Structo wrote:99% of the time when you measure DC voltage on a tube amp, you ground your black lead to the chassis.
This also allows you to probe the amp with one hand on the red probe.
That way you don't take the risk of getting a lethal shock through both hands with your heart in between.
Yep... That's how I do it.... Looking at the 5751 #1 voltages in your experience would you say something is amiss??? should they have a better match to #'s 3 and 4 voltages?? and the plate voltage on 5751 #3 of 305v is that normal?? I cannot find any info on what the pin voltages should be.. any ideas on determining what the volts should be??
sure do appreciate all the Help so far...... Thanks!!!!
Have you tried posting over at the Ceriatone forum?
Or is that you there with the name Telemad?
That's me the one and only...... Thanks again Tom, I will get this thing figured out.. channel 1 sounds great.. I just ordered a new Dario miniwatt ef86 and should have it mid week and I will start from there.. also, think I might re-solder a few pins even though I'm getting continuity point to point...
Also, I will flip nik an e-mail and ask him even though I believe he doesn't get involved with the build questions.... It guy's like you and others here that make this fun
I mean come on, somebody there has had to measure the voltages and written them down, right?
Good luck, it will probably turn out to be something simple or is perfectly normal for that amp but to me the voltages seem off.
You are exceeding the cathode to heater voltage, so tube life will be minimal.
Let me take a stab at this: on an EF86, pin #1 is the screen grid and should have much higher voltage on it than you show. In pentodes (and tetrodes) the screen functions as the anode of the tube in terms of controlling the way the tube works. The plate catches all the electrons flowing from the cathode, but they "see" the voltage on the screen, because it is much closer than the plate. A low screen voltage almost shuts off the tube because the electrons have no incentive to move from the cathode. Pull the EF86 and remeasure your voltages. If pin #1 is still low, check the 2M2 resistor and and solder joints on anything connecting to pin #1 of the EF86. If the voltage goes way up with the tube removed, then it is probably a bad tube.
As to the high voltages on your #3 5751 -- that's wired as a cathode follower so you should see high voltages on pins 1, 6, 7 & 8. You shouldn't see anything like 120 volts on pin #3. Check your wiring. On the other hand, your cathode voltages on the #4 5751 are way out of whack too. You should see maybe 2 volts there, so there may be an issue with your meter.
"You are exceeding the cathode to heater voltage, so tube life will be minimal."
I e-mailed nik at ceriatone and he got back to me within an hour He will send me a DC30 voltage chart Monday..... He also said cathode voltage of 100+ volts was way off... He asked if I was sure I grounded the C/R on the cathodes?? what is C/R??
Thanks!!!
Last edited by playonit on Sun Jul 26, 2009 10:52 pm, edited 1 time in total.
" Pull the EF86 and remeasure your voltages. If pin #1 is still low, check the 2M2 resistor and and solder joints on anything connecting to pin #1 of the EF86. If the voltage goes way up with the tube removed, then it is probably a bad tube."
I pulled the ef86 and voltage shot up to 257v... looks to be a bad tube...
Got one major hurdle figured out... The Buss bar supplied in the kit was to short it did not connect the 2 25uf 25v caps together on the board it stopped a couple of turrets short, which left a gap and did not connect the ground making a continuous path. Two major things occurred when I completed the path.. cathode volts dropped from over 100v to 1.5v and all noise is gone ...you can hear a pin drop>>>> I have a bad ef86 to replace and heater pins are only seeing 2.8v but, I think I might be measuring it wrong... nik is sending a voltage chart tomorrow I think I see light at the end of the tunnel.... Also.. this thing gained a huge amount of volume I can't believe how loud it's going to be..... How should I be measuring heater voltage???
Thanks!!!!
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playonit wrote:He asked if I was sure I grounded the C/R on the cathodes?? what is C/R??
C/R is the Cap / Resistor in parallel that connect from the cathode to ground. He wanted to make sure you had a good ground there.
To measure heater voltage, set your meter to Volts AC and measure between the heater pins (e.g. pins 4/5 and pin 9 for a 12AX7). You should see ~6.3 VAC.
Would you also remeasure and post all the voltages for the EF86. Be sure to measure all the pins (except 4, 5 which are the heaters and 2, 7 which are the internal shield). I'm curious what DC voltage you get on the control grid (pin 9).
