Primary impedance of original jtm 45 ot?

[Ray Barbee]

Anyone know the correct primary impedance on the kt66 jtm 45s? Thanks in advance.

[Roe]

Anyone know the correct primary impedance on the kt66 jtm 45s? Thanks in advance.

it varied from 5.7k to 8k, depending on tranny and tap

[neskor]

I have one right know.
Impedance is around 6.5K

[Ray Barbee]

Thanks!

[pdf64]

The first year or 2’s production mostly used the RSDeluxe, hard wired for 6k6 primary and 15 ohm secondary.








Subsequently the Drake 784-103 was mostly used, 8k primary to 8, 16 & 100V secondary, typically hard wired to 16 ohms.
See Marshall database
http://marstran.com/Historic%20Data%20Base.htm

[pdf64]

I have one right know.
Impedance is around 6.5K

Have you checked the high frequency to ultrasonic frequency and phase response of your’s?
Mine has a weird resonant peak and phase shift around 40kHz.

[neskor]

[/quote]
Have you checked the high frequency to ultrasonic frequency and phase response of your’s?
Mine has a weird resonant peak and phase shift around 40kHz.
[/quote]
I didn't
I don't have balanced signal generator, maybe runing the secondary with SG and solid state amp will work, but never tried.
I think the only valid measurments will be if we put OT in the circuit.

[Roe]

I have one right know.
Impedance is around 6.5K

on the 15 ohms output arrangement, not the 7/8 ohms out?

[neskor]

on the 15 ohms output arrangement, not the 7/8 ohms out?

it is measured on 8 ohm tap with 8R resistor on secondary

[bepone]

The first year or 2’s production mostly used the RSDeluxe, hard wired for 6k6 primary and 15 ohm secondary.

nice data, i see how in the past all important data were given for calculating freq. response like inductance and leakage inductance, nowadays all those data are hiden, or manufacturer even doesnt know what and how to make it

[bepone]

I have one right know.
Impedance is around 6.5K

hi neskor, can you explain what exactly you are measuring = 6.5k ohms here?

when you have this trafo on hand , how much is parasitic capacitance between P and S? any tap is ok

[neskor]

hi neskor, can you explain what exactly you are measuring = 6.5k ohms here?
when you have this trafo on hand , how much is parasitic capacitance between P and S? any tap is ok

6.5K is primary impedance with 8R on secondary
I tried to measure parasitic capacitance between P and S but results vary to much depends on which pin I connect the probes, if you have some sugestion how to wire and connect probes, please let me know

[bepone]

6.5K is primary impedance with 8R on secondary

understand that, but is the same like inserting voltage on primary and measure sec. , calculate by hand? did you check and confirm ?

I tried to measure parasitic capacitance between P and S but results vary to much depends on which pin I connect the probes, if you have some sugestion how to wire and connect probes, please let me know

put 1khz C setting and try from Ub+ to secondaries.. should be around 1-5nF if is good trafo, if doesnt measure try via normal multimeter, on C selector, usually is somewhere there.. this parasitic measuremnt i use like indicator, if is 20nF or so, then insulation is too small and bandwith is too narrow, 1-5nF is ok, less than 1nF means maybe too much highs

[neskor]

understand that, but is the same like inserting voltage on primary and measure sec. , calculate by hand? did you check and confirm ?

put 1khz C setting and try from Ub+ to secondaries.. should be around 1-5nF if is good trafo, if doesnt measure try via normal multimeter, on C selector, usually is somewhere there.. this parasitic measuremnt i use like indicator, if is 20nF or so, then insulation is too small and bandwith is too narrow, 1-5nF is ok, less than 1nF means maybe too much highs
[/quote]

With 1Khz C settings and from Ub+ to secondaries I'm getting 1440pF
If I apply 400hz AC signal 1V RMS on secondary, on primary I'm getting 26.65V RMS, so it should be OK with 6.5K/8R relation

[neskor]

With 1Khz C settings and from Ub+ to secondaries I'm getting 1440pF