Wet 1969 ITT-KB junior battery radio

[paulsherwin]

They didn't waste money on fancy transistors in radios like these, so you will find any general purpose types you have to hand will be OK. For the output pair you can use a BC327/337 or 2N2222/2907, and for everything else you can use BC548s, 2N3904s or 2N2222s (and zillions of others of course).

Check the transistor leadouts to see if they follow 'US/European standard' or 'Japanese standard'.

[audion_1908]

Originally Posted by paulsherwin

They didn't waste money on fancy transistors in radios like these, so you will find any general purpose types you have to hand will be OK. For the output pair you can use a BC327/337 or 2N2222/2907, and for everything else you can use BC548s, 2N3904s or 2N2222s (and zillions of others of course).

Check the transistor leadouts to see if they follow 'US/European standard' or 'Japanese standard'.

I plan to reuse any survivor transistors, but they seem to have thinner legs with obviously more susceptible to corrosion, I am not buying any fancy transistors for a £1.49 radio.
The audio output uses germanium transistors in push pull, and there are meny cheaper subs, and I will research this deeper if either of push-pull pair dead, but it's the audio driver, phase shifter or whatever you want to call it the bt1 it's completely rusted, two legs have fallen off and has a hole in its head, I have no clue what it's electrical parameters are, the internet has come up dry on a datasheet, I don't want another bt1 even if I could find one I want a good sub

All I have is this https://www.radiomuseum.org/tubes/tube_bt1.html
I have a pack of npn me4003 transistors bc108 equivalents, I will have to check if useful elsewhere in the radio?

[paulsherwin]

The output pair are indeed Ge. The BT1 in the Radiomuseum link appears to be Ge too, and acting as a stabiliser to adjust the output pair bias as the heatsink temperature changes.

[ekjdm14]

EDIT- scratch that, what i found was an RF amp nothing to do with AF. Did say it was an NPN too

https://html.alldatasheet.com/html-p...C3930-BT1.html

The one shown on RMorg says it's a PNP planar silicon device. at least that much is the same on those haha

[paulsherwin]

That's a modern surface mount transistor - unlikely to be found in a 50 year old transistor radio.

[ekjdm14]

Originally Posted by paulsherwin

That's a modern surface mount transistor - unlikely to be found in a 50 year old transistor radio.

Yes I noticed, was wondering if it was a progression of the original package though since it stated issue 'M'... Doubtful though, and I'd have expected a Germanium there also even if RMorg says silicon.

[audion_1908]

Originally Posted by paulsherwin

That's a modern surface mount transistor - unlikely to be found in a 50 year old transistor radio.

It may still work if I could get it to fit? Lol
I think all I need to know about the the bt1 transistor is silicon or germanium to be confirmed, orientation of the semiconductor sandwich be confirmed PNP Vs npn, it's hfe and capacitance, to find a sub, but I am no electronics engineer, I could just randomly throw something generic and modern in, got some likely to have audio distortion

[paulsherwin]

A number of designs from that era used an odd sounding Ge transistor as a temperature compensator - Hacker did in some of their models. They may have been mainstream types which were out of spec somehow so were marked with odd codes. You could probably replace them with any small signal Ge type - OC71, AC126 etc.

[audion_1908]

Originally Posted by ekjdm14

EDIT- scratch that, what i found was an RF amp nothing to do with AF. Did say it was an NPN too

https://html.alldatasheet.com/html-p...C3930-BT1.html

The one shown on RMorg says it's a PNP planar silicon device. at least that much is the same on those haha

How radiomuseum.org know about the bt1?

[ekjdm14]

There's an example circuit shown on there too which might help confirm some of what's needed to be known of course https://www.radiomuseum.org/tubes/tube_bt1.html

If germanium you could always go for one of those Russian flying saucers as a test I suppose. Now I look closer, RM says silicon in the text but example circuit looks Ge...

[audion_1908]

Originally Posted by paulsherwin

A number of designs from that era used an odd sounding Ge transistor as a temperature compensator - Hacker did in some of their models. They may have been mainstream types which were out of spec somehow so were marked with odd codes. You could probably replace them with any small signal Ge type - OC71, AC126 etc.

The BT1 does share a heatsink, sandwiched between the two germanium output transistors radiomuseum.org lists the BT1 is used in 35 radios in the same place, I did wonder if the BT1 was like universal transistor like a ton?

[audion_1908]

Originally Posted by ekjdm14

There's an example circuit shown on there too which might help confirm some of what's needed to be known of course https://www.radiomuseum.org/tubes/tube_bt1.html

If germanium you could always go for one of those Russian flying saucers as a test I suppose. Now I look closer, RM says silicon in the text but example circuit looks Ge...

I like the idea of installing Russian flying saucers, the price is good as well, shango066 had good luck
https://youtu.be/wet7QameYc4
Thermally bonding them could be a challenge

I have also messaged the radio museum website asking for more info on the bt1 transistor

[ekjdm14]

That was precisely the video I was thinking of when I mentioned those! Yes getting them tied to the outputs thermally might be a challenge but I've seen (have got) some in a slightly different package that look like they'd fit. They still have the "flange" part but the body is much taller and slimmer and not too dissimilar to the shape of the ones in the set.

[audion_1908]

Originally Posted by ekjdm14

That was precisely the video I was thinking of when I mentioned those! Yes getting them tied to the outputs thermally might be a challenge but I've seen (have got) some in a slightly different package that look like they'd fit. They still have the "flange" part but the body is much taller and slimmer and not too dissimilar to the shape of the ones in the set.

Would it work wrapping solid core copper cable round the 3 transistors binding the transistors together, maybe some thermal glue? It's looking like I might not be using the cool looking copper heat spreader, I am still cleaning the rust off with wine vinegar

[ekjdm14]

I wouldn't write it off just yet, but I'd imagine solid copper wire would perform much the same function wound closely around the bodies in a kind of conjoined-double-figure-8 manner. Hopefully though the solution will fit in the original, assuming it can be liberated intact.

[audion_1908]

I printed out the radio data sheet and was going over it and the cool reject transistor as a diode the cd0000 is gone, rotted off and lost, it's easy to sub just sad.
I am not giving up

[Philips210]

Hi.

It sounds worse than a basket case, it truly is an oxidised relic . I have a load of spare germanium transistors and diodes. It's a case of trying to establish what could be subbed for the ones required. It's hard to find data on the BT1 for example.

Regards,
Symon

[audion_1908]

The cap trimmer c314 seems to have a bodge green ceramic cap on the back of the PCB? That's not in the schematic?

[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.

[audion_1908]

forgot to post these
Before cleaning agen





After I Scrubed corroded PCB with an old toothbrush and toothpaste as it's a micro abrasive