Metropoulos Forum

Finally finished building my amp, powered it up to test voltages as per Metro JTM45 instructions, and I'm not getting 5 volts on pin 8 of my rectifier socket. Powered down, disconnected wire from tab A on the PT (Marstran 1202-118) which was connected to pin 8, powered back up and tested again. Now it reads 80 something volts on tab A and B on the PT and 5ish between the two. I know very little about the specifics on how transformers work, so... Is this normal? Hooked tab A back up to pin 8 and checked again. Still no 5 volts on pin 8. Checked a few other things before calling it a night. Not sure where to go from here. Any suggestions?

Tried to attach a picture of the wiring diagram for the transformer. No luck there. Also, am I posting in the right section?

Thanks!

give us all the AC voltages on the primary and secondaries

I'm not at home right now but I can ballpark it.
Since I can't get the diagram on here, here's the pin out list and roughly what the voltage is.
Supposed/Actual
A 5vAC
B 5vAC / 5V
C HT high / 340ish
D HT low / 290ish
E 0
F HT low / 290ish
G HT high / 340ish
H common
I 3.15 / 3.12ish
J 0
K 3.15 / 3.12ish

120vAC from the wall.

I'll double check everything when I get home, but I'm 97% certain this is correct.

I'll get it sorted out eventually. I just want to figure out if the transformer is bad so I don't wind up chasing my tail.

Actual voltages:
power on / power & standby on
A 83.0 / Nothing
B 86.6 / 5.204
C 337.7 / 338.2
D 300.9 / 300.1
E Ground
F 300.4 / 299.7
G 338.9 / 337.8
H 121.7 / 121.4
I 3.322 / 3.310
J Ground
K 3.321 / 3.308

Do I need to kept searching for the root, or is my transformer faulty?

double check the 5v taps and the grounding/common perhaps

I've done that. Taps A & B are the 5v taps. Tap B puts out 5.204v when the power switch and standby are both on. Tap A does not. I get a signal on my meter like I do when I measure between grounds, but when I put it on continuity, there is no continuity between tap A and ground. With the standby switch off, I get 83v from tap A and 86.6v from tap B and if I measure between tap A and B, I get 5v again. This is the part that I want to know if it's normal or not. The rest of the voltages from the other taps do not change.

What you are getting seems correct to me

A-B is one coil with no ground or centre tap. If you measue A-B you should get 5vac, these are soldered to the heater taps on your rectifier (pins 8 and 2) suggest you double check the pin layout of the socket.

Pin 8 is connected to the HT switch as it is the output of the rectifier.

Your pins C to ground to G is your HV supply (337-0-337vac) with a centre tap to ground, so total of about 670vac which rectified will give you about 425vdc

PIns D to ground to F are your LV option (300-0-300vac) and again it has a centre tap to ground, to give 600vac which rectified would give you about 380vdc

On a JTM45 typically the HT fuse goes between the centre tap and the ground lug.

The octal and 9-pin heaters do have a centre tap (grounded near the PT)written as 3.3-0-3.3, and the J to round to K voltage of 6.6vac is a little high but will work fine.

Hope that makes sense.

I put a 0.05uF 600v or 1000v cap between pin 8 and ground as well (stops HT pops).