84 ever made.

 

[edgarallanpoe]

Seems I'm in for a rebiasing, either cap replaced or pot. ANYWAY......

The LSS is a cathode biased amp and should not need rebiased IIRC.

 

[Strat N My Stuff]

Are you serious? What do I do then about the red plating Tungsram's that I bought????

 

[edgarallanpoe]

Are you serious? What do I do then about the red plating Tungsram's that I bought????

Not sure. Talk to a tech about that, but I know that a cathode biased amp is very different from a fixed bias. You do not rebias a cathode biased amp.

 

[LerxstLee]

Are you serious? What do I do then about the red plating Tungsram's that I bought????

Important technical note on EL84/6BQ5s

Most guitar amps that use these tubes are cathode biased (aka "self biasing") and generally don't require rebiasing when installing new EL84s. However, it is always best to check that the idle power of these tubes does not exceed the maximum rating (12watts) in your amp. Be sure to check or have your amp tech check the idle current/power when installing new EL84s. With some pairs/quartets (any brand, NOS or new production) the tubes will run too hot and have a very short life. If the tubes run too hot, a larger value cathode resistor must be installed.

Some modern guitar amp manufacturers have used Pin 1 on their EL84 sockets as "tie points" for connections. This scheme will not allow NOS EL84s to work properly. Some of the amps known for this situation are: Hiwatt DC40, Lexicon Signature 284 and Mesa 50 Caliber. The Laney VC30 seems to have been wired incorrectly as well. If you know of others let me know.

In order for NOS EL84s to work in these amps, the connections from pin 1 of the EL84 sockets must be removed.

Bad Cat, Matchless, Dr Z, Fender Blues and Pro Jr, Vox, Gibson Goldtone GA15s, Mesa Lonestars and other amps will work fine with NOS EL84s with no modifications to pin1 but should still be checked for idle current/power. The only way to avoid checking this is to order a "low current", AKA, "cool" pair.

Cathode bias is different than fixed bias in the fact that you can 1 order mesa spec'd tubes , they will bias correctly .
Or you can check plate and currect and change the cathode resistor to fix your bias to the tubes you have .
When buying N.O.S ask for "cooler tubes" mesa spec'd .
/cheers