Sylvania 6550 tubes...information

[Stevem]

If you have that many tube amps sitting around, then its high time to invest in at least a 150 buck used emissions type tester like a Eico or a Heathkit model.
At least these can check for shorts and also when you test with these at lesser heater voltages you can get a good feel for how much life is left in a tube even if its on the weak side!

[Butterbone]

Well it might make sense if this was something that I will keep running into, but most of this is a fluke.

Once the batch of stuff I have is gone, I don't plan to seek this stuff out again. While it could be lucrative, I have no passion for it, so it won't be much of a hobby if I find it annoying and don't care about it.

So investing money in something I am dealing with on this occasion alone isn't a good plan.

I've found that most people who are passionate about a hobby end up being very good subject matter experts even for short term or limited information.

I feel strongly that I didn't approach this subject or the sme's in the right way on this information.

At the moment I'll just try to limit the depth of the losses and move on.

[gldtp99]

I have a pair of these Sylvania 6550's in a 1981 JMP Marshall 2204:

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The Sylvania 6550's came to me in an old General Dynamics (Stromberg-Carlson) 70 watt PA head.
They looked to be in good condition and biased up pretty closely matched.
And they sound very good in this stock JMP 2204----- the 6550's will probably last a very long time in this amp because 6550's aren't pushed very hard in a Marshall 2204----and, mostly, because this amp sits in storage instead of being in regular playing rotation in my shop---- last month I did take it to my shop and several players cranked it up and put it through it's paces for a couple of days----two players made lowball offers to buy it.
It is sitting happily back in storage----
I wouldn't give a huge amount for untested, possibly unmatched, Sylvania 6550's-------they aren't GE 6550A's-----and there's no guarantee that they could be used as a pair in an amp.
Maybe put them up on ebay and see what the market is for them----they would be a gamble for me to buy them-----and I have four new quads of Shuguang KT88's sitting here and I know they sound great in high wattage amps----- here's a 2203 clone I recently built with Shuguang KT88's:

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[Firestorm]

The one caveat with 6550s in a 2204 circuit (besides the biasing) is the series resistance in the grid circuit (g1-k). 6550s can be very fussy about this; the "book" maximum value is 50k. 2204s set up for EL34s have 5k6 plus 220k here. KT88s are more forgiving, especially if plate plus screen grid power is under 35W.