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Old 8th Apr 2020, 11:35 am   #61
PJL
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Default Re: Pilot U650

Looks like the new rectifier has improved the HT. Suggest you measure V5 anode, screen and cathode voltages to check all is well. The audio output valve can cause major damage to mains and output transformers so it is important to check it is working to specification.
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Old 8th Apr 2020, 11:50 am   #62
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Default Re: Pilot U650

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Originally Posted by Devon60Ben View Post
Changed rectifyer to langrex - rectifier heater AC voltages are 9.5 & 10.5 on pins 1 & 4 - should these not be 5V?
Now getting 343Vdc on pins 1&4 and 310Vac on pins 2&3.
Chances are that if you are measuring pins 1 and 4 successively to chassis, the meter is indicating harmonicky HT ripple on one pin and partial cancellation of that ripple by 50Hz AC heater volts on the other. You need to measure across the pins to see the effective heater/filament voltage.
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Old 8th Apr 2020, 6:36 pm   #63
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Default Re: Pilot U650

Quote:
Originally Posted by Station X View Post
Given that two voltages (9.5 and 10.5) are given for pins 1 and 4, I assumed these were measured wrt to chassis.
Yes, was measuring to chassis ground - DOH! will re-measure and let you know how it looks
Thanks to Graham also for the same prompt
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Old 8th Apr 2020, 6:41 pm   #64
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Default Re: Pilot U650

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Originally Posted by PJL View Post
Looks like the new rectifier has improved the HT. Suggest you measure V5 anode, screen and cathode voltages to check all is well. The audio output valve can cause major damage to mains and output transformers so it is important to check it is working to specification.
Thanks PJL and Turretslug your help is invaluable. Yes the new rectifier seems to be better. Will look into the above and other previous suggestions ref the speaker coil etc.

I am not getting anything if hooking up the ipod to the pick-up input - should it just be a case of plugging in to the jack or do I need to do anything else. If I max the volume when doing this I can just hear the faintest of sound to recognise that the ipod is playing.

Ideally I want to get this section sorted before moving on to do any radio alignment stages.
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Old 8th Apr 2020, 7:29 pm   #65
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Default Re: Pilot U650

Re pickup, yes you just plug in a mono 6.35 jack and it should play. The radio output mutes automatically

1. Make sure the phone is in mono mode (it's under settings->smart settings->accessibility)
2. Did you buy the cable I recommended? I tried a few before I found one that works.

Gabriel
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Old 8th Apr 2020, 7:57 pm   #66
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Default Re: Pilot U650

I have the same volume issue with a USB bluetooth adaptor and have ordered some 99p LM386 mono amplifiers with preset gain control from china that should do the trick.
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Old 9th Apr 2020, 5:58 am   #67
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Default Re: Pilot U650

PJL, I have the same model and regularly play via my phone or other devices via PU Jack without the need for an amplifier. It should work right out of the box.
Gabriel
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Old 9th Apr 2020, 7:13 am   #68
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Default Re: Pilot U650

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Originally Posted by Gabe001 View Post
PJL, I have the same model and regularly play via my phone or other devices via PU Jack without the need for an amplifier. It should work right out of the box.
Gabriel
Thanks Gabe - I have the right jack plug which is a convertor from 6.3mm to 3.5mm and it plugs in successfully. The previous one was too big to go in far enough it is probably 6.5mm but the end was long enough.
My phone has a different menu (Iphone):
settings / general / accessibility / mono audio
I have turned mono on but no difference. there is a slider bar to adjust between left and right which is in the middle - will try either end and see if there is any difference.
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Old 9th Apr 2020, 4:07 pm   #69
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Default Re: Pilot U650

Ben, I have tried a 3.5 to 6.35 stereo to mono converter jack as well and it didn't work for me either.
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Old 9th Apr 2020, 5:53 pm   #70
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Default Re: Pilot U650

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Originally Posted by Gabe001 View Post
Indeed the dial lights up in quadrants and it looks quite impressive. Day and night pics below. The magic eye lights up too, although I was told that mine is quite dim.

Light yours up when ready and let me know if you get a faint mechanical hum (not speaker hum) when you do. It's inaudible when the radio is playing.
I can listen to radio 3 and radio 4 only at the moment Gabe but there is no mechanical hum whatsoever - so potentially you may have some transformer de-lamination as someone suggested
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Old 9th Apr 2020, 6:04 pm   #71
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Default Re: Pilot U650

Quote:
Originally Posted by Gabe001 View Post
Ben, I have tried a 3.5 to 6.35 stereo to mono converter jack as well and it didn't work for me either.
Have just ordered off the Big South American River Site for 1.88 with free shipping as you recommended Gabe:
kenable 008903
Fingers crosses and many thanks for the info

Last edited by Devon60Ben; 9th Apr 2020 at 6:04 pm. Reason: Wrong Price
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Old 9th Apr 2020, 8:05 pm   #72
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Default Re: Pilot U650

Quote:
Originally Posted by PJL View Post
Looks like the new rectifier has improved the HT. Suggest you measure V5 anode, screen and cathode voltages to check all is well. The audio output valve can cause major damage to mains and output transformers so it is important to check it is working to specification.
V5 anode with reference to ground is 202vdc and the screen voltage is also 202vdc, the cathode is 10.2vdc

measuring accross the rectifier heaters now shows 4.8vac
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Old 9th Apr 2020, 8:26 pm   #73
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Originally Posted by turretslug View Post
At least there is an even consistency to the lowness across all stages (apart from the high V4 anode voltage, this could be a sign of a slightly tired triode section, it's an almost trivial current consumption stage, so something of a "back burner" issue for the moment). One thing that could cause this is a tired rectifier valve- in which case it could have been acting as a fortuitous current limiter with the earlier shorting wire problem, protecting components like the field coil and mains transformer! The input to the rectifier being a little low could be slightly excessive current consumption, or simply a mains tapping/low incoming mains voltage thing (Sunday morning ovens syndrome!). You could measure the voltage across the field coil smoothing and apply Ohm's law to check that HT current isn't excessive, bearing in mind that oscillator anode and mixer screen are fed from the rectifier cathode via their own filter network.
Accross field coil is 139.2VDC
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Old 9th Apr 2020, 8:30 pm   #74
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Default Re: Pilot U650

Voltage accross Cathode resistors
R5 1.65vdc 8mvac,
R7 3.36vdc 3.0vac,
R14 3.02vdc 4.0vac,
R20 1.75vdc 10.85vac,
R25 9.85vdc 10.78vac,
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Old 9th Apr 2020, 11:15 pm   #75
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Default Re: Pilot U650

What is the value of R25 Ben?- I can't see it on the Trader sheet! (I may of course have overlooked it). That'll give you the cathode current in the output valve, which should be around 42mA- at the moment, it looks as though main HT current is somewhat excessive judging by the 139V across what is quoted as the 1400 ohm field coil. There's a bit of detective work needed to suss out whether it's because the output valve is taking too much current, or whether it's because of something else amiss. So far, the DC cathode voltages for the other valves earlier in the chain don't look too far out of kilter, except that I'm puzzled by the large AC voltage on V4 cathode (in particular)- even if there was oscillation resulting from instability somewhere, the cathode bypass capacitor should prevent too much AC component being apparent here.

Colin.
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Old 10th Apr 2020, 10:12 am   #76
David G4EBT
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Default Re: Pilot U650

Quote:
Originally Posted by Devon60Ben View Post
Quote:
Originally Posted by Gabe001 View Post
Ben, I have tried a 3.5 to 6.35 stereo to mono converter jack as well and it didn't work for me either.
Have just ordered off the Big South American River Site for 1.88 with free shipping as you recommended Gabe:
kenable 008903
Fingers crosses and many thanks for the info
From my experience, having trodden this path, it's unlikely that the output level of an MP3 player such as an I-pod, i-pad, phone etc would be sufficient to give the required volume level when fed into the gram socket, but much will depend on the signal level required at the gram socket. Back in 2015, I wanted to connect an MP3 player to a Pye Fenman1 and Bush AC41. Even with the set volume and I-pod turned up high, all that could be hear was the faintest sound. I trawled internet looking for solutions, and found all sorts of simple circuits which it was claimed would do the trick, but they didn't. I've attached one such circuit at pic 1.

Rather than dwell on what won't work, I'll say what will. Namely, a small preamp. When I say 'small' I mean 1.5cm x 4cm. They're ludicrously cheap (three for 2.00 from China), a bit more expensive from the UK. EG:

https://www.banggood.com/3Pcs-LM386-...r_warehouse=CN

They have a pre-set volume control on board, so what I did was to adjust the set volume as I would if listening to a station, connected the MP3 player to the preamp and then adjusted the pre-set pot of the preamp to give the required output to the radio.

Velleman do a nice little cheap mono preamp kit No K1803, which I've also used for a set used by my (adult) son.

To quote Velleman:

"This kit was developed as module for a number of audio applications where the input signal is too weak.
Applications such as a microphone pre-amplifier or for signal level correction".

End quote.

4.32 plus post plus VAT from ESR electronics. You'll find the construction manual at this link too:

https://www.esr.co.uk/velleman/k1803.htm

Pic 1: Useless suggested circuit.
Pic 2: How to connect your device to your radio whether directly or via a preamp.
The two resistors combine the stereo output from your device to mono.
The capacitor isolates your device from the radio, whilst allowing audio signals to pass.
Pic 3: A Velleman K1803 pramp I built into an ABS box.
Pic 4: Box with the lid on.
Pic 5: Showing 100mV 20 kHz p-p sine wave into the preamp, and undistorted 4V out.

It would of course be possible on an AC only set to put the preamp inside the cabinet, powered from the rectified 6.3V heater to provide approx. 9V DC with the preamp input to the gram socket, so that whenever the set is switched on, the preamp is powered up. I'm not suggesting anyone does that as it means modding the set a little, and a separate plug-in preamp can be used with different radios that have a gram input.

Having written this post, I've discovered that I covered this groud in a thread back in 2017! See post #9 here:

https://www.vintage-radio.net/forum/...+to+old+radios

Hope that helps.
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Old 10th Apr 2020, 10:44 am   #77
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Default Re: Pilot U650

Quote:
Originally Posted by turretslug View Post
What is the value of R25 Ben?- I can't see it on the Trader sheet! (I may of course have overlooked it). That'll give you the cathode current in the output valve, which should be around 42mA- at the moment, it looks as though main HT current is somewhat excessive judging by the 139V across what is quoted as the 1400 ohm field coil. There's a bit of detective work needed to suss out whether it's because the output valve is taking too much current, or whether it's because of something else amiss. So far, the DC cathode voltages for the other valves earlier in the chain don't look too far out of kilter, except that I'm puzzled by the large AC voltage on V4 cathode (in particular)- even if there was oscillation resulting from instability somewhere, the cathode bypass capacitor should prevent too much AC component being apparent here.


Colin.
R25 is 410 ohms on the sheet, actual measurent out of circuit was 459 so it has gone a bit high.
The speaker is a replacement magnavox item that measuures 3k ohms so quite a bit different than the standard
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Old 10th Apr 2020, 11:03 am   #78
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Default Re: Pilot U650

With R25 measuring 459R and 9.85VDC across it, the calculated combined anode and screen current is around 21mA which is around half what it should be.

Has the replacement speaker simply been wired in place of the output transformer primary? Is the 1400R energising coil measuring correctly?
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Old 10th Apr 2020, 11:25 am   #79
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Default Re: Pilot U650

Measure the resistance of the field coil as Graham suggests. It is probably over 2000 ohms.

Assuming it is high and you are happy with the results then I would leave it as is. If you replace the output valve with one with better emissions it will create another problem by reducing the HT volts.
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Old 10th Apr 2020, 11:27 am   #80
Devon60Ben
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Default Re: Pilot U650

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Originally Posted by Station X View Post
With R25 measuring 459R and 9.85VDC across it, the calculated combined anode and screen current is around 21mA which is around half what it should be.

Has the replacement speaker simply been wired in place of the output transformer primary? Is the 1400R energising coil measuring correctly?
The coil measures 3k ohms wired to pins 3&4 of the speaker socket
The output transformer is wired separately to pins 1&2 of the speaker socket
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