Replacement Transistors Mullard LP1156

[poppydog]

I am currently in the process of repairing an Ekco A455 and have removed the Mullard LP1156 as I am not picking up any stations. So far I have found shorts on the AF117s but the AF115 is fine. Searching the forum has come up with being able to replace the AF115s and the AF117s with the GT322b.

My question is: Can I use the GT322b to replace them all, i.e. would it work with 3 of the same? As I don't really want to end up doing this again .

I am assuming that the tin whiskers is going to get them all eventually.

Regards
Poppydog

[paulsherwin]

Yes, that should be fine, though the transition frequency would be a bit marginal in a VHF set.

[Herald1360]

Just beware of the GT322b pinout. It's different from both AF11x and AF12x types.

[poppydog]

Thanks for the confirmation/replies, I will let you know if its a success

[Sideband]

To be honest, I wouldn't take a chance with possible 'marginal' transistors when repairing these modules. It can't be properly tested until fitted back in the radio and if doesn't work, it has to come out again (and some of them are not easy to remove). Far better to fit known good transistors in a once-and-for-all repair. The AF124, 125, 126 and 127 are direct replacements for the AF114 - 117 series and I fit those every time. I seem to recall that Langrex have good stocks of these for a reasonable price so worth giving them a try. Watch the lead-outs as they are different.

[paulsherwin]

The transition frequency won't be a problem in the AM module. It might be where an AF115 is being used as a VHF mixer, but that's not the case here.

[Herald1360]

In any case, Ft for GT322b is 80MHz vs 75 MHz for AF115. Voltage and power ratings are slightly lower but nothing that would matter with less than 20V supplies.

https://alltransistors.com/transisto...ansistor=21718

https://alltransistors.com/transisto...ansistor=36080

[poppydog]

The Russian transistors have been installed, the leads are extremely contorted due to the configuration of the transistor being very different to the AF series (the leads being very short didn't help either). It was a lot harder than I expected, especially making sure it was right first time. I have got a couple more things I need to check in the module then I will reinstall it over the next few days.

Regards
Poppydog

['LIVEWIRE?']

The GT322bs I bought, admittedly a few months ago, all have leads about 25mm long, which made it easier to use them in a 60s transistor radio (admittedly this one didn't use the Mullard module, and I've yet to try using them in a LP1156) Given the need to keep the transistor leads short in order to close the module when replacement transistors have been fitted, they might be a bit difficult to fit in a module, as you have found, Poppydog, but no more difficult than AF127s surely?

[Herald1360]

Depends- leadout on GTs is different from AF12x so leg crossing may be worse.

[tri-comp]

You should at least check the 10uF AGC electrolytic cap. for high ESR and loss of capacitance.
Half a century passed since it left the factory so most likely it's far beyond spec's even if it's a Philips part.
I recently had a similar cap' that had completely lost it's capacitance in a Philips 4822 214 50075 stereodecoder of roughly the same age.

[poppydog]

Originally Posted by 'LIVEWIRE?'

but no more difficult than AF127s surely?

After you had said about that I had a look in my manual at the lead out configurations between the AF127 and the GT322b, and as Chris (Herald) states, the transistor legs crossing each other is much more extreme than if it were an AF127 replacing an AF117. I remember replacing the AF117s with the GT322b in my Roberts R300 and that turned into a circus. If I had used AF127s in the module it probably would have taken me half the time. It was much more difficult in the module as the leads had to be kept short and also I had to insulate all of them apart from the screen lead.

Originally Posted by tri-comp

You should at least check the 10uF AGC electrolytic cap. for high ESR and loss of capacitance.

That's what I did, I lifted one end of MC8 and it was absolutely fine, I ended up replacing quite a few of those low value Philips type on the amp board as they were not good. I also replaced C22, the blue Philips type coupler to the volume control, as that was not good either. I also put the meter across the OA90 diode and that was fine.

It's all working , it's picking up everything on both wave bands, however there is an issue with the speaker which has put a massive dampener on everything It seems there is rust or something in/around the speech coil. I removed it and when you gently press on the cone it sounds like its full of gravel. Don't know if this can be fixed.

Regards
Poppydog

[Herald1360]

If you can get some, PTFE sleeving is good for this sort of job. It's thin, tough and doesn't melt when a soldering iron touches it. It comes in handy sizes too.

[Boater Sam]

Speaker.
If you're lucky it just muck, if not lucky could be rust or wire wool/filings and being magnetic are a sod to get out.
Carefully pack the back of the cone with tissue or cotton wool to bring the coil as far out of the magnet as you dare. Watch the connecting braids.
Pick off the central dust cover with a point, they come off quite easily in one piece.
Than try a vacuum cleaner, dry air line or air can repeatedly. A gentle wipe in the gap with a thin plastic strip, like a piece or margarine tub or water bottle may help.
If all else fails, soak the outer edge of the cone off the chassis with alcohol, IPA, meths. It will become very fragile whilst wet. Disconnect the braids from the tags and lift out the cone.
Now you can clean out the gap with white spirit and pieces of cardboard until you are sure there is nothing in there. If you have metallic bits that won't wipe out, use a steel strip, feeler gauge with a Neodymium magnet (broken hard drive?) to pull them out.
Clean and check the speech coil and reassemble with 3 plastic spacers in the coil to magnet centre gap to centralise the coil. weight the cone so that the coil is well into the gap.
Re glue the cone edge and cardboard ring with contact adhesive. Let it all dry out and re glue the dust cover in the cone.
A tricky repair but quite easy to do.

Transistors.
I sleeve the leads and fit the transistor upside down, can onto the PCB. Its then easier to get the leads to bend over and down into the correct holes, they are usually long enough this way as you are not crossing them over.

[poppydog]

Thanks for the replies. It's a bit of a shame really as the cone is in very good order but I have nothing to lose. It sounded like there was a bunch of keys in with the speaker I have never heard one like that before. When tried with another speaker it's very good.

Regards, poppydog.

[Boater Sam]

Have a go, its easier than it sounds. When you soak the cone off, let it dry before you touch it too much, that's really the only tricky part.
It may just vacuum out.

[poppydog]

Well the attempted speaker repair didn't go as planned so I will put a request out for a speaker, bit of a shame but at least I didn't balls up the module repair.
regards poppydog

[m0cemdave]

I'd advise against trying to blow dirt out of a gap (air duster or compressed air) You are just as likely to blow it deep into the magnet assembly where it will be even harder to remove.

A vacuum cleaner hose is the best way, especially if you can make a reducing nozzle with several layers of heatshrink over the end of the tube.

The standard way to clean a gap is with masking tape - use 2 or 3 layers to get enough stiffness. Work the tape around the gap so the sticky side picks up the grit. When I regularly did recones at work (at a loudspeaker company) I found some tape called Tesakrepp was ideal. Like masking tape but with a crepe texture. No idea if it's still available.

When reassembling, don't forget to line up the lead-in wires over the terminals before gluing the cone down ...

[poppydog]

Thanks for the reply m0cemdave, but I am afraid this one is beyond repair.

Regards
Poppydog