Tandberg Solvsuper 3 (1941)

[Murphyv310]

Hi.
Spurred on by Nowhere Man’s DDR radio I have decided to bring out the 1941 Tandberg Solvsuper 3 and carry on with the restoration that I shelved a couple of years ago.
The Solvsuper was unusual as it was a wartime product not of the basic designs that both Germany and Britain made. Norway of course wasn’t aligned to either side as such.

The set itself uses side contact valves which includes the rather odd EFM1, a dual valve incorporating a triode tuning indicator and a vari mu AF pentode, there is good reason for this layout as it reduces the valve count. The circuitry is odd, the control grid is DC coupled from the AGC diode and AC coupled from the volume control, the varying DC level plus the use of the vari mu characteristics mean the G2 volts (fed from a high value resistor from HT) will change with the AGC potential thus giving the tuning indicator varying drive.
Sadly the valve wasn’t a success and was withdrawn quickly.
Mine is duff so am EM34 and separate AF amp will be substituted.
The RF tracking on MW & LW is way off and I think its all down to dampness in the coils.
I’ll post up some pictures in due course.

[Murphyv310]

           
Hi.
As promised some pictures. One of the upper chassis, one underneath with some work already done, I'll be restuffing the original caps in this instance and tidying up the work once the set performs like it should, the last picture of the odd tuning indicator valve.
Next is to fix the tuning although it may be OK now as it's had two years to dry out. Then work out the best way to replace the suspect valve with say an EM34 and perhaps an EF85 Vari mu for the audio.

[Murphyv310]

Hi.
This set has sent me on a merry dance. It's rest of two years seems have greatly improved the tracking, the tuning is now nearly spot on but the other AGC problem has left me scratching my head
Initially I had bad distortion on strong stations and only about -2v AGC. Since I have had another go I have replaced the EBF2 double diode vari mu pentode with an EF9 and strapped in two germanium diodes and have -3.5v AGC now, I'm sure it's too low though. The IF's are 465Khz on this set and I did a full realignment to no avail. I have been around the circuit with a fine toothcomb with no success, the set is sensitive and pulls in weak stations with ease, audio quality is spot on on the weaker stations.
One thing does come to mind and that is the odd EFM1 combined tuning indicator and AF amp, the tuning indicator is duff with nothing seen, voltages seem fine but I am now thinking of using an EF92 as the AF amp (it needs to be Vari MU due to the circuit design) and seeing if doing that may help, I'm not hopeful though.
I have a copy of the circuit from the Radio Museum but I don't think I should post it here due to copyright.
Perhaps if someone has the sheet then I'd like to post it here.

Any ideas fellas?

[Murphyv310]

Hi.
I have downloaded the circuit and have put it on Photobucket so it isn't on the forum's gallery. I'm sure it should be OK to link it here but Mods please remove if not allowed.

[radioman]

Hi Trevor,
Have you changed the AGC de-coupler (C24) ?

Andy

[Murphyv310]

Hi Andy.
Yes indeed I have. I've been right through the AGC circuit, even the DC content on the right hand diode is low (AF detector) at 3-4v negative on the local here (The audio is loud and good quality except the very strong stations where it distorts). I'm going to have a look at it on the scope tomorrow. It's a really odd one and no doubt it'll be an obvious fault when I find it.

[Crackle]

Hi Trevor
I am sure you know this, but I have found that some local AM radio stations can distort heavily. At one time I could receive Gold from their Southend (I think) transmitter and from London. On some valve radios one TX was distorted and the other was not, both seemed about the same strength. I believe it is to do with the amount of "modulation"
It would be nice to know why some circuits cant cope with the high modulation, and how it can be fixed.

Mike

[Murphyv310]

Hi Mike.
Many thanks for your input. The distortion though is just as bad on BBC Radio Scotland on 810Khz, the modulation on this station has never been an issue on anything else. TBH the negative AGC volts rarely gets to 4v which is way too low. I'm hoping to crack on with the set tomorrow as It is getting professional cabinet restoration, it's a set I like and it's sufficiently rare in the UK to be interesting.
I'll revert to the EBF2 which I'm sure is fine and go back to using the valves diodes. I'll also do something with the EFM3 and most likely go for a hidden EF92 and a standard magic eye. The problem could still be something to do with the EFM3, perhaps showing some grid current dragging down the AGC........... We will wait and see.

[Geordie McBoyne]

Hi Trevor,
              The EFM1 soon became obsolete and there was a time when Mullard simply suggested that the valve should be replaced by an EF39. just leave the tuning eye out of the circuit. This is not satisfactory and later on Mullard came up with this modification by using the vari-mu EF39 and the EM34, the latter is now becoming scarce and expensive. The EM4 is electrically identical and has the side contact base the same as the EFM1, this might be a good thing for the Tandberg because it maintains almost near originality.   Other Philips-Mullard tuning eyes are the EM1/TV6 and EM3, the former requires only -5volts and the latter -21volts for 90 degrees defection. Other tuning eyes to consider would be the American 6G5 and 6U5 but these are not very sensitive tuning eyes, requiring -21 volts for full deflection.
The Solvsuper must be the only non Philips set to use the EFM1
The attachment shows the information found in the 1958 Mullard Maintenance Manual about replacing the EFM1 with the EF39 and EM34.  The EM4 was not suggested as a replacement because it was considered obsolescent 1958.
Interestingly, at least one vari-mu audio amplifier valve was made, the EF83.
From the Radiomuseum: http://www.radiomuseum.org/tubes/tube_ef83.html
EMI-Capitol used the EF89 in certain record players, by varying the cathode bias in a differential manner to adjust the stereo balance, not nice really.  
I do have some funny valves upstairs so it might be worth a search for an EFM1, I know there is an ELL1 up there, even Mullard doesn't list it in any publication.

Geordie McBoyne.

[Murphyv310]

Hi.
Well I think the EFM1, is the problem, will the valve out the audio at the grid is spot on on the G1 connection, with it in its badly clipped, just on strong signals. With the G1 disconnected there is 10v on it. I have a new EM4 so that and an EF92 will be fitted.