max plate voltage question for 12ax7,...please help.

[tonequester]

Greetings nashvillebill.

I know that 22nf id 22 nanofarad. My point was that on the Blackstar schematic it reads 22n, with the n, looking more like an upside down u. I thought nf was standard. I am sure that their 22 "whatever", is nanofarad. On some of the vintage schematics the numbers close to the described caps were voltage ratings like : 400, or 600. Other times the numbers were like " 275,360,or 380, and I'm sure these were voltage readings. Your point about the Blackstar cap reading is right, IT IS a cap voltage rating.

Thanks for your help, in trying to help me better understand what I thought to be standardized, but now know needs careful inspection and thought. tonequester.

[tonequester]

Greetings jazz P Bass, and thanks for replying.

I have known for a long time that the Blackstar is a cheaply built hybrid, backed with very poor quality assurance, as it took me three tries to get an amp that didn't blow up, had all features functional, or in the last case, came complete with an unmounted speaker, and interior cabinet damage. Of course, by that time the company was no longer talking studio/practice amp, but was talking entry level amp. I fixed the last one myself, voiding the warranty, but(knock on wood) it hasn't yet gone up in flames and smoke yet(the third amp has made it 4 months). I found out about the signal path from Enzo. I WAS stupid enough to NOT research, before purchase. I trusted the dealer who pointed me to the HT-1R, when I told him that I wanted a small tube type practice amp. When I checked out the reverb without springs, and the Infinite Sound Feature, I knew that there was digital "under the hood", but I didn't know that op amps and transistors were intermixed with the tubes, "all the way". I had 2 email correspondence with the head engineer of Blackstar, who told me that each amp was subjected to a strenuous, multi point inspection before shipping. He did not further reply, after I asked him how a completely non-functional reverb would pass this inspection process. Then I got the one I now have, which had the speaker only mounted to one threaded stud out of four, with punctured speaker, and much broken particle board inside as well. Thus my inspiration to build an amp.

Best regards....tonequester.

[tonequester]

Greetings defaced. I don't know how i could post a coipy of this schematic, but I think I have been straightened out about this now. The high voltage readings I was finding, turned out to be on 12ax7's that were in reverb and tremelo circuits. Why these circiuts push the "envelope" I do not know, but it was stupidity on my part to miss this.

Thanks for the reply and interest, sorry to waste your, and the others time. tonequester.....that means newbie dumb s---!

[tonequester]

Greetings Enzo, and thanks for your reply.

As it turns out, the high voltage readings that I was seeing on the vintage schematics, turned out to be tremelo and reverb circuits. Stupid is, as stupid does ! Well, I learned something alright. I apologize to alk, for my missing such a thing. as to WHY tremelo and reverb circuits SOMETIMES show at least higher voltages than pre amp tubes, I haven't a clue.

Best Regards. tonequester.

[tonequester]

Stupid!!!....ME !

Greetings Enzo, and thanks for your reply.

Unfortunately, I wasted everyone's time here. It turns out that the high voltage readings that I was yammering about, are for 12ax7 tubes that are in tremelo and reverb circuits. I apologize to you and everyone else for such an elementary mistake. Of course, now I wonder why SOMETIMES these circuits have higher voltages at plate than pre amp tubes do in the same amp ! Your info on "ball park" analogy is well taken, and to be remembered.

Best Regards. tonequester.

[tonequester]

Hey Again Jazz P Bass.

DUMB ! DUMB ! DUMB ! You are right. The high voltages are on 12ax7's in either reverb or tremelo circuits. I wasted everybody's time here, and apologize. However, now I wonder why tremelo and reverb circuits are pushed harder than the pre amp tubes are, in the same amp !

Thanks fro getting to the bottom of my screw up ! Best Regards......dumbquester......I mean tonequester.

[Dave H]

I expect the voltage is high on the reverb driver 12AX7 because it's transformer coupled to the reverb unit and the transformer primary has much less resistance than the 100k plate load of a preamp tube.

I'm not sure about the trem circuit but the voltage readings were probably taken with the trem turned off which grounds the tube grid (to stop the oscillator) turning the tube off so the plate goes high.

[tonequester]

Greetings Dave H, and thanks for the enlightenment concerning those high voltages in reverb and tremelo circuits. This forum is turning out to be a great learning experience for me. I've started a notebook, and bought a printer cartridge to get all of this good advice and info down, before I forget any of it.

Thanks again, for setting me straight on something that I hadn't even thought of yet ! Best Regards...Glad to "meet" you here......tonequester.