UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 13th Jul 2019, 10:34 am   #1
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default Tandberg Huldra 8-55 FM in mono only

Found myself a Tandberg Huldra 8 after spending a considerable time searching for one. Judging by the amount of dust build up inside the device it is likely to be in original condition and probably not been serviced since new.

When FM mode selected and mono select p.b. released I get no music but instead get a clicking sound at say 60 ticks a minute. When I select mono using the push button the FM sound comes through OK.

LC radio band works OK. Turntable connected to radio produces good quality sound albeit with one channel down on volume.
Running the unit on 8 ohm speakers even though spec says 4 ohm, but am lead to believe this has no impact on functionality of radio.

Is there a forum member that could help me on my way with this problem, would love to be able to get the unit back working A OK. As I am a grey haired engineer rather than an electronics guru, help this form can offer me will enable me to decide if it is worth travelling the country to have it fixed.
Tandbergfan is offline  
Old 13th Jul 2019, 12:37 pm   #2
orbanp1
Heptode
 
Join Date: Nov 2009
Location: London, Ontario, Canada
Posts: 672
Default Re: Tandberg Huldra 8-55 FM in mono only

Just curious, does your radio have the stereo decoder installed?
It looks like it is a unit that was installed later on.

Hifiengine has the documentation on it:
https://www.hifiengine.com/manual_li...huldra-8.shtml

Regards, Peter
orbanp1 is offline  
Old 13th Jul 2019, 1:51 pm   #3
Mike. Watterson
Heptode
 
Join Date: Dec 2014
Location: Limerick, Ireland.
Posts: 901
Default Re: Tandberg Huldra 8-55 FM in mono only

The 8 Ohms will only limit the power.

Peering inside should reveal if the decoder is fitted.
Mike. Watterson is offline  
Old 14th Jul 2019, 8:27 am   #4
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default

Thanks Peter/Mike, do not believe there is a decoder installed. Bit strange that the unit has a stereo indicator light on the left hand side of the front panel but would not have produced a FM stereo output without such a decoder.

Have attached a picture of the inside
Attached Thumbnails
Click image for larger version

Name:	inside2.jpg
Views:	480
Size:	92.6 KB
ID:	186654  

Last edited by Station X; 14th Jul 2019 at 9:14 am. Reason: Posts merged.
Tandbergfan is offline  
Old 14th Jul 2019, 10:46 am   #5
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Tandberg Huldra 8-55 FM in mono only

Quote:
Originally Posted by Tandbergfan View Post
Thanks Peter/Mike, do not believe there is a decoder installed. Bit strange that the unit has a stereo indicator light on the left hand side of the front panel but would not have produced a FM stereo output without such a decoder.

Have attached a picture of the inside
There's a link to a manual below if you haven't got one:

http://sportsbil.com/tandberg/huldra-8-sm.pdf

You can see from the schematic where the FM stereo decoder would plug in, the bulb's sink for FM stereo indication is on the second connection down on the socket, on the schematic it shows that it isn't connected to anything but when a stereo decoder is fitted a link wire would be connected between that connection and the ground side of R6, the indicator bulbs dropper.

On the decoder a transistor switches that side of R6 to ground when an FM stereo transmission is tuned in correctly.

With the mono switch out, the stereo indicator bulb indicates stereo when either the phono or tape functions are selected or when FM is selected and a stereo transmission is being received with a decoder fitted.

I can't give a direct link to the stereo decoder schematic I have but if you look in the Tandberg section of vintageshifi you will be able to find it there and download it for free then you can see for yourself where the link wire would be connected with the decoder installed.

Hope that helps.

Lawrence.

Last edited by ms660; 14th Jul 2019 at 10:51 am.
ms660 is offline  
Old 14th Jul 2019, 11:15 am   #6
Mike. Watterson
Heptode
 
Join Date: Dec 2014
Location: Limerick, Ireland.
Posts: 901
Default Re: Tandberg Huldra 8-55 FM in mono only

Very normal to have Stereo decoder an option, especially on exported models as it's considerable expense. So only fitted for markets with a complete stereo roll out.
Stereo MPX was maybe 1962 in USA or earlier? I know some Grundig models of that era only had the stereo decoder fitted to models for export to USA.
I'm thinking it might have been 1971 when stereo reached Belfast, though some parts of UK didn't have VHF at all till 1980s.
Certainly stereo was an option on some other German models. One German "Stereo" model has a B7G test socket and a later model with a similar chassis simply had that rewired for the optional decoder. That was a model with motorised tuning and switching Push Pull EL84 mono to single ended for an external stereo source such as a record player or tape recorder. Quite a few late 1950s and early 1960s radio models sold with stereo badges that couldn't take a decoder at all. Stereo was for tape & disc.
Mike. Watterson is offline  
Old 14th Jul 2019, 12:47 pm   #7
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
Default Re: Tandberg Huldra 8-55 FM in mono only

You can add a stereo decoder fairly easily, as long as you don't mind cheating a bit with silicon.

In many 1980s "boom boxes", the FM stereo decoder functionality was provided by a single IC on a small, separate PCB; probably so the same radio tuner section could be used in a mono offering. Even on single-board machines, a separate decoder IC was usually used, as opposed to shoving all the radio functionality into a single dedicated IC. At any rate, the stereo decoder IC can be identified by its connection to the stereo indicator LED. Only a few types were used, and data sheets can be found online.

The "postage stamp" self-contained decoder PCB is the best sort, if you can find one; it just needs some power arranging (from an output valve cathode resistor, or the heater circuit) and the mono input and left and right outputs connecting up (possibly also the disconnection of one resistor and capacitor), and an LED positioning so as to shine out of the right aperture on the front. But the ICs are fairly easy to unsolder and don't need many support components, so if you have to steal one from an all-in-one PCB, it is not too big a deal.
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments.
julie_m is offline  
Old 19th Jul 2019, 9:09 am   #8
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default Re: Tandberg Huldra 8-55 FM in mono only

Thanks very much to all people that have responded to my query. Very interesting to be taken back to the times when FM and stereo transmissions were a novelty. Also neat to understand reason why the likes of Tandberg only installed decoders in units that went to markets where FM stereo transmissions were taking place. Have decided to keep the unit original rather than trying to fit a non Tandberg decoder.
Thanks Lawrence for explaining the function of the Stereo indicating light, even with a new bulb it does not light up when selecting phono or tape. Seems like a simple circuit. Lampholder is Ok, wires seem to be connected, maybe the resistor in the circuit has failed. Will leave it to persons more qualified to check this issue out. All the Best, Jacques van Selm, New Zealand
Tandbergfan is offline  
Old 19th Jul 2019, 11:47 am   #9
SteveCG
Nonode
 
Join Date: Jun 2009
Location: Herefordshire, UK.
Posts: 2,495
Default Re: Tandberg Huldra 8-55 FM in mono only

A thought:

I understand that New Zealand only had mono FM for a long time. Perhaps that explains the absence of a Stereo Decoder in a model presumably intended for the NZ market?
SteveCG is offline  
Old 16th Dec 2019, 5:35 am   #10
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default Re: Tandberg Huldra 8-55 FM in mono only

When I received my Huldra 8 I brought up the issue of stereo FM not working. Forum members pointed out that that was possibly due to the absence of a decoder in my unit (which was indeed the case) As part of the thread forum member Lawrence Mms660 pointed out that the stereo indication light is activated through either the decoder or through the phono and tape switches.

In my case the stereo light did not work at all. First replaced the bulb, no change, I then decided to take some time to translate the Tandberg service manual from Norwegian and found that the bulbs for the panel lights are different from the stereo indicator light. Managed to source the proper bulb in the Europe so now the stereo indicator light is working.

In my earlier approach to the forum I mentioned that that when listening to FM or AM with the selector switch in stereo (up) I hear a regular pop/crackle at a frequency of around 200 pops a minute. The pop disappears when I select mono.

With my new bulb in place playing FM or AM (stereo/mono button in stereo) the light flashes at the same frequency as the pop crackle. The light comes up solid when I select mono (while listening to radio) The light comes up solid when I select tape or Phono and both these inputs produce good quality sound (albeit that one channel is down on volume and possibly sounds a bit muffled)

Looking at the wiring diagram I note that with tape and mono switches off and stereo/mono switch to stereo there appears to be no path to earth for the bulb circuit, still the bulb lights up 200 times a minute in sequence with the crackle/pop. Cannot imagine there is an issue with C11 in the 33V power supply as the tape/phono sound is OK. Lawrence mentioned that there should be a third wire on the lamp socket, cannot find this wire in my set. Any advice that could help me solve this mystery would be very much appreciated.

Jacques, New Zealand
Tandbergfan is offline  
Old 16th Dec 2019, 11:45 am   #11
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Tandberg Huldra 8-55 FM in mono only

Quote:
Originally Posted by Tandbergfan View Post
Looking at the wiring diagram I note that with tape and mono switches off and stereo/mono switch to stereo there appears to be no path to earth for the bulb circuit, still the bulb lights up 200 times a minute in sequence with the crackle/pop. Cannot imagine there is an issue with C11 in the 33V power supply as the tape/phono sound is OK. Lawrence mentioned that there should be a third wire on the lamp socket, cannot find this wire in my set.
I did not say there was a third wire on the lamp socket, what I explained in that post was that if a stereo decoder was fitted there should be an additional wire that would be connected between the 2nd pin down (in the schematic) of the stereo decoder plug/socket and the ground end (contacts "b" of the Tape and Phono switches) of the stereo indicator bulbs series resistor (R6)

The 2nd pin down is marked on the PCB layout with an X in the manual I posted a link to.

In mono there should be no circuit path for the stereo indicator bulb, if there is there's probably a short to ground somewhere on the ground side of the bulb.

Lawrence.
ms660 is offline  
Old 16th Dec 2019, 7:49 pm   #12
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default Re: Tandberg Huldra 8-55 FM in mono only

Sorry Lawrence, should have read your first post with more care. Your post was very helpful in improving my understanding of the circuit. I had a closer look at the various switches involved and they are all quite dirty.Bit weary about taking the PB assembly out (for cleaning) for fear of ending up with springs and levers flying in all directions. Do you feel that the fact that light is pulsing suggests that the earth fault involves a capacitor?
Tandbergfan is offline  
Old 16th Dec 2019, 11:15 pm   #13
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
Default Re: Tandberg Huldra 8-55 FM in mono only

You will need to trace out the wiring and correlate the diagram with real life, to see where the current might be going. How easily could you disconnect pins C of the tape and phono switches from chassis?
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments.
julie_m is offline  
Old 17th Dec 2019, 12:58 am   #14
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default Re: Tandberg Huldra 8-55 FM in mono only

Have done some further investigation, with the stereo indicator light removed there is no pop crackle and radio works fine.
I note there is a capacitor and some wiring associated with the three switches(stereo/mono, tape and Phono) that do not appear in the diagram I have.
A 2muF capacitor is connected between connector B on tape switch and e on mono/stereo switch. A black wire runs from f on the mon/stereo switch to the MF board 2.
An additional blue wire runs from connector B on the tape switch to a point on MF board no.2 Blue and black wire are twisted together.
Will be doing an internet search to see if I can find out more about the stereo decoder and how it should be wired in. Have a suspicion that these wires are associated with such a decoder.
Tandbergfan is offline  
Old 17th Dec 2019, 1:52 am   #15
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default Re: Tandberg Huldra 8-55 FM in mono only

Looks like the unit is fitted with a stereo decoder after all. Way back I was looking for the PCB as shown on the decoder manual front page rather than an aluminium box. Could it be that the capacitor C12 mentioned in my previous posting and shown in the decoder manual causes the popping symptoms and the flashing stereo light. Can anyone tell me if the aluminium cover comes off together with the decoder PCB (i.e is the PCB somehow plugged in to a connector)
Tandbergfan is offline  
Old 17th Dec 2019, 5:40 pm   #16
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Tandberg Huldra 8-55 FM in mono only

Quote:
Originally Posted by Tandbergfan View Post
Looks like the unit is fitted with a stereo decoder after all. Way back I was looking for the PCB as shown on the decoder manual front page rather than an aluminium box. Could it be that the capacitor C12 mentioned in my previous posting and shown in the decoder manual causes the popping symptoms and the flashing stereo light. Can anyone tell me if the aluminium cover comes off together with the decoder PCB (i.e is the PCB somehow plugged in to a connector)
The "popping" at 200Hz (approx.) on FM and AM could be due to instability in the decoder (including the external circuit of the indicator bulb, series resistor, C12 etc) Might be worth replacing C12 and the B+ de-coupler on the decoder board (C830, 8uF)

On the other hand it could be due to instability somewhere else that's finding it's way into the decoder.....hard to say for sure.

Reading the decoder instructions seems to suggest that the decoder is a plug in job.

Lawrence.
ms660 is offline  
Old 18th Dec 2019, 12:46 am   #17
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default Re: Tandberg Huldra 8-55 FM in mono only

For completeness: tested C12 and came up as 1 muF verfied test using a new cap of same value. so problem unlikely to have been caused by that component.
Tandbergfan is offline  
Old 18th Dec 2019, 5:06 am   #18
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: Tandberg Huldra 8-55 FM in mono only

Quote:
Originally Posted by SteveCG View Post
A thought:

I understand that New Zealand only had mono FM for a long time. Perhaps that explains the absence of a Stereo Decoder in a model presumably intended for the NZ market?
In fact NZ had stereo FM from the beginning of FM broadcasting here, which started (quite late by world standards) in the early/mid 1980s.

A 1960s Tandberg receiver might well have been a private import.


Cheers,
Synchrodyne is offline  
Old 18th Dec 2019, 5:43 am   #19
Tandbergfan
Diode
 
Join Date: Jul 2019
Location: Tauranga, New Zealand
Posts: 9
Default Re: Tandberg Huldra 8-55 FM in mono only

Hi John, yes brought the unit in from the Netherlands last year.
Tandbergfan is offline  
Old 20th Dec 2019, 10:56 pm   #20
Chris55000
Nonode
 
Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 2,853
Default Re: Tandberg Huldra 8-55 FM in mono only

Hi!

Certainly it's a very novel design of the likes I've never seen before, a valve RF amp and mixer/osc. and a transistor IF preamp in the FM front end, a valved IF strip with a magic eye and then all transistors in the audio!

I've not come across an EAF801 diode/pentode anywhere before, but don't give yourself a headache trying to locate a spare, the much more commonly found EBF89 is pin compatible, the second diode on pin7 of the EBF89 is simply left unused!

Chris Williams
__________________
It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

Last edited by Chris55000; 20th Dec 2019 at 11:01 pm.
Chris55000 is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 11:34 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.