Extended Foreplay 3 Help

[Paul Birkeland]

The "I" on the B side is the ground, don't look too hard into that

At this point, you could actually listen to your preamp, which is good, but the regulation is still off.

Is there any way you can post a photo of the center C4S board?

Also, it is good to double check that the wires leaving the Kreg pads are going to the appropriate tube socket pins. 

-PB

 

[John EH]

Yeah I saw that when I saw the wire running to the center tube socket!  Ha ha.

It's working and sounds damn good.

Stand by for the photo

 

[John EH]

Photo.  Only thing of note is the LED I subbed which I mentioned in the first post.  Radio shack 276-026a. 

 

[John EH]

Oh yeah K wires go to R3 and R8

 

[John EH]

In the photo the B end upper LED is the one not lit.  The other three are very dim.  My subbed LED is dim.  Ohm meter diode setting says they are installed correctly.

I followed the trace at the top of the board to the last LED leg in the line and got 1.8v with the diode checker.

They all seem to have 166 (or so) volts on both sides of each one.

 

[Paul Birkeland]

Oh yeah K wires go to R3 and R8

Yes, they should, but if you have them switched, things fall apart.

You can set your meter to the continuity beep, then put one probe on + on the A side.  Either pin 1 or pin 6 will beep for that connection.  Now move your probe to the K pad on that side, then move to the accompanying cathode (3 for 1, 8 for 6) and you should get continuity. 

If they are switched, the regulators can't keep things in balance.

That dim LED could be from the adjacent R1 not being well soldered.

-PB

 

[John EH]

Oh yeah K wires go to R3 and R8

Yes, they should, but if you have them switched, things fall apart.

You can set your meter to the continuity beep, then put one probe on + on the A side.  Either pin 1 or pin 6 will beep for that connection.  Now move your probe to the K pad on that side, then move to the accompanying cathode (3 for 1, 8 for 6) and you should get continuity. 

If they are switched, the regulators can't keep things in balance.

That dim LED could be from the adjacent R1 not being well soldered.

-PB

On + pin one beeps.  Moving to K makes pin 3 beep.

I'll reheat the R1's

 

[John EH]

Reheated the R1's and K's.  Same same.  3 dim LED lights.  Voltages the same.

 

[John EH]

Regulator tube PLENTY hot too

 

[Paul Birkeland]

Can you swap in a different 12AU7 to the center socket?  Everything looks just spot on, but the 12AU7 is not cooperating.

 

[John EH]

Great minds think alike.  I just rolled in a couple different known good tubes.  I have a TV7 tester.

 

[John EH]

I should have added that it didn't fix the problem.

 

[Paul Birkeland]

You don't happen to have a pair of PN2907's instead of TL431's?

It's odd, something is not allowing the plate to pull current from the cathodes.  I'd say double check that the grids on the 12AU7's are grounded (through those 220 Ohm resistors), but even if those floated up, your Kreg voltages would be higher than 1.

-PB

 

[John EH]

You don't happen to have a pair of PN2907's instead of TL431's?

It's odd, something is not allowing the plate to pull current from the cathodes.  I'd say double check that the grids on the 12AU7's are grounded (through those 220 Ohm resistors), but even if those floated up, your Kreg voltages would be higher than 1.

-PB

Not sure what you mean.  I do have two 2907a's as Q1 as per the manual

The two regulator chips are LM 431 also per the manual.  The photo I posted before shows.

I'm starting to think I for sure have one bad LED.  When I put the meter across the LED's individually I can get them to light up.  One absolutely will not and then of course I have the subbed LED.

Would one crap LED cause the regulation problem?

I asked Eileen to send me four new ones via email earlier.  Right track?  Wrong station?

 

[Paul Birkeland]

Well, you can have one regulator that's totally not working, but the other side should still be spot on.

There is something either missing on that center PC board, or something very wrong with the center 9 pin socket.  Can you triple check that you get 6V from 4/5 to 9 on that center tube socket?

Can you twist that board up vertically a bit and snap a 2nd pic? (I've been staring at the first one for over an hour now, lol)

 

[John EH]

Hold up a sec on the pics.  I'm on roll.  One in a row.  I removed that bad LED on the B end and sure enough I have the B end lit up brightly now.

I suspect the subbed LED in the A end is dead too.  My daughter says she can't see a peep of light on it when I cross it with the diode checker.

Cross my fingers.  And yours.

 

[John EH]

How 'bout dem apples.  All LED's lit.  Once Eileen sends me the new ones I'll put the HLMP's in.

One more question.

12 - 155v
15 -99v

21 - 163v
32 - 75v

Is that any kind of a problem or varies with the tube?

Thanks for all your help. I do really appreciate it.

 

[Paul Birkeland]

You can check those by swapping the outboard tubes.

What are the voltages at I/O/Kreg pads on the center PC board?

 

[John EH]

You can check those by swapping the outboard tubes.

What are the voltages at I/O/Kreg pads on the center PC board?

Sorry had to go outside and live life away from the soldering iron a bit.

Here's what I have and factor in that I hooked to my main stereo system and my mains power there is now 120 where everything I fed you before was 100v mains.

12 -150
21 -150

15 -70
15 -80

A side
K -2.2
I - 215
O - 150

B side
K - 2.3
I - 217
O - 150

I'm good right?

Thanks again so much.  It sounds stupid great.  Better than my other Foreplay 3 Extended.  Not sure why that is but it's good!

John

 

[Paul Birkeland]

You're right on the ragged edge of where the TL431 will opeate.  I think you'll want to see 3+V on Kreg, but we can now see that it's over 1V, so the 12AU7 cathodes are spewing some electrons.

I'd swap in another 12AU7 or two and see if you can get that voltage to pop up a bit.  If all your 12AU7's are behaving in the same manner, I would replace the TL431 regulators (I've blown my fair share of them, they are an amazing chip, but somewhat sensitive).

-PB