5F6A low volume

[Pedro Vecino]

With all secondaries disconnected (HT and bias), measure the resistance between the high voltage windings and the center tap to see if they are identical or very close (37 and 37 Ohms).

[J M Fahey]

Thanks, almost there, letīs complete the measurements.

Yes, some are redundant, repetitive, "not necessary" .... and thatīs the point, we are trying to catch where/which the error is.

So please measure and post AC voltage across:

1) Red_T>Red_B (I call Red_T the top one, Red_B the bottom one, please attach a little piece of tape to wires to label them, "Red" alone does not tell me which is which and this is important)

2) Red_T>Red/Yellow

3) Red_B>Red/Yellow

4) Red/Green>Red/Yellow

5) Red_T>Red/Green

6) Red_B>Red/Green

Unless I forgot some, these are all possible High Voltage winding combinations, our main problem today; in theory they "should" add up and yield consistent results, but your earlier measurments did not match, at all, so we are testing the transformer "clean" to verify.

After we are certain of what we have there, we can go on with other tests.

[Reader]

- - -I have not measured between Bias and center tap because last night while I was measuring the 500mA fusein bias wire is burned, then I'm scared. I suspect the problem is at 50 VAC out winding.- - -

Since you were able to measure the voltage at all the other secondary windings and the transformer doesn't seem to be in distress (Such as heating up excessively or blowing the main primary fuse) it should be OK to measure the remaining voltages.

Specifically, measure the voltage between the Red/Yellow wire and each of the red wires and measure the voltage between the Red/Yellow wire and the Red/Green wire.

Note that the 500mA fuse in the bias circuit doesn't blow because of a transformer problem. It blow because of excess current draw due to something in the downstream circuit. Could also blow because of a slip with a test probe causing a short.

Edit: Oh - I see that Juan Fahey has posted while I was writing. Follow his instructions of course.

[vinceg]

Thanks, almost there, letīs complete the measurements.

Yes, some are redundant, repetitive, "not necessary" .... and thatīs the point, we are trying to catch where/which the error is.

So please measure and post AC voltage across:

1) Red_T>Red_B (I call Red_T the top one, Red_B the bottom one, please attach a little piece of tape to wires to label them, "Red" alone does not tell me which is which and this is important) 690

2) Red_T>Red/Yellow 340

3) Red_B>Red/Yellow338

4) Red/Green>Red/Yellow50.5

5) Red_T>Red/Green290

6) Red_B>Red/Green396

Unless I forgot some, these are all possible High Voltage winding combinations, our main problem today; in theory they "should" add up and yield consistent results, but your earlier measurments did not match, at all, so we are testing the transformer "clean" to verify.

After we are certain of what we have there, we can go on with other tests.

Here I am. It is I who thank you and everyone else.

[vinceg]

With all secondaries disconnected (HT and bias), measure the resistance between the high voltage windings and the center tap to see if they are identical or very close (37 and 37 Ohms).

Yes, it is identical.

[eschertron]

340 + 338 = 678 pretty close to the measured 690 (little more than 1% off)
290 + 396 = 686 even better.
I'll let Juan do the final assessment, but I think you will not need to buy a new PT

[Helmholtz]

340 + 338 = 678 pretty close to the measured 690 (little more than 1% off)
290 + 396 = 686 even better.
I'll let Juan do the final assessment, but I think you will not need to buy a new PT

Depends on what happens, if RED/YEL is connected to chassis ground/ORG. I suspect voltage between RED/YEL and ORG/transformer core.

[vinceg]

Depends on what happens, if RED/YEL is connected to chassis ground/ORG. I suspect voltage between RED/YEL and ORG/transformer core.

Can I check with multimeter if there is voltage between RED/YEL and ORG?

[vinceg]

Depends on what happens, if RED/YEL is connected to chassis ground/ORG. I suspect voltage between RED/YEL and ORG/transformer core.

Unfortunately, your suspicion is founded. I measured the voltage between RED / YEL and ORG and it is 94VAC. So the transformer is gone?

[Helmholtz]

Can I check with multimeter if there is voltage between RED/YEL and ORG?

You might, but the reading will not be very reliable, because of capacitive leakage in the transformer. But you can measure resistance between RED/YEL and ORG (after disconnecting from mains!), should read infinite/open.
But I recommend to wait for Juans reply, because I assume that he is going to guide you through a more systematic and instructional analysis.

[vinceg]

You might, but the reading will not be very reliable, because of capacitive leakage in the transformer. But you can measure resistance between RED/YEL and ORG (after disconnecting from mains!), should read infinite/open.
But I recommend to wait for Juans reply, because I assume that he is going to guide you through a more systematic and instructional analysis.

Oops, I measured before reading your comment. Ok, I measured resistance and it's open (multimeter display show 0L)

[J M Fahey]

So far I think transformer is fine, all voltages and specially their combinations match perfectly; remember normal meters guarantee 2% precision, expensive ones 1% ... of full scale value, (just check datasheet) so less than full scale measurements have less than "official" precision ... yet these match incredibly well.

Letīs go through this first: *maybe* a turn is touching the core laminations, we canīt discard that at least from safety considerations, letīs check it one way or another before going on:

a) measuring voltage between a winding and core is a way, but sadly very high meter impedance makes usually very weak losses/undesired_coupling look larger than they are.
Iīd connect a neon bulb if you have one from Red/Yel>Org , with, say, 100k in series, and check whether it lights bright (for a Neon)/weak/none.

If unavailable, replace neon with a bright or extrabright LED (best if crystal clear) in anti-parallel with any 1N400x type diode you have: Led Cathode to diode anode, Led anode to diode cathode; the couple in series with a 100kresistor.
I have found this to show visible light even with tiny current through it.

or: Plan B, the (safe) brute force approach, and which I trust better, because it mimics actual use:

b) connect Red/Yel to Orange , plug amp into mains , always through lamp bulb limiter and turn it on:

* if lamp lights full brightness, transformer is shorted unusable

* if it blinks and then becomes dark red or orange, the transformer is probably fine, weīll continue with other tests.


Note: Iīm suggesting nothing new or unusual, just applying my OCD to a noble cause
The old: "leave no stone unturned" or Enzoīs: "never search for reasons NOT to check something"

Including:"but I already measured that"

[vinceg]

or: Plan B, the (safe) brute force approach, and which I trust better, because it mimics actual use:

b) connect Red/Yel to Orange , plug amp into mains , always through lamp bulb limiter and turn it on:

* if lamp lights full brightness, transformer is shorted unusable

* if it blinks and then becomes dark red or orange, the transformer is probably fine, weīll continue with other tests.

Remembering that at the moment the transformer is disconnected from the amp circuit, do you mean that i have to connect Transformer to circuit or test only the transformer?
For 220VAC voltage at wall what wattage for the bulb? Incandescent bulb are hard to find, I have one of 60W.

[vinceg]

Unfortunately the time zone does not allow us to be awake at the same time, but in Italy it is daytime and I can not stay still.
So I connected Red/Yel to Orange and together to chassis, then plug transformer into mains through lamp bulb limiter (I used a 60W incandescent lamp) and turn on. The lamp does not light up. While transformer is turn on I redid the same measurements and I get:

Red_T > Red_B 644 V
Red_T > Red/Yel 329 V
Red_B > Red/Yel 329 V
Red/Yel > Red/Green 48 V
Red_T > Red/Green 280 V
Red_B > Red/Green 375 V

I'm waiting for your response

p.s. Before all above operations I test for continuity between Red/Yel and Orange and there is not continuity.

[J M Fahey]

Hey, we are only 4 hours away!!!
Italy +1 GMT ; Argentina -3 GMT

Back to the transformer, it seems to be perfect


So now weīll reconnect it step by step.

Start by reconnecting filaments .... *ONLY*
Do not "save time" connecting anything else.

1) Test first with bulb limiter that we have filament voltage across proper tube pins at every tube. No tubes plugged in.

2) Now that each tube pin has about half that relative to ground.

3) Now repeat tests with tubes in their sockets, *still* through builb limiter.
I donīt care you will now have way less than 6.3V at each filament, we are just testing winding does not collapse/short under real load.

Post results.