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Old 12th Jul 2019, 7:01 pm   #1
Mike. Watterson
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Default Brownlee assembled Pilot Mariner II Radiogram

The radio only version has no ferrite rod. The Radiogram does.
Except the rod had fallen off snapping most of the coil wires!
Also the label shows a 12AH8, 6BA6, 6AT6, 6BW6, 6X4 like the table radio only version (in a Blue Peter style case and similar size chassis) which I restored for someone a couple of years ago. It's more like the UK Pilot 85 series than the Blue Peter or UK Mariner. Perhaps even like T854 for radio only and T85M for radiogram.

Why would it have an ECH81? I'll see next if the heaters are wired for ECH81 rather than 12AH8.
There's not a big difference between a 6BJ6 (UK models) and a 6BA6?

Is it feasible that the third coil at the end of the rod goes between aerial and earth? It's the only one I'm not sure of. I think the MW and LW coils are correct, going between 0V and the wavechange and RF trimmers for MW & LW (based on switch position).

About 5 paper caps to change. Maybe in the morning. I've only the chassis, not the cabinet & turntable. Doing this FOC for a friend.
Click image for larger version

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Coils
Aerial ----- MW ------bracket ----------- LW
Click image for larger version

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Old 12th Jul 2019, 7:38 pm   #2
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

The Radiogram https://www.radiomuseum.org/r/pilot_...radiogram.html
The similar but not identical radio https://www.radiomuseum.org/r/pilot_...r_mk_iimk.html

Photo of the radio only version I did a couple of years ago
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It had a bit of veneer missing. I photoedited and laser printed the missing part, glued on card and varnished.
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Old 12th Jul 2019, 10:36 pm   #3
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

I was curious.
So I took out the 6X4 (rectifier) and powered up. The ECH81 lit. Which it wouldn't if socket was wired as per chassis label of 12AH8?

Decided the caps are easy to change and no crumbly sorts so easy to scrape case and read values:
I replaced one at a time starting at output.
10nF from Anode 6AT6 to grid 6BW6 (o/p). The removed one was 4uA leakage at 30V.
25nF from Anode 6AT6 to tone circuits (this model has several tone settings and Gram on one switch)). 10uA leakage at 30V. I replaced with 10nF in parallel with 15nF.
So I didn't even bother getting out the high voltage leak tester. The bench PSU was for Electrolytic tests.
2nF from 6AT6 grid to coax, probably from volume wiper. I didn't have any high voltage 2.2nF except one 1KV part for Tone Correction (for some other set) or 2.7 so I put a 10nF. It's not critical and I could have put a 50V ceramic.
A 100nF on the AGC line.
A 100nF to 6BA6
A 100nF to ECH81.

The 25uF @ 25V cathode decoupler on 6BW6 was fine.
The pair of HT electrolytics just needed a minute or two of reforming.
A pilot lamp replaced.

Noise on MW. LW has RTE and BBC R4.
Added the end coil on ferrite to aerial and earth wires on the tag board and 7m of wire produced noise on SW.

No glow on 6U5 magic eye.
Tuning caps very crackly and switches seem tricky. I've no knobs! Why did he not give me the knobs?
I wonder what turntable it is?

So more to do, but now some life.

Mystery of the ECH81, looks like original wiring.

Should I replace 2 core flex with 3 core?
What does the trailing coax aerial wire connect to? Some sort of SW wire in the cabinet?
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Old 12th Jul 2019, 10:39 pm   #4
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

Need to check if the 6e5s Russian is pin compatible. It's not with an EM34. I've an idea grid and anode are swapped? Need to check carefully. I have one in stock. He'll have to pay for replacement I think.
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Old 12th Jul 2019, 10:55 pm   #5
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

Only a jumper wire needed to make Octal socket work for Russian 6e5s (6E5C) and octal 6U5. Likely the "empty pins" on the 6U5G socket are used as tags so it will be a little more complicated.
https://www.radiomuseum.org/tubes/tube_6u5g.html
https://www.radiomuseum.org/tubes/tube_6e5s.html
The EM34 is tricker, also it's a dual shadow, dual sensitivity, so the Russian part hasn't same function.

Cleaning switches and tuning vanes will help a lot.
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Old 13th Jul 2019, 1:42 am   #6
Synchrodyne
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

Quote:
Originally Posted by Mike. Watterson View Post
There's not a big difference between a 6BJ6 (UK models) and a 6BA6?
As I understand it, the 6BJ6 was intended to essentially replicate 6BA6 characteristics, but with a marked improvement (lower noise) at VHF to make it suitable for use as an FM RF amplifier; and to do that with half the heater power.

Its 6.3-volt, 150 mA heater made it a “low consumption” valve, particularly suitable for mobile equipment such as two-way VHF radiotelephones. It also made it suitable for use in American AC-DC receivers with 150 mA heater strings and where heater voltage needed to be conserved, as it were, such as in AM-FM receivers. Zenith used the 6BJ6 extensively as FM RF amplifier in its FM-only and FM-AM table receivers. It also served as AM RF amplifier on those FM-AM modes that had a three-gang AM front end (I think that most of Zenith’s FM-AM and AM-only chassis of the period came in both two-gang and three-gang versions as far as the AM side was concerned.)

The 6BH6 was the sharp cutoff counterpart to the 6BJ6, also with a 6.3-volt, 150 mA heater and essentially replicating 6AU6 characteristics with better VHF performance.

Quote:
Originally Posted by Mike. Watterson View Post
Why would it have an ECH81?
I should not be too surprised if some chassis that started life with the 12AH8 were changed over to the ECH81 once the latter became established and swept all before it. The 12AH8 looks to have been fairly lacklustre, with a 0.5 mA/V conversion slope as compared with the 0.75 mA/V or thereabouts of later triode heptodes. The 12AH8 may have been something of a “hospital pass” on Brimar’s part, when it realized that many setmakers were not going to accept the (relatively noisy and not-so-good-at-HF 6BE6/12BE6. So fairly soon after the B9A base was introduced, it cobbled together a triode heptode with a dual heater system (6.3-volt, 300 mA and 12.6-volt, 150 mA) to avoid the need to offer two of them.

I think that a similar fate befell the Osram X79, even though that was a better valve, with some setmakers – and commercial/industrial receiver makers such as Marconi -switching to the ECH81 (X719). Osram’s initial receiving miniature “77” range included the 6BE6 (as the X77, later as the X727) and a 100 mA heater variant, the X107. But almost right away it recognized the need for a triode heptode, and “squeezed” one on to the B7G base by having the cathode share one of the heater pins. This was the X78 with 100 mA version X108. Soon after the B9A base became available the same valve was reissued as the X79/X109, without the compromised pinout.


Cheers,
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Old 13th Jul 2019, 8:47 am   #7
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

I agree the ECH81 makes more sense. Curious though that it seems original wiring and yet the printed label stuck on the chassis has 12AH8.
I shall have to add a note on the chassis.
I think too that the 6BW6 is really a miniature version of the 6V6?
It's curious that the metal work is more like the Blue Peter chassis than the 85 series chassis. Seems like poor layout and wasted space, though it's made/punched for the B7G and B9A sockets rather than using adaptors.

Thanks for the thoughts on the ECH81. I must test and see how similar the cheap NOS Russian version is. I was thinking of an entire radio & Push pull audio out using them. Or maybe a 12V set using transistor outputs. The ECH81 apparently "works" down to under 6V HT if the grids are biased positive.
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Old 13th Jul 2019, 1:04 pm   #8
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

Cleaned tuning caps and crackle gone.
Hmm... it died.
Cleaned switches, valve sockets, swapped ECH81 etc...
Then it just came back.
Either an intermittent connection on LO on waveswitch or a short on LO Tuning? I wondered was it the main HT dropper resistor as it's very burnt looking. Only some red paint on the end. I was puzzled as to how this was fed as it's NOT directly between the caps.
Investigation revealed the primary of audio TX is fed direct from main HT on the 6X4 and cap, and then a connection off that feeds dropper which feeds 2nd cap and all HT except RF/IF. A second dropper at the 6BA6 off that supply feeds that and the ECH81.

However it wasn't the dropper. No idea what it was. I've left it running.

The Russian magic eye lights up and a 6U5G should still work, as I simply added a link, the target on the Russian eye is NC on a 6U5G and vice-versa.

I've established by looking which trimmers are RF and LO and the bands. Nothing except the signal generator on SW with the medium long wire, but that might be true anyway today.
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Old 13th Jul 2019, 4:32 pm   #9
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

Still working. Radio China briefly somewhere around 12MHz. Seemed very deaf on SW so tried 3 other S/H ECH81, one was maybe better and the other two only pickup the signal generator.

No movement on Magic Eye, though VVM says AGC line going from -1V to -2.5V on RTE1 LW.

One IF core was badly out (Top, 1st IF). I used top of volume control to feed wobulator. Simply feed in Wobbulator on aerial socket with RF set to end of MW. IF must be similar to the 85 series (It's 471kHz) as the "centre" of the frequency knob is about 455KHz and it looked like about 471 KHz was correct. People rarely twiddle LOWER cores

R4LW seems OK.

Still don't know why it went dead for a while.

I'm puzzled by the Magic Eye and AGC. Even with big signal from generator the AGC line doesn't seem to go bigger than -2 approx. I can test eye by feeding from isolated PSU and see does it match spec. There is 1M in series with eye grid.
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Old 13th Jul 2019, 7:03 pm   #10
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

I checked the "eye" by putting -Ve PSU to grid, which was also then feeding AGC line via the 1M series resistor.
Eye closed about -4.7V. Fully open about -0.5V.
So I examined wiring on AGC line and last IFT. The gram/radio/tone switch is fed via a tag, this has a three leg thing that looks like a ceramic tube capacitor. One end goes to IFT and 1M resistor that feeds AGC line. The other end, where a capacitor lead would be, goes to 0V/ chassis. The third extra wire from inside goes to tag wired to gram/radio/tone switch and then to volume control (500K). The extra wire measures about 47K to the IFT end. I thought this might be touching another wire? Anyway, re-dressed all parts with long bare wires and now AGC / Eye working.
Also picking up Radio Romania International on 25m band without any aerial! Good SW reception now with aerial connection to foil on my workshop ceiling.
RTE1 now on LW almost closes eye.
Just interference on MW. During daytime a VERY good battery set will get Five Live from UK and used to get Radio Devon and Spirit on MW from Cavan border (Limerick City is at end of Shannon River where it becomes tidal estuary, I'm about 9km as crow flies further west).
I'll try MW at night.

I'm tempted to draw up schematic. At least diagrams of trimming and voltages on a working one.

So maybe something was partially shorting under chassis?
It's loud and lively now. It has a big audio transformer.
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Old 13th Jul 2019, 9:22 pm   #11
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

Arrgh. Found another evil lurking paper TCC. A 5nF. No idea what it's for really.
Cleaned 60 years muck off inside and outside of glass.
Starting to pickup UK MW.
So I'll take it to other side of Limerick on Monday and discover what the audio style coax on rear of AE sockets is for. I can see it come out of exact same chassis hole on several photos on web, like Maitu's on RMorg and one on Adverts.ie
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Old 14th Jul 2019, 11:05 am   #12
Mike. Watterson
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Default Re: Brownlee assembled Pilot Mariner II Radiogram

A mystery. The 5nF cap on the top of the chassis isolates the tuning cap from the ECH81 g1H. That's normally done if the AGC is fed there via a 1 M Ohm from the decoupled AGC line.
Alternate arrangement is to feed AGC via "earthy" end of all the coils, in which case the cap isn't needed.
But the wire to waveband switch from ECH81 RF grid goes direct! The other end of all the RF coils seem to be earthed. This requires further investigation!
Has the capacitor been fitted in the wrong place due to a lack of a tag? Its leads stretched from ECH81 grid via small chassis hole to the tuning cap.
Is the 1M resistor accidentally been left out? Easily would go from ECH81 pin to point where the 100nF decouples AGC line near where it feeds the IFT connecting to IF amp.

Perhaps this is cause of the intermittent SW performance and variable LW gain.

I think I should isolate the RF coils by connecting that wire to the tuning cap, if the earthy end is really at earth/0V/Chassis and not fed by AGC voltage?

Voltages:
6X4: 253V
HT after audio transformer and 2K5 resistor: 180V
HT after 2K resistor fed from 180V: 82V
6BW6 cathode: 8.2V on 270 Ohms
6AT6: Audio preamp & detector. Cathode maybe 15mV on 33 Ohms? Not sure.
6BA6 = EF83: 0.75V on 62 Ohms
ECH81: Not sure if the 220 Ohms is to the cathode? It has 2.2V

There is feedback from the audio transformer secondary to the 6AT6 via 220 Ohms, assuming the 33 Ohms is on the cathode. That and size of it may be why there is no specific snubber/tone correction capacitor. The split primary with all HT to rest of circuit via 2K to 2.7K (don't know what it was originally, paint burnt off) will cancel the class A bias current to the 6BW6 and also reduce hum. A number of better KB models also use this scheme. In theory if you know the current of the rest of the set vs o/p bias current the ratio of the split can cancel the DC magnetisation of the core entirely, so no air gap is needed. Sort of like class A push pull with only one one valve driven.

So I think more investigation tonight of the ECH81 circuit?
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