View Full Version : What must "match" on output tubes?
12-13-2004, 08:41 PM
I'm sorry if this is a silly question, but I'm hunting EBAY, for some NOS (most likely Mullard/Philips or GE), EL84's for a Marshall DSL201 and I'm confused.
Sellers list all kind of readings and I'm not sure which one needs to match. Is it milliamps, plate voltage or triodes or something else.
I really appreciate the help.
12-13-2004, 09:26 PM
milliamps. The seller usually measures the current at a given plate voltage + bias voltage, and writes the current in milliamps on the tube box.
Don't get too hung up on matching power tubes, though; mismatches sound really good sometimes.
12-13-2004, 10:38 PM
The advantage to matched tubes is that they've been tested for current draw and you know it's possible to bias them to work in an amp. They express the match in a number of different ways (mhos of transconductance, mA for a given bias and plate voltage) but it's just the fact of the bad ones being weeded out thats most useful.
12-14-2004, 05:03 AM
Thanks for the help.
Old Tele man
12-14-2004, 07:10 AM
drbob1--gets it right! Give that guy a beer!
12-14-2004, 11:38 AM
How close do the numbers have to match for it to be acceptable? I have seen that within 3 millamps is OK.
Is this correct?
Old Tele man
12-14-2004, 11:59 AM
3mA out of 30mA is 10%...
rule of thumb:
20% = normal
10% = good
5% = very good
<3% = excellent
1% = perfect (but for how long)
...just because they'r "matched" now is no guarantee they'll remain that way after break-in / use...tubes DO drift!
12-14-2004, 05:48 PM
The GE EL84's I just got were 23.7 and 22.0 so I'm thinking thats OK.
Thanks again for the help.
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