375-0-375 PT a bit high?

[mini612]

Hello everyone!  This is my first post here.  I recently bought an amp from an old record player which appears to be from a RCA Victor Model A-108.  It has 1 5y3gt, and 2 6v6.  My newbie question is on the PT.  Firstly, the wire colors do not match the schematics.  I did label the wires prior to removing it from the chassis, so the 6.3v, 5v, and HV are labeled correctly despite the colors of the leads.  I have pics attached for your view.  When I tested the PT for continuity; I get it on the 6.3 and 5 leads but NOT on the HV.  When I tested the PT, the 6.3v and 5v was confirmed to be true, but the HV is quite high with 375-0-375.  Since I am new to amp building and still have a lot to learn, I have not run into this situation yet; is this PT going bad since there is no continuity on the HV and the voltage being very high, or this is normal?   I would like to add that the size of this PT is small, not like the ones on organs.  My last project, the PT was the same size and was rated at 250-0-250.

Any suggestion is much appreciated, thank you.

[shooter]

there is no continuity on the HV and the voltage being very high

those 2 conditions can't exist together unless you metered something wrong.
when you measured VDC was it PT lead to ground or PT lead to PT lead?
does the secondary have a CT ground for the B+ windings?

[mini612]

there is no continuity on the HV and the voltage being very high

those 2 conditions can't exist together unless you metered something wrong.
when you measured VDC was it PT lead to ground or PT lead to PT lead?
does the secondary have a CT ground for the B+ windings?

Hi Shooter, thanks for your response and questions.  My multimeter is a HF AMES DM1000 (could be my meter going bad).  I measured lead to lead.  And yes the HV winding does have a CT.

[pdf64]

'Continuity' has no standard definition, eg at what resistance does a wire cease to exhibit it?
HT windings may have a higher resistance than your meter thinks is reasonable.
I suggest that you measure resistance, rather than leaving it up to the meter to decide on stuff.
PT secondary windings are rarely rated at their open circuit voltage. More normally, it's x volts when loaded with y current.
So when HT current is drawn, the voltage across the HT winding will fall, eg a 10% reduction will turn it into a 675V winding.

[tubeswell]

What pdf64 ^said^


You can ‘simulate’ a secondary load on the PT with some chunky resistors connected across the windings, and if this load resistance is estimated accurately, the secondary voltages should drop to within an expected loaded ballpark voltage.  The best winding(s) to simulate such a load on are the heater winding and rectifier filament winding. Calculate the total current draw you expect on these windings, then work backwards (using ohms law) to calculate the resistor value(s) you need to simulate a loaded winding. The PT’s load regulation should kick in when you fire it up.


Make sure that the resistor(s) you use is sufficient to safely dissipate the power that will result when you fire up the PT.

[mini612]

This is really awesome and thanks everyone for your inputs.  I will try as suggested! 

[PRR]

Very high-turns windings will confuse many digital meters. Don't go by "continuity", that is for trailer lights. Use Ohms and read the number. 300 Ohms is high for a trailer light but low for a small tube HV winding. Also (especially on output transformers), -short- a low-voltage winding (use a clip-lead) while you measure the OHMS of a high voltage winding, to damp the inductive kick. (Remove shorts right after this test!)

[mini612]

Ran home from work and did a quick measurement with the meter in ohms. Here is the results:
Secondary winding:
496.8 ohms total across CT, from CT to one of the HV is 240.2 and 257.5 ohms.
1.0 ohms for the heater
1.1 for the rect filament

Primary winding is 9.4 ohms.

Do the numbers above look correct?

[sluckey]

OK

[PRR]

.......
1.0 ohms for the heater
Do the numbers above look correct?

Actually, the heater winding is less than 1 ohm. But most meters do not handle real-low Ohms well. Read it as "1 Ohm or less". Compare with probes pressed together tight.