50 watt high voltages, no cathode voltage v1 v2

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RockinRocket
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by RockinRocket » Tue Dec 11, 2018 6:28 pm

This is why I do 69 style boards with the wire wrapped around the lugs on top of the board.
You'll never be able to fix a joint underneath the board!

It also makes it hard to tell if everything is wired correctly.


Did you check the pins of the tubes for the correct voltages?
Are the pots securely bolted to complete the ground connection?
The mechanicall conection could be decieving and could possable act up latter as Ive hadhappen once.

And not to be harsh but I would seriously practice making good solid solder joints. Most every joint is questionable.
Solder should flow freely in the joint and flow to the heat not directly to the tip of the iron.

danman
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by danman » Tue Dec 11, 2018 6:42 pm

I looked over the photos but there was a shadow over the preamp end of the board so I wasn't able to make out some of the connections. Earlier you had mentioned checking the v1 and v2 cathode grounds with your meter and they all read zero. If you were taking a reading from pin 3 and 8 to ground, you should be seeing the value of the cathode resistor that you used for each stage. If you are reading zero, that may be the issue.

whopperplate
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by whopperplate » Tue Dec 11, 2018 10:55 pm

Thank you, I appreciate reality checks RockinRocket, important to stay honest and strive for better when shown our errors. I admit i rushed some on this one.

Dan man, I was referring to the resistance from the component leads to ground and to the tube pins. I get zero resistance, which is ideal of course, which is the same for all the connections in the amp, including the ground bus to chassis connection. I crank down the connections securely with a socket wrench. At this point I have tested every connection at least thrice if not more. Sorry my wording is confusing

The pre 69 board is what it is, but that’s what mirrors are for. If I have to I can unsolder the pot side easy enough and fix anything questionable, which I am tempted to fo just as something yo try. Will I do this again in the future? Don’t know

Per the advice from my good ol tube amp book , I removed the coupling capacitor and 1M from the turret and measured the voltage on the isolated leads. Indeed the stray 15vdc on p2 V3 is coming from the 1M side, even with the nfb resistor disconnected from the OT secondary.

I am seriously perplexed , I feel a bit out of options. Seems like every solution suggested would be the remedy but here I am still .

I thank you all for taking your time and very much appreciate your help , much love
Musicians are like a bowl of cereal
If they aren't Fruits or Nuts they're Flakes

danman
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by danman » Wed Dec 12, 2018 8:23 pm

It may be a good idea to take the resistance reading from pin 3 and 8 directly to ground to see if your cathode resistance value is actually showing. You may have good continuity from one point on a lead to the other but we need to know that there is a solid connection from the tube's cathode to ground through the resistor.

I couldn't be sure from the photos if your chassis is bare metal or has some type of coating or paint applied. If so, it may be causing a grounding problem. A bad ground (or connection) through the cathode circuit would be the only thing preventing two tubes from drawing current if they both have DC voltage at their plates.

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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by danman » Wed Dec 12, 2018 8:42 pm

When taking the resistance reading from the socket's cathode pin to ground, try grounding your black meter lead to a point on the chassis away from the actual grounding lug that you grounded the cathode to. You meter may be reading a solid connection to the grounding lug but the actual lug may not be perfectly grounded to the chassis.

whopperplate
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by whopperplate » Thu Dec 13, 2018 12:34 am

Danman, everything checks out :what:

It just doesn’t make any sense. I almost feel like taking photos or videos of me probing to show you all so I don’t think I am crazy :stars:
Last edited by whopperplate on Thu Dec 13, 2018 1:11 am, edited 2 times in total.
Musicians are like a bowl of cereal
If they aren't Fruits or Nuts they're Flakes

whopperplate
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by whopperplate » Thu Dec 13, 2018 1:02 am

I am still trying to figure out the stray dc voltage hitting the grids in v3...seems like a red flag as grids are not ever receive dc voktagr, right?...with v3 being the only point where current is being drawn i figure this would be the place to look :|


FYI chassis is galvanized steel from valveStorm
Musicians are like a bowl of cereal
If they aren't Fruits or Nuts they're Flakes

RockinRocket
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by RockinRocket » Thu Dec 13, 2018 1:50 am

I know you have a good set of ears on you for fine tuning but Id just finish the joints with solder.

If that doesn't work. Check each connection to the schematic. You might have to unbolt the pots and jacks and lift the board forward to make sure the under board connections are in the right spots and soldered well,

whopperplate
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by whopperplate » Thu Dec 13, 2018 11:41 am

I have pulled the board up and confirmed wiring, but I will likely just shot gun blast solder the whole thing and see what happens, though I don’t understand how anything verifiably mechanically connected with full continuity would be causing any issues, but alas I have tried most everything else.

In all reality based on the symptoms I could remove the un soldered signal capacitors and still receive the same readings, as evidenced by already removing the .022 if cap before the grid of V3. They block dc voltage when working, as they are verifiably doing so, and the tubes should be drawing current regardless of their inclusion; correct me if I am wrong please.

All in all it seems like a ground problem, but I nothing adds up.
Musicians are like a bowl of cereal
If they aren't Fruits or Nuts they're Flakes

danman
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by danman » Thu Dec 13, 2018 8:14 pm

In some cases, a slight layer of oxide is enough to prevent a complete electrical connection from occurring. The flux in the solder helps to remove any unseen oxide and form a perfect electrical joint. There are times when taking a voltage reading with my meter and I see a zero reading where I know there is voltage. It can take a little extra pressure to get the tip of the lead to break the oxide layer and give a proper reading. Not saying that this happens every time but occasionally there is just enough of a layer to prevent a solid connection. The voltage on the grid of v3 is odd but I would really try to get v1 and v2 working properly before focusing on v3. That issue may resolve itself once those other two stages are working properly. Just keep at it. It's usually something so simple that it is easily overlooked while troubleshooting.

whopperplate
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Re: 50 watt high voltages, no cathode voltage v1 v2

Post by whopperplate » Fri Dec 14, 2018 12:04 am

Thanks for the words of encouragement danman, :toast: very much appreciated. I am sure if it was a snake I would have been bit by now.
Musicians are like a bowl of cereal
If they aren't Fruits or Nuts they're Flakes

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