Before you possibly damage/destroy more EL84's, could you measure, with all the EL84's removed, what voltages you have on positions 7 and 9 on the tube sockets for the EL84's?
In line with the advise/question of OldHector in post # 33: Could you check if the four cathode resistors of the EL84's are connected properly (are they all connected to ground on one side?) and if they, and the decoupling capacitors parallel to them, are still OK?
With the amplifier off and the 6BQ5's out, please measure the resistance between each socket pin #3 and ground. Did you install the resistors R7, R8, R9, R107, R108, R109 properly?
Best regards!
Best regards!
With a tube tester, but you probably don't have one (else you would have tested them already).
If there are realy no faults in the amplifier (you could check if the secondaries/outputs are not shorted) than I think it must be that all four EL84's are dead.
What puzzles me the most, is that one of the EL84's still seems to draw some current, but there is no sound at all. I would think that you would still have to hear something (weak/distorted) but maybe that EL84 is damaged in a way that none of the current flows to the anode, but all to the screengrid. I find it hard though to imagine such a situation inside that tube unless the connection from the anode to the pin is no longer there.
Addition: Or the screengrid could be shorted to the cathode.
If there are realy no faults in the amplifier (you could check if the secondaries/outputs are not shorted) than I think it must be that all four EL84's are dead.
What puzzles me the most, is that one of the EL84's still seems to draw some current, but there is no sound at all. I would think that you would still have to hear something (weak/distorted) but maybe that EL84 is damaged in a way that none of the current flows to the anode, but all to the screengrid. I find it hard though to imagine such a situation inside that tube unless the connection from the anode to the pin is no longer there.
Addition: Or the screengrid could be shorted to the cathode.
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If there were shorts from the screens to the cathodes, considerable current would flow and destroy the cathode resistors, and/or the PSU filter resistor - or, as I said before, the internal cathode to pin #3 or screen to #9 jumper wires.
Best regards!
Best regards!
But how can the cathode connection of the EL84 that seems to pass some current (5 V on its cathode + more current through the 330 Ohm resistor than the 12AX7 is taking) be broken? Than current flow in the tube would be impossible, or?
Correct. I think we're shooting in the dark until OP provides the measurements that I suggested before.
Best regards!
Best regards!
I don't have any experience regarding the frequency of occurrence. Anyhow, I see that the internal cathode jumpers usually were made from thin flat wire, which I interpret that they may act as fuses in the case of some major incidence. Of course I don't know what has happened with the OP's tubes.
Best regards!
Best regards!
Still we await the results of the measurements asked for in posts #46 and #47. If they also turn out to be OK, than it must be the EL84's (or 6BQ5's or even an other substitute?). Are they new production? Or NOS? Or were they used ones?
Just to be sure: Did you maybe use one or more of the contacts for pins 1, 6 and 8 on the tube sockets of the EL84's as points to solder parts in? Depending on the manufacturer of the EL84's, sometimes one or more of these pins are internaly connected with one or more electrodes in an EL84, so they could create problems if you use them.
Could you post some pictures of your amplifier?
Just to be sure: Did you maybe use one or more of the contacts for pins 1, 6 and 8 on the tube sockets of the EL84's as points to solder parts in? Depending on the manufacturer of the EL84's, sometimes one or more of these pins are internaly connected with one or more electrodes in an EL84, so they could create problems if you use them.
Could you post some pictures of your amplifier?
I just bought new tubes, also from China, claimed to be military grade. Once the tube arrive I will post the results. In the mean time I will recheck all connections and values of all components. Since I reported very small sound coming from the loudspeaker and I just measured the resistance of the winding of the opts, the opts should be OK.
Do you have a variac to bring the power up slowly? That is a good way to get confidence that the voltages are in the right ballparks. It is quite stressful applying power for the first time!
Due to the OP's refusal of providing us the important infos we've asked for, can we assume that his unit is already working perfectly?
I think it's time for me to leave the party.
Best regards!
I think it's time for me to leave the party.
Best regards!