If the first tube is pulled out and after power up the amplifier is silent, the problem is around the 6N1P socket.
Maybe the socket pins damaged.
Turn off the amplifier, pull out mains cable.
Pull out 6N1P.
If the 6N1P grid is floating, the bias of the tube is undefined (no grid leak resistor? == damaged potentiometer, or damaged grid stopper resistor, or damaged socket pin).
Try to measure resistance from pin 2 of socket (on tube's side) to ground.
If it changes between 1k...101k (depending of potentiometer's rotation), the grid leak resistance is OK.
Repeat it with pin 7 and ground.
Check the cathode resistors.
Try to measure resistance from pin 3 to ground: 0.96...1k is OK.
Repeat it with pin 8 and ground.
Maybe the socket pins damaged.
Turn off the amplifier, pull out mains cable.
Pull out 6N1P.
If the 6N1P grid is floating, the bias of the tube is undefined (no grid leak resistor? == damaged potentiometer, or damaged grid stopper resistor, or damaged socket pin).
Try to measure resistance from pin 2 of socket (on tube's side) to ground.
If it changes between 1k...101k (depending of potentiometer's rotation), the grid leak resistance is OK.
Repeat it with pin 7 and ground.
Check the cathode resistors.
Try to measure resistance from pin 3 to ground: 0.96...1k is OK.
Repeat it with pin 8 and ground.
Pulling and pushing on tube sockets can create bad solder joints and PC board cracks. So when the amp started humming it suggests the loss of filtering which could have created the dropout of one channel. It also has the sound of Motorboating now. That is an issue of too little capacitance or a bad decoupling or no decoupling capacitor in the driver stage. And it seems that both channels are now sending the same noise signal to both channels coming from both speakers so I don't think you have an OPT issue. One bad OPT would create still show a difference between channels. So, I would start looking closely for a cracked PC board trace or broken solder joint at the driver branch of the power supply filtering and maybe suspect a blown cap that you cannot see the bottom of because it's on the PC board tightly. Examine the caps for swelling. Since you have been pulling and pushing on the tube socket I would suspect it's more likely you have a broken trace or solder joint or bad cap you cannot see the issue with.
Could the volume pot be damaged? What's it rated for? Would the lack of a grid leak resistor cause too much current to flow thru the pot?
I have a new tube socket set to arrive tomorrow. Once that is installed I will check the current on the tubes and follow the recommendations posted here.
Regarding the suggestions about PC boards and volume pot, this amp is point to point wired and I didn’t use a volume control.
Regarding the suggestions about PC boards and volume pot, this amp is point to point wired and I didn’t use a volume control.
How does the signal enter the driver stage? In the schematic you posted there's a volume pot, but there's no "grid leak resistor" that is typical for most cathode-biased tube stages. It should be after the pot, connecting the signal wire to ground with a large resistor, something like 470K, before the 1K grid stopper. As drawn, your amp uses the volume pot as the grid leak resistor, so the current that keeps that grid at ground potential has to pass through the pot.
And you're saying there is no volume control in this amp? No pot? That means there's no way for the grids of your input stage to be referenced to 0 volts. That's a problem.
And you're saying there is no volume control in this amp? No pot? That means there's no way for the grids of your input stage to be referenced to 0 volts. That's a problem.
The 1k resistors connecting to pins 2 and 7 on the input tube connect directly to the RCA input center pin. Perhaps that’s the problem? Does there need to be some kind of resistor there? The amp ran fine for months until I swapped out the input tube with the 5670 adapter.
"Perhaps that’s the problem?"
Surely.
It's imperfect design.
If no grid leak resistor as I wrote in #21 post, the tube is in undefined state.
If it has potentiometer, its viper_to_gnd resistance is act as grid leak (not good solution, but working .... if no bad contact wiper).
If both of them (grid leak resistor or potentiometer) omitting, the previous stage (preamplifier) loading resistor (100k...470k) act as grid leak ... if the stages connected together with interconnect.
Use few hundred kOhm grid leak resistor from 1k grid stopper to ground.
Surely.
It's imperfect design.
If no grid leak resistor as I wrote in #21 post, the tube is in undefined state.
If it has potentiometer, its viper_to_gnd resistance is act as grid leak (not good solution, but working .... if no bad contact wiper).
If both of them (grid leak resistor or potentiometer) omitting, the previous stage (preamplifier) loading resistor (100k...470k) act as grid leak ... if the stages connected together with interconnect.
Use few hundred kOhm grid leak resistor from 1k grid stopper to ground.
Why
Completely unrelated.
In any case, plug the original tube, the original way, it should work as it always did.
Why would you think output transformer trouble when you messed with the input tube socket?
Completely unrelated.
In any case, plug the original tube, the original way, it should work as it always did.
I understand the theory of the grid leak resistor but following the logic of diagnosing the failure I don’t understand why the amp has worked without it and stopped working after using the different tube. I’ll try it either way, once the new tube socket is installed.
Also, just noticed that pin 9 on the driver tube is floating- shouldn’t that be grounded?
Also, just noticed that pin 9 on the driver tube is floating- shouldn’t that be grounded?
Someone inquired about the 5670 adapter earlier in this thread. It’s a cheap Chinese adapter from eBay, no brand. It has extremely long “gold” pins. I have been using it for years without issue, just not in this specific amp.
Because after checking all the components and not finding a problem I was left wondering how to check the output transformer.
Original tube “should” but doesn’t. Thanks.
6N1P pin 9 is the screen between halves.
If you grounded it, may will less crosstalk between channels.
The operating of tube independent of this.
One more time: USE grid leak resistors!
If you grounded it, may will less crosstalk between channels.
The operating of tube independent of this.
One more time: USE grid leak resistors!
Although we don't know the schemactics (me at least doesn't know it...), we have to assume that there are grid leaks where they're necessary. Why else should have the amp worked correctly up to the moment he plugged in the omimous adapters and (wrong) tubes)? I'm repeating myself, as I suspect these adapters. Remember that the only pins that correspond between both tube types are #6, #7, and #8.
Best regards!
Best regards!
I had an issue with a Quad II that I modified by installing a decoupling capacitor on the input. There was still a resistor to ground before the cap, but I forgot to add a grid leak after the cap. It used to work fine with the EF86 1st stage tube, but if I disconnected the input it would become unstable, make a lot of noise. I would turn it off, and then it would not work after turning back on. Then the following morning it was fine again! So I think the capacitor I added was charged in some way, the tube was biased so that it was off, and it only worked again after the charge leaked from the capacitor by itself.
So I think that not having the grid leak resistor can make the operation of the amplifier unpredictable and could easily contribute to the symptoms you see when changing the 1st stage tube.
So I think that not having the grid leak resistor can make the operation of the amplifier unpredictable and could easily contribute to the symptoms you see when changing the 1st stage tube.
gorgon53,
You are right about floating the Suppressor Grid, g3.
That is called the Hazen Mod.
The Hazen Mod is a Magic Idea that helps to increase sales, but does not solve any other real problem, but potentially creates problems.
Just my opinion, your arcing, current run-away, variable sounding performance . . . all may vary in your amplifier.
If I had a Decware amplifier, working, or not working, the very first thing I would do is:
Connect the output tubes suppressor grids, g3, to their cathodes. Pin 1 to Pin 3.
Careful!
Not all output tube types that have been used in those sockets, have the same tube elements connected to Pin 1 and Pin 3. Check the tube type base connections in a tube manual.
If the voltage rating of the Hazen Mod 0.1uF capacitor is only 100V, it is Cheap. Throw it away, I have no idea where it can be used to good advantage.
You are right about floating the Suppressor Grid, g3.
That is called the Hazen Mod.
The Hazen Mod is a Magic Idea that helps to increase sales, but does not solve any other real problem, but potentially creates problems.
Just my opinion, your arcing, current run-away, variable sounding performance . . . all may vary in your amplifier.
If I had a Decware amplifier, working, or not working, the very first thing I would do is:
Connect the output tubes suppressor grids, g3, to their cathodes. Pin 1 to Pin 3.
Careful!
Not all output tube types that have been used in those sockets, have the same tube elements connected to Pin 1 and Pin 3. Check the tube type base connections in a tube manual.
If the voltage rating of the Hazen Mod 0.1uF capacitor is only 100V, it is Cheap. Throw it away, I have no idea where it can be used to good advantage.
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I’m not sure how often people admit they are idiots here but I will raise my hand.
I’m not sure what happened when I used the tube adapter, but I replaced the socket and things are working.
However, when I was testing components to see what and if anything blew I rewired the power supply wrong. So a majority of my problems were there. It is now rewired and all is well. I did add a 200k grid leak resistor on the input as recommended, too. Thanks for the help everyone. To the critics of this schematic, this really is an amazing sounding amp.
I’m not sure what happened when I used the tube adapter, but I replaced the socket and things are working.
However, when I was testing components to see what and if anything blew I rewired the power supply wrong. So a majority of my problems were there. It is now rewired and all is well. I did add a 200k grid leak resistor on the input as recommended, too. Thanks for the help everyone. To the critics of this schematic, this really is an amazing sounding amp.
Now you have a better idea of how the whole thing works. Good stuff.
w
w
I heard the early version of the Decware Amplifier at one of the first VSAC in Silverdale Washington (Vacuum tube State of the Art Conference).
It sounded very good.
It is amazing how good simplicity sounds, especially when all the stereo components are picked together to produce positive synergy.
(all the way from the signal source to the loudspeaker)
It sounded very good.
It is amazing how good simplicity sounds, especially when all the stereo components are picked together to produce positive synergy.
(all the way from the signal source to the loudspeaker)