Question for the amp techs

[famous beagle]

Hey y'all,

I'm building a Marshall 18 watt clone, and I decided to treat myself with NOS tubes for the first time. I got a matched pair of GE EL84's (as well as NOS 12AX7's), and I F***ing dropped one of the EL84 boxes, and the tube broke.

Here's my question:

Is it as important (or important at all) to have a matched pair of power tubes if the amp is cathode-biased (which my amp is)?

Thanks much

 

[ranjam]

Matching what? Socks? Even though it is Cathode-biased, electrically similar tubes in a push-pull configuration should then each amplify the sine-wave..... similarly. They'll add up at the OPT and give you the maximum output power. However, even though I can open a can of worms the size of Texas at the drop of a hat, I won't right now . So, let's move along.
If you have a good tube tester, you can half-assed match them up before they get into the amplfiier. If you have the skills, open the Plate connection and meter the idle Plate current. Within a few milliamperes of each other is fine. I've purchased many EH tubes and had them run all over the map, so making good matched pairs was a hassle. Buying matched from someone like The Tube Store is just smart. But an NOS GE? Good luck. I have mixed GE with Westinghouse or whatever, and as long as they measured the same idle Plate current I didn't care.

 

[Milnoque]

Did the whoever sold you the tubes mark the test vales on the box? If so you may be able to get an NOS verdor to send you a single that matches the one you have.
I'm not an amp tech but I have years of time in keeping my vintage amps going. so what follows is just my opinion based on my experience. Take it with a grain of salt.

Back in the day manufacturer commonly made tubes under a variety on brand names. Your GE tubes were not necessarily made by GE. I agree with the previous poster that you can mix/match brands.

Running unmatched tubes will not harm the amp. (let the flames begin) In fact matching tubes is a relatively recent practice. I think Groove Tubes popularised it. Mismatching the tubes is an interseting tone experiment.

Cranking your amp with badly mismatched tubes can shorten tube life somewhat, but not as much as is often claimed.

Do yourself a favor and bring your amp up on some cheap modern tubes and work out whatever bugs you find before you put the NOS tubes in.

Good luck to you. I've ordered a kit to build my first amp.

Very Excited

 

[famous beagle]

Did the whoever sold you the tubes mark the test vales on the box? If so you may be able to get an NOS verdor to send you a single that matches the one you have.
I'm not an amp tech but I have years of time in keeping my vintage amps going. so what follows is just my opinion based on my experience. Take it with a grain of salt.

Back in the day manufacturer commonly made tubes under a variety on brand names. Your GE tubes were not necessarily made by GE. I agree with the previous poster that you can mix/match brands.

Running unmatched tubes will not harm the amp. (let the flames begin) In fact matching tubes is a relatively recent practice. I think Groove Tubes popularised it. Mismatching the tubes is an interseting tone experiment.

Cranking your amp with badly mismatched tubes can shorten tube life somewhat, but not as much as is often claimed.

Do yourself a favor and bring your amp up on some cheap modern tubes and work out whatever bugs you find before you put the NOS tubes in.

Good luck to you. I've ordered a kit to build my first amp.

Very Excited

I think I'm going to have to do that. The only other matched pair of EL84's I have is JJ's.

I know that mismatched tubes won't hurt the amp, and I realize that some people purposely use mismatched tubes for the tone. I was just wondering whether or not it makes a tonal difference in a cathode-biased amp. But I'm guessing it does.

 

[Milnoque]

I just noticed that we were neighbors.

Howdy nieghbor.

JJ Makes a good EL84

Check your PMs

 

[dementedchord]

i suspect that matched outputs are less of an issue in cathode biased amps... the reason being that it essentialy floats above that ground as a function of it's own internal resistance... as opposed to being forced through use of a bias voltage to some operating point and expecting two tubes to behave the same...