Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Buxton_Flux on November 15, 2024, 07:05:11 pm
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Sounds like you mis-wired something, maybe a few things.
This is a great way to double check a builds wiring;
https://el34world.com/Forum/index.php?topic=17701.msg178630#msg178630
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Your going to have to go through every single connection, 1 at a time until you find it/find them.
There are no short cuts, sorry.
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Is a light bulb limiter being used, fitted with a rather lower wattage bulb?
Once valves are fitted, with a 50ish watt amp, LBL bulb wattage could be 60W minimum, perhaps 100W.
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Is a light bulb limiter being used, fitted with a rather lower wattage bulb?
Once valves are fitted, with a 50ish watt amp, LBL bulb wattage could be 60W minimum, perhaps 100W.
Yes using a 60 watt light bulb limiter. With all tubes in, brightens up on start then dies down to dim. With only rectifier tube, dims down to barely perceptible.
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then that test passed, if it failed the light would stay bright all the time, remove then check VDC's again.
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then that test passed, if it failed the light would stay bright all the time, remove then check VDC's again.
Voltages are:
- 460v on B+ 1,2,3,4 with only rectifier
- With rectifier and power tubes, starts around 340 and drops to 275 or so. Same voltage on B+ 1,2,3,4
- With rectifier and one preamp tube (no power tubes), it's around 440. With each preamp tube added it gets lower
- Bias voltage as stated in original post, 52v with only rectifier, drops to 30-ish with other tubes added
No load/no tubes/only rectifier, 460dcv. As soon as you put the 2 x 6L6's in dcv drops to 340 and keeps dropping down to 275dcv.
That sure seems to look like either, the 6L6's are drawing WAY TOO much current or that there's a short/miss-wired power tube sockets.
If their drawing way too much current, the 6L6's should be red plating and you've probably taken the life out of those tubes.
Look and see if you see the metal plates inside those tubes turning red.
Did you put in 1 ohm R's on the power tubes K to ground connection?
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Put the light bulb under the bench and plug the amp straight into the wall.
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The power tubes are not/have not red plated. (Light bulb limiter prevent that?). Have used the light bulb limiter each time starting up.
Your NOT being clear.
Shooter just told you that once the amp passes the test with the light bulb limiter, you don't use it any more.
Now you post new dcv's but say that "The power tubes are not/have not red plated. (Light bulb limiter prevent that?). Have used the light bulb limiter each time starting up."
Your amp passed the LBL test, you don't need to use it every time you turn on the amp.
So do you still have the amp plugged into the LBL when you took the new dcv's?
Voltages also drop if I put in only rectifier + preamp tubes.
Yes, I read that. I was starting with the power tubes, divide and conquer.
And that is WAY to vague, doesn't mean much, no numbers, not clear.
I can't find a short to ground from any power tube socket pin except cathode to ground, nor a short between any two pins. Same, preamp sockets. Still looking. The circuit board is new, not the sockets, so I think the problem is there.
I said a short/miss-wired power tube sockets. If there's no short, then something mis-wired. Either the tube socket or on the board.
You need to use the double check method that I posted the link to. Go through it 1 solder connection on 1 wire, 1 cap, 1 jack, 1 resistor, etc. at a time and mark it checked off on the layout drawing with the high liter. And make absolutely sure everything goes to the correct tube socket pin. It's the easiest and fastest way. Your looking for a short cut, there is no short cut, do the work. You probably have several mistakes, things mis-wired.
Is that K as in Cathode? The cathode pins go straight to ground. Screen and grid stopper resistors are newer and test good.
Yes, K = cathode.
I didn't ask you about the screen grid and control grid stoppers.
Using a 1 ohm R from the tube socket's K pin to ground lets you measure for current on the power tube safely, no high B+dcv.
You should have those. I was asking because if you had them, you could measure how much current it being pulled through the tube. That would be good to know right now.
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Use this;
Sounds like you mis-wired something, maybe a few things.
This is a great way to double check a builds wiring;
https://el34world.com/Forum/index.php?topic=17701.msg178630#msg178630 (https://el34world.com/Forum/index.php?topic=17701.msg178630#msg178630)