Belco Tokyo Test Oscillator TE-16A (Palace). - UK Vintage Radio Repair and Restoration Discussion Forum

Gordon71 · 31st Mar 2020, 11:33 am

Hi everyone, sometime ago i purchased the above at a car boot sale. Now with plenty of time to kill I decided to dig it out and see if it works.

Unfortunately the battery leads were detached from the PCB. I obtained a circuit diagram from radio museum.org which appears to show the pos. going to ground via the power switch. The neg. going to the circuit board. I think one or both of the transistors may have been blown by me (if not already blown) by trying the battery neg/pos to ground and on/off switch. I have new transistors on their way which should arrive by the weekend. Not wanting to replace and blow them I'm hoping someone on the forum can advise correct polarity (pos.to ground looks odd to me !).

Any help appreciated.

Andrewausfa · 31st Mar 2020, 1:28 pm

Hi Gordon,

The equipment uses PNP transistors so positive ground wouldn't be unusual.

Better prepare your wallet if you've blown them, £8-10 a go based on a cursory look.

Andrew

orbanp1 · 31st Mar 2020, 1:38 pm

Hi Gordon,

You are correct, positive goes to the ground through the switch!
The transistors are PNP, that gives the polarity of the battery.

Chances are that the transistors survived the application of the reverse polarity battery.
The 2SA942 is in the RF oscillator stage, it is a Si transistor, so a 2N3906 or similar would do fine there.
The 2SB175 is a Ge PNP audio transistor, any similar transistor harvested from an old transistor radio should work there.
You could even try a 2N3906 there too, the biasing set up is the same as for the RF oscillator.

electrotanya has the manual too, though it is called differently, in case you did not download all the pages from RM.
(The quality of the schematics in the elektrotanya document is quite poor though.):
https://elektrotanya.com/itoka_produ.../download.html

Regards, Peter

Gordon71 · 31st Mar 2020, 2:01 pm

With thanks to you both, Andrew and Peter. I've tried both polarities without success and assume something else may be going on. I sourced new transistors from Littlediode Ltd on e-bay £11.08 for both, postage free. Decent makes for both, 2SA942 NEC; 2SB175 MOTOROLA.
I'll now rewire battery leads and try again fingers crossed. New transistors due at weekend so can replace if it's still not working. Many thanks again to both

best wishes ian

Orakle42 · 31st Mar 2020, 5:52 pm

Attached is a circuit diagram of my TE-16A in case you also have a legibility problem.
The transistors are PNP and it is definitely +ve ground\chassis.
I have found it a useful bit of kit if you can get it going.

Orakle42

Gordon71 · 31st Mar 2020, 8:00 pm

Greetings Orakle42 and thanks for your assistance.
This is turning in to a voyage of discovery !
Firstly thanks for the circuit diagram i did actually manage to get this version by registering with radio museum.org. However you may like to note on your copy that the RF oscillator tranny shown as 2SA942 is actually a 2SA342 which is noted at radiomuseum.org on the opening page of the Belco TE-16A Test Oscillator.
Whoever notorised the circuit diagram must have misunderstood the the notes or miss translated from the Japanese !!
Fortunately Littlediode Ltd, from whom i mistakenly ordered a 942 had not yet despatched and were able to change it for the 342.
Since receiving confirmation of the correct polarity i have rewired the battery connections and got it working ,of sorts !! It would now appear that the 2SA342 was updated (upgraded to ?) an SA279 which i was able(just !) to read with a torch and magnifying glass. This would appear to give a higher frequency response from 100Mhz to 150Mhz.
The other major difference between the OEM and mine is the replacement of the output potentiometer from 2K with a 5K pot.This i think is the reason for what is a somewhat erratic output as measured on my frequency counter. This looks to be a previous owner bodge rather than an OEM upgrade.
So i've now ordered a new 2K pot.
No longer a car boot bargain !! but its helping to fill in lock- down time.
Hopefully i receive the parts this weekend and can get it working accurately without having to instal the two trannies which i can use in later projects.
My thanks again to all for the help, i'll let you know how it's gone next week with a bit of luck

31st Mar 2020, 11:33 am	#1
Gordon71 Diode Join Date: Mar 2020 Location: Neston, Cheshire, UK. Posts: 3	Belco Tokyo Test Oscillator TE-16A (Palace). Hi everyone, sometime ago i purchased the above at a car boot sale. Now with plenty of time to kill I decided to dig it out and see if it works. Unfortunately the battery leads were detached from the PCB. I obtained a circuit diagram from radio museum.org which appears to show the pos. going to ground via the power switch. The neg. going to the circuit board. I think one or both of the transistors may have been blown by me (if not already blown) by trying the battery neg/pos to ground and on/off switch. I have new transistors on their way which should arrive by the weekend. Not wanting to replace and blow them I'm hoping someone on the forum can advise correct polarity (pos.to ground looks odd to me !). Any help appreciated. Last edited by Station X; 31st Mar 2020 at 12:31 pm. Reason: Poll removed.

31st Mar 2020, 1:28 pm	#2
Andrewausfa Octode Join Date: Dec 2010 Location: St Ives, Cambridgeshire, UK. Posts: 1,180	Re: Belco Tokyo Test Oscillator TE-16A (Palace). Hi Gordon, The equipment uses PNP transistors so positive ground wouldn't be unusual. Better prepare your wallet if you've blown them, £8-10 a go based on a cursory look. Andrew __________________ Invisible airwaves crackle with life. Or they should do. BVWS Member

31st Mar 2020, 1:38 pm	#3
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: Belco Tokyo Test Oscillator TE-16A (Palace). Hi Gordon, You are correct, positive goes to the ground through the switch! The transistors are PNP, that gives the polarity of the battery. Chances are that the transistors survived the application of the reverse polarity battery. The 2SA942 is in the RF oscillator stage, it is a Si transistor, so a 2N3906 or similar would do fine there. The 2SB175 is a Ge PNP audio transistor, any similar transistor harvested from an old transistor radio should work there. You could even try a 2N3906 there too, the biasing set up is the same as for the RF oscillator. electrotanya has the manual too, though it is called differently, in case you did not download all the pages from RM. (The quality of the schematics in the elektrotanya document is quite poor though.): https://elektrotanya.com/itoka_produ.../download.html Regards, Peter

31st Mar 2020, 2:01 pm	#4
Gordon71 Diode Join Date: Mar 2020 Location: Neston, Cheshire, UK. Posts: 3	Re: Belco Tokyo Test Oscillator TE-16A (Palace). With thanks to you both, Andrew and Peter. I've tried both polarities without success and assume something else may be going on. I sourced new transistors from Littlediode Ltd on e-bay £11.08 for both, postage free. Decent makes for both, 2SA942 NEC; 2SB175 MOTOROLA. I'll now rewire battery leads and try again fingers crossed. New transistors due at weekend so can replace if it's still not working. Many thanks again to both best wishes ian

31st Mar 2020, 5:52 pm	#5
Orakle42 Pentode Join Date: Nov 2015 Location: Maidstone, Kent, UK. Posts: 131	Re: Belco Tokyo Test Oscillator TE-16A (Palace). Attached is a circuit diagram of my TE-16A in case you also have a legibility problem. The transistors are PNP and it is definitely +ve ground\chassis. I have found it a useful bit of kit if you can get it going. Orakle42 Attached Thumbnails

31st Mar 2020, 8:00 pm	#6
Gordon71 Diode Join Date: Mar 2020 Location: Neston, Cheshire, UK. Posts: 3	Re: Belco Tokyo Test Oscillator TE-16A (Palace). Greetings Orakle42 and thanks for your assistance. This is turning in to a voyage of discovery ! Firstly thanks for the circuit diagram i did actually manage to get this version by registering with radio museum.org. However you may like to note on your copy that the RF oscillator tranny shown as 2SA942 is actually a 2SA342 which is noted at radiomuseum.org on the opening page of the Belco TE-16A Test Oscillator. Whoever notorised the circuit diagram must have misunderstood the the notes or miss translated from the Japanese !! Fortunately Littlediode Ltd, from whom i mistakenly ordered a 942 had not yet despatched and were able to change it for the 342. Since receiving confirmation of the correct polarity i have rewired the battery connections and got it working ,of sorts !! It would now appear that the 2SA342 was updated (upgraded to ?) an SA279 which i was able(just !) to read with a torch and magnifying glass. This would appear to give a higher frequency response from 100Mhz to 150Mhz. The other major difference between the OEM and mine is the replacement of the output potentiometer from 2K with a 5K pot.This i think is the reason for what is a somewhat erratic output as measured on my frequency counter. This looks to be a previous owner bodge rather than an OEM upgrade. So i've now ordered a new 2K pot. No longer a car boot bargain !! but its helping to fill in lock- down time. Hopefully i receive the parts this weekend and can get it working accurately without having to instal the two trannies which i can use in later projects. My thanks again to all for the help, i'll let you know how it's gone next week with a bit of luck