Blown Capacitor in EL34

The circuit or design itself is good. It was published in Mullard's Tube Circuits For Audio Amplifiers.  The circuit is on page 30 and the charts for Harmonic distortion and output/input characteristics, Intermodulation and 'beat-note' distortion characteristics and Frequency response, loop-gain and phase-shift characteristics are shown on page 38.  According to the author, EF86 was chosen for input stage because it provides high-gain, about 120 times.  I built this amp almost 20 years ago and I was quite satisfied with it.  Later, I came across another one which is the best, I think, pp amp circuit published in the Sound Practices, Summer 1993 copy.  The author Bill Kleronomos explained why he chosed 6DJ8 for amp/phase splitter and 12BH7 as the pp driver stage.  His logic is wonderful.  I take his idea to build amps by using 6L6, KT66 and 807 and am so impressed with the result.  Now, 6DJ8/6922 and 12BH7A are my favourite tubes.

Hello Cat,

Thank you so much for telling me how to use the digital camera.  I took the picture on my book again by turning  the "flower " sign on.  It works this time.  I am going to post it here.

I would agree with Accphoto that the "noise" is most properly from  wiring or grounding if you are sure that the power tubes are not weak. Since your amp is built on circuit board, you may pay more attention to the solder joints.  Yes, before your amp runs good or in stable condition, don't put those "expensive" tubes on for testing or measuring voltage.  From what he said, I believe that Accphoto is an experience guy with ample knowledge on tube amp.  Trust on him.

If you really want to go into the tube amp DIY deep, you may consider to own some basic equipments; like signal generator, oscilloscope, tube tester and capacitor checker as well as the tube handbook which will definitely help in troubleshooting and design your own circuit.