Dynatron T10a Ether Pathfinder

[DTEC1966]

Hello all. My first post as a new member!
I have just acquired a Dynatron T10A tuner as a separate.

I was hoping to link it up to the input of a Dynatron Mazurka via the rear input.
I have used this input for CD and it works fine.
My problem is this. The T10a is rated at 240VAC and has 4 cables associated with the power.

Red, Black, Blue, Green which are linked to a 5pin output socket.
There is also the signal output lead which has an coax termination.

So I'm thinking

RED-LIVE
BLACK-NEUTRAL
BLUE-NEUTRAL
GREEN-EARTH

I have removed the 5 pin socket to expose the individual cables.


Using a Variac output I connected the RED and BLACK, and the GREEN back to the Variac Earth.

Slowly cranked up the Variac checking the chassis didn't become live.

Nothing. No bulbs, No heating valves, No hiss.

Did the same with the secondary Blue and Black together. Nothing.

I am aware that the blue line may be the lower voltage for the bulbs but again nothing.

Any thoughts!!!

[Graham G3ZVT]

I see no mains transformer, so my best guess is it needs approx. 200v DC HT and 6.3v AC on some combination of those pins.

A variac is unsuitable to provide either, and will likely cause damage.

https://www.radiomuseum.org/r/dynatr...inder_t10.html shows the valve line-up as EF89 ECH81 EF89 EF89 EM80 D77 D77 ECC85 which rules out a live chassis AC/DC arrangement, not that I would have expected that.


https://picclick.co.uk/Vintage-DYNAT...210672410.html




It shouldn't be difficult to reverse engineer the connections, but I'm sure someone will be along soon with chapter & verse.

[Paul_RK]

Yes - the Ether Pathfinder tuner was generally found in radiograms such as the RG11, RG13 and RG16 - scroll down to see them

http://www.dynatronmuseum.org.uk/1950's.htm -

where it derived HT and LT supplies from the amplifier which sat on the cabinet floor. It's unfortunate that the maker's plate fixed on the tuner itself suggests 200-250 volt AC operation, I'll not speculate on the damage the variac may have wrought beyond saying that it could be extensive. Details of the power supply wiring and requirements should be available in a service manual covering the equipment, for instance

https://www.service-data.com/section...g16sa-berkeley

Paul

[Station X]

Here you go. It wouldn't surprise me if your Variac has wrecked the tuner though.

[DTEC1966]

Ok. Thanks for the comments.
Everything now makes more sense. It is confusing putting the 250v ac sticker on the frame.
So some good news. Checked all the valves this morning against a working Hacker Mayflower and a Bush for the am tube. All survived! Not sure how to check the 2 final d77 rectifier diodes {EB91}, but the tube schematic is in the download so I think it will be a multimeter process. Yes they seem o.k. Only pin 4+5 connected and everything else isolated. I may have had a stroke of luck in that at the end of the fateful session yesterday. The variac had blown a fuse, so it may be that I did the initial test with a non operative variac. The bulbs also survived.
Had a good look at the Hacker Mayflower transformer to see if it could be used to piggyback the T10a. They are very similar in that they use the HT /DC @200v.
Downloaded the schematic for the Berkeley.
Implies:220V DC and Ground for two wires and 6.3v / 4A for the other pair. The 4A seems high for the other pair but I will continue to investigate. Would this be the heaters?

Nice to meet you all.

[Paul_RK]

Originally Posted by DTEC1966

...and 6.3v / 4A for the other pair. The 4A seems high for the other pair but I will continue to investigate. Would this be the heaters?

Yes, plus (I expect, without having the schematic in front of me at the moment) the scale illuminating lamps.

[Silicon]

If you draw HT and heater current from a power supply in a radio or amplifier you need to consider the voltage and the current.

Drawing too much current from an external power supply could damage it.

[John Caswell]

According to the service manual you are going to need 4A for the heaters and about 50mA at an HT village of 250-300V.
I would suggest that you knock up a PSU, using something like a 5Z4 as the HT rectifier to give the unit a nice slow warm up.
As this unit is now pretty old, I would suggest going through the Rs and Cs and change any wildly out of specification and if you are not au fait with things don't go at it mob handed change one or two components at a time, just so you know where you may have made an error. The M1 rectifiers are now not available.
If you are not familiar with aligning AM/FM radio receivers leave all IFT and coils/trimmers well alone, especially the variable inductance tuned FM tuner head. Be careful with the tuning scale they are unobtanium, be very careful cleaning the printed side if at all, a careful clean/lubrication of all drive pulleys will help the tuning knob and pointer run smoothly.
If you pm me with an email address I will scan the schematics and send them to you.

John

[DTEC1966]

Thanks for all the considerate and informed discussion.
Having done a few Hacker Mayflowers and Bush record player and various other valve projects, I thought the T10a one would be a challenge!
I've had a good look at the schematics and agree with everything that has been submitted so far. As I do not have a L15/ EL84 amp lying around to collect the H/T from Pin 5, I was looking to draw the H/T from the valve of another amp to power the Tuner, then send the tuner output signal of to any pre/amp to amp combo for reproduction.

I agree though with the PSU and HT rectifier as a more user friendly option.
Thanks for the 5Z4 pointer.
I suppose the heaters are on a separate supply.
It suggests originally sourced direct from the L15 transformer output?

Just as a reminder to myself.

Looking at the back of the L15 photo, the output to the Tuner is clearly showing

6.3V / 3.4A between what was the Red and Black Cable
250V/50mA and Earth Between what was the Blue and Green Cable.

/Users/hafwen/Desktop/vintage-dynatron-stereophonic-power_360_61c7c5528900638e4c3778f824f24a7d.jpg

Clockwise from earth, the corresponding wiring was:
Blue...Ground
Red...6.3V / 3.4A
Green....250V / 50mA
Black....6.3V/3.4A

Ok my brain is fried!!!

[DTEC1966]

A yes! A single transformer that does the Ht220V and 6.3v at the same time.
Then 1/2 rectified sent to T10A and 6.3v direct?

[Graham G3ZVT]

A couple of observations about this Dynatron kit.

I do like the tuner styling, it's somehow "serious", almost communications receiver style.
But why is the dial marked M/CS? don't they mean Mc/s, Megacycles per second


Also another idiosyncrasy, the amplifiers make use of Belling Lee sockets for audio.


and it seem the "Car aerial" connector is used for audio too.

[rontech]

Originally Posted by rambo1152

A couple of observations about this Dynatron kit.

I do like the tuner styling, it's somehow "serious", almost communications receiver style.
But why is the dial marked M/CS? don't they mean Mc/s, Megacycles per second
Attachment 234200

Also another idiosyncrasy, the amplifiers make use of Belling Lee sockets for audio.
Attachment 234205

and it seem the "Car aerial" connector is used for audio too.
Attachment 234208

I used to have a Leak TL10 and associated preamp. The rear audio sockets were "Car aerial" type. I think the front panel tape and aux were 1/4" PO jack type

[John Caswell]

The sort of transformer you require has secondaries of 250-0-250 at about 50-60mA for HT, a single 0-5v 2-3A for the rectifier heater (if you are using say a 5Z4) and finally a 0-6.3V 4A for the radio valve heaters and the dial lamps. This is what I run my T10a on.
As has been described the audio comes out on cable terminated in a car aerial plug but there is enough room on the chassis where the audio cable exits to fit a good quality insulated phono socket.
I suggest that you also change the 5 pin power plug for something a little more modern.

John

[DTEC1966]

Thanks John. It is good to know someone has completed the power up phase of the T10a with success. The combined knowledge of the group is a credit to you all. I have a few transformers on a watch list. Your definitive answer will make the choice easier, There is one that has the rectifier valve attached. An old Phillips if I recall. Listed as a Full wave rectifier though! I suppose if this valve is suitable for the rectifier stage, it would perfectly suit the criteria with just the two output stages recommended.

Yes having removed the original terminal plug, I will invest in a nice alternative.

Once the power up stage is looking ready for testing, It will be very tempting to have a quick go, using the variac at the front end of this new arrangement.
I suppose I would like to see or hear some output from any from anywhere before recapping and checking resistors. The advice given about small incremental changes is sound advice.

Checked the isolated bulb array yesterday. 6.2V AC on the variac. All four lit up. One a bit dim but I think it was an old 12v!

Ok thanks for all the comments. I am enjoying the progress being made and at least our efforts are recorded and remain for the benefit of others.

[DTEC1966]

Ref 5 pin power plug. I couldn't see that the centre pin had any function wrt the four cables. I suppose it was just a redundant pin?

[DTEC1966]

Just thinking out loud.

Sourcing the transformer is opening a few avenues.
A few suitable ones in the pipeline.

Some may be disregarded due to:

Would a 200V rated Input transformer be overwhelmed by U.K mains supply.
This one gives the 6.4v @ 4A. That would be perfect for the Heaters, Bulbs and very close to the Rectifier { +1.4 V }

That might do the Job?

[John Caswell]

I think that a 200v primary would not last long on 250v, and bear in mind that with, say, 250 v into 200v that is 25% higher so the 6.3v would also be the same 25% higher - well outside valve manufacturers ±10%.
If possible look for a tx with multiple primary taps.

John

[DTEC1966]

Ok. Took apart an old Hacker record player that was lying round yesterday to look at the guts.
It looks promising. There is an Ez80 ( or EZ81 if needed ) in the line up rated at 90m/A and a 2 pairs of black / brown feeds directly off the main transformer. One set to a single bulb at 6v a.c. which is operational and the other pair to the heater pins 4 and 5 on the Ez80. The EZ 80 is operational.



Pin 1 ---Anode 1
Pin 7---Anode 2
Pin 4--- Heater
Pin 5--- Heater

Pin 3 ---Cathode ( Off to Large Capacitor at present)

Ground Casing back to transformer and Large capacitor.

I think this may be resolved tomorrow with a cup of tea and a multimeter!

[Synchrodyne]

By way an observational comment, the Dynatron T10a certainly had what might be called “generous” circuitry.

On the AM side, it was of the one RF stage, two IF stage type, with a three-gang front end. AGC delay was done by a “third” diode, thus avoiding differential distortion, and AGC bias was applied to the RF, MX, and 1st IF stages, but not the 2nd IF stage, so modulation rise in the 2nd IF stage was likely not a problem. Also, the 1st IF stage had degeneration, and was switched to lower gain on LW and MW than on SW. Overall, perhaps the AGC system was not quite as good as that on the Chapman S6 and S6BS tuners, but it was not far off.

The demodulator output was well tapped-down, so minimizing distortion arising from differential AC and DC loads. The output level, 100 mV at 30% modulation, was UK de facto norm at the time. I think that much of the T10A AM side followed the general pattern of the earlier T99 and T139 units, including the four-position selectivity. Although unlike those, the T10a does not seem to have had a 9/10 kHz notch filter. Perhaps had Dynatron not been turning towards a down market direction at the time, this would have been included on a future iteration.

On the FM side, it had a two-valve front end with three-gang tuning. (The T10a was “one-up” on the preceding T10, in that the latter had had only a basic single-valve FM front-end.) The three-gang feature was uncommon in UK FM tuners of the time. Others that come to mind are the Pye HFT111 (essentially the RF section of the FenMan II radio receiver) and the (rather obscure) Jason AM/FM2. (Leak did not go to three gangs until the Troughline II of 1959.) Even less common was the four-stage IF strip, achieved by using the EF89 AM RF amplifier as an FM 1st IF amplifier, meaning that the ECH81 heptode section served as 2nd IF amplifier on FM. The only other 1950s UK FM tuner with a four-stage IF strip that comes to mind is the Jason AM/FM2; Radford did use a four-stage IF strip in the 1960s though, albeit with a basic front end. In the T10a, the final FM IF stage was configured as a limiter, and it looks as if the 3rd stage would have been a partial limiter. Given the high-gain IF strip with good limiting, it could have been that a wide-band ratio detector was used, sacrificing AM rejection for lower distortion. The FM tuning indicator provided both signal strength and centre-channel indications using a conventional magic eye, this done by using a rectifier bridge to add the modulus of the detector DC output (zero at centre-channel) to the limiter grid DC (proportional to signal strength). Several makers of the period took the trouble to get this aspect right, albeit by different means.

There was no AFC. Either the FM oscillator had exceptional stability, or Dynatron was being optimistic. The evidence is that AFC was preferable for valve tuners. Leak used AFC on the Troughline despite heroic efforts to avoid it, and Quad also had to add mild AFC to its original FM design.

Perhaps had there been a successor variant, Dynatron might have refined the design by adding a cathode follower output, by using a cascode FM RF amplifier in place of the pentode, and by including AFC.

Be that as it may, the evidence is that T10a was quite a tour-de-force as British hi-fi tuners went in the second half of the 1950s. Perhaps its very limited visibility in that pantheon stemmed from the fact that although it was available as a separate item, it was probably sold mostly as part of Dynatron integrated systems. Nonetheless, the Dynatron components were sometimes advertised as such, e.g. in Wireless World 1959 March.





Cheers,

[DTEC1966]

Thanks Synchrodyne, a very informative analysis that I am sure will prove to be useful during the latter stages of refining the T10a performance.
When I hear such informative posts, I feel a sense of regret that so much knowledge may be lost to the iPod generation who are forced, or inclined, to throw away their tech rather than attempt to fix it.