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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 8th Feb 2019, 11:18 pm   #1
GW4FRX
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Default BFW58/88 substitutes?

Having recently finished restoring a Radford SPA.50 power amplifier, the time has come to start on the associated SC.24 control unit. This is in generally better condition than the SPA.50 but still needs a lot of TLC.

The SC.24 uses BC149, BFW58 and BFW88 transistors throughout -- which are of course the dreaded Lockfit devices. Since all the PCBs need refurbishment I'm thinking in terms of progressively replacing them all along with some very tired electrolytics. The BC109 seems a sensible replacement for the BC149 but has anyone any particular suggestions for the others?
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Old 9th Feb 2019, 1:08 am   #2
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Default Re: BFW58/88 substitutes?

My ECA book lists for the BFW58:

BC939, BSX33, 2N2221A, 2N2222A - not listed but maybe BC337

and for the BFW88:

BC327, BC638, BSW24, 2N2906, 2N2907
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Old 9th Feb 2019, 1:22 am   #3
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Default Re: BFW58/88 substitutes?

I agree, the BC337/327 are likely to be valid replacements for the BFWs (as will be the 2N2222/2N2907) and any general purpose low noise transistor like a BC549 will be OK for a BC149. These are all just general purpose transistors, so any other GP type which meets the parameters will be OK.
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Old 9th Feb 2019, 9:10 am   #4
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Default Re: BFW58/88 substitutes?

For the benefit of anyone else daft enough to think about restoring an SC.24 it's worth noting that as often seems to happen with Radford products, the schematics show something different from the actuality. The schematic for the SC.24 shows 2N2483s in several (although not all) positions where there are BC149s and other oddities instead of the Lockfits. A number of capacitor values are either wildly different or not on the PCBs and several are but don't feature on the schematic at all.
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Old 9th Feb 2019, 10:07 am   #5
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Default Re: BFW58/88 substitutes?

A mixture of design changes, production shortages and previous repairs?

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Old 9th Feb 2019, 10:25 am   #6
GW4FRX
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Default Re: BFW58/88 substitutes?

Unlike the SPA.50, this particular SC.24 doesn't seem to have been hacked about and the track sides of most of the boards still look pristine. The only exception is the +60V regulator board where some kind soul has swapped out practically every component using what looks like the trusty kettle-mender and Baker's Flux. A new PCB is called for.

So yes, assorted undocumented design and production changes.
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Old 9th Feb 2019, 11:13 am   #7
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Default Re: BFW58/88 substitutes?

Given the transistor types don't appear to be critical, it's likely that Radford just used whatever suitable types were available and cheap at the time of production. This would explain why the relatively obscure BFW types have been used.
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Old 10th Feb 2019, 2:38 pm   #8
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Default Re: BFW58/88 substitutes?

Radford weren't the only manufacturer to basically use whatever suitable device types were available at the time of production. Radiomobile sometimes did this, especially towards the end of UK Manufacturing, no doubt because, if at all possible, the production line must keep going, not stop until fresh supplies of the listed component are available.
Besides this, printed circuit layouts were often altered between publication of the service manual and a particular production date. I'm currently finding that with a NAD 3020 amplifier I've been asked to repair.
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Old 10th Feb 2019, 5:07 pm   #9
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Default Re: BFW58/88 substitutes?

Quote:
Originally Posted by GW4FRX View Post
The only exception is the +60V regulator board where some kind soul has swapped out practically every component using what looks like the trusty kettle-mender and Baker's Flux. A new PCB is called for.
I was once asked to have a look at an old Sommerkamp (Yaesu) HF rig that had been through the hands of some naughty CBers who'd tried to change it onto their naughty band.

Holding up the crystal/mixer board, I cleared my throat and announced: "It was the Marx Brothers, in the Kitchen, with the Blow Lamp"

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Old 11th Feb 2019, 4:54 pm   #10
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Default Re: BFW58/88 substitutes?

Hmm. Must have been the same people who tried to "fix" the SPA-50 power supply and the regulator board of the SC.24.

Incidentally it seems the notion that Radford (and others) who used whatever was available to keep production going may not be far from the truth. I had an e-mail this morning from someone whose SC.24 makes use of BC107s and BCY70s with nary a Lockfit in sight. Come to think of it, they sound like rather good choices for mine!
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Old 12th Feb 2019, 3:38 am   #11
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Default Re: BFW58/88 substitutes?

Don't forget the BFW88 is PNP.
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Old 12th Feb 2019, 9:47 am   #12
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Default Re: BFW58/88 substitutes?

As is the BCY70, which presumably is why Radford substituted it. On paper that or the BCY71 look like reasonable alternatives to the BFW88.
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Old 12th Feb 2019, 10:40 am   #13
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Default Re: BFW58/88 substitutes?

Arrrgh... need to wear my glasses when reading the fine print in these data books - I was thinking about one ('58) and looking at the other while assuming there was a complimentary pair in there that needs replacing
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Old 12th Feb 2019, 2:32 pm   #14
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Default Re: BFW58/88 substitutes?

If it's any consolation I know the feeling well. Spent a while the other day thinking that some BC177s in the spares box would be good substitutes for BC149s. Then a colleague said "Isn't that a PNP device...?"
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