A little more information

The two main activities in my life: Helping the hungry in the late hours of the night and helping guitar players sound better one amp at a time.

I always try to remember that in order to do good one has to take action and actually do something.

I was born and raised in Los Angeles. I have watched the city and Southern California change for well over half a century.

I can be found on facebook at www.facebook.com/mylesr or on twitter at www.twitter.com/myles111us or on my own Guitar Amplifier Blueprinting website at www.mylesrose.com

Los Angeles Architectural History

Los Angeles Architectural History
1935 Art Deco at some of its finest: No. 168 - Griffith Observatory- (click on the photo for information)

Thursday, February 23, 2012

Tube Test - JJ ECC803S

Test results of the JJ ECC803S Long Plate vacuum tube.

Today I spent a bit of time working with Mike Franceschini over at 65 Amps.  Mike wanted a bit of data on some of the tubes used in the new Producer from the folks at 65 Amps.

In one of the positions of the design they use a JJ 803S.  There were some anomalies that were thought to be tube related.  I was asked to investigate.

Click on "read more" for the full report.

The below test is courtesy of the folks over at 65 Amps ( www.65amps.com )

Bottom line; plate resistance of the tube was too low causing low gain. 

Tolerances were quite wide.  This is not good and shows a lack of manufacturing control and QA/QC which was not effective.

Expected design specification is 62.5k ohms at spec test voltages. This tube was below that number.  In some amp circuits a plate resistance of below 50k ohms might exhibit problems such as noise, crosstalk and interaction of the two sides of the dual triode which are not desired.  Some of you may recall issues with the GT 12AX7M in some runs where the gain was lower than a 12AY7 and plate resistance was below 40k which made these tubes very problematic.

I went back and looked at my last test of the JJ 803S which was performed last month.  Dan Boul and Mike Franceschini have me look at every batch of tubes that come into their shop.  A database is kept on the results.  

I asked Dan if he would like me to start posting this information for folks out there and he said he would like that very much.  I guess you can consider this the first of a series supplied by the folks at 65 Amps.  Even though I do not work for them and they are the owners of my data on their tubes based on agreement Dan has given the go on publishing this data.  When I was at Groove Tubes I used to publish these reports and monitor quality of current production tubes.  Much of my data appears in the deluxe edition (hard cover) of The Tube Amp Book.

You can download a design spec sheet of a 12AX7/ECC83 here:
The last batch test results of the JJ 803S (12AX7):

If you click on the image you should see a larger version.


  1. cool! thanks for posting this.

  2. Thanks to all involved. You are da' man, Myles!

  3. I will be posting ongoing tests in the future.

  4. I bought one of these and the filaments lasted 14 hours of playing time. The next gig I get to, when I turned on the standby, four very loud pop pop pop pow....occurred. I've sent 3 letters to JJ tubes in Serbia with no response. It's going on 3 weeks now. My amp...1968 Fender Twin Reverb-Amp.