Hacker Herald RP35 - UK Vintage Radio Repair and Restoration Discussion Forum

GrahamN · 17th Oct 2008, 5:25 pm

Apologies if this is a bit basic...

I am currently working on renovating a Herald RP35 which only picks up one station very quietly on MW and nothing on LW. I have downloaded the service sheet from up there, and see that the IF section has 4 x AF117 transistors. It seems that someone has already replaced these, but with 2 x BF194 and 2 x BF195.

Should I expect this to work? Or should I replace the replacements before looking elsewhere? I have a few AF125 and some BF450 transistors here - if I need to replace, are either of these any good? Or can someone recommend a better alternative?

If the replacement transistors are OK (I assume they were replaced by someone who knew what they were doing as it's a very neat job), can anyone recommend any checks to try and isolate the problem?

I've looked around the aerial coils, etc. and there doesn't seem anything obviously amiss.

Thankk you

Darren-UK · 17th Oct 2008, 5:41 pm

I think the BF194/5 is used in later equipment and, without actually comparing specs to verify, it doesn't surprise me they don't function too well in an AF-version RP35.

When replacing Germanium AF117's with Silicon, as far as I'm aware the only really suitable replacement is the BF450.

However, although I've never done this change to a Hacker I understand the BF450 doesn't perform too well in these (unlike in Roberts sets where the BF450 performs very well).

Probably best using AF125's (the 127 maybe better if you can get hold of some but try 125's as you have some to hand). I'm sure our resident Hacker expert will be able to comment further.

I'd also check to see if the BF conversion has also entailed some changes to resistors and biasing, also see if the IFT's have been twiddled.

Paul_RK · 17th Oct 2008, 9:57 pm

Are you sure the transistors are replacements? From serial number 19001 onwards (July 1968) the RP35 was fitted with a different IF board using BF194/BF195 - I'd guess you have a later set and are looking at an early version of the manual.

Paul

mark pirate · 17th Oct 2008, 9:58 pm

Hi, i have a rp35 for spares & this set is fitted with bf194/5 transistors, are you sure your set originaly used af series transistors?
If you want it i have a chassis free to good home

Mark

GrahamN · 17th Oct 2008, 10:43 pm

Quote:

Are you sure the transistors are replacements?

No. I'm still getting used to transistor sets, and just went by the service data I downloaded from up top. There is no serial number plate or label I can see on the set, but the transistors could well be original - in which case back to the drwaing board.

Quote:

If you want it i have a chassis free to good home

Mark - I may well take you up on this if I may. I would prefer to get the board working if possible, rather than replacing it, as that way I may learn something! If I can't fix it over the next few days , though, I will get back to you if that's OK?

Thanks

Paul_RK · 17th Oct 2008, 10:56 pm

If you open the back of the set and look upwards inside, the serial number should be stamped faiirly centrally on the aluminium plate behind the tuning dial. Alternatively, the later all silicon board will be marked "TYPE 503" in the top right corner, i.e. behind the set's volume control. Electrolytics are likely culprits for low gain, not least the big fellow - perhaps a red TCC - again at the top right of the board as it's fitted in the set.

Paul

GrahamN · 18th Oct 2008, 8:08 am

Found the serial number - 25493

So a later set then.

The large electrolytic fitted is a blue 400uF 10V and the nearest value I have is a much smaller (physically) 470uF 10V - presumably that will be OK to fit? I did check with a DMM across the cap while in circuit, and saw a gradually increasing resistance which is similar to that which I get across the replacement and which I assume is due to the capacitor charging, though I don't know if that really proves anything!

I'm unlikely to be able to do anything more on this now until sunday, so any suggestions of tests etc. are welcome.

Thanks again

Darren-UK · 18th Oct 2008, 8:27 am

For quickness you could disconnect one end of the existing 400uF cap and just hold the 470 across the junctions to see if that cures the problem. The smaller physical size should be ok; modern caps usually are smaller.

Presumably the aerial coils mentioned in post #1 are in their correct positions on the ferrite rod? Presumably, too, you've also checked the wavechangers are clean and contacting properly?

GrahamN · 18th Oct 2008, 8:53 am

Coils look OK. The coils and wires are held by plastic tape which looks original and doesn't allow more than a millimeter or two of movement. The switches look OK too, though I haven't removed them to test out of circuit.

I've just changed the cap, with no difference. I'm out of time now today, so will check back this evening to see if anyone has any other ideas.

Thanks again

Graham

petervk2mlg · 18th Oct 2008, 9:09 am

With low gain I'd be thinking of leaky capacitors, resistors gone high and then alignment.
See if you can take some voltage readings on the transistors and compare with figures given on the schematic diagram.

Someone might also have fiddled with the IF transformers so it would be worthwhile seeing if you can peak them up if voltage readings are as per circuit.
Aerial and oscillator trimmers might also need attention.
A signal injected into the volume control that only results in very weak audio can pinpoint a faulty audio output stage.
An RF signal injected into various points in the RF section of the set also can pinpoint a weak RF/IF stage.
I'm not familiar with this particular set so my points are just generic ones.
Peter

Paul_RK · 18th Oct 2008, 11:30 am

You don't of course have the schematic for the set, and probably I shouldn't furnish it as everything you need is available via the usual button: except it's the RP25A Sovereign manufacturer's data you'd need to buy, not the RP35 Herald. That's the original (germanium) RP25 manual with addenda covering the silicon RP25 and the RP25A: with each change the Herald remained essentially the current Sovereign less its FM components. What Paul (Stenning) is offering for the RP35 is the Newnes R+TVS entry for the model as first issued, so half the purchasers wouldn't be getting what they need for their radio: the service is a fine one, but possibly this could be clarified?

Hacker's RP25A manual is more comprehensive than the R+TVS info - running to 34 pages in the version I have, though of course you don't have the FM bits in your Herald - and well worthwhile if simple capacitor checks etc. don't deal with your problem or if you've any thoughts of meeting more of the sets it covers - everything for RP25, 25A, 35, 37 and 37A is there.

Paul

GrahamN · 18th Oct 2008, 4:30 pm

Thanks Paul

I've now purchased and downloaded the RP25A info, so I'll look again at this hopefully tomorrow. Maybe I'll get a bit further on with the correct circuit details

GrahamN · 14th Nov 2008, 5:26 pm

Thanks for all the help - I ordered some BF194/195 transistors, ad I just got back to this today. After injecting a signal into the base of the transistors as suggested by the manual, I was able to isolate the problem pretty quickly. One of the BF195 transistors had failed, and after replacing it, the radio is now working well.

All I need to do now is clean it up a bit and re-aasemble.

17th Oct 2008, 5:41 pm	#2
Darren-UK Retired Dormant Member Join Date: Apr 2003 Location: Blackpool, Lancashire, UK. Posts: 4,061	Re: Hacker Herald RP35 I think the BF194/5 is used in later equipment and, without actually comparing specs to verify, it doesn't surprise me they don't function too well in an AF-version RP35. When replacing Germanium AF117's with Silicon, as far as I'm aware the only really suitable replacement is the BF450. However, although I've never done this change to a Hacker I understand the BF450 doesn't perform too well in these (unlike in Roberts sets where the BF450 performs very well). Probably best using AF125's (the 127 maybe better if you can get hold of some but try 125's as you have some to hand). I'm sure our resident Hacker expert will be able to comment further. I'd also check to see if the BF conversion has also entailed some changes to resistors and biasing, also see if the IFT's have been twiddled.

17th Oct 2008, 9:57 pm	#3
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Hacker Herald RP35 Are you sure the transistors are replacements? From serial number 19001 onwards (July 1968) the RP35 was fitted with a different IF board using BF194/BF195 - I'd guess you have a later set and are looking at an early version of the manual. Paul

17th Oct 2008, 9:58 pm	#4
mark pirate Dekatron Join Date: Mar 2008 Location: Worthing, West Sussex, UK Posts: 5,185	Re: Hacker Herald RP35 Hi, i have a rp35 for spares & this set is fitted with bf194/5 transistors, are you sure your set originaly used af series transistors? If you want it i have a chassis free to good home Mark

17th Oct 2008, 10:56 pm	#6
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Hacker Herald RP35 If you open the back of the set and look upwards inside, the serial number should be stamped faiirly centrally on the aluminium plate behind the tuning dial. Alternatively, the later all silicon board will be marked "TYPE 503" in the top right corner, i.e. behind the set's volume control. Electrolytics are likely culprits for low gain, not least the big fellow - perhaps a red TCC - again at the top right of the board as it's fitted in the set. Paul

18th Oct 2008, 8:08 am	#7
GrahamN Hexode Join Date: Jun 2008 Location: Burnham on Crouch, Essex, UK. Posts: 391	Re: Hacker Herald RP35 Found the serial number - 25493 So a later set then. The large electrolytic fitted is a blue 400uF 10V and the nearest value I have is a much smaller (physically) 470uF 10V - presumably that will be OK to fit? I did check with a DMM across the cap while in circuit, and saw a gradually increasing resistance which is similar to that which I get across the replacement and which I assume is due to the capacitor charging, though I don't know if that really proves anything! I'm unlikely to be able to do anything more on this now until sunday, so any suggestions of tests etc. are welcome. Thanks again

17th Oct 2008, 5:25 pm	#1
GrahamN Hexode Join Date: Jun 2008 Location: Burnham on Crouch, Essex, UK. Posts: 391	Hacker Herald RP35 Apologies if this is a bit basic... I am currently working on renovating a Herald RP35 which only picks up one station very quietly on MW and nothing on LW. I have downloaded the service sheet from up there, and see that the IF section has 4 x AF117 transistors. It seems that someone has already replaced these, but with 2 x BF194 and 2 x BF195. Should I expect this to work? Or should I replace the replacements before looking elsewhere? I have a few AF125 and some BF450 transistors here - if I need to replace, are either of these any good? Or can someone recommend a better alternative? If the replacement transistors are OK (I assume they were replaced by someone who knew what they were doing as it's a very neat job), can anyone recommend any checks to try and isolate the problem? I've looked around the aerial coils, etc. and there doesn't seem anything obviously amiss. Thankk you

18th Oct 2008, 8:27 am	#8
Darren-UK Retired Dormant Member Join Date: Apr 2003 Location: Blackpool, Lancashire, UK. Posts: 4,061	Re: Hacker Herald RP35 For quickness you could disconnect one end of the existing 400uF cap and just hold the 470 across the junctions to see if that cures the problem. The smaller physical size should be ok; modern caps usually are smaller. Presumably the aerial coils mentioned in post #1 are in their correct positions on the ferrite rod? Presumably, too, you've also checked the wavechangers are clean and contacting properly?

18th Oct 2008, 8:53 am	#9
GrahamN Hexode Join Date: Jun 2008 Location: Burnham on Crouch, Essex, UK. Posts: 391	Re: Hacker Herald RP35 Coils look OK. The coils and wires are held by plastic tape which looks original and doesn't allow more than a millimeter or two of movement. The switches look OK too, though I haven't removed them to test out of circuit. I've just changed the cap, with no difference. I'm out of time now today, so will check back this evening to see if anyone has any other ideas. Thanks again Graham

18th Oct 2008, 9:09 am	#10
petervk2mlg Heptode Join Date: Jan 2007 Location: Parkes, NSW Australia Posts: 877	Re: Hacker Herald RP35 With low gain I'd be thinking of leaky capacitors, resistors gone high and then alignment. See if you can take some voltage readings on the transistors and compare with figures given on the schematic diagram. Someone might also have fiddled with the IF transformers so it would be worthwhile seeing if you can peak them up if voltage readings are as per circuit. Aerial and oscillator trimmers might also need attention. A signal injected into the volume control that only results in very weak audio can pinpoint a faulty audio output stage. An RF signal injected into various points in the RF section of the set also can pinpoint a weak RF/IF stage. I'm not familiar with this particular set so my points are just generic ones. Peter

18th Oct 2008, 11:30 am	#11
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Hacker Herald RP35 You don't of course have the schematic for the set, and probably I shouldn't furnish it as everything you need is available via the usual button: except it's the RP25A Sovereign manufacturer's data you'd need to buy, not the RP35 Herald. That's the original (germanium) RP25 manual with addenda covering the silicon RP25 and the RP25A: with each change the Herald remained essentially the current Sovereign less its FM components. What Paul (Stenning) is offering for the RP35 is the Newnes R+TVS entry for the model as first issued, so half the purchasers wouldn't be getting what they need for their radio: the service is a fine one, but possibly this could be clarified? Hacker's RP25A manual is more comprehensive than the R+TVS info - running to 34 pages in the version I have, though of course you don't have the FM bits in your Herald - and well worthwhile if simple capacitor checks etc. don't deal with your problem or if you've any thoughts of meeting more of the sets it covers - everything for RP25, 25A, 35, 37 and 37A is there. Paul

18th Oct 2008, 4:30 pm	#12
GrahamN Hexode Join Date: Jun 2008 Location: Burnham on Crouch, Essex, UK. Posts: 391	Re: Hacker Herald RP35 Thanks Paul I've now purchased and downloaded the RP25A info, so I'll look again at this hopefully tomorrow. Maybe I'll get a bit further on with the correct circuit details

14th Nov 2008, 5:26 pm	#13
GrahamN Hexode Join Date: Jun 2008 Location: Burnham on Crouch, Essex, UK. Posts: 391	Re: Hacker Herald RP35 Thanks for all the help - I ordered some BF194/195 transistors, ad I just got back to this today. After injecting a signal into the base of the transistors as suggested by the manual, I was able to isolate the problem pretty quickly. One of the BF195 transistors had failed, and after replacing it, the radio is now working well. All I need to do now is clean it up a bit and re-aasemble.