Wet 1969 ITT-KB junior battery radio - Page 8 - UK Vintage Radio Repair and Restoration Discussion Forum

Philips210 · 5th May 2020, 2:49 pm

Hi

I did a few checks with the signal generator and with reference to the pic in post #140 I connected the RF signal generator to pins D and E and the oscilloscope to the tuned winding pins A and C. I set the signal generator to around 450kHz. Looking at the sinewave on the 'scope and varying the frequency around 450kHz I noticed an increase to maximum amplitude at resonance. Resonance is not that sharp but is clearly noticeable. Altering the ferrite adjustment screw moves the resonant frequency as expected. I used the second channel (with no input) on the 'scope to place the horizontal trace at the peaks of channel 1's signal to assist in finding the point of resonance as it's not easy to see as the sinewave is opening and compressing as the frequency is altered. Having a fixed bright line marker makes it easier to see when the peak occurs. I found that resonance was about 452kHz though I should use the frequency counter to prove this.

I also similarly tested a TOKO IFT from a later Roberts radio. That had a much sharper peak than the one in the ITT. Resonance occured around 455KHz.

I'll have a look at the BFO circuit when time permits. My assumption is if it's used closely coupled to a radio with the same IF there should be a heterodyne effect, perhaps whistles/silence if the test IFT is adjusted around the same frequency as the radio's IF. If this proves to be the case, then resonance is occuring and the IFT should be fit for service.

Regards,
Symon

audion_1908 · 6th May 2020, 2:08 pm

Quote:

Originally Posted by Philips210

Quote:

Originally Posted by audion_1908

Test setup
Attachment 204824

Attachment 204825

Tests side with 2 pins 4.7ohm 0.11mH with ferrite on, 4.7ohm 0.08mH without.
Tests side with 3 pins outer set 7.5ohm 0.35mH, 0.43mH with ferrite.
5.3ohm 0.10mH center to one side 4.2ohm 0.11mH to the other, both with ferrite

It looks like there is a tubular ceramic capacitor in the base, but doesn't seem to show up on the test?
The tubular ceramic capacitor appears to be wired across the outer of the three pins on the other side.
This seems to show the wires are good, but I don't know how to read the uncalibrated test gear results.
I think I'll consider all the other IF can good until proven otherwise as it's likely to destroy the PCB taking them all off! As the copper track has a tendency of coming off the PCB

I am waiting for some solder wick to turn up

And the ferrite core turns freely! It is a surprise that the cores seems to be ok

Hi.

I have done a few L and R checks for a TOKO 10T1 4603 IF transformer removed from my ITT Junior 21 see attached pic for details. Incidentally, does your screening can still have any legible markings left on it?

I'll try to do some checks with the RF signal generator and 'scope later when I have the time. I'll also try out that BFO circuit and see if it will work in practice. These tests are going to be more meaningful than static L and R checks.

Regards,
Symon

sadly no markings, they where lost when I was scraping the corrosion off

audion_1908 · 9th May 2020, 11:57 am

I have bort a new soldering iron tip and tip restorer, just waiting on the post

5th May 2020, 2:49 pm	#141
Philips210 Nonode Join Date: May 2007 Location: Redruth, Cornwall, UK. Posts: 2,573	Re: Wet 1969 ITT-KB junior battery radio Hi I did a few checks with the signal generator and with reference to the pic in post #140 I connected the RF signal generator to pins D and E and the oscilloscope to the tuned winding pins A and C. I set the signal generator to around 450kHz. Looking at the sinewave on the 'scope and varying the frequency around 450kHz I noticed an increase to maximum amplitude at resonance. Resonance is not that sharp but is clearly noticeable. Altering the ferrite adjustment screw moves the resonant frequency as expected. I used the second channel (with no input) on the 'scope to place the horizontal trace at the peaks of channel 1's signal to assist in finding the point of resonance as it's not easy to see as the sinewave is opening and compressing as the frequency is altered. Having a fixed bright line marker makes it easier to see when the peak occurs. I found that resonance was about 452kHz though I should use the frequency counter to prove this. I also similarly tested a TOKO IFT from a later Roberts radio. That had a much sharper peak than the one in the ITT. Resonance occured around 455KHz. I'll have a look at the BFO circuit when time permits. My assumption is if it's used closely coupled to a radio with the same IF there should be a heterodyne effect, perhaps whistles/silence if the test IFT is adjusted around the same frequency as the radio's IF. If this proves to be the case, then resonance is occuring and the IFT should be fit for service. Regards, Symon Last edited by Philips210; 5th May 2020 at 2:59 pm. Reason: Additional info

9th May 2020, 11:57 am	#143
audion_1908 Hexode Join Date: Nov 2009 Location: Chertsey, Surrey, UK. Posts: 456	Re: Wet 1969 ITT-KB junior battery radio I have bort a new soldering iron tip and tip restorer, just waiting on the post