All capacitors are changed. But I might change the big cap on it in the silver tube. It might be this that is causing me channel cut out issues
Your latest symptom reports are not inconsistent with a leaky coupling cap. They leak more as they get warmed up, and the leakage can have a strong dependence on voltage. Get those coupling caps to the grids of the output tubes replaced and add those 10 ohm resistors so that each tube current can be monitored. Get that done before anything else. You will likely not need to do anything else unless the output tubes have been damaged.
Good luck
Good luck
I will do. Thanks. Are you able to provide a diagram or say which connections the 10 Ohm resistors are to have.
Which is the coupling cap? All capacitors on the boards have been replaced. And it is then that I started having this issue. Could it be that one of these new caps is faulty?
That main power supply filter capacitor is shared between channels.
Your problem is most likely still bad connections or solder joints on the pcb.
Which coupling capacitors did you use? Check all their solder joints.
A problem happening just after that work is likely due to the work.
You can buy replacement pcbs to restore the circuitry. Most would do that because of the age.
Those should be ok. But even with one cap left out entirely, you should still get some sound in that channel.
Also check both ends of all wires to the pcb.
Also check both ends of all wires to the pcb.
Just seeing those tube sockets raises concerns. Looks like lots if oxidation. These should be cleaned and treated with products like deoxit, or suitable replacements found. Intermittent connections that can be caused by bad sockets cause baffling and changing problems.
Time for new pcbs with all new parts. Only a few bucks.
https://www.dynakitparts.com/shop/pc-13-st-35-mf-resistors/
https://www.dynakitparts.com/shop/pc-13-st-35-mf-resistors/
Dave Gillespie also offers boards:
http://www.tronola.com/html/daves_store.html
All good fortune,
Chris
http://www.tronola.com/html/daves_store.html
All good fortune,
Chris
I did not have time to look at the schematic. So, I do not know the exact EL84 cathode connection(s) and part(s) to ground.
EL84 connections:
Pin # 2 is g1 (G1) control grid.
With the amplifier warmed up and running for at least 15 minutes, check the DC voltage from g1 to ground.
Should be at or Very near 0 Volts (Zero Volts).
Let us know what the voltages on each G1 are . . .
Pin # 3 is the cathode (K) and G3 connection.
If this already connects directly to circuit ground, then install a 10 Ohm resistor in series from the K/G3 connection to ground
(if present, you have to cut the trace that goes from pin # 3 directly to ground, and install the 10 Ohm resistor across the cut trace (carefully scrape the traces, and solder it there). When the amplifier is warm, measure the voltage from Pin # 3 to ground.
If instead, Pin # 3 connects through self bias resistor(s) to ground, you need the 10 Ohm resistor to go across the cut trace between the cathode and the rest of the circuit (harder to measure across the 10 Ohm resistor, because both ends are floating above ground).
Now you know one of the reasons to use Individual self bias resistors . . .
Voltage from the cathode to ground/ individual self bias resistor to ground = current V/R = I
You measure the voltages with original tubes, new tubes, and 6months or a year later if you are curious to see how the current is the same, or changed with age.
Finding the space for 4 resistors, and 4 bypass caps is not fun.
Measuring the circuit currents as often as you want is EASY.
Hint:
Whenever you re-solder a PCB, change parts, etc. . . . Be sure to clean All the rosin off the board (rosin, environment, and time becomes a resistor.
A 'parasitic' resistor from one Pin to another? Yes
A 'parasitic' resistor from one part to another? Yes
Never operate a circuit that has not had the rosin removed.
EL84 connections:
Pin # 2 is g1 (G1) control grid.
With the amplifier warmed up and running for at least 15 minutes, check the DC voltage from g1 to ground.
Should be at or Very near 0 Volts (Zero Volts).
Let us know what the voltages on each G1 are . . .
Pin # 3 is the cathode (K) and G3 connection.
If this already connects directly to circuit ground, then install a 10 Ohm resistor in series from the K/G3 connection to ground
(if present, you have to cut the trace that goes from pin # 3 directly to ground, and install the 10 Ohm resistor across the cut trace (carefully scrape the traces, and solder it there). When the amplifier is warm, measure the voltage from Pin # 3 to ground.
If instead, Pin # 3 connects through self bias resistor(s) to ground, you need the 10 Ohm resistor to go across the cut trace between the cathode and the rest of the circuit (harder to measure across the 10 Ohm resistor, because both ends are floating above ground).
Now you know one of the reasons to use Individual self bias resistors . . .
Voltage from the cathode to ground/ individual self bias resistor to ground = current V/R = I
You measure the voltages with original tubes, new tubes, and 6months or a year later if you are curious to see how the current is the same, or changed with age.
Finding the space for 4 resistors, and 4 bypass caps is not fun.
Measuring the circuit currents as often as you want is EASY.
Hint:
Whenever you re-solder a PCB, change parts, etc. . . . Be sure to clean All the rosin off the board (rosin, environment, and time becomes a resistor.
A 'parasitic' resistor from one Pin to another? Yes
A 'parasitic' resistor from one part to another? Yes
Never operate a circuit that has not had the rosin removed.
Thabks for the great write up.
I did a quick clean of the contacts with anti corrosion even the driver tube socket. I also tightened the rod holders in the socket. Been playing all evening without a drop in volume. Shall see how it continues. But might be wise to change the sockets. And put the resistors in for the bias. But recently all tubes have been glowing the same amount. 1 step at a time and see what the changes bring. Thanks all for comments
I did a quick clean of the contacts with anti corrosion even the driver tube socket. I also tightened the rod holders in the socket. Been playing all evening without a drop in volume. Shall see how it continues. But might be wise to change the sockets. And put the resistors in for the bias. But recently all tubes have been glowing the same amount. 1 step at a time and see what the changes bring. Thanks all for comments
Glad it’s working now. Those 10 ohm cathode resistors ( no need for individual cathode bias resistors) will help with any diagnostics in the future and are low enough in value not to effect the original design performance. They can also be used to check tube matching.
Hi all. I have taken readings on the error side. They are enclosed.
On V2 pin 7. I get a value of 350. When the sound goes all that I need to do is touch the pin with the volt meter prong and it comes back.
Any ideas? Faulty transformer?
On V2 pin 7. I get a value of 350. When the sound goes all that I need to do is touch the pin with the volt meter prong and it comes back.
Any ideas? Faulty transformer?