Really disappointed with TAD EL34's

CEG85

CEG85

Active member
I Just finished installing TAD EL34B-STR tubes in my Marshall 1959 Plexi.
These tubes all have a "matching" plate current of 31.

I've installed and biased at least 5 different sets of tubes in here. I've never had them be this mismatched.

Dropped them in, hooked up the bias probes, and went to work.
Only 2 of the tubes were closely matched, (within 1ma)
The other 2 were 6ma off!!
2 or 3ma I can deal with, but a 6ma difference is ridiculous.

Total disappointment.
It sucks even more because I bought these tubes months ago and can't return them.

I'm just putting the word out there.
 
I think the 'trick' is to get new tubes from dealers who do additional burn-in and matching. You could try getting these TADs or similar Ruby STRs from valvequeen.com.
 
For sure, definitely trying out valve queen next.
I bought these from reputable dealer, but I really don't blame them.
Tube depot has been my go to spot for years and I've always happy with them.

Gonna Pick up a quad set of Rubys next time.
 
Well 20% is normal tolerance from what I understand. I had a set of JJ's from Tube Depot that were 12ma apart, that is not matched..
 
First off, 6 ma is a pretty tight spec for a guitar amp. These aren't Hi Fi stereos we are talking about. Tube matching to 1 ma was never something ever considered in guitar amps until the audio-fool world started to creep in. Most guitars amps up until about 15 years ago 5-10 ma was perfectly acceptable. Then the audiofool and internet work crept in.

Also here is what most guitar players don't know...... Companies that match power tubes match them by plate current (okay so you know that) but your typical run of the mill bias probe measures plate current and screen current. Yep, so you are not comparing apples to apples here. So the tubes could indeed be perfectly matched but using a bias probe that measures cathode current and most do, then you are adding something else, (screen current into the equation) just like everything else, the screens will draw different current levels from tube to tube. Also the plate voltage the tubes were matched at also makes a difference.

Bias probes are only good for setting a close enough bias setting and not for determining that tubes are matched. Now some bias testers do only read plate current, but those are not as common and generally more expensive. Yes Eurotubes make a cheap plate current bias probe, but you better have a good meter (fluke) because you are putting 400+ volts into it and the cheap meters will have too much inductance and effect the reading. Now the more expensive bias units they sell would work pretty well.
 
CEG85":3ojcttiv said:
I Just finished installing TAD EL34B-STR tubes in my Marshall 1959 Plexi.
These tubes all have a "matching" plate current of 31.

I've installed and biased at least 5 different sets of tubes in here. I've never had them be this mismatched.

Dropped them in, hooked up the bias probes, and went to work.
Only 2 of the tubes were closely matched, (within 1ma)
The other 2 were 6ma off!!
2 or 3ma I can deal with, but a 6ma difference is ridiculous.

Total disappointment.
It sucks even more because I bought these tubes months ago and can't return them.

I'm just putting the word out there.
Click to expand...
You are aware that in a 100w amp that the tubes don't operate independently aren't you?
 
Yes, I've checked the PV numerous times (450v +/-)
The tubes sounded totally fine but noticed, v3 and v4 were both red plating.
tried out 2 other sets of tubes the same day, same story.

Amps at the shop getting repaired, any guess what the problem might be?
 
HilltopExplosion":1ktzlqt4 said:
Bad screen grid resistor... Bias too high.. :dunno: :dunno:
Click to expand...

Ya I'm thinking bad screen grid resistor too.
Played around with the bias.
Set it between 32-35ma on all sets of tubes.

Hopefully I'll get the amp back in this week, and know what the issue was.

Update:
Got the amp back.
Changed 4 out of 6 capacitors.
I had 2 bulging and another 2 that were puffy, so replaced all of them.
Replaced 5W1Kohm resistors.
Whole board was re-soldered.

All in all, the amp is way more quiet then it used to be.
More importantly, no more red plating. :)
 
Can't say anything about the red-plating issue. But as far as matching goes, I've found most amps actually sound better when the tubes are mis-matched. Adds more flavor, character, and musicality to the sound. But YMMV.
 
FourT6and2":304mn7x5 said:
Can't say anything about the red-plating issue. But as far as matching goes, I've found most amps actually sound better when the tubes are mis-matched. Adds more flavor, character, and musicality to the sound. But YMMV.
Click to expand...

I'm gonna try that out.
Ive got an extra set or 2 of EL34's but don't know if they're closely matched or not.

Dropped the amp back off at the shop.
Still getting slight red plating on V4/V5. (I mentioned V3 and V4 earlier on my post by mistake, but its actually V4 and V5)

My tech went through it again and found i have a bad output transformer.
We initially went through the whole amp top to bottom.
Re soldered everything, no loose connection anywhere.

So we put in a order for a Mercury Magnetics 0100JM.
Hopefully ill get the amp back either this week or early next week.
 
Seems like every time I've ordered from Tube Depot the tubes aren't as closely matched. Been using Tubeandmore.com last couple years and all of them have been great. And yes I agree with the above statement... the closest matched set I've ever got was from Valve Queen, she does a great job and takes pride.

The TAD's are my favorite current production EL34 cause they seem more open and have a tight even frequency response. They seem to lift a little blanket off that JJEL34 tend to drape over the speakers.
 
Adambomb":1i1x3xbk said:
The TAD's are my favorite current production EL34 cause they seem more open and have a tight even frequency response. They seem to lift a little blanket off that JJEL34 tend to drape over the speakers.
Click to expand...

Give the Ruby EL34BSTR tubes a shot. It's probably the very same tube as the TAD (although I haven't compared them myself).
 
Ya, probably gonna try ruby or give TAD another shot when I need replacing.
For now were throwing in a set of JJ EL34L's.

Took the amp to my tech.
Apparently I had a bad OT, which is being replaced with a Mercury Magnetics 0100JM.
I guess it was feeding too much current to V4 and v5 for some reason.
Should be getting back soon.
Also getting a master volume mod so I can use the amp without my Rock Crusher.
Cant wait to get it back.
 
I have been buying tubes from the same Ebay seller for 2 years now,they do Apex matching and 2 quads of JJ's 6l6 GC's and also their JJ El-34's,lots of el-84's etc..all matched sets have come at no more than 2 ma difference..I have never had that happen before,so I stay with them and the prices are very good.
 
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