Wet 1969 ITT-KB junior battery radio

[audion_1908]

Originally Posted by Refugee

From what I remember from Mullard books the bias transistor was just an out of spec PNP of the same type as the PNP output transistor. The important thing is that it is of the same internal construction as the output ones.
The easy solution is to replace it with another one of the same type as the PNP output transistor as it is the VBE variation with temperature that is important. The gain is not important so they used any that were too low for the output position and marked them with a number that would stop them ending up in the wrong place.

Sometimes the answer is so simple that it gets forgotten with time, so I could just use an in spec audio output transistor!
So BT-1 = bias transistor 1!
So in my case my bt1 is a basically a 2sb364!

[Refugee]

With silicone transistors they had become so cheap and tightly specified that they were able to use a smaller full spec driver transistor.

[audion_1908]

I have started to remove the damage components, I have found my £6.47 soldering iron is the worst I have ever used! I miss my temperature controlled solder rework station that my father got for me, its stuck in storage that I can't get to

Sadly 2 bits of track lifted, luckily not critical, it looks like only 3 transistors intact enough to work! I just need to find my universal component tester! I will start on the resistors with a dvm later, why do these transistors have such thin legs? The resistors are about twice as thick, the headphone jack I thought was a complete loss it was so corroded, but I removed it from the PCB and soaked in vinegar and attacked it few times with cotton wool buds and now now looks fully functional! A success!

I have one new style resistor that the end has broken off, and numerous chiped ceramic disk capacitors, on the plus side I found a box of salvaged capacitors may be of some use! I'm starting to get a bit worried about how far this is going to go, at least it gives me a chance to clean all the hard to get too nooks and crannies of the PCB.
I also found the electrolytic capacitors replacements, I got these for another project but should work great.

[audion_1908]

Mystery BT-1 transistor used in ITT-KT radios audio output

https://www.vintage-radio.net/forum/...d.php?t=166248

[Philips210]

Originally Posted by audion_1908

So BT-1 = bias transistor 1!
So in my case my bt1 is a basically a 2sb364!

Or Broken Transistor 1 .

I had a look out for a 2SB364 and the nearest I had was a 2SB365 which has a slightly lower hFE. In my TVT data books it suggests either AC128, AC153 or AC188 to sub the 2SB364.

Regards,
Symon

[ekjdm14]

Will have a look through my stash & see if there's a working AC128 in there, if a replacement is needed for the 2SB364 then?

I think I prefer Symon's expansion of the BT1 acronym

[audion_1908]

Originally Posted by ekjdm14

Will have a look through my stash & see if there's a working AC128 in there, if a replacement is needed for the 2SB364 then?

I think I prefer Symon's expansion of the BT1 acronym

Lol broken transistor 1

I think a usable 2SB364 in the right size can is £7 in eBay! But I have not completed my research on subs, I don't want to use up your expensive germanium transistors, I am thinking of fitting Russian transistors, they are cheap and mil spec, it's a generous offer, I still need to test my transistors first.

The radio used mostly silicon transistors, and they should be easy to find substitutes, it's the strange push-pull germanium audio section that is the tricky bit

[ekjdm14]

"Broken Transistor 1" If there's a 128 that tests good & the 2SB364 turns out dead then it'll go in the envelope anyway as it'd be an old used one that I won't need (unused replacements are from £3 anyway, nothing in the big scheme of things).

Would be an interesting experiment to sub all the dead ones with the Russian ones though, I wonder if it'd pick up the Kremlin afterwards?

[audion_1908]

Originally Posted by ekjdm14

"Broken Transistor 1" If there's a 128 that tests good & the 2SB364 turns out dead then it'll go in the envelope anyway as it'd be an old used one that I won't need (unused replacements are from £3 anyway, nothing in the big scheme of things).

Would be an interesting experiment to sub all the dead ones with the Russian ones though, I wonder if it'd pick up the Kremlin afterwards?

From what I've read the Russians kept evolving germanium transistors when others abandoned the tech so I could put far superior transistors in than original, some of the Russian germanium transistors can go to a gigahertz! Not that I need that, Also it would look cool, in 1969 the cold war was going on!

Maybe with a big enough antennae maybe I will get the Kremlin, are they still on am?

[ekjdm14]

I like the cool/irony factor of using Russian parts in a cold-war era set yes! Careful with those super-UHF types though, you might end up with a 5G radio!!!

Not sure if it's Government owned but Radio Rossii is on 873Kc/s... Radio Mayak sadly is reportedly not on AM any more, but I definitely heard Russian language programming on 31m band a few nights ago...

[audion_1908]

I found my components tester and for fun put the 10v 200uf 51 year old electrolytic capacitor in and it tested 522uf! 7.2% loss ESR 3.4ohm? For fun I had done a basic reforming on my dvm on the 2mohm resistance range the other day, of course I was not planning to reuse the cap just interested. It's the only electrolytic cap without his legs rotted off.
I have tested one transistor the 2sb364 push-pull audio output it tests PNP hfe 75, uf 202mv so works!
The 2sd104 tests Npn hfe 6 uf 79mv, so bad I tested it a few times and taped it's case and it got better, and tested hfe 7, uf 188mv but still bad, the why is the forward voltage going up

[audion_1908]

So the 2SB364 could be the new bt-1 just need a new germanium push pull output matched pair!

https://www.web-bcs.com/transistor/tc/2sd/2SD104.html
Lists 2sb364 pnp subs ac128, ac153, ac188, 2n1190, 2sb475
And it's complementary 2sd104 non sub ac127, ac176, ac187, 2sd72, 2sd352
But I have not looked up Russian germanium transistors yet

[audion_1908]

How closely dose the hfe of the germanium transistors need to be? some say 50% is ok, Mallard apparently sold matched-pairs back in the day of 20% and some articles say that transformers less audio output with feedback it doesn't really matter? if it doesn't matter much and I don't have to buy spares for matching?

[audion_1908]

I have managed to remove most of the rotted off components legs from the PCB using a mix of liquid flux, lead tin solder, and the bad soldering iron, I even removed the black top IF transformer T313, but with great difficulty I also removed the stock bodge caps from the back of the pcb, maybe they are what makes a Mark 1 and 2 Mark 2?
the 2 dark green ceramic caps are to small for my universal component tester to test it one ad 25 on it?

How do you open the IF transformer now!

[audion_1908]

http://kbmuseum.org.uk/itt_service_m...10_service.pdf
lists the bt-1 as a bias stabiliser as used in the itt-kb kr610

[audion_1908]

the cs9018 only has 2 legs but tests ok as a diode 2pf 0.877mv so maye sub the cd0000? as its a silicone diode.
the cs1312 also only had 2 legs but dead as a door nail.
so out of 8 transistors and 2 diodes I have 1.5 good transistors 2sb364 and half the cs9018, the cd0000 diode is lost but I have not tested the 1n60 but that diode has a dry joint, and it fell apart as I tried to remove it.

[audion_1908]

Under the band switch it was packed with wax and rust goo, so had to go.
The radios PCB is looking very barren now, but I'll be able to start putting components back on now, starting with the capacitors.








Sorry for the bad pics

I found a Russian sub for the AC128 that is a sub for the 2sb364, the Russian sub a gt402 comes a few flavours with the same shape as the original 2sb364

[audion_1908]

I think the 2sd104 ge sub is an AC176 that is sub gt404j, and still fit the original triple heat sink, but I will double check before buying them.

[Philips210]

Originally Posted by audion_1908

How do you open the IF transformer now!

Hi.

It's not too difficult but can be awkward especially if the can is corroded.

If you look under the can, and either side of the two screening can pins is a small tab. I find if you gently splay the screening can pins outwards that will be sufficient.
The following is far from ideal and I've never had a problem using this method but it's a case of using a blunt tool to apply gentle pressure on top of the ferrite adjustment screw. That should push the whole assembly out of the can. It usually comes out without having to apply too much force but could be difficult if the can is corroded. If shouldn't need so much force as to cause the screw to crack. Tapping around the base of the can first might help.
Once the assembly is out the polythene carrier has two tabs that can be splayed to free it from the base which had the winding. Under the base you'll notice the tuning cap. In the attached pics it should be clear how it is assembled. Note I've unscewed the ferrite screw for clarity, it's not necessary to have to do this. If you were to do the same then note its approximate position first so it's somewhere near the correct setting when reassembling it.

Others may have other ways to dismantle these IFTs.

Hope this helps.

Regards
Symon

Regards

[Philips210]

Hi.

Out of curiousity, do you have any pics of the loudspeaker showing to what extent it's corroded?

Regards,
Symon