Latest JJ 803S info and test results

[myles]

Just letting folks know that the current run on the JJ 803S long plate tested a bit differently than the last batch.

Expected Plate current 1.2mA
Expected Transconductance 1600
Expected Plate reistance 62.5K ohms
Expected gain 100

The above figures are design spec by RCA, Sylvania, RFT, Mullard, Telefunken, GE, etc. Tested at 250 plate volts as per spec with a 2 volt bias.

The actual test results were as follows:

Average plate current 2.2mA (it will run hotter than expected)

Average transconductance 2090 (more abrupt tone, faster reacting so to speak) Less input signal required for a given output voltage is another way of expressing this.

Plate resistance 39.2K. This is very low and the reason for the high plate current and low gain. This low plate resistance can also contribute to crosstalk between the two sides of a tube where the two sides are used for different purposes (which is generally the case) in some amps.

Gain on average is 82, about average today for production 12AX7 tubes. In past runs the gain was at least five points higher on average with many in the 90+ to 95 range.

Hopefully JJ will resolve this in future runs.

 

[myles]

Thanks for the info.

Maybe they can work on the "tone" as well

You are welcome.

 

[D-Rock]

Never tried an JJ ECC803S, but love the ECC83S in my amp.
Is the 803 not supposed to be lower gain than the 83S? Running at 90-95mns for an 803S seems quite high.

 

[myles]

Never tried an JJ ECC803S, but love the ECC83S in my amp.
Is the 803 not supposed to be lower gain than the 83S? Running at 90-95mns for an 803S seems quite high.

The ECC83S and 803S were very close in gain in the past. They were the two highest gain 12AX7 types currently in production. When their specs are close the 83S is more of a midrange tube in character, compresses faster than the 803S and is not as smooth. The 803S also handles higher input levels before compressing such as when pedals have their output levels set higher.

The both sound different so in the end it is really personal taste.

True actual gain of these tubes in curcuit, not just on a text fixture used to be the same or quite close but this last batch of 803S tubes dropped about 15% in actual gain over the last ECC83S batch or the prior three batches of 803S production.

 

[stephen sawall]

Interesting .... thank you as always myles.

 

[myles]

Interesting .... thank you as always myles.

You are welcome.

 

[crwnedblasphemy]

Hey Myles.....have you ever had a go with the gold pin JJ's? They state on Eurotubes to be more smooth, and run about $22 a pop, but I have never known anyone to try them, let alone see them anywhere?

 

[myles]

Hey Myles.....have you ever had a go with the gold pin JJ's? They state on Eurotubes to be more smooth, and run about $22 a pop, but I have never known anyone to try them, let alone see them anywhere?

No difference at all in gold pins vs non-plated pins.

And ... when folks talk up gold grids .... most tubes have gold plated grids already.

In the tube bizz making gold plated pins is cheap and easy and an easy way to raise price to the end user and make a larger profit. This was discussed many times over the years at GT for the 12AX7M as an option.

 

[Giga]

Thanks Myles. I only have experience with the older batches of 803's. I like them in the PI-spot in most amps. To me they sound like a "bigger" Chinese tube and they stay cleaner at higher signals.

Giga.

 

[scottcrud]

I could be wrong but isn't the 803 built for lower gain applications? I had two and both went microphonic within a month in my Boogie head...

 

[myles]

I could be wrong but isn't the 803 built for lower gain applications? I had two and both went microphonic within a month in my Boogie head...

I don't know where that lower gain application commentary comes from ... perhaps some smoke and mirror marketing or something. The tube spec sheet from JJ is little more than a reprint of a standard 12AX7 spec sheet and the 803S is just one more 12AX7 option for players out there.

 

[scottcrud]

Just saying I was under the impression that that particular tube was not built for High gain Amp heads... Like I said, could be wrong, wouldn't be the first time.

 

[JMP2203]

thanks for the info

did you tried the new mullard style TAD?

http://www.tubeampdoctor.com/product_in ... ts_id=1749

 

[myles]

thanks for the info

did you tried the new mullard style TAD?

http://www.tubeampdoctor.com/product_in ... ts_id=1749

Tad has their tubes made buy Shuguang, who also made the GT 12AX7m Mullard tube. I wonder if these are similiar.

If the tube by TAD is any relation to the GT 12AX7M there may be many problems. I may be wrong but I think that Fender who now owns what is left of GT is not even trying to produce the tube anymore. When things ended last August the 12AX7M was still nowhere close to being proper.