Express build bias - strange outcome

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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Mark
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Re: Express build bias - strange outcome

Post by Mark »

Yeah, you'd think the the voltage would be lower after going through the 18K resistors in the power supply.
Something strange going on there.

Also where are you measuring the bias voltage. Are you measuring the other side of the resistor or on the valve socket.
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Mark Abbott
Rnb716
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Re: Express build bias - strange outcome

Post by Rnb716 »

On the phase invertor, check your resistor color code multiplier... 100r, 1k, 10k, 100k(brown/black/yellow)? Verify with DMM. Its under the wire so I can't see it in the picture.

On the bias, IMO, suspect that the zero volt leg is shorted to ground or the 220kr is open. What resistance reading do you get from the zero volt side of the 220kr to ground?
resistor-color-chart.jpg
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MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

Rnb716 wrote: Mon Apr 24, 2017 4:32 pm On the phase invertor, check your resistor color code multiplier... 100r, 1k, 10k, 100k(brown/black/yellow)? Verify with DMM. Its under the wire so I can't see it in the picture.

On the bias, IMO, suspect that the zero volt leg is shorted to ground or the 220kr is open. What resistance reading do you get from the zero volt side of the 220kr to ground?

resistor-color-chart.jpg
I pulled the other side of those resistors off the board, they're now 150k. Resistance to ground is about 400 ohms with power on.
MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

Mark wrote: Mon Apr 24, 2017 8:12 am Yeah, you'd think the the voltage would be lower after going through the 18K resistors in the power supply.
Something strange going on there.

Also where are you measuring the bias voltage. Are you measuring the other side of the resistor or on the valve socket.
I tried measuring everywhere, I even pulled the other ends of the resistors off the board and checked. Still the same issue, left side has bias and right side 0.
Rnb716
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Re: Express build bias - strange outcome

Post by Rnb716 »

That is strange indeed. did you re flow that solder joint. Is there bias voltage on the resistor leg on the supply side up close to the body of the resistor?
MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

Ok so I just checked voltages again on open ends of those resistors. Suddenly I have the same bias voltage on both! It's -74 vdc, which is exactly what the bias circuit b- lead was sending.

But the b+3 phase inverter voltage which comes in at 480 vdc is wrong. It goes through the 82k resistor to pooh 1 inverter plate - measures 368 vdc. And the other side goes through the 100k resistor to pin 6 inverter player - measures 178 vdc. Shouldn't they be closer in value? How can it split into those uneven voltages?

I must at least have a bad joint re the bias thing and maybe poking around fixed it temporarily. I'll reflow all of them as I've been adding and pulling resistors etc.
MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

Ok scratch that issue - I was pushing down hard with the meter probe and suddenly saw the right voltages appear.....momentarily. They both went to around 210 vdc. Slight variation between them due to that little difference in resistor values, which I think is exactly right.

Must be crap joints or something....
MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

Very frustrating.....re soldered everything. Bias voltage now gone on one side. In the pic the right leg resistor is floating. I get bias voltage there. If I connect it to the yellow wire which runs to the output tube pin the voltage disappears. The left leg works perfectly and sends bias voltage to the other tube pin. No issues with that side.

I can't believe this is not a common build issue, followed the schematic and layout exactly....

Any clues?
MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

rps20170424_142130_877.jpg
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MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

Clearer pic
rps20170424_142341_770.jpg
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MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

It must be grounding somewhere......I'll rip it all out build it again lol
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Re: Express build bias - strange outcome

Post by pompeiisneaks »

Hey, looking at that last picture (The earlier one was too hard to see what's going on) I've downloaded and circled in red some things that seem confusing to me.

First off, please don't consider this as overly negative or ripping on you, I still make tons of solder mistakes too, and I'm just noting things I've done wrong before as well, in an effort to help.

I'm attaching my edit, and basically it's like this:
rps20170424_142341_770.jpg
Starting from the bottom two circles - both seem like they have potentially poor soldered connections (and what is the black spot? is it flux or a gap in the solder?)

Middle of the two 470 ohm high wattage... that seems like they may be joined and possibly soldered to the pot below? Not sure. but I don't see any physical connection there between those two?

Upper Yellow wire and loose wire. They seem broken? Am I missing something?

Other base of 470 ohm high watt resistor... That looks like something isn't well connected?

The large electrolytic. Seems like maybe a resistor is there, but I don't see a solid soldered connection there as well.

Seems like there are a few other soldered connections that are grey instead of shiny that implies dry soldered connections.

Lastly, I just noted one other and added it top center is two resistors that seem to be in series, but again I see what looks like just two wires solder tacked together. If you don't make a solid connection with those types and it has a dry soldered connection you can get really inconsistent results. It's always better to twist the leads together prior to soldering, to ensure a solid physical connection, then solder to hold in place.

I don't know this particular layout exactly, I will go look up the schematic of the express and see if it makes sense to me there.

Don't get too flustered, it will end up working!

~Phil
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pompeiisneaks
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Re: Express build bias - strange outcome

Post by pompeiisneaks »

I just looked up the schematic and layouts again, and definitely think I get what you're doing, you're trying to setup a dual bias for both sides of the tubes? If you could put a schematic of what's going on, it would help.

I also mentioned 470 ohm incorrectly, seems it is 47k per the schematic, I thought that third band was brown, 10ohm so 47x10 = 470, but in the drawings I'm looking at it says 47k and has an orange band, so either yours may be wrong, or the color is just off a bit on those carbon comp high wattage resistors.

~Phil
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MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

pompeiisneaks wrote: Mon Apr 24, 2017 9:53 pm I just looked up the schematic and layouts again, and definitely think I get what you're doing, you're trying to setup a dual bias for both sides of the tubes? If you could put a schematic of what's going on, it would help.

I also mentioned 470 ohm incorrectly, seems it is 47k per the schematic, I thought that third band was brown, 10ohm so 47x10 = 470, but in the drawings I'm looking at it says 47k and has an orange band, so either yours may be wrong, or the color is just off a bit on those carbon comp high wattage resistors.

~Phil
Thanks, this is the schematic I was working from, the express Kelly 90s:
rps20170424_170026_468.jpg
And I used Todd Heplers turret board layout because I wasn't sure how to relate all the schematic to a board:


rps20170424_170243_349.jpg


I thought that was supposed to be a 470 ohm resistor, I'll check some other schematics
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MikeR670
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Re: Express build bias - strange outcome

Post by MikeR670 »

pompeiisneaks wrote: Mon Apr 24, 2017 9:44 pm Hey, looking at that last picture (The earlier one was too hard to see what's going on) I've downloaded and circled in red some things that seem confusing to me.

First off, please don't consider this as overly negative or ripping on you, I still make tons of solder mistakes too, and I'm just noting things I've done wrong before as well, in an effort to help.

I'm attaching my edit, and basically it's like this:

rps20170424_142341_770.jpg

Starting from the bottom two circles - both seem like they have potentially poor soldered connections (and what is the black spot? is it flux or a gap in the solder?)

Middle of the two 470 ohm high wattage... that seems like they may be joined and possibly soldered to the pot below? Not sure. but I don't see any physical connection there between those two?

Upper Yellow wire and loose wire. They seem broken? Am I missing something?

Other base of 470 ohm high watt resistor... That looks like something isn't well connected?

The large electrolytic. Seems like maybe a resistor is there, but I don't see a solid soldered connection there as well.

Seems like there are a few other soldered connections that are grey instead of shiny that implies dry soldered connections.

Lastly, I just noted one other and added it top center is two resistors that seem to be in series, but again I see what looks like just two wires solder tacked together. If you don't make a solid connection with those types and it has a dry soldered connection you can get really inconsistent results. It's always better to twist the leads together prior to soldering, to ensure a solid physical connection, then solder to hold in place.

I don't know this particular layout exactly, I will go look up the schematic of the express and see if it makes sense to me there.

Don't get too flustered, it will end up working!

~Phil
Much appreciated Phil, I've been pretty rough here as it's got to all be put into a new chassis with new turret boards etc, if I end up with something worthwhile :)

But good points you made - and I'll sort those dry joints etc out.

I posted the schematic here just now but only a phone screenshot, so it's not clear...I can't seem to post a download shot. I'm pretty sure I found it here originally in the trainwreck files though.

It's all beginning to make more sense......gradually:)

Thanks for all the input and encouragement - I'll keep at it... :x :lol:
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