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Old 25th Nov 2021, 6:09 pm   #1
HoverJohn
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Default Dynatron Ether Pathfinder….

Hi I’m now at the stage where I need to get the radio for the Berkeley ready to use again, it’s an Ether pathfinder and very complex. I’m aware I should inly change the bare minimum so as not to mess up it’s calibration etc.
There was no known faults with this part except the glass supports has perished and the glass was touching the indicator bar and damaged the paint on the back of the glass. I’ve packed this out and cleaned off the nicotine and electrolysed the switches, but do I just swap the last output cap to protect the pre amp and leave the rest or go full monty?

There quite a few wax caps I’ve been over the diagram and not actually sure what’s what yet also some mega tiny electrolytic caps….

What to do??
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Old 25th Nov 2021, 6:31 pm   #2
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Default Re: Dynatron ether pathfinder….

I would instinctively replace the wax-caps, only because I know from experience that the majority of them _will_ be leaky!

Likewise the electrolytics: after half a century or more they will either have become leaky, or dried-out and now only delivering a pale shadow of their intended capacitance.

Apart from that, it looks an 'interesting' radio - on the 'trawler-band' SW range you may be able to hear some of us hams who still persist in using double-sideband-and-full-carrier AM around 3.60-3.62MHz!
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Old 25th Nov 2021, 9:16 pm   #3
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Default Re: Dynatron ether pathfinder….

By mega tiny electrolytic caps do you mean the ones on the rear mounted tag strip?
They're selenium diodes I think, M1 or M3.
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Old 25th Nov 2021, 10:52 pm   #4
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Default Re: Dynatron ether pathfinder….

By all means change the grid feed cap and then power up via a lamp limiter. Just wanted to say that it has the prettiest front I've ever seen. Absolutely gorgeous ...

My only wish is that all those stations were still available.
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Old 26th Nov 2021, 12:04 am   #5
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Default Re: Dynatron ether pathfinder….

My only wish is that all those stations were still available.

Hmm, let's see. 1MHz of bandwidth, so a sampling rate of three or 4 MHz would be good, maybe 16 bits of depth. That's 4*16 =64 megabits/second. I've got a 256gigabyte flash 'drive' from a dismantled desktop kicking around 256E9*8/64E6 = 32,375 seconds = 8.99 hours.

So allowing for inefficiencies, parity and doodads, it could make a player that played a full medium wave of stations and repeated every four or five hours. Of course, all the stations would be in permanent lock-step with no variety. You could fake fading and interference in making the big file. Ideally you'd want to go back in time and record the real thing. But it looks like you could use re-purposed junk and have a full medium wave.

Just musing!

So pensioned off Flash hard drive, an FPGA to soak up the logic and be the controller.

Hey! you're no longer tied to 9kHz channels and the hamstrung bandwidth associated with it... hifi AM on some signals!

This is the crude full-frontal approach. More sophisticated would just be a multi-file audio player into a multichannel modulator. Do-able in a large FPGA, just add a DAC for re-construction.

A battery of pantry transmitters. Battering RAM?

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Old 26th Nov 2021, 1:25 am   #6
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Default Re: Dynatron ether pathfinder….

Quote:
Originally Posted by Kentode View Post
My only wish is that all those stations were still available.
Also back in the day, the UK AM transmitter bandwidths were limited by their respective landline feeds, not by brickwall filters. I understand that Brookmans Park HS had 15 kHz landlines from the late 1940s, and I’d guess that Daventry 3P had the same. Elsewhere I think it was around 8 kHz, although variable by location. Internationally, 10 kHz was the CCIR “music circuit” bandwidth, taken as a benchmark for AM broadcasting. The Alloius LW transmitter had a specially designed aerial system to allow ±10 kHz radiated bandwidth. (Droitwich LW bandwidth was somewhat lower – a form of British understatement, perhaps.) Commensurately, the Dynatron Ether Pathfinder T10A tuner had an AM frequency response to above 10 kHz at its widest IF bandwidth setting.


Cheers,
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Old 26th Nov 2021, 9:14 am   #7
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Default Re: Dynatron ether pathfinder….

So the waxy cylindrical ones are ok to change (they mainly seem to go from HV to LV) - but I’m going to leave the square waxy ones they look like mica? I think every thing else is ceramic?

Edit this is based on the ones that go to earth are less likely to affect it than if I were to change the ones accross inductors/coils etc.
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Old 26th Nov 2021, 9:36 am   #8
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Default Re: Dynatron ether pathfinder….

Waxy cylindrical ones need changing, they're almost certain to have gone leaky.
Flat, rectangular ones, covered in wax will be found in the RF, LO and IF sctions. These are silver-mica and usually reliable. Any changes will most probably cause a large disturbance of RF/IF alignment.

I wouldn't expect there to be many ceramic capacitors. Most of that era were tubular types, looking like a little dog bone resistor usually with a hole down its centre and wire leads wrapped on at the ends. The first ones were seen as a bit exotic and used for controlled temperature coefficient to temperature compensate tuned circuits, most usually local oscillators. I think disc-ceramic types came a bit later and were at first only in materials with high dielectric constant and poor thermal stability - they got used as RF decouplers. Ceramics are fairly reliable compared to waxed paper and electrolytics.

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Old 26th Nov 2021, 10:23 am   #9
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Default Re: Dynatron ether pathfinder….

Is there any provision for selecting a gramophone input?
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Old 26th Nov 2021, 10:27 am   #10
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Default Re: Dynatron ether pathfinder….

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Originally Posted by rontech View Post
Is there any provision for selecting a gramophone input?
The Gram selector is part of the pre-amp and not on the tuner.

See this thread https://www.vintage-radio.net/forum/...d.php?t=184865

Cheers

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Old 26th Nov 2021, 11:33 am   #11
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Default Re: Dynatron ether pathfinder….

Hi,

I actually just finished restoring mine. Only needing an alignment now, and although not original and might upset some, I will add an ECC82 under the chassis, to raise the gain a bit with one half, and let the other half act as a cathode follower to reduce output impedance.
Since I am going to use this tuner a lot, I decided to replace the resistors as well. Probably no need for that, but I found that a lot of them were far beyond tolerances, so I did it anyway. Also the ones inside the FM front end... - not a lot of space in there btw... Valves were also replaced, since most of them were weak. I think this tuner was used a lot. Some valves were almost completely dead.

About alignment, my experience is, that it is practically always needed on old equipment. Even if only a few parts are being replaced, or it had a lot of use over time, or having just been sitting unused for decades. Of course, it will probably work anyway, but I found that an alignment is always needed to get the best sensitivity, and on FM to make sure the discriminator operates on 100% alignment with the IF.

I replaced the small metal diodes, MR1 to MR5, with 1N4148. If you don't like the more "modern" appearance, you can use OA81. It is not that critical, and they will for sure be better than the original ones, which are probably small selenium "buttons".

Best regards,

Jan
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Old 26th Nov 2021, 2:10 pm   #12
HoverJohn
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Default Re: Dynatron ether pathfinder….

Thanks all, ok so looks like I will take a light touch on this aiming to leave the resistors- the only ones I changed in the amp (separate thread)were the ones that would unbalance the pair of EL84s in the power amp.
There are quite a few disc ceramics in there Erie 0.01ufs

Jan looks good I’ve not disturbed the FM unit as the diagram looked to contain no large caps so left it alone. Interesting that the valves get weak I suppose they are powered up all the time it’s on. I found the resistors on the circuits with duff caps in the amp to be the worst I might test a few later - did u identify any totally dead ones? Also did u swap the 5pf cap a tiny waxy thing? I’ve ordered gold paint to fix a scratch on the back of the dial where the indicator fixing screws touched the glass. Mines in an RG Berkeley so not in a stand-alone path finder. Let us know how it goes.
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Old 26th Nov 2021, 8:26 pm   #13
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Default Re: Dynatron ether pathfinder….

@jan FYI following up on your comment about valves getting tired I just popped a new set in the pre amp and amp and the improvement of the gram is phenomenal. I think the main difference was the el84s I put in some cheapo sovtec ones I got to keep as spares and they are great.
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Old 26th Nov 2021, 9:51 pm   #14
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Default Re: Dynatron ether pathfinder….

Hi John,

The output valves, in this case EL84, are the ones that wears out first. It is common that that they need to be replaced.

As for the tuner itself (I only have the tuner chassis), the two duo diodes D77 did almost not move the needle on my valve tester. I replaced them with new 5726's. E91AA or EAA91 are equivalents as well and can be used without any kind of modifications. I am sure the are easier to find than D77.
The ECC85 in the FM tuner was also close to dead. The rest was still giving quite good test results, but since I had a complete set of new ones and also replaced all resistors and paper caps already, I went for a set of all new valves throughout, including the EM80 tuning eye. I think russian equivalents are available if it is impossible to find a NOS genuine EM80.

BTW I have and early danish produced Mørch turntable with built in tuner and amplifier, using 2 x EL84 in the amp section, and I replaced those with russian types as well. It plays perfect and it has been used many hours already and shows no sign of instability or other problems. They did not even drift away from each other (was purchased as a matched pair). And they run pretty hard in that amplifier.

You are right, there are no paper (waxy) caps inside the FM tuner, and it is quite a challenge to remove it from the main chassis.

I am not sure which tiny 5pF wax capacitor you mean. I did not replace any with that small value. Normally a capacitor with that value would be a ceramic type. Can you post a picture of it, or maybe specify the number on the schematic, so I can identify it?

Best regards,

Jan
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Old 27th Nov 2021, 8:51 am   #15
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Default Re: Dynatron ether pathfinder….

The cap is literally the top right most component in the picture I posted above - the service manual that was kindly sourced by a member here has some modifications it might be one of those- this is a ‘56 model year.
I’m more likely to use the gram and the AF input so asking as I can get a few fm stations it will be fine but I will look at sourcing new valves.
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Old 27th Nov 2021, 10:17 am   #16
Jan Zodiac
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Default Re: Dynatron ether pathfinder….

Yes, that is C64 in the schematic and it's ceramic. You can leave that in there. It is in the AM section btw.

I'm sure you will get FM stations even without replacing valves. Maybe you will have lower sensitivity and maybe it will be a bit off in the discriminator, but this can only be corrected by alignment anyway. On the other hand, not a lot of prgrammes of value are available on FM anymore. Not in my country anyway.
If someone in your area could test the valves, it would be a good help. There is no need to replace the ones still working. I'm sure not all are weak.

Maybe you can help me out with a capacitor. It is the one referred to as C44 in the schematic/chassis bottom view plan. In your picture it is the far left bottom (on the large tag strip). It is a small electrolytic capacitor. I can't read the value from the schematic, it is a bit blurry. I would guess it to be 5uF as is usual for this capacitor, but it could look like it says 8uF in the schematic.
Someone replaced it with a 47uF - 250V and that is for sure not correct. So if you could read the actual value + voltage rating on the capacitor, it would be a great help.
The flywheel on the tuning shaft was also removed on mine at some point, so I have to fit one from another radio.

My tuner must be a pre 1958 also, since the modifications shown in the manual was not carried out. I implemented those mods, since I was doing a lot of work on it anyway.

Best regards,

Jan
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Old 27th Nov 2021, 10:57 am   #17
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Default Re: Dynatron ether pathfinder….

It’s 8uf @ 150v see image

I’ve ordered 8uf at 450v as a replacement from cricklewood electronics
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Old 27th Nov 2021, 11:50 am   #18
Jan Zodiac
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Default Re: Dynatron ether pathfinder….

Quote:
Originally Posted by HoverJohn View Post
It’s 8uf @ 150v see image

I’ve ordered 8uf at 450v as a replacement from cricklewood electronics
Great! Thanks a lot
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Old 5th Dec 2021, 7:19 pm   #19
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Default Re: Dynatron ether pathfinder….

Thanks for the help folks it’s all recapped now and I’ve just touched up the glass front. Time to pop it back in the cabinet!!
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Old 12th Dec 2021, 3:29 pm   #20
Jan Zodiac
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Default Re: Dynatron ether pathfinder….

In case this could be helpful to others, I mounted a cathode follower to the output of my own T10A. This is because I have the tuner chassis only, and will be using it with another preamplifier (home build mono project). This cathode follower stage can be used in a lot of other applications as well.
In general I am not a fan of tampering too much with original equipment, but if it can be made so it looks like it could have been done by a technician around the same era as from when the equipment was made, I don't really have anything against it.
As for the T10A tuner (and a lot of other vintage tuners as well), it has a relatively low AF output, as well as being high impedance also.

The first ECC82 triode gives an amplification factor of around 8 (can be increased my shunting the cathode resistor with a capacitor). The second is connected as a cathode follower (gain a little less than 1), and gives a siginificantly lower output impedance. I did not calculate it, since I then have to look up how it is done. I don't remember it just from my mind. I took the stage from the schematic of my preamp project. The output impedance is probably in the region of 1kOhm or so.

I loaded its output with 100kOhm and did a frequency sweep. 3dB roll of at 600kHz. My signal gen. does not go below 10Hz on the low end, and at 10Hz there was still full signal, so I was not able to reach the -3dB point at the low end. I would say that is all adequate for a tuner like this...
Another advantage is, that it takes quite a large input signal before distortion appears.

B+ around 250V can be taken from any supply available. B+ current is only a little over 4mA.

Kind regards,

Jan
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