12th Apr 2020, 1:24 pm | #101 |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Thanks Turretslug,
Just been planning ahead to the IF and band alignment and located the adjustment points but have run into a serious problem that may be a showstopper. The IF adjusters are fine but the band adjusters - C31 to C46 seem to have been butchered in the past so that many of the screw heads are damaged an unable to turn except 1 out of the 12. Currently I can't think of a potential solution! |
26th Apr 2020, 7:43 am | #102 |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Finally the post arrived with a large 1500 ohm resistor to substitute for the field coil for testing purposes. The current Magnavox FC is 3200 ohms, std speaker was 1400 ohms.
With the resistor in place all plate voltages improved by 50V & Screens by around 20V so all much more in the ball park to the spec sheet. Fitted a new output valve and the volume has now roughly doubled when on max and drawing less current with plate voltage increasing by 10V. NOS magic eye arrived and looks great but doesn't open & close very much - staying around 3/4 open so need to look into that. The "Kenable" PU Jack lead has also arrived so will test this out and report back. So, should I be looking for a replacement speaker at around 1400 ohms? are there other options? Can the 3200 ohm remain? thanks |
26th Apr 2020, 8:39 am | #103 |
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Ipod now playing well through the pickup without anything in between at the moment - just switched to mono mode on the ipod. The speaker is poor but at least its all working.
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26th Apr 2020, 10:03 am | #104 | |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,737
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Re: Pilot U650
Quote:
This article, from the National Valve Museum site, originally from Radio Constructor March/April 1969, cites the 6U5G to explain how magic eyes work, so you might find it of interest: http://www.r-type.org/articles/art-137.htm As an aside, I restored a Pye 'Fenman 1' which sounded well enough at good volume on the internal wire aerial, but the EM80 magic eye didn't vary whether on or off tune. As EM80s are mercifully quite cheap, I took the easy option of fitting a new one, which made no difference. I made a little EM80 tester to vary the voltage on the grid to see how much it needed to go negative to vary the display. That proved that both the new and old eyes were working fine. It then dawned on me to plug in an external aerial, which gave a swing of several volts on the AGC line, and hence on the grid of the EM80. An interesting learning experience which cost me several hours of my life which I'll never get back! Likewise, I restored a Unitra 'Figaro Special' which has a DM70 magic eye. (The 'exclamation mark' display). The set has an internal ferrite rod aerial on which it performs very well at good volume. However, the AGC varies little when off tune or tuned into a strong station. The set has an external aerial socket too, and when I plug an aerial into it, the AGC voltage swings by -9V and the display shrinks to just a dot. Hope that might help a bit.
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David. BVWS Member. G-QRP Club member 1339. |
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26th Apr 2020, 10:11 am | #105 | ||
Tetrode
Join Date: Mar 2020
Location: Newton Abbot, Devon, UK.
Posts: 73
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Re: Pilot U650
Quote:
This is how it looks currently. Don't know anything about aerials yet - just have a coil of wire on the aerial feed and nothing on the earth. |
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26th Apr 2020, 10:12 am | #106 | |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
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Re: Pilot U650
Quote:
Options would seem to be: Stay with 3,200R if you're happy with the set's performance with this in place. Look for a replacement aroiund 1,400R. Would be nearer to original. Rewind the 3,200R speaker with slightly thicker magnet wire to reduce its resistance. Lot of effort and might not be as loud. Leave the 1,500R resistor in place and fit a PM speaker. Might sound better but very non original though could be regarded as a typical "period" repair. Polish it up and put it on a shelf secure in the knowledge that you could have restored it if you wanted to It's really up to you at this stage......
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