i've had trouble free experiences putting together 3 bottlehead kits in the past, and so am finding myself confused and a little frustrated with my construction of the foreplay 3 kit i'm working on. i'm having a couple of problems, but i'd like to take the questions 1 at a time. i am not getting correct voltage readings for the heater supply; i have 3.3 - 3.4 VAC at transformer terminals 4 & 5, and i am reading 6.4 VDC at H2 and 0 at H1. i have checked my diode and cap orientation and layout configuration step by step 4 times now, and reheated my solder joints 2 or 3 times each, and am developing a headache trying to figure this out. is it possible this 23 watt iron isn't hot enough to adequately heat these diode connections? i am completely stumped, and any helpful suggestions would be much appreciated.
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foreplay 3 construction help! request
- Thread starter khingila
- Start date
OK, I don't know this circuit, so I can't be of much help to you. But, I cannot help but wondering if you're having a measurement issue rather than an actual problem.
When you are measuring AC Voltage on the transformer terminals 4 & 5, what is your reference point? Is it circuit ground? Have you measured AC Voltage between terminals 4 & 5? Finally, since I don't have this information, what numbers were you expecting when you took this measurement?
If it's OK with you, we'll stick with those questions to start with, and maybe someone who knows the circuit will happen along.
When you are measuring AC Voltage on the transformer terminals 4 & 5, what is your reference point? Is it circuit ground? Have you measured AC Voltage between terminals 4 & 5? Finally, since I don't have this information, what numbers were you expecting when you took this measurement?
If it's OK with you, we'll stick with those questions to start with, and maybe someone who knows the circuit will happen along.
Grainger49
New member
khingila,
The transformer puts out 6.3V AC then with the diodes, capacitor and resistor produces about 6.3V DC. But if you measure to ground from the transformer terminals or from the tube pins you will get an odd reading. The heater voltage rides on top of some of the B+ that feeds the plates.
What matters is what you get from either pin 4 or 5 to pin 9. That is one meter lead on pin 4/5 and the other on pin 9. That should be 6.3V DC. If you have that plus or minus 0.2V you are good.
The transformer puts out 6.3V AC then with the diodes, capacitor and resistor produces about 6.3V DC. But if you measure to ground from the transformer terminals or from the tube pins you will get an odd reading. The heater voltage rides on top of some of the B+ that feeds the plates.
What matters is what you get from either pin 4 or 5 to pin 9. That is one meter lead on pin 4/5 and the other on pin 9. That should be 6.3V DC. If you have that plus or minus 0.2V you are good.
thanks for the replies, jc and grainger; the construction manual says i should be reading 26.3 VDC at H1 and 32.6 VDC at H2, both referenced to ground. i am reading 0 at H1, 6.3 at H2, both referencing circuit ground. ACROSS transformer 4 and 5, i read 3.3 VAC, and ACROSS H1 and H2 i read 6.3 VDC. at the tube sockets, i am reading 6.6VDC across pins 4/5 and 9, in both cases. those sound like appropriate heater voltages, correct? at this point i am wondering if the specs for H1/H2 in the manual are a misprint.
Grainger49
New member
Ok, what you don't have is the B+ bias on the heater circuit. H1 and H2 are the output of the heater circuit and should have a bias voltage on it. There should be a short measured from A9 to 22U. That is on page 31 second step.
Yes, the heaters have the right voltage across them. But you seem to be missing the bias voltage. BTW, H1 to H2 should read exactly what tube pins 4 to 9 reads since they are wired to each other on page 19. But if your meter probes are not well contacted to the terminals or tube pins you can get a difference.
Yes, the heaters have the right voltage across them. But you seem to be missing the bias voltage. BTW, H1 to H2 should read exactly what tube pins 4 to 9 reads since they are wired to each other on page 19. But if your meter probes are not well contacted to the terminals or tube pins you can get a difference.
ah! got it; thanks very much. yes, the next question i am going to address is the B+ issue; i've got proper voltages up until the terminals with the last cap. i was going to post that issue here tonight, if i haven't figured it out after i have a chance to go through the layout and resoldering 3 or 4 times. i appreciate the help.
Grainger49
New member
If the voltage on the 46uF Edit that should read 47uF (terminal 10) and the voltage on the 1.0uF (mustard colored cap terminal 22) is good and the voltage at the 0.1uF (Octal socket pin 5) is off then you might have a problem with the OD3.
with regard to my B+ supply, i find that my resistance to ground readings from transformer terminals 6, 7, 9 & 10 are all approx. 4 M and declining, rather than infinity. my voltage readings referenced to ground at terminal strip points 1, 2, 4 & 6 are all a little higher than spec'ed @ 247VDC rather than 217; 5 & 9 are 0; 7 is 494 rather than 434, and i got nothing at 10. everything looks to be wired, oriented, and soldered properly, but obviously something is wrong...needless to say, i'm getting nothing downstream of 10, either. any suggestions would be much appreciated.
Grainger49
New member
A declining resistance reading often means there is a capacitor and a charge on that capacitor in play. A reading in excess of 500k is considered infinity. So your readings are good.
High voltages are expected when the B+ circuit is open downstream. Everything tends to float to the highest voltage because there is no current, the tubes are not on, the resistors that should drop the voltage are not passing the proper current (not dropping as much voltage).
You are right on path. Getting nothing at terminal 10 is a big clue! Check continuity of the 2.7k resistor (Rpsu) from terminal 7 to terminal 10. Try measuring resistance from the top of the terminals so you don't touch the resistor leads. If there is a problem, wet both T7U and T10U.
I'm going to have to transfer terminal numbers to the schematic I have to tell where in the power supply you are losing it.
I will post back if no one else finds it in the mean time.
High voltages are expected when the B+ circuit is open downstream. Everything tends to float to the highest voltage because there is no current, the tubes are not on, the resistors that should drop the voltage are not passing the proper current (not dropping as much voltage).
You are right on path. Getting nothing at terminal 10 is a big clue! Check continuity of the 2.7k resistor (Rpsu) from terminal 7 to terminal 10. Try measuring resistance from the top of the terminals so you don't touch the resistor leads. If there is a problem, wet both T7U and T10U.
I'm going to have to transfer terminal numbers to the schematic I have to tell where in the power supply you are losing it.
I will post back if no one else finds it in the mean time.
Grainger49
New member
You are welcome.
Grainger is my given name. Like in my signature. Well, in the old South folks were called Mr. and their given name but that was a hundred years ago. Grainger was my grandmother's maiden name.
Grainger is my given name. Like in my signature. Well, in the old South folks were called Mr. and their given name but that was a hundred years ago. Grainger was my grandmother's maiden name.
to satisfy my curiosity, i disassembled this wirewound resistor, and found inside the 'ceramic' insulation what i assume is some sort of non-conductive core, a metal cap with attached lead on each end of it, and...nothing connecting them. there is a spiral groove on the core in which i'd guess should be laid the wound wire tieong together the ends, but there's nothing.
Grainger49
New member
Depending on where you are you might be able to get that fast locally. Call the Queen Monday morning and Bottlehead will probably, most likely, mail it to you Monday.
Click on the Bottlehead badge at the left top of any page and it will take you to an index. Contact information is a link on that index page.
Click on the Bottlehead badge at the left top of any page and it will take you to an index. Contact information is a link on that index page.
Grainger49
New member
For the most direct service call on Monday. That will get it out fastest.
Paul Joppa
Moderator
I am not up-to-date on parts substitutions, which have been pretty common the last year or two as the economic problems have forced supplier inventories down. With that caution, I am guessing this is one of those square cross section "cement" resistors. Those are bulk metal oxide at higher resistances, and wirewound at lower resistances. The exact cutoff varies with the manufacturer, and with the power rating, but it's usually pretty low, less than 1200 ohms IIRC. So this one is probably a metal oxide type, not wirewound.khingila said:to satisfy my curiosity, i disassembled this wirewound resistor, and found inside the 'ceramic' insulation what i assume is some sort of non-conductive core, a metal cap with attached lead on each end of it, and...nothing connecting them. there is a spiral groove on the core in which i'd guess should be laid the wound wire tieong together the ends, but there's nothing.
a new 5w2k7 courtesy of bottlehead picked up at the impressive new facility and inserted into the circuit results in all resistance and voltage readings tolerably close to specs. thanks very much to all who assisted. soon as i walk the dog, the foreplay III will be inserted into the system.
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