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Old 29th Apr 2021, 7:36 pm   #1
Phil_C_
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Default Help sought with a Pye Fenman 1

Hi.

I'm hoping someone might be able to help me to progress with the repair of a Pye Fenman that I bought a few months ago. This is the first radio I've opened up and it's given me great satisfaction so far, although I haven't made a huge difference to it! I've freed up the tuning mechanism which had seized up where the shaft between the drive drum and the tuning capacitors passes through their housing. This revealed that MW and LW were working but that FM wasn't. I've 'cleaned' the band selector switch mechanism with contact cleaner and lots of turning it back and forth. I've replaced loads of capacitors (all the electrolytics, brown Hunts ones and the greasy fluff-coated wax ones) including the C64 (Trader 1257 sheet numbering) that links the anode of the EABC80 (V4) to the EL84 (V5). MW and LW still work, to much relief! and sound better. I've tried phono input and that sounds great.

So it's the FM that I need help with the most. I'm aware that ECC85 valves can often need replacing but I want to make sure that there are no other problems before I buy another one. Having measured some voltages and resistances, I can see that:-

The tuning indicator (EM80) pin9 and V5 (EL84) pin9, which should be at 220V are at 260V (+18%). Taking into account that my mains won't be the same as in 1955 and that digital voltmeters read higher, is that a reasonable voltage for the 'top rail'?

Many of the other voltages I've measured are high, usually by low-teens percent. But my biggest concern is for the V1 (ECC85). I'm reading 170V rather than the listed 106V (+60%) for pin 6 ('b' anode) and 148V rather than 55V (+170%) for pin9 ('a' anode). Yet the resistors that sit between the 'top rail' and V1 are all slightly high (R1 15%, R3 11%, R35 11%) so presumably would drop the voltage as intended if everything else was OK? Would a dud valve give me a high voltage (higher internal resistance?) or was it a high voltage that damaged the valve in this case? I don't want to just destroy replacement ECC85s for the sake of it but if funny voltages are just a sign that the valve is shot that would be worth me knowing!

Two other questions:

The connection from the aerial to the first coupling loop has a capacitor that looks to have had both ends soldered together onto the wire (see pic). I thought at first it had been twisted around itself but it's definitely soldered. Should I be concerned about this? What does this capacitor do?

Finally, am I right in thinking that this tuning indicator isn't displaying quite as it should? I include two photos of it between stations and on a fairly strong station. There isn't a massive difference. On station, should the two bright parts come closer to the middle?

Sorry for so many questions. Although I've been lurking for a while and reading lots of the old posts I am very much a novice.

Phil
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Old 29th Apr 2021, 9:56 pm   #2
cathoderay57
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Default Re: Help sought with a Pye Fenman 1

Hi Phil, you've achieved some good work on the Fenman - well done. The HT rail voltage you have measured seems reasonable. The biggest effect on HT will be the EL84 because it is the most power hungry part of the circuit. If the valve has lost some emission it will be drawing a bit less current. When the EL84 draws less current the HT voltage goes up. How does the cathode voltage compare with the expected 7.2v? That will give you an indication of whether the EL84 is drawing more, less or about the right current. It looks as if you have a dud ECC85 but you should clean the valve pins and sockets in case you have an open connection on anode or cathode pins, or if the heater isn't lighting up. If there is an open circuit or if the valve has virtually lost all emission then there will be next to no current flowing through R1 and R3 apart from a tiny amount powering your DVM hence the anode voltages will indeed read high. It's hard to be certain but it looks like the red ceramic capacitor (20pF?) could be C1 (from Trader Sheet #1257). If so then assuming the coax goes to the FM aerial socketry then that should be L2/L3 that we are looking at, in which case the coax braid should be connected to one end of C1 and the other end of C1 to L2, the centre core of coax going to the other end of L2, which will have only a very small number of turns. It looks like somebody has bodged the aerial connection in an attempt to get more signal? That's a nice bright magic eye. Presumably the indication is on AM. Try using an external aerial and see if you get a full deflection on a strong signal. If not then check R37 (470k) in case it has gone high. Probably not - the AM alignment might be slightly off or you might have a low emission ECH81 or EF85. Hope that helps. Cheers, Jerry
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Old 30th Apr 2021, 6:06 am   #3
Gabe001
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Default Re: Help sought with a Pye Fenman 1

Hi Phil, good to have a fellow enthusiast close by.

I've never managed any significant tuning indicator deflection indoors on AM. As Jerry said AM aerials were typically long wires running the length of the garden, which received much stronger signals than what you would get with a few feet inside the house.

On FM however, once you get this working, you should get full deflection on a strong signal. I would reassess the tuning indicator deflection once you've got FM up and running.

Gabriel
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Old 30th Apr 2021, 9:56 am   #4
PJL
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Default Re: Help sought with a Pye Fenman 1

It looks like the aerial coupling capacitor has been taken out of circuit but I would not expect that to stop reception.

It's best to avoid working on the VHF front-end as stray capacitance between components and to the chassis can have a significant impact on performance so just moving a wire or component can mess things up.

Higher anode feed resistors should increase the voltage drop across them and so lower the measured anode voltages. The high anode voltages will in part be due to a high HT and us of the DMM but low emission from the ECC85 will also cause this due to the reduction in anode current.

A replacement ECC85 is the only way forward I am afraid.
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Old 11th May 2021, 8:25 pm   #5
Phil_C_
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Default Re: Help sought with a Pye Fenman 1

Thanks for all the advice!
I quickly determined that the tuning indicator was fine by using my long washing line, which has a steel core, as an aerial to give me better AM reception. The TI responded by behaving more as I had been expecting.
I heeded the advice to leave the aerial coupling capacitor alone.
Not much has happened for a while but I now have a replacement ECC85 and FM is working - yay! The only problem now is that the stations are all shifted to the wrong places, so R2 sits at ~96.8 MHz and R3 at ~99.9 MHz; R4 is off the scale. The pointer travels the full distance as the variable capacitor moves from fully opened to closed so it's not strung wrong, plus MW and LW stations are where they should be. But all the screws for adjusting the cores are covered in loads of grime and don't look like they've been messed with - are there simpler things I should consider first?
Thanks again, Phil
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Old 22nd May 2021, 4:49 pm   #6
Phil_C_
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Default Re: Help sought with a Pye Fenman 1

Would it be worth me getting an FM transmitter to allow me to work out whether my scale is shifted or stretched? It's a bit difficult with only two stations. It might make it easier to suggest what to check/adjust/fix next. I've seen as well how you can 'chase' a signal from one of these to make small adjustments but my radio is way out, so perhaps not realistic.
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Old 23rd May 2021, 12:38 pm   #7
cathoderay57
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Default Re: Help sought with a Pye Fenman 1

Quote:
Originally Posted by Phil_C_ View Post
Would it be worth me getting an FM transmitter.
In a word (or two), probably not. Since you seem to be able to receive R2 FM than you should be able to use that as a signal reference instead for around 89 MHz. Follow the FM RF alignment instructions in the service sheet. It is possible that the FM IF alignment is out but I would leave it alone for the time being and see if you can shift the tuning range via RF realignment, which is a bit simpler. I've never played with a Fenman but do be careful with the coil tuning slugs since they are very easily damaged. Ideally use a plastic tool such as an old knitting needle or a toothpick whose tip you have filed to the correct profile. If the slug won't move, don't force it. Oh, and before you start make sure that the tuning cord or the pulley on the VHF tuning capacitor hasn't slipped. The easiest way to check this is to verify that the AM stations are appearing where you expect to hear them on the dial, and assuming that the AM and FM sections of the tuning capacitor are ganged together, as they usually are. If you are attempting RF realignment then start with the receiver tuned into R2, albeit at the wrong point on the dial, and adjust the trimmers and cores as detailed in the service data very slightly and check in which direction the tuning has moved. Keep going until you reach the right point on the dial, peaking for signal strength as instructed as you go if the signal starts to disappear. Hope that helps. Jerry

Last edited by cathoderay57; 23rd May 2021 at 12:49 pm.
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Old 23rd May 2021, 8:47 pm   #8
Phil_C_
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Default Re: Help sought with a Pye Fenman 1

So instead of doing this:

F.M. R.F. and Oscillator Stages
20. Reconnect D.C. voltmeter across C55 (for A.M. generator alignment) or reconnect output meter across " Ext. L.S." sockets (for F.M. generator alignment).
21. Transfer signal generator leads to F.M. aerial sockets, connecting the earthy generator lead to the lower socket. Feed in an un-modulated signal if using A.M. generator, or a signal deviated by ±100 kc/s if using F.M. generator.
22. Set C12 (J4) to minimum capacitance, and set C6 (J3) to mid-capacitance. Set the cores of L5 (J3) and L7 (J4) flush with the tops of their formers.
23. Tune receiver to 19 on substitute tuning scale. Feed in a 99 Mc/s signal and adjust C6 (J3) and C12 (J4) for maximum output.
24. Tune receiver to 83.5 on scale, feed in an 89 Mc/ s signal and adjust the core of L7 (J4) for maximum output.
25. At the same frequency, adjust the core of L5 (J3) for maximum output.
26. Repeat operations 23, 24 and 25 until calibration is correct.
27. With receiver still tuned to 83.5 on scale, feed in an 89 Mc/s signal and adjust the core of L3 (A1) for maximum output.
28. Repeat F.M. I.F. adjustments in operation 17, feeding in a 10.7 Mc/s signal.


Do I
1. Tune to R3
2. Set C12 (J4) to minimum capacitance [will that be obvious?], and set C6 (J3) to mid-capacitance. Set the cores of L5 (J3) and L7 (J4) flush with the tops of their formers.
3. Refind R3 then shift dial position slightly towards where it should be from where it is.
4. Carefully adjust C6 (J3) and C12 (J4) until I can hear it again [will both have a similar effect? will it be one of these that shifts the position but I won't know which until I try?]
5. Repeat 3. and 4. many times until it's about right.
6. Tune to R2 and if it's not quite right position the dial slightly towards where it should be and adjust the core of L7 (J4) until ?I can hear it? and then adjust the core of L5 (J3) until??

And then just keep repeating things until it all falls into place? (perhaps doing steps 1-5 for R4 instead of R3 if it ever appears?).
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Old 24th May 2021, 3:16 pm   #9
cathoderay57
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Default Re: Help sought with a Pye Fenman 1

Hi Phil. try this:
1. Tune to R3 at the point where you can hear it on the dial.
2. Adjust C12 (J4) slightly, retune the dial to pick up R3 again. If the dial has gone up in frequency then reverse the adjustment of C12 and keep going until you can hear R3 at about 90.8 MHz (I think that's correct for your location). If you lose the signal or reach the end of the trimmer then adjust L7 (J4) and C12 until you can get R3 in the right position on the dial. The adjust C6(J3) and L5(J3) for max signal.
3. The key point to remember is that C12 and L7 comprise the oscillator and are the means of changing the dial frequency setting. C6 and L5 comprise the RF amplifier and will affect signal strength.
4. Tune to R2 and if it's not quite right adjust the core of L7 (J4) until the dial position changes to about 88.6 MHz and then adjust the core of L5 (J3) for max signal strength.
Cheers
Jerry
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Old 24th May 2021, 9:09 pm   #10
Mr 1936
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Default Re: Help sought with a Pye Fenman 1

Hi Phil C

I second the advice given by cathoderay57. It's possible that your replacement ECC85 has a slightly more stray capacitance than the original. If that's the case, simply adjusting the oscillator trimmer C12 for less capacitance should restore normality, assuming it has enough adjustment range.

You need to get the LO tuning correct (stations appearing at the right place on the dial) before worrying about peaking the RF stages to improve sensitivity.

Unless the set's been "got at" the IF stages are probably OK, and would be the lowest priority for re-tweaking.
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Old 26th May 2021, 9:09 pm   #11
Phil_C_
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Default Re: Help sought with a Pye Fenman 1

Thanks again!

I had been far too terrified of adjusting any of these things for fear of doing some damage that I couldn't put right. All of the trimmers and cores appeared to have the original waxy stuff sealing them so I thought that there must have been something faulty elsewhere. Only when I looked more closely at C12 and C6 did I realise that what I thought was a seal wasn't over the part that moved and that the whole of the top of the thing rotated. C12 was very loose and it would have been very easy to turn it as my fingers pushed past it at some stage during my capacitor replacement work. I was quickly able to bring the FM back to where it should be. I had a quick play with C6 but it seemed about right so I returned it to its original position and left everything else alone.

So I think I'm finished! I was going to replace the 2-core mains cable with a 3-core and earth the chassis but I've got continuity between the neutral pin of the plug and the chassis (and it trips my RCD), which I read means that the transformer has some faulty insulation somewhere.

Although I've no plans to play with another radio right now I'm sure I'll take on another one at some point as I've enjoyed the challenge so much and keep seeing so many beautiful radios! In the meantime I'll content myself with reading about all of your projects.

Cheers, Phil.
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Old 27th May 2021, 9:40 am   #12
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Default Re: Help sought with a Pye Fenman 1

Quote:
Originally Posted by Phil_C_ View Post
I was going to replace the 2-core mains cable with a 3-core and earth the chassis but I've got continuity between the neutral pin of the plug and the chassis (and it trips my RCD), which I read means that the transformer has some faulty insulation somewhere.
Transformers do break down between the windings and the core, but it would be most unusual for the resistance to be so low that it shows up on a "continuity test". Normally a Megger insulation tester or mains voltage would be required to break down the insulation.

I think the fault is elsewhere and suggest you investigate further.
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Old 27th May 2021, 11:28 am   #13
cathoderay57
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Default Re: Help sought with a Pye Fenman 1

Well done, Phil. Re: RCD tripping, although none are shown in the circuit, make sure nobody has fitted a mains interference suppressor capacitor between any of the primary winding connections and chassis. Unlikely, but possible. Such components can and do leak mains to chassis. I would then disconnect all the mains wires from the transformer primary and recheck the insulation resistance between the primary windings and chassis. If there is still leakage at the transformer terminals, it is possible that you have leakage between the primary winding and the transformer screen connection, which is earthed. Identify the screen to chassis connection, disconnect one end, and check to see if the leakage is between primary and screen. If so, you could consider leaving the screen disconnected but still earthing the chassis. However, note that the transformer screen is provided for a purpose which is to prevent mains getting to the secondary windings when insulation fails so it's not ideal. If the transformer is dodgy then Ed Dinning might be able to help. Cheers, Jerry
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Old 27th May 2021, 6:19 pm   #14
Phil_C_
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Default Re: Help sought with a Pye Fenman 1

I should've checked the obvious things before I started getting ideas about transformer leakages! The wire leading from the on/off switch to the transformer via the voltage selector had been crushed under the nut holding the transformer to the chassis (see pic). Although it's sheathed red, it connects through the switch to the incoming neutral, which is why I was seeing continuity to that plug pin. I wonder if it's been like that for all these years?
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