Hacker Super Sovereign RP75 woes

[darren brown]

I am a newbie and therefore on a steep learning curve.

I recently picked up a Hacker Super Sovereign RP75 fairly cheap and I am a happy man but a little confused. The set works fine on long, medium and FM bands with impressive performance, but is somewhat lacking when i am tuning round the two short wave bands. The set seems to respond when I attach a long wire antenna to the external socket.

Is this common? Any ideas gratefully received.

[SeanStevens]

I would set it on a SW station (without any additional aerial), then touch the tellescopic aerial with your hand, then a metal object.

If the sound changes and/or you can hear the metal touching the aerial, the radio is using the tellescopic aerial. If not, it may not be connected to the tuner.

If no change is detected, the radio is probably not using the tellescopic aerial at all. It will work fine on LW because it uses the ferrite (internal aerial)


SEAN

[SeanStevens]

So Sorry, forgot to say WELCOME to the forum.





Is the FM working REALLY well? Is it possible it is only picking up stong signals?


SEAN

[darren brown]

Sound advice Sean. Looks like there are some dry joints and I will check for continuity.

I noticed another little problem though on PCB B/211/2 there are three transistors attached to a heat sink with coloured sleeves on the leads which are white, green and orange. These must have overheated in the past and probably why the set was so cheap.

Although the set still works I would feel better if the three metal transistors were replaced.
Any ideas of their types or dare I say modern replacements that would work in place of the burnt originals?

[Ian E G7OLT]

The telescopic aerial is used on FM and SW. If you insert a plug into the external FM aerial socket, it disconnects the telescopic aerial. The external AM aerial socket was intended for use in a car. A long-wire aerial connected to either socket improves SW reception. The SW2 band will be livelier than SW1, you'll hear more stations after dusk.

I assume when you're referring to the white, green and orange sleeving on the output transistors, that this is where you're seeing evidence of over-heating, presumably because the sleeving has melted? If so, where? At the end where the leads are attached to the PCB or along the entire length? If at the attached end only, this may be where someone has left a soldering iron on the joint for too long.

Before you condemn the OP transistors, check the mid point voltage on the output pair - measured at the junction of R13/14 it should be 5.85 Volts. (Set supplied with 12 Volts). RP1 adjusts.

Check also the quiescent current. Remove the test link and insert an ammeter, reading should be 3 mA with no audio on the amplifier input. RP2 adjusts. Amplifier total quiescent current should be around 13/14 mA.

The output pair TR5/6 are an AC187 and an AC188 respectively. TR3, the other transistor on the heat sink is a type "T2" - and I have no idea exactly what that is or if there's any equivalent. Anyone know? It doesn't appear in any of my Mullard/Philips data books, although I can tell you it measures as PNP. There's a picture below.

Good luck.

Regards,

--
Ian

[Ian E G7OLT]

Sorry, picture went AWOL for some reason.

[Herald1360]

Originally Posted by darren brown

Although the set still works I would feel better if the three metal transistors were replaced.
Any ideas of their types or dare I say modern replacements that would work in place of the burnt originals?

The Audio amp is similar to that in the RP37A VHF Herald; this thread might be interesting.....

https://www.vintage-radio.net/forum/...r+Herald+RP37A

In any case, the same devices could be used, with suitable biassing changes as required.

You may also find that the Hackerradiogroup on Yahoo is worth a close look, esp the files section

[darren brown]

Thanks Ian and Herald1360, some very good advice.

I dare not disturb these three transistors on the heatsink. I'm going to upload a pic so you can all see. Frankly I'm surprised the set works at all.

Cheers.

[mhennessy]

Ouch!

Could the transistors have got hot enough to have done that? Perhaps at the ends, but other the whole length of the leads? Could it be something else - external heat source or chemical attack. Never seen anything quite like that...

Mark

[Ian E G7OLT]

Darren,

I've never seen anything quite like it either! There must have been a lot of smoke.

You say this is an RP75 which has a DC power jack on the back, unlike the RP75MB which doesn't. There are no fuses. My guess would be that someone has connected it to a car battery and got +ve and -ve the wrong way round. Frankly I'm amazed that the output transistors survived at all and looking at the damage your picture shows, I would be inclined to replace all three.

Running from left to right in your picture, the transistors are TR5: AC187, TR3: T2 and TR6: AC188. The leads are sleeved white for collector, orange for emitter and green for base.

This leaves the problem of identifying TR3 a type T2. From looking at other Hacker amplifiers in other examples of their radios, I guess that T2 is something like an AC128 that's been selected for certain thermal characteristics. There's a partial circuit attached, perhaps someone else would like to comment?

Having just done a quick search, all three types are available for about £1 each plus postage. When they have been replaced, you need to run through the alignment procedure posted above.

Good luck.

[saxmaniac]

I have one of these, the heat damage looks like a bit of clumsy soldering iron damage, if the output stage works ok then there is nothing wrong. If you need, I may have NOS of these transistors if you give me type nos

[saxmaniac]

Ian, do you happen to have all the circuit as a file by anh chance? I cannot find one anywhere. Just as a note, the SW gain seems to be poor on mine & I dont think there is anyting wrong with it, it needs a decent aerial, at the end of the day it aint really a SW reciever

[Herald1360]

Originally Posted by Herald1360

You may also find that the Hackerradiogroup on Yahoo is worth a close look, esp the files section

Since I can't see a RP75 datasheet up top, it's worth being more explicit- join the hackerradiogroup and scroll down through the files section. There's a RP75 pdf Hacker manual buried in there.....

[amp_mangler]

T2 is "most" likely to be an AC126, which I have
AC187 and AC188 I have
this looks like a standard Mullard 3watt amp I have alla the bits
it was ONE of the first sand projects I made, around 1965
if ya want a set of transistors PM me your address, BUT !!!! ya owe me a pint of Guinness !!
Ive only had the local made stuff
best regards
Joe

[darren brown]

cheers to all for sound advice which is allways welcome.
ian your thoughts on pumping too many milliamps through its dc socket was one of my theories looking inside a sovereignIII today i noted that the same output board is used and the mains transformer is rated 200milliamps max
when you think of a car battery 35 amphours
bang! sort of springs to mind well certainly lots of smoke.

cheers darren

[mhennessy]

If incorrect polarity was applied, I wonder if there's any further damage? The LT regulator, T2 on the switchboard, might be vulnerable - it would be worth checking that the voltage on its emitter is 6V. Perhaps the easiest way without dismantling is by checking the voltage on the red wire on the FM tuner.

I'm sure it'll be fine (there is 100 ohms in series withT2), but you never know...

I like to fit a protection diode to sets with DC input sockets. But that wouldn't do much when confronted with a car battery

[Herald1360]

If the protestion diode is in series with the set it will protect it just fine. For an inverse parallel diode to be any use, it would have to be paired with a suitable fuse with a lower IsquaredT rating than the diode.

[mhennessy]

A 1n400x will easily "win" against a cheep wall-wart, or even a less cheep one with foldback current limiting. Obviously I instruct people to remove power the instant they realise it's not working, but these things come with thermal fuses should the worst happen. At 12V the drop of a series diode is rather undesirable, but the very real possibility of finding itself connected to a car battery is something I'd leave up to the individual to consider. Of course, there are tricks involving relays, MOSFETs and other such things - countless articles and "circuit ideas" have been published over the years - but a simple diode that can be hidden behind the volume pot gives me enough peace of mind while retaining originality to a large enough extent.

BTW, every 12V "cigarette lighter" lead that I've seen comes with a fuse in the plug. I'm sure there are exceptions

[saxmaniac]

Do you need a manual? I can send you a PDF but I think it would have to go to your direct email if the file is too big for the site?

[darren brown]

hi to all
after looking at the hacker radio groug's site i did find the service manual pdf
makes very interesting reading.
at the local council reclaimation site i was suprised to find part of an old phillips reel to reel tape recorder with ac187/188 and a t3 these three have different colour sleeves namely red yellow and blue will this matter?
not had time to de solder them so i can check to see if they are any good yet, i'll let you know.

been having problems with a dodgy bass control so it looks like that will have to be replaced dont like the look of the one i ordered from maplins horrid plastic shaft.

cheers for advice

darren