8th Apr 2020, 11:35 am | #61 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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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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8th Apr 2020, 11:50 am | #62 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
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Re: Pilot U650
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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8th Apr 2020, 6:36 pm | #63 |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
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8th Apr 2020, 6:41 pm | #64 | |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
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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8th Apr 2020, 7:29 pm | #65 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,612
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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 |
8th Apr 2020, 7:57 pm | #66 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
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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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9th Apr 2020, 5:58 am | #67 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,612
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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 |
9th Apr 2020, 7:13 am | #68 | |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
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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9th Apr 2020, 4:07 pm | #69 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,612
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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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9th Apr 2020, 5:53 pm | #70 | |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
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9th Apr 2020, 6:04 pm | #71 | |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
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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9th Apr 2020, 8:05 pm | #72 | |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
measuring accross the rectifier heaters now shows 4.8vac |
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9th Apr 2020, 8:26 pm | #73 | |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
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9th Apr 2020, 8:30 pm | #74 |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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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, |
9th Apr 2020, 11:15 pm | #75 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
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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. |
10th Apr 2020, 10:12 am | #76 | ||
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,737
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Re: Pilot U650
Quote:
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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David. BVWS Member. G-QRP Club member 1339. |
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10th Apr 2020, 10:44 am | #77 | |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
The speaker is a replacement magnavox item that measuures 3k ohms so quite a bit different than the standard |
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10th Apr 2020, 11:03 am | #78 |
Moderator
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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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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
10th Apr 2020, 11:25 am | #79 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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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. |
10th Apr 2020, 11:27 am | #80 | |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
The output transformer is wired separately to pins 1&2 of the speaker socket |
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